DE102009045767A1 - Method for commissioning process for purified separation of acrylic acid crystals from suspension of its crystals in mother liquor with device having hydraulic washing column that has process chamber limited by a cylindrical lateral wall - Google Patents

Abstract

The method for commissioning a process for purified separation of acrylic acid crystals from a suspension of its crystals in mother liquor with a device having a hydraulic washing column that has a process chamber rotationally symmetrical to its longitudinal axis running from top to bottom, is claimed. The process chamber is limited by a cylindrical lateral wall (28) and two ends opposite to each other to the symmetrical axis. Several filter tubes extend through the process chamber from the upper end of the process chamber parallel to its longitudinal axis. The method for commissioning a process for purified separation of acrylic acid crystals from a suspension of its crystals in mother liquor with a device having a hydraulic washing column that has a process chamber rotationally symmetrical to its longitudinal axis running from top to bottom, is claimed. The process chamber is limited by a cylindrical lateral wall (28) and two ends opposite to each other to the symmetrical axis. Several filter tubes extend through the process chamber from the upper end of the process chamber parallel to its longitudinal axis, taper to the lower end of the process chamber opposite to the upper end and have a filter in the half of the process chamber turned to the lower end of the process chamber and are led outside of the process chamber from the washing column, where the filter forms a direct connection between an interior of the filter tube and the process chamber. The quotient of the distance between the upper and lower ends of the process chamber and the diameter of the process chamber is = 2, where the distance is 3 m. The washing column connects itself at the lower end of the process chamber and is downwardly aligned to a crystal melting chamber, where a rotatable discharging device (16) is integrated between the process chamber and the crystal melting chamber and a crystal melting circuit (31) is guided through the crystal melting chamber. The crystal melting circuit comprises a first conveyor pump (11), a first conveyor connector, a second conveyor connector and a heat exchanger, which are present outside of the crystal melting circuit. The first conveyor pump is present outside of the washing column and has a suction side and a pressurized side. The first conveyor connector guides the washing column from the crystal melting circuit to the suction side of the first conveyor pump. The second conveyor connector reguides the washing column from the pressurized side of the first conveyor pump into the crystal melting circuit and has an outlet from the crystal melting circuit with regulatable discharge. The first conveyor connector from the crystal melting circuit to the suction side of the first conveyor pump or the second conveyor connector from the pressurized side of the first conveyor pump into the crystal melting circuit is guided over the heat exchanger. A distribution chamber is upwardly mounted to the upper end of the process chamber and is separated from the process chamber bay a base, which has passages that guide into the distribution chamber at the side of the base turned to the process chamber and at the side of the base turned away from the process chamber. A second conveyor pump (12) having a suction side and a pressurized side and a source of suspension are present outside of the washing column. An independent claim is included for a process for purified separation of acrylic acid crystals from a suspension of its crystals in mother liquor with a device hydraulic washing column connects to the commissioning process.

Description

• – sich vom oberen Ende des Prozessraums parallel zu dessen Längsachse ein oder mehrere Filterrohre durch den Prozessraum erstrecken, die auf das dem oberen Ende gegenüberliegende untere Ende des Prozessraums zulaufen, und in der dem unteren Ende des Prozessraums zugewandten Hälfte des Prozessraums wenigstens ein Filter F, das die einzige direkte Verbindung zwischen dem jeweiligen Filterrohrinneren und dem Prozessraum bildet, aufweisen sowie außerhalb des Prozessraums aus der Waschkolonne herausgeführt werden,
• – der Quotient Q = L/D aus dem Abstand L zwischen dem oberen und dem unteren Ende des Prozessraums und dem Durchmesser D des Prozessraums 0,3 bis 4 beträgt,
• – sich am unteren Ende des Prozessraums nach unten gerichtet der Kristallschmelzeraum der Waschkolonne anschließt, wobei zwischen den beiden Räumen eine rotationsfähige Abtrageinrichtung integriert und durch den Kristallschmelzeraum ein Kristallschmelzekreis hindurchgeführt ist, der außer dem Kristallschmelzeraum
• – eine außerhalb der Waschkolonne befindliche Förderpumpe P1, die eine Saug- und eine Druckseite aufweist,
• – eine erste Förderverbindung G1, die vom Kristallschmelzeraum der Waschkolonne zur Saugseite der Förderpumpe P1 führt,
• – eine zweite Förderverbindung G2, die von der Druckseite der Förderpumpe P1 in den Kristallschmelzeraum der Waschkolonne zurückführt und einen Auslass A aus dem Kristallschmelzekreis mit regelbarem Durchfluss aufweist, sowie,
• – einen Wärmeübertrager W, über den entweder die Förderverbindung G1 vom Kristallschmelzeraum zur Saugseite der Förderpumpen P1, oder die Förderverbindung G2 von der Druckseite der Förderpumpe P1 zum Kristallschmelzeraum geführt ist, umfasst,
• – dem oberen Ende des Prozessraums nach oben gerichtet ein Verteilerraum vorgelagert ist, der vom Prozessraum wenigstens durch einen Boden B getrennt ist, welcher Durchgänge U aufweist, die auf der dem Prozessraum zugewandten Seite des Bodens B in den Prozessraum und auf der vom Prozessraum abgewandten Seite des Bodens B in den Verteilerraum führen,
• – sich außerhalb der Waschkolonne eine Förderpumpe P2, die eine Saug- und eine Druckseite aufweist, und eine Quelle QS der Suspension S befinden, wobei
• – eine erste Förderverbindung E1 von der Quelle QS zur Saugseite der Förderpumpe P2, und
• – eine zweite Förderverbindung E2 von der Druckseite der Förderpumpe P2 in den Verteilerraum führt,
• – sich außerhalb der Waschkolonne gegebenenfalls eine Förderpumpe P3, die eine Saug- und eine Druckseite aufweist, und eine Quelle QT einer Steuerlauge befinden, wobei
• – eine erste Förderverbindung C1 von der Saugseite der Pumpe P3 zur Quelle QT, und
• – eine zweite Förderverbindung C2 von der Druckseite der Pumpe P3 in den Verteilerraum und/oder in den zwischen seinem oberen Ende und den Filtern F der Filterrohre gelegenen Längsabschnitt des Prozessraums führt, und wobei man bei der Durchführung des Trennverfahrens in seinem stationären Betrieb
• – mit der Pumpe P2 kontinuierlich einen Strom ST der Suspension S von der Quelle QS durch die Förderverbindungen E1, E2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne führt,
• – gegebenenfalls mit der Pumpe P3 einen Strom SL der Steuerlauge von der Quelle QT durch die Förderverbindungen C1, C2 über den Verteilerraum und die Durchgänge U hindurch und/oder direkt in den Prozessraum der Waschkolonne führt,
• – über die Filter F der Filterrohre insgesamt einen Strom SM umfassend Mutterlauge und gegebenenfalls Steuerlauge als Ablaugestrom in das Filterrohrinnere hinein- und über die Filterrohre aus der Waschkolonne herausführt, und diesen aus der Waschkolonne herausgeführten Ablaugestrom SM als die Quelle QT für die Steuerlauge verwendet,
• – durch die Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum der Waschkolonne die Ausbildung eines Kristallbetts an Acrylsäurekristallen aufrechterhält, das eine dem oberen Ende des Prozessraums zugewandte Aufbaufront (die Aufbaufront bezeichnet den Übergang von der Kristallsuspension zum (verdichteten) Kristallbett und ist durch einen relativ abrupten Anstieg des Kristallgehalts je Volumeneinheit gekennzeichnet) aufweist, an der sich kontinuierlich Kristalle des zugeführten Stroms ST der Suspension S (des Suspensionsstroms) ans Kristallbett anlagern,
• – das Kristallbett durch die aus dem hydraulischen Strömungsdruckverlust der Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum resultierende Kraft von oben nach unten an den Filtern F vorbei auf die rotierende Abtrageinrichtung zuführt,
• – mit der rotierenden Abtrageinrichtung vom auf sie stoßenden Kristallbett Acrylsäurekristalle abträgt,
• – den Strom der abgetragenen Acrylsäurekristalle durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei in den sich in Förderrichtung des Kristallbetts an den Prozessraum anschließenden Kristallschmelzeraum führt, und in dem durch den Kristallschmelzeraum geführten Kristallschmelzekreis (vereinfacht häufig auch nur „Schmelzkreis”) durch Eintrag von Wärme mit dem Wärmeübertrager W zu einem Kristallschmelzestrom aufschmilzt, und
• – den Durchfluss des Auslasses A so regelt, dass, bezogen auf die Stärke des vorgenannten Kristallschmelzestroms, vom Kristallschmelzeraum ausgehend ein Teilstrom an Kristallschmelze als Waschschmelzestrom durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei gegen die Bewegungsrichtung des Kristallbetts in den Prozessraum zurückströmt, wo er im abwärts geförderten Kristallbett aufsteigt und dabei von den Kristallen im Kristallbett verbliebene und mit diesem unter die Filter F geförderte Mutterlauge abwäscht und zurückdrängt, wobei sich im von den Filtern F bis zum unteren Ende des Prozessraums erstreckenden Längsabschnitt des Prozessraums im Kristallbett eine Waschfront ausbildet, die das Kristallbett von oben nach unten in eine Mutterlaugezone und in eine Waschschmelzezone aufteilt, und der restliche Teilstrom des vorgenannten Kristallschmelzestroms den Kristallschmelzekreis durch den Auslass A verlässt.

The present invention relates to a method of starting up a separation process for the purification separation of acrylic acid crystals from a suspension S of their crystals in mother liquor with a device comprising a hydraulic wash column having a rotationally symmetrical to its running from top to bottom longitudinal axis process space, of a cylindrical Mantle wall and two on the symmetry axis opposite ends is limited, wherein

• - extending from the upper end of the process space parallel to the longitudinal axis of one or more filter tubes through the process space, which run towards the upper end of the opposite end of the process space, and in the lower end of the process space facing half of the process space at least one filter F, which forms the only direct connection between the respective filter tube interior and the process space, and are led out of the wash column outside the process space,
• The quotient Q = L / D from the distance L between the upper and the lower end of the process space and the diameter D of the process space is 0.3 to 4,
• - Directed at the bottom of the process chamber down the crystal melt space of the wash column, wherein between the two spaces integrated a rotatable Abtrageinrichtung and through the crystal melt space a crystal melt cycle is passed, which except the crystal melt space
• A conveying pump P1 located outside the washing column and having a suction and a pressure side,
• A first conveying connection G1, which leads from the crystal melt space of the washing column to the suction side of the feed pump P1,
• A second conveying connection G2, which leads back from the pressure side of the feed pump P1 into the crystal melt space of the washing column and has an outlet A from the flow control circuit with variable flow, and
• A heat exchanger W via which either the conveying connection G1 from the crystal melt space to the suction side of the feed pumps P1 or the feed connection G2 is guided from the pressure side of the feed pump P1 to the crystal melt space,
• - Upstream of the upper end of the process space, a distribution space is upstream, which is separated from the process space at least by a bottom B, which has passages U, which on the process space facing side of the bottom B in the process room and on the side facing away from the process space lead the floor B into the distributor room,
• - Be outside the wash column, a feed pump P2, which has a suction and a pressure side, and a source QS of the suspension S, wherein
• A first delivery connection E1 from the source QS to the suction side of the delivery pump P2, and
• A second conveying connection E 2 leads from the pressure side of the feed pump P 2 into the distributor space,
• - Outside the scrubbing column optionally a delivery pump P3, which has a suction and a pressure side, and a source QT of a control liquor, wherein
• A first delivery connection C1 from the suction side of the pump P3 to the source QT, and
• A second conveying connection C2 leads from the pressure side of the pump P3 into the distributor space and / or into the longitudinal section of the process space located between its upper end and the filters F of the filter tubes, and in the steady-state operation of the separation process
• - With the pump P2 continuously a stream ST of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and through the passages U passes into the process space of the wash column,
• Optionally with the pump P3, a flow SL of the control liquor from the source QT through the feed connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column,
• Via the filter F of the filter tubes a total of a stream SM comprising mother liquor and optionally control liquor as Ablaugestrom in the filter tube inside and leads out via the filter tubes from the wash column, and this led out of the wash column Ablaugestrom SM used as the source QT for the control liquor
• - Maintains the formation of a crystal bed of acrylic acid crystals by the mother and optionally Steuerlaugeführung in the process space of the wash column, which faces the upper end of the process space build-up front (the construction front refers to the transition from the crystal suspension to (compacted) crystal bed and is characterized by a relatively abrupt increase of the crystal content per unit volume indicated), at which crystals of the supplied stream ST of the suspension S (of the suspension stream) continuously accumulate on the crystal bed,
• - the crystal bed by the force resulting from the hydraulic flow pressure loss of the parent and possibly Steuerlaugeführung in the process space force from top to bottom on the filters F passes over to the rotating removal device,
• - with the rotating removal device from on she pushes off abutting crystal bed acrylic acid crystals,
• The current of the ablated acrylic acid crystals passes through the rotating removal device and / or past the rotating removal device into the crystal melt space adjoining the process space in the conveying direction of the crystal bed, and in the crystal melt circuit guided through the crystal melt space (often also simplifies only "melt circle") by melting heat with the heat exchanger W melts to a crystal melt stream, and
• - Regulates the flow of the outlet A so that, based on the strength of the aforementioned crystalline melt stream, starting from the crystal melt a partial stream of crystal melt as a wash melt stream through the rotating removal device and / or past the rotating removal device against the direction of movement of the crystal bed back into the process space , where it rises in the downwardly promoted crystal bed and thereby washes from the crystals remaining in the crystal bed and funded under this filter F mother liquor and pushed back, wherein in the extending from the filter F to the lower end of the process chamber longitudinal section of the process chamber in the crystal bed a wash front which separates the crystal bed from top to bottom into a mother liquor zone and into a wash melt zone, and the remaining substream of the aforesaid crystal melt stream leaves the crystal melt circuit through the outlet A.

Acrylic acid, either alone or in the form of their salts or their esters, is in particular for the preparation of polymers for various fields of application (eg adhesives, superabsorbents, Binder) of importance.

at the synthesis of acrylic acid is usually the same not as a pure product, but as part of a substance mixture, that in addition to the desired in high purity target compound still unwanted components such. For example, solvents, Contains starting compounds and by-products. Often this is the substance mixture is a liquid.

For example, acrylic acid is obtainable by catalytic gas phase oxidation of glycerine, propane, propene and / or acrolein. These starting compounds are in the gas phase, usually diluted with inert gases such as molecular nitrogen, CO ₂ and / or water vapor, passed in admixture with molecular oxygen at elevated temperatures and optionally elevated pressure over transition metal mixed oxide and oxidatively converted into an acrylic acid-containing product gas mixture ,

By Condensative and / or absorptive action is the acrylic acid hereinafter usually in the liquid (condensed) Phase in which already one Basic separation of acrylic acid from them in the product gas mixture accompanying compounds is achieved.

Under Application of various combinations of thermal separation processes (as such, for example, the rectification, the extraction, the Stripping, distillation, desorption, etc.) the acrylic acid finally in high purity separated the above-mentioned liquid phases. component such process combinations is often the process of suspension crystallization.

cools one is in its fluid state of aggregation, Acrylic acid-containing mixture from, and thereby causes the formation of crystals of acrylic acid, so is the Suspension crystallization is a possible method to to separate the acrylic acid from the mixture.

there One makes use of that during the growth of the acrylic acid resulting crystals in the liquid mixture in addition to acrylic acid constituents often Be be displaced from the crystal lattice and remain in the mother liquor (The term mother liquor should be understood in this document as that it both melting (in them accounts for a weight share of ≥ 50% by weight of the acrylic acid) from acrylic acid and impurities as well as solutions of acrylic acid and these optionally accompanying impurities in solvents or in solvent mixtures (on the acrylic acid in them a weight fraction of <50 wt .-%) with the proviso includes that when it cools down (i.e., upon cooling of the mother liquor) the acrylic acid crystallized).

Sometimes one already obtains in a single-stage suspension crystallization process high purity crystals of acrylic acid. If necessary, the Suspension crystallization can also be carried out in several stages.

The process of suspension crystallization for the crystallative separation of acrylic acid is known (cf. DE-A 10 2007 043758 . DE-A 10 2007 043748 . DE-A 10 2007 004960 . DE-A 10 2007 043759 and DE file number 10 2009 000987.6 ).

application point It is useful with the help of a secondary space and at least one primary room having indirect Heat exchanger (cooler or crystallizer) carried out.

By the transfer of heat from the the secondary space supplied (and this usually flows through), the acrylic acid-containing liquid mixture through the secondary space and the at least one primary space separating material partition (the heat transfer surface) through into a flowing in the at least one primary space Coolant into it, cools the liquid Substance mixture until its saturation limit exceeded with acrylic acid is and the liquid mixture of supersaturation by formation (by precipitation) of acrylic acid Counteracts crystals.

is the desired degree of crystallization (the term crystallization degree means the mass fraction or mass fraction of the in the resulting Suspension of crystals of acrylic acid in (liquid) residual mother liquor contained finely divided crystals reached on the total mass of the crystal suspension), the crystal suspension led out of the secondary room.

By Separating the acrylic acid crystals formed from the mother liquor can the acrylic acid in appropriate purity from the Isolated crystal suspension.

One crucial step, the purity of the separated acrylic acid significantly influenced, is the case for the Separation of the acrylic acid crystals from the mother liquor, the components other than acrylic acid in Enriched form as the uncrystallized portions containing acrylic acid, applied separation methods. This separation process can be multi-level, at least in the Often the last stage is preferably a separation with one hydraulic wash column is applied.

The Separation with a hydraulic wash column can but also the form the only separation stage. Basically, the separation comes with a hydraulic wash column the task to the contaminated Mother liquor as quantitatively as possible from the acrylic acid crystals to separate.

Separation processes for the purifying separation of acrylic acid crystals from a suspension of their crystals in mother liquor by means of a hydraulic scrubbing column are known (cf. DE file number 10 2009 000987.6 . WO 2006/111565 . DE-A 10 2007 004960 . EP-A 1 448 282 . US-A 2009/018347 . WO 03/041832 . WO 01/77056 . WO 04/35514 . WO 03/41833 . WO 02/9839 . DE-A 100 36 881 . WO 02/55469 . WO 03/78378 and the prior art cited in these documents).

A sample of a hydraulic wash column ( 0 ) show the 1 this font. It has a process space (B) which is rotationally symmetrical with respect to its longitudinal axis extending from top to bottom (all alphabetic or numerical addresses in brackets in this document refer to the figures enclosed with this document).

This is from a cylindrical shell wall ( 28 ) and two ends lying opposite each other on the axis of symmetry, whereby from the upper end ( 29 ) of the process space (B) parallel to its longitudinal axis one or more filter tubes ( 6 ) through the process space (B), which are at the end opposite the upper end ( 30 ) of the process space (B) (without piercing it), and in the half of the process space (B) facing the lower end of the process space (B) at least one filter F ( 7 ), which forms the only direct connection between the respective filter tube interior and the process space (B), and outside the process space (B) from the wash column (FIG. 0 ) are led out.

At the lower end of the process space (B), the crystal melt space (C) of the hydraulic wash column closes downwards (FIG. 0 ), wherein between the two rooms a rotatable removal device ( 16 ) and through the crystal melting chamber (C) a crystal melt cycle ( 31 ) is passed.

The removal device ( 16 ) is usually on a drive shaft ( 18 ), which is driven by a drive unit for rotation about its longitudinal axis, wherein it for the rotation of the removal device ( 16 ) transmits required torque to this.

The crystal melt circle ( 31 ) comprises, in addition to the crystal melt space (C), one outside the wash column ( 0 ) located feed pump P1 ( 11 ) having a suction and a pressure side. A first conveyor connection G1 ( 5 ) leads from the crystal melt space (C) of the wash column ( 0 ) via a heat exchanger W ( 9 ) to the suction side of the feed pump P1 ( 11 ). A second conveyor connection G2 ( 12 ) leads from the pressure side of the feed pump P1 ( 11 ) in the crystal melt space (C) of the wash column ( 0 ) back. It comprises an outlet A ( 3 ) with a controllable ( 10 ) Flow.

Upstream of the upper end of the process space (B) there is a distributor space (A) upstream of the process space (B) at least through a bottom B ( 32 ), which passes U ( 26 ), which lead on the process space side facing the bottom B in the process space (B) and on the side facing away from the process space (B) side of the bottom B in the distribution space (A).

Outside the hydraulic wash column ( 0 ) is a feed pump P2 ( 8th ) having a suction and a pressure side. A first conveyor connection E1 ( 33 ) leads from a source QS ( 1 ) of the suspension of acrylic acid crystals in mother liquor to the suction side of the feed pump P2 ( 8th ). A second conveyor connection E2 ( 34 ) leads from the pressure side of the feed pump P2 ( 8th ) in the distribution chamber (A) of the hydraulic wash column ( 0 ).

Outside the wash column ( 0 ) is usually (but not necessarily) in addition a feed pump P3 ( 13 ) having a suction and a pressure side. A first conveyor connection C1 ( 35 ) leads from the suction side of the pump P3 ( 13 ) to a source QT for so-called control liquor (as the control liquor is via the at least one filter tube ( 6 ) (spent) waste liquor used (see, eg. WO 2006/111565 )).

A second conveyor connection ( 36 ) leads from the pressure side of the pump P3 ( 13 ) in the distribution chamber (A) of the hydraulic wash column ( 0 ) and / or in between its upper end ( 29 ) and the at least one filter ( 7 ) of the at least one filter tube ( 6 ) located longitudinal section of the process space (B).

When carrying out the separation process in its stationary operation, the pump P2 ( 8th ) continuously a stream of the suspension of crystals of acrylic acid in the mother liquor through the conveyor connections E1 ( 33 ), E2 ( 34 ) via the distributor space (A) and through the passages U ( 26 ) through into the process space (B) of the wash column ( 0 ) (if necessary, in addition with the pump P3 ( 13 ) Control liquor through the conveyor connections C1 ( 35 ), C2 ( 36 ) via the distributor space (A) and through the passages U ( 26 ) and / or directly into the process space of the wash column ( 0 ) guided). The passages U ( 26 ) act on as uniform as possible distribution of the crystal suspension over the cross section of the process chamber (B). The pressure conditions in the filter tube interior as well as in the process chamber (B) are designed so that via the filter F ( 7 ) of the filter tubes ( 6 ) a stream comprising mother liquor and optionally control liquor as Ablaugestrom in the filter tube inside and over the filter tubes ( 6 ) (usually via a Ablaugesammelraum ( 27 ), the z. B. in the soil B can be integrated) from the wash column ( 0 ) (via a corresponding outlet) ( 2 ).

This Leakage current forms the source QT for an optionally used one Control liquor stream.

By the mother and optionally Steuerlaugeführung in the process space of the wash column ( 0 ) (first from top to bottom and then with superimposed cross-flow through the filters ( 7 ) in the filter tubes ( 6 ), the formation of a (compacted) "crystal bed (filter cake) s (for the first time during the start of the separation process) ( 4 ) Constantly updated on acrylic acid crystals and thus the formation of a crystal bed ( 4 ) maintained on acrylic acid crystals, which a the upper end of the process space facing mounting front ( 25 ), in which crystals of the stream of the suspension of acrylic acid crystals in mother liquor continuously fed to the (compacted) crystal bed filter cake ( 4 ) (in the literature, the construction front is often referred to as the filtration front).

Due to the hydraulic flow pressure loss of the mother and optionally control liquor on the flow path in the process space (B) through the crystal bed ( 4 ) resulting force becomes the crystal bed ( 4 ) and from top to bottom on the filters F ( 7 ) over (as a filter cake of the cross-filtration) on the rotating removal device ( 16 ).

With the rotating removal device ( 16 ) are caused by the crystal bed ( 4 ) Acrylic acid crystals continuously removed. The resulting stream of ablated acrylic acid crystals is depending on the design of the rotating removal device ( 16 passing therethrough and / or past the same in the conveying direction of the crystal bed ( 4 ) to the process space (B) subsequent crystal melt space (C), and in the guided through the crystal melt space (C) Kristallschmelzekreis ( 31 ) (or melt circle ( 31 )) by introducing heat with the heat exchanger W ( 9 Alternatively, the heat exchanger W may alternatively be integrated into the conveyor connection G2 for this purpose, and for this purpose more than one heat exchanger may also be integrated into the crystal melt circuit).

The flow rate of the outlet A ( 3 ) is regulated in this way ( 10 ), that, based on the strength of the aforementioned crystalline melt stream, from the crystal melt space (C) going from a partial stream of specifically comparatively lighter (having a lower mass density), and displaced by the crystals conveyed into the crystal melt space, crystal melt as a wash melt stream, depending on the embodiment rotating removal device ( 16 passing therethrough and / or past the same, against the direction of movement of the crystal bed ( 4 flows back (the ascending Waschschmelzemassenstrom is normally not greater than the over the crystal suspension in the process chamber (B) guided crystal mass flow), where it in the downwardly conveyed crystal bed ( 4 ) rises while the crystals in the crystal bed ( 4 ) and with this under the filter F ( 7 ) Waxed and filtered mother liquor while the mother liquor pushes back upwards, whereby in the filter F ( 7 ) to the lower end of the process space ( 30 ) extending longitudinal portion of the process space (B) in the crystal bed ( 4 ) a wash front ( 37 ) forming the crystal bed from top to bottom into a mother liquor zone (extending from the wash front ( 37 ) to the construction front) and into a wash melt zone (extending from the wash front ( 37 ) to the lower end of the crystal bed ( 4 )), and the remaining partial flow of the aforementioned crystal melt stream the melt circuit ( 31 ) through the outlet A ( 3 ) leaves (the feed pump P1 (11) acts as a pure circulation pump).

D. h., By the opposite to the conveying direction of the crystal bed ( 4 ) flowing wash melt is the below the filter F ( 7 ) only with a residual amount of mother liquor impregnated crystal bed ( 4 ) as a result practically in the process space (B) upwardly flowing wash melt pressed (and vice versa) and as a washing action (further possible washing effects are on page 9 of the WO 01/77056 listed in the "Filtration" in the crystal bed ( 4 ) remaining mother liquor simply pushed back by the wash melt to a limited extent. With a corresponding adjustment of the wash melt stream to the boundary conditions of the separation process, a stationary state occurs, so that at a defined height in the process space (B) a so-called wash front (FIG. 37 ) (in fact, a largely stable "phase boundary" between wash melt (pure melt) and mother liquor). The wash front is defined as the height in the section of the process space (B) extending from the lower end of the crystal bed to the upper filter edge, on which the highest temperature and concentration gradients occur, viewed over the process space height.

Above and below the wash front ( 37 ) essentially reach the height-dependent temperatures (concentrations) comparatively quickly (usually within a height change ("wash front" called) of less than ± 5 cm) a height-dependent each no longer changing value.

This is in the area above the wash front ( 37 ) substantially the temperature (the corresponding concentration) of the process space (B) supplied suspension of acrylic acid crystals in the mother liquor and in the area below the wash front ( 37 ) the melting point temperature (the corresponding concentration) of the wash melt (pure melt). The height position of the wash front ( 37 ) can be varied to a limited extent by controlling the ratio of crystal mass flow delivered in the process space to countercurrent wash melt stream. Below a respective minimum length of the wash melt zone, the washing effect (the separation effect) becomes better with increasing length of the wash melt zone. In terms of application, the wash front ( 37 ) 50 to 200 mm, often up to 100 mm below the lower filter edge (below the lower edge of the filter F ( 7 )).

To start up the separation process to be carried out in stationary operation as described above for the purifying separation of acrylic acid crystals from their suspension in mother liquor, the US Pat WO 01/77056 to feed the corresponding Kristallisatsuspension (crystal suspension) directly into the unfilled hydraulic wash column and through the filters of the filter tubes initially only mother liquor dissipate until it has formed in the process space of the wash column in the desired bed height, a crystal fixed bed. Subsequently, removal device and crystal melt circuit are put into operation and after a certain flow with closed flow of the outlet of the crystal melt circuit selbiger adjusted so that the desired position of the wash front results.

adversely in this way of commissioning, however, that is with her in an economically relevant frequency one Blockade of the crystal melt circle is accompanied. This is usually on it attributed to that in case of an immediate feed-in the crystal suspension in the unfilled hydraulic wash column until the time you reach the desired bed height to a greater extent already crystallizate in the Kristallschmelzekreis arrives. If the same is then put into operation, they swirl previously settling crystals (which, while essentially no compression experienced) abruptly, from which the described blockade result (especially if you take into account that the feed pump for the crystal melt cycle (the melt pump) their full capacity first reached after a certain start-up time).

in principle can counteract the appearance described above be that one at the start of the hydraulic wash column First, the melting circle comprising the crystal melt space as well as the process space of the previously unfilled wash column with a starting liquid containing acrylic acid filled so that the filling level of the starting liquid in Process space at least overruns the removal device, and only then the filling of the hydraulic scrubbing column with crystal suspension and optionally Waste liquor continues as a control liquor.

In the case of hydraulic scrubbing columns, the quotient Q = L / D from the distance L between the upper and lower end of the process space and the diameter D of the process space is 0.3 to 4, are in such a procedure in the course of further operation of the separation process with relatively high regularity and after already relatively short periods of operation in the delivery connection E2 and the distribution chamber comprehensive However, space area working pressures occurred that led to the bursting of built-in rupture disk for safety reasons in this area.

The Object of the present invention was in view of the described Problems in finding appropriate remedies.

• – sich vom oberen Ende des Prozessraums parallel zu dessen Längsachse ein oder mehrere Filterrohre durch den Prozessraum erstrecken, die auf das dem oberen Ende gegenüberliegende untere Ende des Prozessraums zulaufen (ohne es zu durchstoßen), und in der dem unteren Ende des Prozessraums zugewandten Hälfte des Prozessraums wenigstens ein Filter F, das die einzige direkte Verbindung zwischen dem jeweiligen Filterrohrinneren und dem Prozessraum bildet, aufweisen sowie außerhalb des Prozessraums aus der Waschkolonne herausgeführt werden,
• – der Quotient Q = L/D aus dem Abstand L zwischen dem oberen und dem unteren Ende des Prozessraums und dem Durchmesser D des Prozessraums 0,3 bis 4 beträgt,
• – sich am unteren Ende des Prozessraums nach unten gerichtet der Kristallschmelzeraum der Waschkolonne anschließt, wobei zwischen den beiden Räumen eine rotationsfähige Abtrageinrichtung integriert und durch den Kristallschmelzeraum ein Kristallschmelzekreis hindurchgeführt ist, der außer dem Kristallschmelzeraum
• – eine außerhalb der Waschkolonne befindliche Förderpumpe P1, die eine Saug- und eine Druckseite aufweist,
• – eine erste Förderverbindung G1, die vom Kristallschmelzeraum der Waschkolonne zur Saugseite der Förderpumpe P1 führt,
• – eine zweite Förderverbindung G2, die von der Druckseite der Förderpumpe P1 in den Kristallschmelzeraum der Waschkolonne zurückführt und einen Auslass A aus dem Schmelzkreis mit regelbarem Durchfluss aufweist, sowie
• – einen Wärmeübertrager W, über den entweder die Förderverbindung G1 vom Kristallschmelzeraum zur Saugseite der Förderpumpen P1, oder die Förderverbindung G2 von der Druckseite der Förderpumpe P1 zum Kristallschmelzeraum geführt ist, umfasst,
• – dem oberen Ende des Prozessraums nach oben gerichtet ein Verteilerraum vorgelagert ist, der vom Prozessraum wenigstens durch einen Boden B getrennt ist, welcher Durchgänge U aufweist, die auf der dem Prozessraum zugewandten Seite des Bodens B in den Prozessraum und auf der vom Prozessraum abgewandten Seite des Bodens B in den Verteilerraum führen,
• – sich außerhalb der Waschkolonne eine Förderpumpe P2, die eine Saug- und eine Druckseite aufweist, und eine Quelle QS der Suspension S befinden, wobei
• - eine erste Förderverbindung E1 von der Quelle QS zur Saugseite der Förderpumpe P2, und
• – eine zweite Förderverbindung E2 von der Druckseite der Förderpumpe P2 in den Verteilerraum führt,
• – sich außerhalb der Waschkolonne gegebenenfalls eine Förderpumpe P3, die eine Saug- und eine Druckseite aufweist, und eine Quelle QT einer Steuerlauge befinden, wobei
• – eine erste Förderverbindung C1 von der Saugseite der Pumpe P3 zur Quelle QT, und
• – eine zweite Förderverbindung C2 von der Druckseite der Pumpe P3 in den Verteilerraum und/oder in den zwischen seinem oberen Ende und den Filtern F der Filterrohre gelegenen Längsabschnitt des Prozessraums führt, und wobei man bei der Durchführung des Trennverfahrens in seinem stationären Betrieb
• – mit der Pumpe P2 kontinuierlich einen Strom ST der Suspension S von der Quelle QS durch die Förderverbindungen E1, E2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne führt,
• – gegebenenfalls mit der Pumpe P3 einen Strom SL der Steuerlauge von der Quelle QT durch die Förderverbindungen C1, C2 über den Verteilerraum und die Durchgänge U hindurch und/oder direkt in den Prozessraum der Waschkolonne führt,
• – über die Filter F der Filterrohre insgesamt einen Strom SM umfassend Mutterlauge und gegebenenfalls Steuerlauge als Ablaugestrom in das Filterrohrinnere hinein- und über die Filterrohre aus der Waschkolonne herausführt, und diesen aus der Waschkolonne herausgeführten Ablaugestrom SM als die Quelle QT für die Steuerlauge verwendet,
• – durch die Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum der Waschkolonne die Ausbildung eines Kristallbetts an Acrylsäurekristallen aufrechterhält, das eine dem oberen Ende des Prozessraums zugewandte Aufbaufront aufweist, an der sich kontinuierlich Kristalle des zugeführten Stroms ST der Suspension S ans Kristallbett anlagern,
• – das Kristallbett durch die aus dem hydraulischen Strömungsdruckverlust der Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum resultierende Kraft von oben nach unten an den Filtern F vorbei auf die rotierende Abtrageinrichtung zu fördert,
• – mit der rotierenden Abtrageinrichtung vom auf sie stoßenden Kristallbett Acrylsäurekristalle abträgt,
• – den Strom der abgetragenen Acrylsäurekristalle durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei in den sich in Förderrichtung des Kristallbetts an den Prozessraum anschließenden Kristallschmelzeraum fördert, und in dem durch den Kristallschmelzeraum geführten Kristallschmelzekreis (bzw. Schmelzkreis) durch Eintrag von Wärme mit dem Wärmeübertrager W zu einem Kristallschmelzestrom aufschmilzt, und
• – den Durchfluss des Auslasses A so regelt, dass, bezogen auf die Stärke des vorgenannten Kristallschmelzestroms, vom Kristallschmelzeraum ausgehend ein Teilstrom an Kristallschmelze als Waschschmelzestrom durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei gegen die Bewegungsrichtung des Kristallbetts in den Prozessraum zurückströmt, wo er im abwärts geförderten Kristallbett aufsteigt und dabei von den Kristallen die im Kristallbett verbliebene und mit diesem unter die Filter F geförderte Mutterlauge abwäscht und zurückdrängt, wobei sich im von den Filtern F bis zum unteren Ende des Prozessraums erstreckenden Längsabschnitt des Prozessraums im Kristallbett eine Waschfront ausbildet, die das Kristallbett von oben nach unten in eine Mutterlaugezone und in eine Waschschmelzezone aufteilt, und der restliche Teilstrom des vorgenannten Kristallschmelzestroms den Schmelzkreis durch den Auslass A verlässt, zur Verfügung gestellt, das dadurch gekennzeichnet ist, dass man bei der Inbetriebnahme des Trennverfahrens zur erstmaligen Ausbildung des Kristallbetts im Prozessraum
• – den den Kristallschmelzeraum umfassenden Schmelzkreis und den Prozessraum der zuvor unbefüllten Waschkolonne mit einer Acrylsäure enthaltenden Anfahrflüssigkeit AT zunächst so befällt, dass die Füllhöhe der Anfahrflüssigkeit AT im Prozessraum wenigstens die Abtrageinrichtung überragt,
• – anschließend die Befüllung der Waschkolonne fortsetzt, indem man mit der Pumpe P2 einen Strom ST* der Suspension S von der Quelle QS durch die Förderverbindungen E1, E2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne und von dem dabei durch die Filterrohre aus der Waschkolonne herausgeführten Ablaugestrom SM* als Quelle QT* gegebenenfalls mit der Pumpe P3 einen Teilstrom als Steuerlaugestrom SL* durch die Förderverbindungen C1, C2 über den Verteilerraum und die Durchgänge U hindurch und/oder direkt in den Prozessraum der Waschkolonne führt, und dies wenigstens so lange, bis der Zeitpunkt t_S erreicht ist, bei dem der Differenzdruck P_D = P_K – P_V, wobei P_K der an einer beliebig ausgewählten Stelle im Kristallschmelzeraum zu einem bestimmten Zeitpunkt der Zufuhr des Stroms ST* jeweils bestehende Druck und P_V der zum jeweils gleichen Zeitpunkt an einer beliebig ausgewählten Stelle im Verteilerraum jeweils bestehende Druck ist, in Abhängigkeit von der Dauer der Zufuhr des Stroms ST* nicht mehr ansteigt oder konstant bleibt, sondern plötzlich abnimmt, und dies mit der Maßgabe, dass
• – bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F, berechnet als der arithmetische Mittelwert des während der Zufuhr des Stroms ST* durch die Filter F der Filterrohre zum jeweiligen Zeitpunkt insgesamt strömenden Ablaugestroms SM* (dies ist der Ablaugegesamtstrom; d. h. die Summe aller in den einzelnen Filterrohren abgeführten Ablaugeströme, wobei über alle Filterrohre summiert wird), geteilt durch die Gesamtfläche aller Filter F, nicht mehr als 80 m³/(m²·h) beträgt,
• – die Acrylsäure enthaltende Anfahrflüssigkeit AT eine solche ist, aus der beim Abkühlen bis zur einsetzenden Kristallisation die sich bei der Kristallisation bildenden Kristalle Acrylsäurekristalle sind, und
• – zwischen der in Grad Celsius angegebenen Kristallbildungstemperatur T^KB dieser Acrylsäurekristalle in der Anfahrflüssigkeit AT und der in Grad Celsius angegebenen Temperatur T^S der Suspension S des Stroms ST* die Beziehung TKB ≤ TS + 15°C

erfüllt ist.Accordingly, a method of starting a separation process for purifying separation of acrylic acid crystals from a suspension S of their crystals in mother liquor with a device comprising a hydraulic wash column having a rotationally symmetrical to its top-to-bottom longitudinal axis process space, of a cylindrical shell wall and two ends opposite to each other on the symmetry axis, wherein

• - extending from the upper end of the process chamber parallel to its longitudinal axis, one or more filter tubes through the process space, which run on the upper end opposite the lower end of the process space (without piercing it), and in the lower end of the process space facing half of Process space at least one filter F, which forms the only direct connection between the respective filter tube interior and the process space, and are led out of the wash column outside the process space,
• The quotient Q = L / D from the distance L between the upper and the lower end of the process space and the diameter D of the process space is 0.3 to 4,
• - Directed at the bottom of the process chamber down the crystal melt space of the wash column, wherein between the two spaces integrated a rotatable Abtrageinrichtung and through the crystal melt space a crystal melt cycle is passed, which except the crystal melt space
• A conveying pump P1 located outside the washing column and having a suction and a pressure side,
• A first conveying connection G1, which leads from the crystal melt space of the washing column to the suction side of the feed pump P1,
• A second conveying connection G2, which leads back from the pressure side of the feed pump P1 into the crystal melt space of the washing column and has an outlet A from the melt circuit with controllable flow, as well as
• A heat exchanger W via which either the conveying connection G1 from the crystal melt space to the suction side of the feed pumps P1 or the feed connection G2 is guided from the pressure side of the feed pump P1 to the crystal melt space,
• - Upstream of the upper end of the process space, a distribution space is upstream, which is separated from the process space at least by a bottom B, which has passages U, which on the process space facing side of the bottom B in the process room and on the side facing away from the process space lead the floor B into the distributor room,
• - Be outside the wash column, a feed pump P2, which has a suction and a pressure side, and a source QS of the suspension S, wherein
• a first delivery connection E1 from the source QS to the suction side of the delivery pump P2, and
• A second conveying connection E 2 leads from the pressure side of the feed pump P 2 into the distributor space,
• - Outside the scrubbing column optionally a delivery pump P3, which has a suction and a pressure side, and a source QT of a control liquor, wherein
• A first delivery connection C1 from the suction side of the pump P3 to the source QT, and
• A second conveying connection C2 leads from the pressure side of the pump P3 into the distributor space and / or into the longitudinal section of the process space located between its upper end and the filters F of the filter tubes, and in the steady-state operation of the separation process
• - With the pump P2 continuously a stream ST of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and through the passages U passes into the process space of the wash column,
• Optionally with the pump P3, a flow SL of the control liquor from the source QT through the feed connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column,
• Via the filter F of the filter tubes a total of a stream SM comprising mother liquor and optionally control liquor as Ablaugestrom in the filter tube inside and leads out via the filter tubes from the wash column, and this led out of the wash column Ablaugestrom SM used as the source QT for the control liquor
• - Maintains the formation of a crystal bed of acrylic acid crystals by the mother and optionally Steuerlaugeführung in the process space of the wash column, which has a the upper end of the process space facing the mounting front, at which continuously crystals of the supplied stream ST of the suspension S ans Kris attach a tall bed,
• - Promotes the crystal bed by the force resulting from the hydraulic flow pressure loss of the parent and possibly Steuerlaugeführung in the process space from top to bottom on the filters F on the rotating Abtragageinrichtung
• - removes acrylic acid crystals from the crystal bed impinging on them with the rotating removal device,
• - Promotes the flow of the ablated acrylic acid crystals through the rotating Abtragageinrichtung and / or on the rotating Abtragageinrichtung in the subsequent in the conveying direction of the crystal bed to the process space crystal melt space, and in the guided through the crystal melt space crystal melt (or melt circle) by the entry of heat melts with the heat exchanger W to a crystal melt stream, and
• - Regulates the flow of the outlet A so that, based on the strength of the aforementioned crystalline melt stream, starting from the crystal melt a partial stream of crystal melt as a wash melt stream through the rotating removal device and / or past the rotating removal device against the direction of movement of the crystal bed back into the process space , where it rises in the downwardly conveyed crystal bed and thereby washes off the crystals remaining in the crystal bed and with this under the filter F funded mother liquor and pushed back, wherein extending from the filters F to the lower end of the process space extending longitudinal section of the process chamber in the crystal bed A wash front is formed which divides the crystal bed from top to bottom into a mother liquor zone and into a wash melt zone, and the remaining part stream of the aforementioned crystal melt stream leaves the melt circuit through the outlet A, provided, which is characterized in that at the start of the separation process for the first-time formation of the crystal bed in the process room
• - the melt cycle comprising the crystal melt space and the process space of the previously unfilled wash column are initially filled with an acrylic acid-containing start-up liquid AT such that the filling level of the start-up liquid AT in the process space exceeds at least the removal device,
• - Subsequently, the filling of the scrubbing column continues by passing with the pump P2 a flow ST * of the suspension S from the source QS through the conveyor connections E1, E2 through the distributor space and through the passages U in the process space of the wash column and of the case the filter tubes from the wash column led out Ablaugestrom SM * as a source QT * optionally with the pump P3 a partial flow as Steuerlaugestrom SL * through the conveyor connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column leads, and this at least until the time t _{S is} reached, at which the differential pressure P _D = P _K - P _V , where P _K of at any selected point in the crystal melt space at a given time of supply of the current ST * each existing pressure and P _V of each at the same time at any selected point in the distribution space existing Dru ck is, depending on the duration of the supply of the current ST * no longer increases or remains constant, but suddenly decreases, and this with the proviso that
• - up to the time t _{S is} the average surface loading of the filter F, is calculated as the arithmetic average of the * through the filters F of the filter tubes at the time a total of flowing Ablaugestroms SM * (during the supply of the stream ST this is Ablaugegesamtstrom, ie the sum of all in the individual filter tubes discharged leaching flows, being summed over all filter tubes), divided by the total area of all filters F, not more than 80 m ³ / (m ² · h),
• The starting liquid AT containing acrylic acid is one from which, on cooling to onset of crystallization, the crystals forming on crystallization are acrylic acid crystals, and
• - Between the specified in degrees Celsius crystal formation temperature T ^{KB of} acrylic acid crystals in the start-up liquid AT and the specified in degrees Celsius temperature T ^{S of} the suspension S of the stream ST * the relationship T KB ≤ T S + 15 ° C

is satisfied.

According to the invention, the arithmetic mean value (also referred to in this document as "average filter surface load" or "mean surface load of the filters F") of the total bleed flow stream SM * flowing through the filters F of the filter tubes at the time of supply of the stream ST * is divided by the total area of all filters F, not more than 75, and more preferably not more than 70 m ³ (m ² · h) until time t _S.

In general, the aforesaid arithmetic mean normalized to the total area of all filters F (the average filter area load) will be at least 5 or at least 10, with advantage at least 15 and with particular advantage at least 20 m ³ / (m ² .h).

D. h., According to the invention favorable ranges for the aforementioned normalized to the total area of all filters F arithmetic mean (the average filter surface load) are the ranges> 0 to 80 m ³ / (m ² · h), preferably 5 to 75 m ³ / ( m ² · h), particularly preferably 10 to 70 m ³ / (m ² · h), very particularly preferably 15 to 65 m ³ / (m ² · h) and with particular advantage 20 to 50 m ³ / (m ² · H).

Everything The aforementioned and all other statements made in this document apply in particular then if the quotient Q = L / D ≥ 0.5 or ≥ 0.7 is. Of course, all of the above and Everything else in this document also said, if L / D ≤ 3.5, or ≤ 3, or ≤ 2.5, or ≤ 2. Not too large quotients Q = L / D are advantageous according to the invention. This also against the background that during transport of the crystal bed in the process space along the contact surface between crystal bed and inner wall of the process space to be overcome frictional resistance, based on the volume of the crystal bed, with a decreasing Q drops.

application point expediently, the distance L between the upper and the lower end of the process space ≥ 0.5 m, preferably ≥ 0.8 m and particularly preferably ≥ 1 m. Usually will L, however, ≤ 5 m and often ≤ 4 m or ≤ 3 m be.

Cheap Inner diameter D of a process space of a suitable according to the invention hydraulic wash column are in the range of 300 to 3000 mm, preferably in the range of 700 to 2000 mm.

In the process according to the invention, favorable process space internal volumes accessible to the crystals amount to 0.05 to 20 m ³ , advantageously 0.2 to 10 m ^3, and particularly advantageously 1 to 5 m ³ .

Under the surface of a filter F is in this document Inflow area (not its "open" filter area, d. h., not the "free holes" of the porous material) understood. That is, a filter extends F at an outer radius r of the associated filter tube and a height a of the filter F over the entire Pipe circumference, the relevant according to the invention Surface of the filter F thus 2π · r · a.

Of the Diameter D of the process space in this document means its inner diameter. Of the Distance L between the top and bottom of the process space means in this document the clear distance between the bottom of the passages U having bottom B and the surface of the rotating body described by the rotary removal device.

If, during the startup of the separation process according to the invention, the bleed stream SM * flowing through the filters F of the filter tubes of the hydraulic scrubbing column at the time t _S at time t _s is plotted as ordinate against time t as abscissa the area in the time range t = 0 (beginning of the supply of the current ST *) up to the time t = t _S under the resulting curve divided by t _S , the arithmetic mean value used in this document during the supply of the current ST * up to the time t _S through the filter F of the filter tubes at the respective time total flowing Ablaugestroms SM *. Dividing it by the total area of all filters F yields the mean surface loading of the filter F.

In this document, the crystallization temperature T ^{KB of} a start-up liquid AT is understood to mean the temperature at which the formation of acrylic acid crystallization begins from this liquid during its cooling (the possibility of the occurrence of supersaturation phenomena being disregarded). Alternatively, the crystallization temperature T ^{KB of} a starting liquid AT is the temperature which is present in the starting liquid AT at the moment which is reached if, starting from a crystal suspension or crystallizate suspension (suspension of acrylic acid crystallizate) produced from the starting liquid AT by cooling the same. under constant (ideally ideal) mixing heat to melt the acrylic acid crystals contained in the Kristallisatsuspension and the last acrylic acid crystal is just melted (it is sometimes referred to in the literature as the dissolution temperature or crystallization initiation temperature).

In accordance with the invention, the temperatures T ^KB and T ^S advantageously fulfill the relation T ^KB ≦ T ^S + 10 ° C. and, particularly advantageously, the relation T ^KB ≦ T ^S + 5 ° C.

In principle, the crystal formation temperature T ^{KB of} the starting liquid AT can also be below the temperature of the stream ST * of acrylic acid crystals in mother liquor fed in the commissioning of the hydraulic scrubbing column according to the invention.

As a rule, however, T ^KB in the process according to the invention will not be more than 20 ° C., usually not more than 10 ° C., and often not more than 5 ° C. below T ^s . As starting liquid AT come for the inventive method z. B. separated from the suspension S (eg., By filtration) mother liquor, or re-molten after its production suspension S, or that liquid from which the suspension S has been generated by cooling, or the melt of a Suspension S previously in a (the) hydraulic scrubbing column cleaning separated acrylic acid crystals (ie pure melt), or mixtures of two or more of the above-mentioned possible starting liquids into consideration.

By the term "pump", this document means pumps for conveying liquids (ie, substantially incompressible media). They have a suction side and a pressure side. By means of a conveying connection connected to its suction side, the feed pump sucks the liquid to be conveyed (or suspension). In the pump, the liquid to be delivered is brought to an elevated pressure and pushed away by a connected with their pressure side conveying connection in the desired conveying direction. From an application point of view, the relevant conveying connections are most simply pipelines (delivery lines) through which delivery can take place. For the procedure according to invention in particular the in the DE-A 10228859 and in the DE Application number 102008054587.2 described feed pumps (especially the centrifugal pumps described in these documents). For the promotion of the suspension S are in particular radial centrifugal pumps with semi-open radial impeller (see. DE Application number 102008054587.2 ). Access to the suction side or pressure side of the respective pump can usually be opened or locked by means of corresponding fittings. In particular, in terms of application technology, the feed pump P2 is advantageously a "speed-controlled" feed pump. D. h., The setting of the resulting flow rate is preferably carried out via an adaptation of the speed and not via an adjustment of the free cross section in the conveyor connection (not via a control valve), since in the latter case, the risk that it comes to a closure of the conveyor connection (eg, by crystal clusters) is increased.

Further it is for the procedure according to the invention beneficial when starting the separation process for the first training of the crystal bed in the process room the the Crystal melt space comprising melt circle (crystal melt circle) and the process space of the previously unfilled wash column with a starting liquid containing acrylic acid AT initially filled so that the filling height the starting liquid AT in the process space at least the Filter F surmounted, preferably at least to the middle the distance L from the bottom to the top of the process space protrudes, more preferably at least until the last quarter of Distance L from the bottom to the top of the process space protrudes, most preferably at least to the upper end of the process space towers, even more advantageous beyond the process room to protrudes into the distributor space and the volume of the same to at least fills in half, and best over the process space extends into the distribution room and the volume completely complies with it (application technology is useful in the latter case additionally the conveyor connection E2 (possibly also the conveyor connection E1) and an optionally held, the pump P3 and the conveyor connections C1, C2 more comprehensive, control circuit with the start-up liquid AT filled).

Does the hydraulic wash column on a rinsing fluid system, as it is z. B. the EP-A 1448282 recommends and the 2 this document shows ( 42 ), the described filling takes place according to the invention preferably via this rinsing liquid system.

With the filling of the process space with the starting liquid AT, a corresponding filling of the filter tubes is simultaneously accompanied in the method according to the invention in the sense of tubes communicating via the filters F with the process space. Like in the WO 2006/111565 1, the pressure on the filters F in the filter tube interior is kept lower than the pressure on the filters F on the process space side during steady-state operation of a separation process in a hydraulic wash column.

This also applies to the commissioning according to the invention as soon as the spaces of the hydraulic scrubbing column are completely filled with condensed phase and subsequently continued with the supply of the stream ST * of the crystal suspension S and optionally the Steuerlaugestroms SL * (up to this time, the in the hydraulic wash column gas phase located displaced and discharged via an onboard washing column head valve (the valve is open for as long as long as the oscillation frequency of an in this respect mounted vibrator a surrounding him gas phase reflects (the differential pressure P _D = P _K - P _V takes initially steadily until the condensed phase reaches that point in the distribution space at which the detection of the pressure P _V takes place, thereafter the differential pressure P _D remains essentially constant initially)).

As detailed Analysis of operations during commissioning of a hydraulic Washing column by the applicant occurs subsequently in the hydraulic wash column probably to the following procedures.

The impressed by the above-described pressure difference liquid flow in the process chamber of the hydraulic wash column from top to bottom and then selbiger superimposed transversely through the filter F into the filter tubes into, leads, with sustained supply of Strom ST * and optionally the Steuerlaugestroms SL *, first to a precoution of acrylic acid crystals in the local environment of the respective filter F. From the resulting as they flow through the increased local pressure loss, a compaction of these alluviums to snowball-like filter cake around the filter F around. These filter cake begin to grow in both the width and in the length (in particular in the amount) in the further course.

If the filter cake (the compacted bed of crystals) extends over the entire cross-section of the process space for the first time in closed form, the differential pressure P _D = P _K -P _V suddenly begins to decrease (previously existing channels which can be overcome for liquid without appreciable pressure loss ( with a comparatively large flow cross-section), through which the crystal melt space and the distribution space were able to communicate with one another virtually undisturbed, are now compacted away). The time at which this is achieved is the time t _S.

Obviously It is now in the relevant area according to the invention the quotient Q = LID not possible, the above Finish the crystal bed without breaking the crystal bed not already at least in a subset of the passes U in or through it has grown through. Will now be in further course of commissioning of the separation process at the transition in the stationary operating state, the transport of the "closed" crystal bed absorbed, can in individual passes U filter cake remain ("get stuck"). The probability for this event obviously grows with the strength of the commissioning per total filter area total outflowing Leakage stream SM *, the degree The compaction in the filter cake determines decisively. remains but filter cake in individual passes U, so be from these in the further course of the separation process themselves in the distribution room in growing snowballs from filter cake.

The latter conditionally one to maintain the separation process above average Increase in the required delivery pressure of the suspension S and finally the bursting of the protective rupture disk.

Accordingly, it is advantageous for the process according to the invention, when at least 50%, preferably 75% or 90% and more preferably during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S and optionally the Steuerlaugestroms SL * until reaching the time t _S , the current at the time through the filter F of the filter tubes total flowing Ablaugestrom SM *, divided by the total area of all filters F (this total area is in this document the sum of the areas of all filters F of not more than 80, preferably not more than 75 and more preferably not more than 70 m ³ / (m ² · h) or not more than 60 m ³ / (m ² · h) is in the process space of the hydraulic scrubbing column filter tubes , Advantageously, the values of the aforementioned at the time by the filter F of the filter tubes total flowing Ablaugestromes SM * (this is the sum of all discharged in the respective filter tubes Ablaugeströme, which is summed over all in the process space of the hydraulic scrubber filter tubes summed), divided by the total area of all the filters F, at least during 50%, preferably during 75% and most preferably during the entire period of supply of the stream ST * of the suspension S and optionally the Steuerlaugestroms SL * until reaching the time t _S in the range> 0 to 80 m ³ / (m ² · h), preferably in the range 5 to 75 m ³ / (m ² · h), particularly preferably in the range 15 to 65 m ³ / (m ² · h) and very particularly preferably in the range 20 to 50 m ³ / (m ² · h). From an application point of view, it is preferred to apply a substantially constant filter surface load during the commissioning according to the invention (from the supply of the suspension S) until the time t _S.

From an application point of view, the arithmetic mean M of the stream of liquid supplied to the process space of the washing column (mother liquor as part of the stream ST * of the stream S) of the suspension S) becomes expedient in the inventive starting up to the time t _S (calculated from the beginning of the supply of the stream ST *) Suspension S and optionally control liquor in the form of Steuerlaugestroms SL *), divided by the free cross-sectional area of the process space (= π · (D / 2) ² , minus, for example, the cross-sectional area of the filter tubes and the cross-sectional area of a possibly inserted in the process chamber central displacement body ) in the range> 0 to 30 m ³ / (m ² · h), preferably in the range 1 to 25 m ³ / (m ² · h), particularly preferably in the range 5 to 25 m ³ / (m ² · h) or 10 to 20 m ³ / (m ² · h).

If, during the introduction of the separation process according to the invention, the flow of liquid supplied to the process space of the wash column at the time t _{S of} the suspension S up to the time t _S at the respective point in time is represented as the ordinate against the time t as the abscissa, then the Time range t = 0 (beginning of the supply of the current ST *) until the time t = t _S under the resulting curve curve divided by t _S , the above-mentioned arithmetic mean M.

According to the invention, it is advantageous if at least 50%, preferably 75% and more preferably during the entire period of time, calculated from the beginning of the supply of the stream ST * of the suspension S and possibly the Steuerlaugestroms SL * until reaching the time in the inventive commissioning t _S , the total of the process space of the wash column at the time supplied stream of liquid, divided by the cross-sectional area of the process space> 0 to 30 m ³ / (m ² · h), preferably 1 to 25 m ³ / (m ² · h) , particularly preferably 5 to 25 m ³ / (m ² · h) or 10 to 20 m ³ / (m ² · h).

Of the Acrylic acid content of the inventive Commissioning via the distribution room of the hydraulic Wash column whose process space supplied suspension S of acrylic acid crystals in mother liquor often becomes ≥ 60 Wt .-%, or ≥ 70 wt .-% or ≥ 80 wt .-%, or ≥ 90 Wt .-%, or ≥ 95 wt .-% amount (in natural Way it is <100 Wt .-%, usually ≤ 98 wt .-%).

Especially relevant is the inventive method of Commissioning then, if the degree of crystallization of the commissioning according to the invention supplied to the distributor space of the hydraulic wash column Crystal suspension S ≥ 0.10, or ≥ 0.20, or ≥ 0.25 is. In general, the aforementioned degree of crystallization when commissioning according to the invention ≤ 0.60, often ≤ 0.50 and sometimes ≤ 0.40. Crystallization levels relevant according to the invention the suspension S are thus z. B. also those in the range 0.2 to 0.3.

Everything What is said in this document also applies in particular if the Longitude of the crystals (the longest rectilinear Direct connection of two on the crystal surface befindlicher Points) majority (more than the numerical half of all crystals) 50 to 1600 microns or 200 to 900 microns.

It especially applies when the acrylic acid crystals a cubic to cuboidal appearance have, and thereby a length to thickness ratio in the range 1: 1 to 6: 1, preferably in the range 1: 1 to 4: 1, and more preferably in the range 1.5: 1 to 3.5: 1 show. The fat The crystals are usually in the range of 20 to 600 microns, often in the range of 50 to 300 microns. The length of the crystals is at the same time usually in the range of 50 to 1500 microns, often at 200 to 800 microns.

With regard to the material nature of the hydraulic scrubbing column to be used for the process according to the invention, the teaching of the invention is advantageous WO 03/041832 to follow. D. h., As wall material is preferably the stainless steel DIN material no. 1.4571 , or 1.4539 , or 1.4462 , or 1.4541 used.

In addition, the hydraulic scrubbing column including the associated crystal melt circuit is preferably as in the US-A 2009/018347 described thermally isolated.

The storage of fixedly connected to the removal drive shaft follows according to the invention advantageously according to the teaching of DE application no. 102009000987.6 ,

As a rotating removal device for the inventive method z. As a passage openings (for the removed crystals) having rotating cutter disk into consideration, as they are z. B. in the EP-A 1 448 282 and in the DE application no. 102009000987.6 is described. The rotation of the removal device can be done both continuously and clocked in time.

Instead of a perforated disc having openings can It is also a single at the rotating removal device (optionally in a shaft incorporated (by a shaft Held)) rotary Abtragmesser act. In this case, flows the removed by the rotating Abtragmesser crystal stream past this into the crystal melt space. In both cases, both in the case of the rotating cutting disc and in the case of the rotating single knife, which separates by the rotating removal device described rotational body (as already mentioned) process space and crystal melt space from each other. Of course comes as a rotating Abtragageinrichtung also any between one Circular through holes having cutter disc and a rotating knife lying transitional shape into consideration. Basically, the geometry of the cutting disc however, be arbitrary.

Since the stream of wash melt rising from the crystal melt space and the stream of acrylic acid removed from the removal device have the same passages connecting the process space and the crystal melt space passing through the removal device and / or past the removal device (the crystals must be opposite to one another) ascending stream of wash melt can flow downwards), the removal device suitably has a not too low opening ratio OV in terms of application technology. In this document, the ratio of the sum of the cross-sectional areas through the removal device and / or that on the removal device is referred to as the opening ratio OV in relation to the removal device in the non-rotating state passing leading passages to the cross-sectional area of the crystal bed understood at its end facing the removal device. If the cross-sectional area of an individual passage through the passage is not constant, the smallest cross-sectional area of the passage must be used for the summation. Usually, OV is at least 0.01, or at least 0.03 or at least 0.05, often at least 0.1 and in many cases at least 0.5 or more (sometimes even at least 0.9). Naturally, OV is <1, usually ≦ 0.95, partially ≦ 0.8 or ≦ 0.5, or even ≦ 0.2.

As already said, is the rotatable removal device the hydraulic scrubbing column in the inventive Method advantageously designed as a knife wheel. Preferably this is (circle) round. As the process room with the crystal melt space connecting passages for those removed from the crystal bed Crystals it expediently allocates slots (through holes) on, at the edge thereof (the outline side facing away from the direction of rotation the slot (for example, a slot) advantageously arranged the knife are. The slits with the knives are over the knife disc preferably distributed so that over the entire of the knife disc facing end of the crystal bed crystals are removed when the blade rotates. Advantageously, the slots are radial aligned and each slot with a slanted blade (a slanted knife) equipped with the crystals are removed from the crystal bed. The distribution the slots over the knife disc is also preferred designed so that with one revolution of the cutter disc through each slot essentially the same mass flow of crystals flows. The respective knife (the respective blade) protrudes over appropriate the surface facing the crystal bed (an optional existing profiling of the same remains unconsidered, d. h., reference point is the highest point of the profiling) in addition (typically 1 to 15 mm, often 2 to 10 mm, or 3 to 5 mm) so that crystals are removed from the blade and fed to the slot opening become.

The radius of inventively suitable cutting discs can be used for large-scale process z. B. 300 to 3000 mm. The aforementioned slots often have a slot geometry (the definition of a slot is found, for example, in US Pat DE-A 102007028333 and in the DE-A 102007028332 ). The slot geometry can also be rectangular, or lie between that of a slot and that of a rectangle.

The hole diameter (distance between the two longitudinal edges of the slot) can be z. B. 20 to 100 mm (typically 50 to 70 mm) and the distance between the two hole centers 100 to 500 mm. The surface of the knife disk facing the crystal bed is also expediently provided with a profile of concentric grooves (the groove cross section is advantageously triangular, the groove depth can be eg 2 to 10 mm, or 3 to 7 mm, the groove width 10 to 15 mm and the spacing of radially consecutive grooves must be such that the associated triangular cross-sections have common corner points). The profiling ensures the most uniform possible distribution of the flowing back from the washing melt space in the process chamber wash over the cross section of the process space. The 5 and 8th of the EP-A 1448282 show exemplary embodiments of a present invention as a removal device suitable cutting disc. The angle γ, which includes the surface of the removal elements of the removal device (eg the removal blades or the removal blades) and the axis of rotation of the drive shaft, is often 20 ° to 70 °, and often 30 ° to 60 °, in the method according to the invention. In the method according to the invention, the drive shaft protrudes from below, advantageously from an application point of view, to the cutting disc (or generally to the removal device). From the drive shaft radially running away, equipped with hole openings slats (webs) wear (support) the cutting disc application technology appropriate (44).

Typical crystal mass feed streams, based on the cross-sectional area of the process space at its feed end, in the process according to the invention are 1 to 20 t / m ² h (t = metric ton). The speed of the drive shaft of the removal device is typically in the range of 2 to 40, often 4 to 20 and often 6 to 15 or 4 to 10 per minute. The length of the drive shaft of the removal device is in particular for large-scale processes 0.5 to 4 m.

Of the Crystal melt cycle is in a hydraulic wash column for an inventive method application technology appropriate so that it is essential larger reservoir of crystal melt than the Crystal Melting Room is able to hold on its own (Relative to the total volume of the crystal melt cycle usually only 30 to 60% by volume or 40 to 50% by volume the volume of the crystal melt space; independently of is in stationary operating state the ratio by circulating in the melt circuit mass flow through the rotating removal device from the bottom of the crystal bed removed and conveyed into the crystal melt space Crystal stream suitable in terms of application technology rule 2 to 30 to 1, and preferably 5 to 20 to 1.

That is, the crystal melt circle has norma Lerweise a low content of not molten eroded acrylic acid crystals, which on the one hand favors his and their promotion. On the other hand, the absolute heat capacity of the liquid portion of the contents of the melt circle is much higher than the absolute heat capacity of the solid portion of the melt circle (phase transition heat is ignored).

Of the the crystal melt space supplied crystal stream is in the crystal melt guided in the same suspended and this suspension subsequently in the melt over a heat exchanger (melter) W led, the indirect (preferred) or direct way to melt The crystals required heat enters into the melt circle. Due to the aforementioned ratios of absolute heat capacities results from reaching the desired melt of the crystals required heat input into the melt circuit only a comparatively low temperature increase, which is which is pronounced to unwanted radical Polymerization-prone acrylic acid due to the attendant only comparatively low thermal load is advantageous.

in the Ideally, the crystal melt located in the crystal melt space in stationary operation of the separation process melting point temperature (or Crystal formation temperature) of the ablated crystals on their melt, on (ideally = 14 ° C). Usually this is in the crystal melt cycle beyond the heat exchanger W by not more than 10 ° C, better not more than 5 ° C, preferably not more than 3 or 2 ° C, and more preferably around not more than 1 ° C exceeded.

With Advantage is the process of the invention the conveyor connection G1 via the heat exchanger W guided.

application point is useful as a heat exchanger W a tube bundle heat transferred used. It is an indirect heat exchanger. D. h., The heat transfer is not in by Mix forced direct contact between fluid heat carrier and the heat input requiring fluid Mixture. Rather, the heat transfer takes place indirectly between the fluids separated by a partition wall.

Such Tube bundle heat exchangers usually exist from a closed wide casing pipe, which is in one another numerous tube bottoms attached to usually smooth or ribbed, transformer tubes small Inside diameter encloses.

Of the Distance from the center of the tube to the center of the bundle tubes is in terms of application, it is expedient to use 1.3 to 2.5 times of the pipe outside diameter. The resulting big one specific heat exchanger surface - as Exchange area per unit of space requirements - is a known preference of shell and tube heat exchangers as a heat exchanger W for the invention Method. Basically, the tube bundle heat exchanger in the process according to the invention perpendicular or be arranged horizontally. According to the invention is preferred he arranged horizontally.

According to the invention preferred the contents of the melt circuit flows within the transformer tubes. The fluid heat carrier (according to the invention advantageous a mixture of water and glycol (e.g., with 10 to 60 weight percent glycol; preferred is a mixture of 70 wt .-% water and 30 wt .-% glycol or 65% by weight of water and 35% by weight of glycol; its temperature is expedient 25 to 40 ° C)) flows According to the invention preferably outside the transformer tubes. Guiding plates for better guidance of the fluid heat carrier in the shell space are favorable according to the invention and usually serve the additional purpose of the transformer tubes to support. The baffles usually increase the flow velocities in the shell space and thus u. a. the heat transfer numbers. After the flow direction of the jacket space fluid with respect to the transfer tubes z. B. Längsstrom- and cross-flow - and cross-flow tube bundle heat exchanger distinguishable. Basically, the fluid heat carrier also meandering around the transformer tubes moved and only over the tube bundle heat exchanger considered in cocurrent or countercurrent to the heat receiving be conducted fluid mixture.

in the Einstromrohrbündelwärmeübertrager moves the material flow of the melt circuit through all transformer tubes in the same (one) direction.

Multi-flow tube bundle heat exchangers contain subdivided tube bundles into individual sections (as a rule, the individual sections contain an identical number of tubes). Partitions divide the tubesheets (through which the transmitter tubes are sealed and attached) to adjacent chambers, which divide the flow of material entering the chamber portion (which absorbs the transferred heat) into a second section and thus back , The heat-absorbing material flow flows through the length of the Rohrbündelwärmeübertragers several times (twice, three times, four times, etc.), depending on the number of sections, at a comparatively high speed in an alternating direction (two-flow, three-flow, four-flow, etc.) bundle heat exchangers. Heat transfer coefficient and exchange path increase accordingly.

As an alternative to the shell-and-tube heat exchanger, a plate heat exchanger (plate heat exchanger) can also be used as the heat exchanger W for the method according to the invention. Plate heat exchangers are usually in the form of filter presses usually from corrugated or otherwise profiled, provided with channels for the fluid heat transfer medium and the heat transfer receiving fluid mixture plates (usually made of graphite or metal, eg., Stainless steel) in a compact design composed. The two heat-exchanging fluids then flow in direct, counter and / or cross-flow as thin layers alternately (eg up and down) through their rows of chambers and are in heat transfer to each other at both chamber walls. The corrugated plate profiles increase the turbulence and improve the heat transfer rates. For the purpose according to the invention usable plate heat exchangers are z. B. described in the EP-A 1079194 , of the US 6,382,313 , of the EP-A 1232004 and the WO 01/32301 , Of course, as a heat exchanger W and spiral tube heat exchangers or other heat exchangers can be used.

With Advantage is for the inventive method as heat exchanger W, a three-flow tube bundle heat exchanger used, through whose tubes the substance mixture of the melt circle forcibly conveyed becomes.

The pipe outside diameter can be 25 mm with a wall thickness of 2 mm of the tubes. With a length of the pipes of 3000 mm, their total number of applications is appropriately 121 or 225 (in each case about one third of the total number of pipes for one flow direction). At the same time, the pipe pitch is advantageously 32 mm (60 ° pitch). By 9 or 20 between the tubesheets (in which the exchanger tubes are mounted) mounted deflecting discs (disc thickness: each 5 mm) of the heat exchanger tubes surrounding cylindrical space (the primary space) in 10 or 21 longitudinal sections (segments) is divided. All pulleys are circular in principle. The circle diameter is 584 or 492 mm. At each of the circular deflection discs, however, a circular section is cut away, the radial depth of the circumferential line is inwardly 82 or 94 mm, so that a corresponding passage for the glycol-water mixture is formed as a heat carrier, said passages are successively alternately mounted opposite each other (Incidentally, the baffles are sealingly fixed to the container wall, where the heat exchanger tubes encounter the baffles, corresponding holes in the baffles.) The entry of the heat carrier and the heat-absorbing substance mixture can be conveniently located on the same side of the heat exchanger The mass flow rate of the heat exchanger supplied is typically from 20,000 to 80,000 kg / h with simultaneously supplied melt stream flows of 50,000 to 200,000 kg / h 2 the working pressure (without consideration of hydrostatic effects) on the suction side of the pump P1 (immediately after leaving the melt circuit of the heat exchanger W) in the inventive method below the pressure in the crystal melt space (C) and is often 0.1 to 4 bar. The working pressure on the pressure side of the pump P1 (indirectly after the outlet of the melt circuit from the pump P1) is in a configuration according to 2 in the process according to the invention often 1 to 10 bar.

Production material of the tube bundle heat exchanger is preferably stainless steel from DIN type 1.4571 , or 1.4541 , or 1.4306 tubular and carbon steels such as 1.0425 or stainless steels like 1.4541 , or 1.4571 , or 1.4306 shell side.

The preparation of the suspension S of acrylic acid crystals for the process of the invention is carried out according to the invention advantageously as in DE-A 10 2007 043748 , and in the DE-A 10 2007 043758 described by cooling suspension crystallization in an indirect heat exchanger.

From the heat exchanger, the suspension of acrylic acid crystals in the mother liquor produced in the same is advantageously first applied to a thoroughly mixed buffer tank PT, as is the case with the DE-A 10 2007 043759 describes. From this buffer container (as a source QS) out the crystal suspension can then be sucked by the feed pump P2 as a suspension S (via the delivery connection E1, which connects the buffer tank PT with the suction side of the feed pump P2).

In the rule is the temperature of the inventive Method supplied to the distribution chamber of the hydraulic wash column Suspension S of acrylic acid crystals in the temperature range of -25 ° C to + 14 ° C, often in the range of -5 ° C to + 12 ° C and preferably in the range of +4 and +6 to + 9 ° C.

Of the Content of the mother liquor contained in the suspension S of acrylic acid will usually be ≥ 70 wt .-%. He can but also ≥ 80 wt .-%, or ≥ 85 wt .-%, or ≥ 87 Wt .-%, or ≥ 90 wt .-%, or ≥ 92 wt .-%, or ≥ 94 Wt .-%, or ≥ 95 wt .-%, or ≥ 96 wt .-%, or ≥ 97 wt .-%, or ≥ 98 wt .-%, or ≥ 99 wt .-% amount.

Already before starting with the method according to the invention is, the distribution space of the hydraulic wash column, a stream ST * of the suspension S from the buffer tank PT as source QS, It is inventively advantageous, the feed pump P2 in operation, and via the conveyor link E1, which is the suction side of the feed pump P2 with the buffer tank PT connects to suck in from the suspension S. Subsequently is the sucked suspension S from the feed pump P2 though pressed into the conveying connection E2, the of the Pressure side of the pump P2 into the distribution chamber of hydraulic wash column leads. In the flow direction on the way from the pressure side of the feed pump P2 to the entrance (Inlet port) of the distribution space of the hydraulic scrubbing column is in front of the entrance to the distribution room in the conveying connection E2 but according to the invention advantageously a first Fitting installed, the conveyor connection E2 first locks.

In addition, according to the invention, advantageously between the pressure side of the feed pump P2 and the first valve of the second conveyor connection E2 branches back a conveying connection E3 (() (in the buffer tank PT 55 ) in 2 ), whose connection with the buffer tank PT can indeed be blocked by a second fitting that is advantageously installed according to the invention in the conveying connection E3, but initially kept open. As a result, the suspension S initially circulates through the conveyor pumps E1, E2 and E3 through the buffer tank PT, already in operation, through the conveyor connections E1, E2 and E3. From the time at which the stream ST * of the suspension S is to be supplied to the distribution chamber of the hydraulic scrubbing column, the second fitting blocks the delivery connection E3 to the buffer tank PT and at the same time the first fitting opens the delivery connection E2 to the distribution space of the hydraulic Washing column (as valves such as valves, flaps or ball valves can be used for locking and opening). Both the mixing in the buffer tank PT and the conveying of the crystal suspension S advantageously takes place in the method according to the invention such that, if possible, no breakage and / or no other change in shape of the suspended crystals results. This applies in particular to the above-described circles of the crystal suspension S.

For the case that in the commissioning according to the invention in advance of the supply of the stream ST * of the suspension S via the Manifold and through the passages U through in the Process space of the hydraulic wash column in both the Crystal melt space comprehensive melt circle, as well as the process space and the distribution chamber and the delivery lines E2 (and optionally E1), C1, C2 and the feed pump P3 completely with the acrylic acid-containing starting liquid AT, and with the supply of electricity ST * the Suspension S into the distribution room accompanying this feed simultaneously also control leach flow into the distribution room and / or directly into the Process room is guided, it is appropriate in terms of application technology, already in advance of the beginning of the supply of the stream ST * of the suspension S in the distribution room, the feed pump P3 in operation too take and a stream of starting liquid AT over the distributor space, process space, filter tube interior, conveyor connection C1, Feed pump P3 and conveyor connection C2 formed Circle to circle.

Becomes in the method of commissioning according to the invention a Steuerlaugestrom SL * co-used, so it is to a recirculated partial flow of over the filter tubes led out of the wash column in total Leakage current SM *. Normally, the aforementioned recycling takes place the bleed-off part stream at substantially the same temperature, with which the Ablaugestrom SM * is led out of the wash column. Usually this temperature corresponds to the temperature with which the suspension S of acrylic acid crystals in mother liquor the distribution of the hydraulic wash column is supplied. Of course can the aforementioned recirculation of Ablaugeteilstroms as Steuerlaugestrom SL * z. B. also has a direct and / or indirect heat exchangers, which the Temperature of the recirculated as Steuerlaugestrom SL * Ablaugeteilstroms increased. Application-wise appropriate should the temperature of Steuerlaugestroms SL * but not to more than 15 ° C, preferably not more than 10 ° C, and more preferably not more than 5 ° C above the temperature of the guided into the distribution space of the hydraulic wash column Current ST * of the suspension S are. The above applies in appropriate Also on the stationary operation of the separation process in the hydraulic wash column too.

A co-used Steuerlaugestrom pursued both in the commissioning according to the invention as well as in stationary operation the purpose of influencing the hydraulic pressure loss and thus the effect on the crystals, the crystal bed acting force (eg., The force acting on the closed crystal bed feed force). If the supply of the suspension S of the acrylic acid crystals in mother liquor is not accompanied by mother liquor flow in this regard unsatisfactory or fluctuates during the supply period to a certain extent with time, this can be compensated by the Steuerlaugestroms (a detailed explanation of the mode of action of Steuerlaugestroms finds in the WO 2006/111565 ). The supply of the Steuerlaugestroms in the process space of the hydraulic wash column can both over the Ver divider space and through the passages U through, as well as on a direct path into the process space into it. In principle, control liquor can be conducted into the process space at different heights of the crystal bed. Normally, however, the supply of control liquor always takes place above the filter F.

Since the position of the build-up or filtration front in the stationary operation of the hydraulic wash column is influenced, inter alia, by the feed rate of the crystal bed in the wash column, the position of the build-up front can be kept stable ("controlled") in the event of disturbances by adapting the control leach flow (cf. , WO 2006/111565 ). An increasing (decreasing) current of the Steuerlaugestroms usually causes a shift of the mounting front down (top). Alternatively, the current strength of the supplied suspension stream ST * would have to be varied. Out in the WO 2006/111565 For reasons explained, the construction front should not be positioned too high or too low in the hydraulic wash column. The part of the crystal bed which extends in stationary operation, starting from the crystal removal to the beginning of the filter F, is also referred to as a washing zone. The overlying part of the crystal bed, which extends to the construction front, is also called concentration zone. This is followed by the so-called suspension zone up to the upper end of the process space. The filter tubes of the hydraulic scrubbing column usually protrude into the scrubbing zone, but are no longer hollow in this region of the scrubbing column (cf. WO 01/77056 . WO 03/41833 and WO 03/41832 ). This part of the filter tubes is also referred to as filter tube displacer.

The Control of the strength of Steuerlaugestroms can z. B. by Adjustment of the speed of the feed pump P3 and / or by an additional control valve done.

in principle may be the supply of the suspension S and the supply of Steuerlaugestrom spatially in the distribution space of the hydraulic wash column done separately. Of course, the feed stream the suspension S and a distributor space supplied Steuerlaugestrom but also already outside the distribution room merged, mixed together and the resulting Mixture flow (as it were over a merged conveying connection E2 / C2) are guided into the distribution space of the hydraulic scrubbing column.

For example the mixing of the two streams can be done by that the two conveyor links E2 and C2 first into a static mixer and behind the same as only one common conveyor connection to the distribution room run the hydraulic wash column.

Alternatively, the conveyor connections E2 and C2 can be designed in front of the feed space of the hydraulic scrubbing column as coaxial feed lines (pipelines). In this case, the suspension S is expediently carried out in terms of application technology in the inner delivery connection (in the inner pipeline) and the control liquor in the outer delivery connection (in the outer pipeline). A mixing section of z. B. 0.5 to 20 m before entering the distribution chamber of the hydraulic scrubbing column, the internally guided pipe runs out and only the outer of the two tubes is then continued as a common conveyor connection E2, 02 to the distribution chamber. According to the invention, the internally routed pipe tapers towards its outlet (usually conical, eg from about 80 mm internal diameter to about 50 mm internal diameter). In this way, the inside expiring pipeline acts as a motive nozzle (see pages 3/4 of DE-A 102006045089 ) with the suspension S as a propulsion jet. As such, it sucks in the flow direction immediately behind the end of the inner pipe from the outside flowing control liquor and mixes with the same to the mixture flow, which flows as such in the distribution space. The inner diameter of the outer pipe can, for the aforementioned dimensioning of the inner pipe z. B. 150 mm. The distance from the inside of the wall of the outer pipe to the outer wall of the inner pipe can be z. 40 to 50 mm (eg 46 mm). The strength of the externally guided Steuerlaugestroms can be 5 to 80 m ³ / h and the strength of the in-guided suspension flow 10 to 50 m ³ / h.

The determination of the pressures P _K and P _V z. B. as the pressure measurements of WO 2006/111565 respectively. From an application point of view, membrane pressure gauges are used for this purpose, which are mounted outside the hydraulic wash column. The transducers communicate with the inside of the column via small, open boreholes (typical borehole diameter = 0.1 to 3 mm), which discharge into a spigot leading to the diaphragm manometer (in principle, the procedure is analogous to those in the DE-A 10211290 and in the WO 2006/111565 procedure). In order to prevent crystallization of the aforementioned bores and nozzles, according to the invention, they and the manometers are advantageously accompanied by a slight heat flow (as a rule, an enclosure of the hydraulic washing column in a heated building is sufficient, as is the case, for example) WO 03/041832 and the US-A 2009/018347 describe). Of course, the differential pressure P _D also directly over a Dif be detected as the pressure WO 2006/111565 also describes. According to the invention are preferred as a manometer M1 and M2 (see. 1 and 2 ) those type 2088 GS membrane sensor, measuring range: 0-10 bar, the supplier Rosemount used. As a differential pressure gauge M3 (see. 2 ) are suitable for the United invention drive preferably those of the type 3051 CD differential membrane sensor, measuring range: 0-500 mbar, the supplier Rosemount.

With Advantage closes the respective hole on the inside the respective space of the hydraulic wash column smooth. Of the Diameter of such open holes is from the column interior As far as practical, it is appropriate for use ≤ 5 mm, often ≤ 3 mm and usually ≥ 0.1 mm. By the Wall can be useful in terms of application technology a to the column interior continuously or stepwise tapered bore diameter can be applied.

Until, in the context of commissioning the invention, the time t _{S is} reached, the heat exchanger W, the feed pump P1 (at least from the beginning of the supply of the suspension stream ST *) and the rotatable removal device according to the invention preferably out of service and the flow of the outlet A preferably blocked.

In principle, however, the aforementioned elements can already be put into operation to a limited extent. If the flow rate of the outlet A has already been opened to a limited extent in advance of the point in time t _S , then this must be taken into account correspondingly in the process of filling according to the invention with the magnitude of the stream ST * and optionally SL *. Furthermore, the rotational movement of the removal device should not be too strong, since it has a negative effect on the process of closing the crystal bed and its further structure. The heat output of the heat exchanger W may already be different from zero in advance of the time t _S in order to melt when filling with suspension S already reaching into the melt circle acrylic acid crystals. It should be suitably but not higher than 50% of the heating power used in stationary operation of the separation process (eg it could be 10% or 20% of that heat output) prior to the point in time t _s . Under heating power while the output to the melt heat flow is understood. It can be adjusted as required by appropriate variation of the temperature of the heat carrier (this moves in the normal case, as already mentioned, in the range 25 to 40 ° C) and / or variation of its current strength.

If the instant t _{S is} reached during the inventive startup, the supply of the stream ST * of the suspension S into the distributor space as well as the supply of an optionally used control leach stream SL * is interrupted (as already mentioned advantageous with first non-rotating discharge device and out of operation melt circuit) , Subsequently, the melt circuit and the rotation of the removal device are put into operation, wherein the sequence of commissioning of their individual elements is essentially arbitrary. Preferably, however, the sequence is as described below.

According to the invention advantageous First, the heat output of the heat exchanger W (relative to an operating pump in operation P1) to about 50 to 80% of its heating power in stationary Operation set. Thereafter, the feed pump P1 and then the rotation of the removal device in operation taken (both are based on their operating value in the stationary State set).

From the time from which the rotation of the removal device in operation is taken, the supply of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and through the passages U through into the process space the wash column resumed. The same applies an optionally used Steuerlaugestrom. The sequence commissioning is irrelevant.

The current intensities are chosen so that the crystal bed and its state (build-up front) begin to move down. Understood that the necessary current levels of suspension and, where appropriate, control liquor flow rate must not be greater in a necessary field than those that have been employed in the inventive start-up until the time t _S (are preferred according to the time t _S over time substantially constant currents and current levels applied). In principle, even with otherwise constant currents, lower current intensities than before the time t _S may possibly be sufficient to ensure that not only the crystal bed but also its state (its construction front) begins to move downwards. This is due to the fact that in the commissioning according to the invention until the time t _S an increasing compression of the forming crystal bed results.

As a consequence, even when maintaining the strength of the Ablaugestroms over the operating time increasing hydraulic pressure loss, which may be sufficient at the restart after passing through the time t _S to set the crystal bed and its state in motion.

In less favorable cases, however, a bleed stream of up to 250 m ³ / (m ² · hr), or up to 320 m ³ / (m ² · h), based on the unit of the total area of all filters F may be required to achieve this Set the crystal bed and its stand (construction front) in motion. Higher values are usually not required.

In particularly favorable cases, even a correspondingly related Ablaugestrom of only 40 m ³ / (m ² · h) may already be sufficient to set the crystal bed and its state in motion. The level of the crystal bed in the process room (the "construction front") begins to fall.

There now already at the bottom of the crystal bed by the removal device Acrylic acid crystals removed, as well as in the crystal melt space promoted and melted in the melt, is now technically useful the polymerization inhibition (Addition of polymerization inhibitor and optionally air or other oxygen-containing gas) of the melt circuit put into operation.

Of course the process of the invention must for reasons safety in the presence of polymerization inhibitors, to an undesirable radical polymerization of acrylic acid excluded.

While the mother liquor of suspension S normally polymerization inhibitors such as phenothiazine (PTZ) and / or the monomethyl ether of hydroquinone (MEHQ) in, by the suspension crystallization used to produce them conditionally, has enriched levels, those in the suspension S suspended acrylic acid crystals usually on polymerization inhibitors depleted, since the same usually does not in the crystal formation be incorporated in the forming crystal.

Become in the melt circle such ablated from the crystal bed crystals melted, this leads where this melting pointy goes from local to a local inhibition of the resulting Melt. Such a lower inhibition has an increased Risk of an unwanted, by the released Heat of polymerization self-accelerating radical Polymerization of acrylic acid, which is why counteracted this risk must become.

In comparatively simple way can counteract such be done by the fact that the melt circuit in the flow direction behind the heat exchanger W (if this in the conveyor connection G1 is integrated) but in front of the suction side the feed pump P1 a solution of the corresponding Inhibitors (with comparatively increased inhibitor concentration) in pure product (in a melt of previously purified separated Acrylic acid crystals) is metered in (a metered addition behind the pressure side of the feed pump P1 would be a increased supply pressure condition is basically however possible).

Advantageously according to the invention, this inhibitor solution can be metered in at the temperature (for example via a T-piece) which the melt circuit has at the feed point. Frequently, however, the inhibitor solution is metered in at a temperature in the range from 15 to 35.degree. Typical inhibitor levels of such an added inhibitor solution are z. B. at 0.1 to 1.5 wt .-% PTZ and / or 0.1 to 5 wt .-% MEHQ. Based on the mass flow rate in outlet A, the mass flow rate of the inhibitor solution metered into the melt circuit is generally 0.1 to 10%, preferably 0.5 to 3%. If inhibited with PTZ, its weight fraction in the crystal melt space and in the outlet A is typically 50 to 500 ppm by weight. When inhibited with MEHQ, its proportion by weight in the crystal melt space is typically 10 to 500 ppm by weight. In particular, when the melt cycle is inhibited by MEHQ polymerization (the type of polymerization inhibition is based primarily on the envisaged use of the pure product taken from the outlet A; is intended to use the discharged pure product primarily in polymerization reactions, the inhibition is preferably carried out with the "Storage inhibitor MEHQ", intended to use the discharged pure product primarily for chemical processes other than polymerization reactions, is preferably inhibited by the process inhibitor PTZ (especially if the chemical process is exposed to thermal stresses)), and co-inhibition by incorporation is additionally carried out (eg, injecting) a molecular oxygen-containing gas into the melt circuit. Mixtures of molecular oxygen and inert gas (eg N ₂ , CO ₂ , He, Ar) are particularly suitable as such molecular oxygen-containing gases (preferably the gas containing the molecular oxygen is free of water vapor (previously dried) and free of solid particles (pre-filtered)). Of course, pure molecular oxygen can also be added. According to the invention, air is metered in as the gas containing molecular oxygen.

According to the invention advantageous the metered addition of the molecular oxygen-containing gas takes place in the melt in the flow direction of the same the pressure side of the feed pump P1 to the outlet A.

For the purpose of metering the molecular oxygen-containing gas into the melt circuit, the crystal melt stream forced away from the feed pump P1 is introduced by means of a T-piece split two partial streams of the same composition. The ratio of their current strengths is expediently by means of two valves ( 50 ) and ( 51 ). The previous blocking of this split is now canceled. The smaller of the two sub-streams (it is usually at least 5, but usually not more than 20% of the pre-division total current, the other sub-stream is called the main sub-stream) then flows through an oxygen introduction path (eg as a jet jet jet (eg see. DE-A 102006045089 ) in which the molecular oxygen-containing gas (preferably air) is sucked in). In the simplest case, the molecular oxygen-containing gas is supplied from a pressure line via a T-piece at the beginning of the introduction path ( 53 ). In this case, the gas containing the molecular oxygen preferably has the temperature which the melt circuit also has at the feed point. However, it often has ambient temperatures (≥ 15 ° C and ≤ 35 ° C).

After a sufficiently long mixing section, the substream containing the molecular oxygen-containing gas stream is passed through a gas separator ( 52 ) to separate off gas dissolved in it again. The purpose of this measure is to prevent gas dissolved in such a way in the course of the process from accumulating in the form of a gas bubble below the lower end of the crystal bed, thereby increasing the wash melt from the crystal melt space into the crystal bed and thus ultimately washing the hydraulic effect Washing column reduces.

In principle, all known types of gas separators can be used as such a gas separator, as well as z. B. in the EP-A 492400 are listed. These include centrifugal separators (eg cyclone separators) as well as gravity separators. The latter are preferred according to the invention due to their simple construction and at the same time satisfactory separation effect. Ultimately, a equipped with baffles container in this regard is sufficient. The aforementioned partial flow is guided in the simplest embodiment in the center of the container on baffles mounted there. At the upper end of the container there is the outlet for the specifically lighter gas deposited in the impact area ( 54 ) and in the lower part of the container is the outlet for the specific heavier liquid phase.

Behind the gas separator will be enriched with molecular oxygen Partial flow and the main part stream merged back into a total flow.

in the Connection to the start of the polymerization inhibition is Advantageously, first the strength of the invention preferably mitzulwendeten Steuerlaugestroms reduced so that the state of Crystal bed does not drop further, but on one desired height sets. Then it becomes application technology expedient the flow of the outlet A is opened. For this purpose, the outlet is normally a valve or a other fitting mounted.

Of the Passage is only opened so far that the crystal melt space still a sufficient flow of liquid in the on the Removal device ascends to moving crystal bed.

Preferably you will initially the flow of the outlet A so far restrict that ascending liquid from the crystal melt space rises up to the filter F and as part of the Ablaugestroms through the filter F and the filter tubes through as a component of the Ablaugestroms is led out of the process space (less Advantageously, the height of rise could by appropriate Regulation of the flow of the outlet A also from the beginning below the lower edge of the filter F are adjusted horizontally).

Now is preferably the temperature control of the crystal melt cycle put into operation and the heat output of the heat transfer W regulated so that the tem perature in the crystal melt circle beyond the heat transfer W by no more than 10 or 5 ° C, preferably not more than 3 or 2 ° C and more preferably not more than 1 ° C (usually however, ≥ 0.0100) above the crystal formation temperature eroded pure crystals out of their crystal melt (14 ° C) (at the beginning, the regulation can still be done by hand before is transferred to the automatic control; the latter becomes realized with the help of appropriate thermocouples or resistance thermometers).

Finally, from an application point of view, the flow rate of the outlet A is progressively increased continuously or at certain time intervals until the crystal bed height envisaged for the desired position of the wash front in the crystal bed below the filter F is selected as the controlled variable, between 14 ° C. and the temperature of the Distributor space supplied crystal suspension lying crystal bed temperature (the target temperature) is present. For example, the arithmetic mean of the two temperatures can be selected as the control variable (setpoint temperature) (cf. DE-A 10036881 and WO 02/09839 ). From this point on, the passage of the outlet A can be automatically controlled by means of the deviation of the temperature measured on the crystal bed height intended for the wash front bed from the aforementioned setpoint temperature the. If the temperature measured on the crystal bed height provided for the washfront is lower than the selected setpoint temperature, the flow rate of the outlet A is reduced. If the temperature measured on the crystal bed height provided for the washfront is higher than the selected setpoint temperature, the flow rate of the outlet A is increased (eg, by opening the corresponding control valve).

For example, by controlling the strength of the invention preferably used Steuerlaugestroms by metrological detection of the state of the crystal bed (the mounting front) according to the teaching of WO 2006/111565 the filtration front can be kept relatively easily at the desired height.

in the further course of the execution of the separation process is From an application point of view, the dosing flow rate of the inhibitor solution in Pure product in relation to the led out of the outlet A. Pure product flow regulated automatically (in the case of molecular Oxygen-containing gas is the excess metering maintained with subsequent excess separation).

By sampling the outgoing from the outlet A stream and analysis of the samples is determined in an appropriate manner, from which time the discharged material stream has the desired purity. From this point on, the outlet flow z. B. be performed in a pure product tank farm. Previously discharged material streams with insufficient purity can, for. B. for the purpose of their recrystallization in the crystallization process for generating the suspension S rückge leads. Alternatively, they can also be recycled to the production of the stream from which the suspension S is formed by suspension crystallization (for example, into the fractional condensation of the product gas mixture of a heterogeneously catalyzed partial gas phase oxidation of propane and / or propylene to produce the acrylic acid) eg in the WO 01/77056 and in the WO 08/090190 for the separated in the hydraulic scrubbing mother liquor is described.

The Separation process has now moved to its steady-state operation.

The number of filter tubes in a hydraulic wash column may be 3 to 200 or more in the case of a large-scale application of the method according to the invention. Based on the unit of the cross-sectional area of the process space of the hydraulic scrubbing column, their number is typically 10 to 100 per m ² . The length of the washing zone is typically 0.5 to 20 times, preferably 1 to 8 times and very particularly preferably 2 to 5 times the distance of the filter tube closest to the jacket wall of the process space to the envelope (as a rule this distance is 25 to 500 mm, often 40 to 250 mm, often 80 to 200 mm).

Typical internal diameters of the filter tubes are in the process of the invention 5 to 200 mm, often 10 to 100 mm, often 20 to 80 mm. The wall thickness of the filter tubes is regularly at 1 to 10 mm. As already mentioned, the filter tubes are suitably provided in terms of application technology at a defined height with a filter F, which generally extends around the entire circumference of a filter tube. The height of the filter elements F is often 20 to 200 mm. The perforation of the filtering effect of the filter element F can be perforated as well as longitudinally slotted. The slot width or the hole diameter are preferably 50 to 400, z. B. 100 to 300 microns in the process of the invention. Outer and inner diameter of a filter tube according to the invention are preferably constant over its length. According to the invention, the filter tubes of a hydraulic wash column which is suitable according to the invention have a uniform shape. Downstream of the filter element F of a filter tube normally, as already stated, is a filter tube displacer ( 38 ) at. No fluid can penetrate into it. It can be made both cylindrical, conical or as a combination of these forms. The outer diameter of the connection is usually identical to the outer diameter of the filter element. According to the invention, the filter tube displacer preferably consists of a material with a low heat conductivity (eg Teflon or polyethylene). The length of the Filterrohrverdränger is regularly 50 or 100 to 500 mm).

The Length of the washing zone is the inventive Procedure usually 50 to 500 mm. The total height of the compacted crystal bed (compacted filter cake) in one hydraulic scrubbing column is in the inventive Method typically 300 to 4000 mm, often 400 to 3000 mm, often 500 to 2000 mm, or 600 to 1500 mm or to 1000 mm.

The motive pressure (indicated as overpressure against atmosphere) in a hydraulic scrubbing column is often up to 10 bar, often up to 8 bar and often 1 to 5 bar or 0.5 to 4 bar. The hydraulic flow pressure loss of the mother liquor of the supplied suspension S is generally ≥ 100 mbar to ≤ 5 bar or ≤ 10 bar. With regard to the distribution of the filter tubes of a hydraulic wash column over the cross section thereof is advantageous according to the invention as in EP-A 1 448 282 recommended procedure. The length of the filter tubes (without incorporation of the filter tube displacers) corresponds to the length L of the process space minus the length specified above for the wash zone.

conditioned by the freezing point depression caused by the impurities is the temperature of the distribution space of the hydraulic wash column fed suspension S necessarily lower, than the crystal formation temperature of the discharged from the outlet A. Pure product (the wash melt). In the area of the wash front comes It therefore leads to a temperature compensation of the cold suspension S originating cold crystals with the wash melt, where the wash melt partially or completely recrystallized (this recrystallization forms another cleaning mechanism). This will at least one Part of the wash melt recovered. The described Recrystallization of the wash melt contributes to stabilization and training the wash front and is more pronounced the further the temperature of the suspension S below the crystal formation temperature the wash melt is. Basically, the aforementioned Difference temperature, which, inter alia, by the selected degree of crystallinity the suspension S, 15 ° C and be more. In many cases, a differential temperature of 4 to 10 ° C and with low impurity content of the mother liquor often set only from 2 to 4 ° C. Succeed quantitative Recrystallization (the wash front is below the lower edge the filter F), can ultimately out of the crystal melt circle 100% of the crystal space supplied to the process space as Pure product stream are discharged (both streams have substantially the same mass flow rate; (no wash-melt is lost). Will the difference be Temperature of the suspension S and the wash melt too large, this can be a closure of the pores in the compacted crystal bed resulting in proper implementation the separation process is detrimental.

With a position of the wash front on the filters F, usually goes one not quantitative recrystallization of the upward rising Associated with wash melt stream. A partial flow of the same is accordingly removed as part of the Ablaugestroms.

If the case of the inventive start-up until the time t _S during the supply of the stream ST * through the filters F of the filter tubes in total flowing at the time Ablaugestrom SM * divided by the total area of all filter F, mainly at particularly low values (e.g., B . <20 m ³ / (m ² · h)), so increases the possibility that at the start of the crystal melt circuit after the time t _S, the wash melt stream unintentionally increases up to the filter F. A recrystallization starting on the same can clog the filter openings if necessary and the application of a in the EP-A 1 448 282 recommended rinsing liquid (usual Spülsäureströme (eg., slightly heated mother liquor) per filter F are at 10 to 1000 l / h, preferably at 50 to 200 l / h) make necessary. Leakage currents 20 m ³ / (m ² · h) normalized to the total area of the filters F are therefore preferred in the commissioning according to the invention.

For carrying out the process according to the invention, it is also advantageous to slightly increase the cross section of the hydraulic wash column shortly before (from above) the rotating removal device (by 5 to 100 mm relative to its diameter). This makes it possible to choose the radial extent of the Abrageinreichung slightly larger than the radial extent of the crystal bed (but may in principle be smaller than this), which favors the uniform removal of crystals over the entire crystal bed cross-section. In order to improve the suspension of the crystals removed by the rotating removal device in the crystal melt located in the crystal melt space, it is helpful to fix it to the drive shaft for the removal device below the latter paddle, which mixes the crystal melt space. Reinforcing elements (for example reinforcing ribs or lamellae, which as a rule have passage openings) can also serve this purpose, which are designed to be large-area between the hub used for fastening the removal device to the shaft and baffles attached to the inner wall of the crystal melting chamber. compare to both elements the 2 of the EP-A 1 448 282 ).

The Passages U that pursue at least one bottom B at inventive method the purpose of one over the cross section of the process space as uniform as possible Supply of suspension S from the distributor room into the process room into it. According to the invention, the passages are advantageous U evenly distributed over the soil B. Preferably, the passages U have circular openings and a longitudinal cross-section of the passage U preferably constant on.

The openings the passages U advantageously have cross-sectional areas which, based on a circular shape, a diameter of 15 to 300, preferably from 50 to 150 mm.

The height (length) of the passages U can be up to 1000 mm in the method according to the invention (in each case measured from the distributor space to the process space). As a rule, it is at least 50 to 200 mm. Often it is 400 to 800 mm. The ratio of the total area of all the process space facing openings of the passages U to the total area of the process space cross section in the process according to the invention is frequently 0.10 to 0.60 and often 0.20 to 0.40.

In addition to the passages U having bottom B, the distribution space according to the recommendation of EP-A 1 448 282 Contain distribution aids that are conducive to the most uniform possible supply of the suspension S (viewed over the cross section of the process chamber) from the distribution chamber into the process space. As such distribution aids come z. B. housed in the distribution room packs into consideration. However, such a distribution aid can also be a stirrer, which stirs the contents of the distributor space and thereby keeps as homogeneous as possible. Other possible distribution aids are z. B. a distribution cone according to 2 of the EP-A 1 448 282 or baffles according to 7 of the EP-A 1 448 282 , As distribution aid, however, nested "funnels" come into consideration, such as the 2 this document shows ( 46 ). The funnel necks in each case protrude into the inlet supports of the distributor space and the funnel heads protrude into the distributor space. Between the spaced surfaces of the funnel heads, the suspension S runs uniformly distributed over the cross section of the distributor space via the same. The placement of a displacer ( 43 ) in the center of the process space of the hydraulic wash column, as is the EP-A 1 448 282 recommends is also advantageous for the comparison of crystal bed formation. The central displacer normally has a circular cylindrical shape whose outer diameter is usually larger than that of a filter tube. In principle, however, the centrally placed displacer at the height of the filter F of the filter tubes may have a filter corresponding height as the filter F and be executed hollow inside, whereby he takes over the action of a larger filter tube. In this case, the displacer for the purposes of the present invention, such as a filter tube to be considered and included. For the inventive method particularly well suited hydraulic wash columns are thus in particular those that the embodiments of the EP-A 1 448 282 as well as the DE Application number 102009000987.6 consequences. An embodiment of such a hydraulic washing column shows the 2 this font.

According to the invention, it is advantageous in the case of the hydraulic wash column ( 0 ) according to 2 the distribution space (A) from the process space (B) through a floor B ( 32 ) and through another floor B * ( 39 ), which in turn define a cylindrical space ren. Both floors have openings (preferably circular holes (holes)), of which the openings of the bottom B * ( 39 ) with a part (the second part) of the openings of the bottom B ( 32 ) via continuous connecting pieces, the passages U ( 26 ) are connected (both openings open into a passage U (2 6 )). About the passages U ( 26 ) the suspension S to be separated passes into the process space (B) of the wash column ( 0 ).

The soil B ( 32 ) additionally has a first part of openings which are not counterparts in the floor B * ( 39 ) and in the filter tubes ( 6 ). Preferably, this second part of openings are circular holes (holes).

This first part of openings is just like the filter tubes ( 6 ), which open into these openings, preferably uniformly over the cross section of the bottom B ( 32 ) distributed, as z. B. the 3 of the EP-A 1 448 282 shows.

Due to this equal distribution predominantly equilateral triangles are defined. Advantageously according to the invention, the second part of the openings of the bottom B ( 32 ) in the center of such triangles. Preferably, this second part of the openings is also uniform over the cross-section of the bottom B (FIG. 32 ). According to the invention, it is advantageous if essentially all triangular centers are occupied by openings belonging to the second part.

The space around the passages U ( 26 ) forms the collecting space ( 27 ) for the waste liquor, which is led out of the wash column ( 2 ).

It is preferred for the method according to the invention if between the Ablaugesammelraum ( 27 ) and the suspension distribution space (A) as a further space a Spülflüssigkeitszuführraum ( 40 ) obtained by drawing in a false floor B ** ( 41 ) can be created. The passages U ( 26 ) are substantially sealingly through the intermediate floor B ** ( 41 ) guided. In addition, the intermediate floor B ** ( 41 ) Openings (preferably circular holes (holes)), in the flushing tubes ( 42 ) in the same way as the filter tubes ( 6 ) are distributed over the cross section and into the lower third of the respective filter element ( 7 ) into an associated filter tube ( 6 protrude). The outer diameter of the rinsing tubes ( 42 ) is suitably chosen according to the invention so that it is 0.3 to 0.6 times the inner diameter of the filter tubes ( 6 ) corresponds. In the lower third are on the outer wall of each flushing pipe ( 42 ) centering cam is advantageously mounted, the centered position of the respective Spühlrohrs ( 42 ) in the associated filter tube ( 6 ) to ensure.

The openings in the floor B ** ( 41 ) are advantageously designed so that they can be either closed or opened. Are they closed, can in the room ( 40 ) any heating medium can be fed to crystalline deposits and Incrustations on the ground B * ( 39 ) and at the entrance to the passages U ( 26 ) melt down. Are openings in the floor B ** ( 41 ) opened, z. B. by using heated, previously led out of the wash column spent liquor, crystalline deposits on the filter elements F ( 7 ) are melted.

Advantageously in accordance with the invention, in the purifying separation of acrylic acid crystals from a suspension S of their crystals in mother liquor by means of a hydraulic wash column, a small, previously heated (at temperatures in the range from 14 to 30 ° C.) is always present both during the start of the separation process and in its steady state operation 20 or to 25 ° C) partial flow (based on the total out of the hydraulic wash column Ablaugestrom up to 40 or up to 25%, usually at least 5%) of the total led out of the wash column Ablaugestroms over all rinsing tubes ( 42 ) distributed as a preventive measure in the associated filter tubes ( 6 ) to prevent the formation of incrustations on their filter elements F ( 7 ) to prevent. The aforementioned heating is suitably made in terms of application technology by forced delivery of the partial flow by means of a corresponding feed pump through an indirect heat exchanger through which a heat transfer medium flows (cf. 7 of the EP-A 1 448 282 ). To the filter elements F ( 7 ) normally close the filter tube displacer ( 38 ) at. In the center of the process space (B) of the wash column ( 0 ) is preferably a circular cylindrical running central displacement body ( 43 ). With regard to its dimensions and material quality is on the remarks of the EP-A 1 448 282 directed. Preferably, the central displacer ( 43 ) at the bottom B ( 32 Static (which usually has no passage, no opening in the mounting area) and protrudes to about 1 to 20 mm on the removal device ( 16 ) (eg a knife disc). However, it can also be firmly connected to the cutting disc and thereby be performed with the same rotating. From the drive shaft ( 18 ) in the crystal melt space (C) radially running away, equipped with hole openings slats ( 44 ) or webs support (support) the removal direction (knife disc) ( 16 ) in terms of application technology.

A combination of a distribution cone ( 45 ) and an arranged above this nesting of spaced-apart funnels ( 46 ) acts in the distribution room A as an additional distribution aid. The necks of the funnels run in the inlet connection ( 47 ) of the distribution space and the heads of the funnels protrude above the distribution cone. A rupture disk ( 48 ) in the conveyor connection E2 ( 34 ) protects against safety-related impermissible overpressures. In the mixer ( 49 ) the conveying connection E2 ( 34 ) and the conveyor connection C2 ( 36 ) merged. The merging of the two conveyor connections E2, C2 is appropriate application technology in the form of coaxially guided pipelines. The suspension S is advantageously guided in the inner of the two pipes and the control liquor in the outer pipe. A mixing section before entering the inlet pipe runs out of the internally routed pipe and only the outer pipe is then continued as a common conveyor connection E2, C2 to the distribution chamber. The internally routed pipe tapers conically towards its outlet and acts at its outlet as a motive nozzle with the suspension S as propulsion jet, which sucks on the adjoining mixing section of the externally guided control liquor and thereby mixed with selbiger.

The pressure gauge M3 is advantageously a differential pressure gauge of the type 3051 CD differential membrane sensor, measuring range: 0 to 500 mbar, the supplier Rosemount, which provides immediate access to the pressure difference between measuring points immediately above a passage U ( 26 ) in the distribution room and immediately below a passage U ( 26 ) in the process room. Incidentally, identical addresses come in the 2 the same meaning as in the 1 to.

The 3 This document qualitatively shows the course of the pressures P _K and P _V and of the differential pressure P _D until the passage through the time t _S. The abscissa shows the time (t _S is usually in the range of 10 minutes to 2 hours) and the ordinate shows the pressures in bar. At the 3 Underlying commissioning was the hydraulic scrubbing column, including its melt circle, initially completely filled with mother liquor of the suspension to be treated S as start-up liquid AT.

The inventive method of commissioning a separation process for purifying separation of acrylic acid crystals from a suspension S of its crystals in mother liquor is in particular then advantageous if the suspension S, based on their molar Content of acrylic acid, a comparatively high molar Total content of components other than acrylic acid having.

Thus, the process according to the invention is particularly suitable for the separation of crystals of acrylic acid which are based on the product gas mixture of a heterogeneously catalyzed partial gas phase oxidation of a C ₃ precursor compound of acrylic acid (eg propane, propylene, acrolein, propionic acid, propanol, glycerol and / or propionaldehyde ) (see eg. WO 2004/035514 . DE-A 10 2007 004960 . DE-A 102 43625 and DE-A 103 23758 ).

Accordingly come as inventively suitable suspensions S z. For example, consider all those in the scriptures DE-A 10 2007 043759 . WO 01/77056 . DE-A 10 2007 043758 . DE-A 10 2007 043748 and DE-A 10 2007 004960 be revealed.

Such suspensions S can, for. B. have one of the following sets of contents:
≥ 70% by weight of acrylic acid,
up to 15% by weight of acetic acid,
up to 5% by weight of propionic acid,
up to 5% by weight low molecular weight aldehydes,
up to 3% by weight of polymerization inhibitors,
0 to 5 wt .-% diacrylic acid (Michael adduct), and
up to 25% by weight of water;

or
≥ 80% by weight of acrylic acid,
≥ 100 wt. Ppm to ≤ 10 wt.% Acetic acid,
≥ 10 wt. Ppm to ≤ 5 wt.% Propionic acid,
up to 5% by weight low molecular weight aldehydes,
up to 3% by weight of polymerization inhibitors,
0 to 5 wt .-% diacrylic acid (Michael adduct), and
up to 10% by weight of water;

or
≥ 90% by weight of acrylic acid,
≥ 100 ppm by weight to ≤ 5% by weight of acetic acid,
≥ 10 wt. Ppm to ≤ 2 wt.% Propionic acid,
up to 2% by weight low molecular weight aldehydes,
up to 2% by weight of polymerization inhibitors,
0 to 3 wt .-% diacrylic acid (Michael adduct), and
up to 9% by weight of water;

or
≥ 95% by weight of acrylic acid,
≥ 100 ppm by weight to ≤ 3% by weight of acetic acid,
≥ 10 wt. Ppm to ≤ 2 wt.% Propionic acid,
up to 2% by weight low molecular weight aldehydes,
up to 2% by weight of polymerization inhibitors,
0 to 2 wt .-% diacrylic acid (Michael adduct), and
up to 4.9% by weight of water;

or
From 93 to 98% by weight of acrylic acid,
From 1 to 5% by weight of water,
0.001 to 3% by weight of acrolein,
≥ 0 to 3% by weight of methacrolein,
≥ 0 to 3% by weight of methacrylic acid,
0.1 to 3% by weight of acetic acid,
From 0.01% to 3% by weight of propionic acid,
0.001 to 3% by weight of formaldehyde,
From 0.001 to 3% by weight of aldehydes other than formaldehyde,
0.01 to 3% by weight of maleic acid, and
≥ 0 to 3 wt .-% protoanemonin.

Everything The above applies in particular when the suspension S at least 0.1 wt .-% water.

Further it is especially true if the suspension S no more than Contains 99 or not more than 98 wt .-% acrylic acid.

Naturally It also applies if both of the above conditions simultaneously are fulfilled.

D. h., for suspensions S, the ≥ 70 to <99 wt .-% acrylic acid and ≥ 0.1 Wt .-% water (often ≤ 20 wt .-%, or ≤ 10 Wt .-% water), is the inventive Method particularly advantageous applicable.

is a separation process for the purifying separation of acrylic acid crystals from a suspension S of its crystals in mother liquor with a hydraulic wash column in a steady state operation (Such a condition is characterized by the fact that the operating conditions depending on the operating time substantially unchanged can be maintained), it may change due to a sudden change Market demand may be required, the throughput through the hydraulic scrubbing column increase or demean to the strength to increase the output of the outlet A pure product stream or mitigate.

Usually is such an increase in throughput necessary with a Increase of the current of the distributor space supplied Stream of the crystal suspension S to a new stationary Value, while the other nature of the suspension S normally remains essentially unchanged. application point advantageous is such an increase in the burden of hydraulic scrubbing column with suspension S implemented as follows. The increase takes place in a step size from 2 to 10% of the respective initial value. After every step is a holding time of 5 to 30 min. respected. When doing so the Bedstand (on the construction front) in its position undesirable changed, a corresponding adjustment of the Steuerlaugestroms performed.

at a decrease in the burden of one, previously in a stationary Operating state operated, hydraulic scrubbing column with suspension S (eg, in response to a decline in pure product demand) can on the other hand, it is advantageous to proceed as follows. When lowering The load (load) can be lowered in one step up to 50% of the respective initial value. One Lowering with correspondingly referenced step sizes from 5 to 20% is also possible. One each subsequent waiting time of 1 to 20 min. is also here appropriate, but not indispensable.

It is advisable to proceed in a similar manner, if in addition or for itself Degree of crystallization of the suspension S and / or the crystal size of the crystals suspended suspended in the suspension S suddenly changes out of a steady state operating condition.

• 1. Ein Verfahren der Inbetriebnahme eines Trennverfahrens zur reinigenden Abtrennung von Acrylsäurekristallen aus einer Suspension S ihrer Kristalle in Mutterlauge mit einer Vorrichtung, die eine hydraulische Waschkolonne umfasst, die einen zu seiner von oben nach unten verlaufenden Längsachse rotationssymmetrischen Prozessraum aufweist, der von einer zylindrischen Mantelwand und zwei auf der Symmetrieachse einander gegenüberliegenden Enden begrenzt wird, wobei
• – sich vom oberen Ende des Prozessraums parallel zu dessen Längsachse ein oder mehrere Filterrohre durch den Prozessraum erstrecken, die auf das dem oberen Ende gegenüberliegende untere Ende des Prozessraums zulaufen, und in der dem unteren Ende des Prozessraums zugewandten Hälfte des Prozessraums wenigstens ein Filter F, das die einzige direkte Verbindung zwischen dem jeweiligen Filterrohrinneren und dem Prozessraum bildet, aufweisen sowie außerhalb des Prozessraums aus der Waschkolonne herausgeführt werden,
• – der Quotient Q = LID aus dem Abstand L zwischen dem oberen und dem unteren Ende des Prozessraums und dem Durchmesser D des Prozessraums 0,3 bis 4 beträgt,
• – sich am unteren Ende des Prozessraums nach unten gerichtet der Kristallschmelzeraum der Waschkolonne anschließt, wobei zwischen den beiden Räumen eine rotationsfähige Abtrageinrichtung integriert und durch den Kristallschmelzeraum ein Kristallschmelzekreis hindurchgeführt ist, der außer dem Kristallschmelzeraum
• – eine außerhalb der Waschkolonne befindliche Förderpumpe P1, die eine Saug- und eine Druckseite aufweist,
• – eine erste Förderverbindung G1, die vom Kristallschmelzeraum der Waschkolonne zur Saugseite der Förderpumpe P1 führt,
• – eine zweite Förderverbindung G2, die von der Druckseite der Förderpumpe P1 in den Kristallschmelzeraum der Waschkolonne zurückführt und einen Auslass A aus dem Kristallschmelzekreis mit regelbarem Durchfluss aufweist, sowie
• – einen Wärmeübertrager W, über den entweder die Förderverbindung G1 vom Kristallschmelzeraum zur Saugseite der Förderpumpe P1, oder die Förderverbindung G2 von der Druckseite der Förderpumpe P1 zum Kristallschmelzeraum geführt ist, umfasst,
• – dem oberen Ende des Prozessraums nach oben gerichtet ein Verteilerraum vorgelagert ist, der vom Prozessraum wenigstens durch einen Boden B getrennt ist, welcher Durchgänge U aufweist, die auf der dem Prozessraum zugewandten Seite des Bodens B in den Prozessraum und auf der vom Prozessraum abgewandten Seite des Bodens B in den Verteilerraum führen,
• – sich außerhalb der Waschkolonne eine Förderpumpe P2, die eine Saug- und eine Druckseite aufweist, und eine Quelle QS der Suspension S befinden, wobei
• – eine erste Förderverbindung E1 von der Quelle QS zur Saugseite der Förderpumpe P2, und
• – eine zweite Förderverbindung E2 von der Druckseite der Förderpumpe P2 in den Verteilerraum führt,
• – sich außerhalb der Waschkolonne gegebenenfalls eine Förderpumpe P3, die eine Saug- und eine Druckseite aufweist, und eine Quelle QT einer Steuerlauge befinden, wobei
• – eine erste Förderverbindung C1 von der Saugseite der Pumpe P3 zur Quelle QT, und
• – eine zweite Förderverbindung C2 von der Druckseite der Pumpe P3 in den Verteilerraum und/oder in den zwischen seinem oberen Ende und den Filtern F der Filterrohre gelegenen Längsabschnitt des Prozessraums führt, und wobei man bei der Durchführung des Trennverfahrens in seinem stationären Betrieb
• – mit der Pumpe P2 kontinuierlich einen Strom ST der Suspension S von der Quelle QS durch die Förderverbindungen E1, E2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne führt,
• – gegebenenfalls mit der Pumpe P3 einen Strom SL der Steuerlauge von der Quelle QT durch die Förderverbindungen C1, C2 über den Verteilerraum und die Durchgänge U hindurch und/oder direkt in den Prozessraum der Waschkolonne führt,
• – über die Filter F der Filterrohre insgesamt einen Strom SM umfassend Mutterlauge und gegebenenfalls Steuerlauge als Ablaugestrom in das Filterrohrinnere hinein- und über die Filterrohre aus der Waschkolonne herausführt, und diesen aus der Waschkolonne herausgeführten Ablaugestrom SM als die Quelle QT für die Steuerlauge verwendet,
• – durch die Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum der Waschkolonne die Ausbildung eines Kristallbetts an Acrylsäurekristallen aufrechterhält, das eine dem oberen Ende des Prozessraums zugewandte Aufbaufront aufweist, an der sich kontinuierlich Kristalle des zugeführten Stroms ST der Suspension S ans Kristallbett anlagern,
• – das Kristallbett durch die aus dem hydraulischen Strömungsdruckverlust der Mutter- und gegebenenfalls Steuerlaugeführung im Prozessraum resultierende Kraft von oben nach unten an den Filtern F vorbei auf die rotierende Abtrageinrichtung zu fördert,
• – mit der rotierenden Abtrageinrichtung vom auf sie stoßenden Kristallbett Acrylsäurekristalle abträgt,
• – den Strom der abgetragenen Acrylsäurekristalle durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei in den sich in Förderrichtung des Kristallbetts an den Prozessraum anschließenden Kristallschmelzeraum fördert, und in dem durch den Kristallschmelzeraum geführten Kristallschmelzekreis durch Eintrag von Wärme mit dem Wärmeübertrager W zu einem Kristallschmelzestrom aufschmilzt, und
• – den Durchfluss des Auslasses A so regelt, dass, bezogen auf die Stärke des vorgenannten Kristallschmelzestroms, vom Kristallschmelzeraum ausgehend ein Teilstrom an Kristallschmelze als Waschschmelzestrom durch die rotierende Abtrageinrichtung hindurch und/oder an der rotierenden Abtrageinrichtung vorbei gegen die Bewegungsrichtung des Kristallbetts in den Prozessraum zurückströmt, wo er im abwärts geförderten Kristallbett aufsteigt und dabei von den Kristallen die im Kristallbett verbliebene und mit diesem unter die Filter F geförderte Mutterlauge abwäscht und zurückdrängt, wobei sich im von den Filtern F bis zum unteren Ende des Prozessraums erstreckenden Längsabschnitt des Prozessraums im Kristallbett eine Waschfront ausbildet, die das Kristallbett von oben nach unten in eine Mutterlaugezone und in eine Waschschmelzezone aufteilt, und der restliche Teilstrom des vorgenannten Kristallschmelzestroms den Kristallschmelzekreis durch den Auslass A verlässt, dadurch gekennzeichnet, dass man bei der Inbetriebnahme des Trennverfahrens zur erstmaligen Ausbildung des Kristallbetts im Prozessraum
• – den den Kristallschmelzeraum umfassenden Kristallschmelzekreis und den Prozessraum der zuvor unbefüllten Waschkolonne mit einer Acrylsäure enthaltenden Anfahrflüssigkeit AT zunächst so befällt, dass die Füllhöhe der Anfahrflüssigkeit AT im Prozessraum wenigstens die Abtrageinrichtung überragt,
• – anschließend die Befüllung der Waschkolonne fortsetzt, indem man mit der Pumpe P2 einen Strom ST* der Suspension S von der Quelle QS durch die Förderverbindungen E1, E2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne und von dem dabei durch die Filterrohre aus der Waschkolonne herausgeführten Ablaugestrom SM* als Quelle QT* gegebenenfalls mit der Pumpe P3 einen Teilstrom als Steuerlaugestrom SL* durch die Förderverbindungen C1, C2 über den Verteilerraum und die Durchgänge U hindurch und/oder direkt in den Prozessraum der Waschkolonne führt, und dies wenigstens so lange, bis der Zeitpunkt t_S erreicht ist, bei dem der Differenzdruck P_D = P_K – P_V, wobei P_K der an einer beliebig ausgewählten Stelle im Kristallschmelzeraum zu einem bestimmten Zeitpunkt der Zufuhr des Stroms ST* jeweils bestehende Druck und P_V der zum jeweils gleichen Zeitpunkt an einer beliebig ausgewählten Stelle im Verteilerraum jeweils bestehende Druck ist, in Abhängigkeit von der Dauer der Zufuhr des Stroms ST* nicht mehr ansteigt oder konstant bleibt, sondern plötzlich abnimmt, und dies mit der Maßgabe, dass
• – bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F, berechnet als der arithmetische Mittelwert des während der Zufuhr des Stroms ST* durch die Filter F der Filterrohre zum jeweiligen Zeitpunkt insgesamt strömenden Ablaugestroms SM*, geteilt durch die Gesamtfläche aller Filter F, nicht mehr als 80 m³/(m²·h) beträgt,
• – die Acrylsäure enthaltende Anfahrflüssigkeit AT eine solche ist, aus der beim Abkühlen bis zur einsetzenden Kristallisation die sich bei der Kristallisation bildenden Kristalle Acrylsäurekristalle sind, und
• – zwischen der in Grad Celsius angegebenen Kristallbildungstemperatur T^KB dieser Acrylsäurekristalle in der Anfahrflüssigkeit AT und der in Grad Celsius angegebenen Temperatur T^S der Suspension S des Stroms ST* die Beziehung TKB ≤ TS + 15°Cerfüllt ist.
• 2. Ein Verfahren gemäß Ausführungsform 1, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F nicht mehr als 75 m³/(m²·h) beträgt.
• 3. Ein Verfahren gemäß Ausführungsform 1, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F nicht mehr als 70 m³/(m²·h) beträgt.
• 4. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 3, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F wenigstens 5 m³/(m²·h) beträgt.
• 5. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 3, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F wenigstens 10 m³/(m²·h) beträgt.
• 6. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 3, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F wenigstens 15 m³/(m²·h) beträgt.
• 7. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 3, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F wenigstens 20 m³/(m²·h) beträgt.
• 8. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 7, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F nicht mehr als 60 m³/(m²·h) beträgt.
• 9. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 7, dadurch gekennzeichnet, dass bis zum Zeitpunkt t_S die mittlere Flächenbelastung der Filter F nicht mehr als 50 m³/(m²·h) beträgt.
• 10. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 9, dadurch gekennzeichnet, dass der Quotient Q ≥ 0,5 beträgt.
• 11. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 9, dadurch gekennzeichnet, dass der Quotient Q ≥ 0,7 beträgt.
• 12. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 11, dadurch gekennzeichnet, dass der Quotient Q ≤ 3,5 beträgt.
• 13. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 11, dadurch gekennzeichnet, dass der Quotient Q ≤ 3 beträgt.
• 14. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 11, dadurch gekennzeichnet, dass der Quotient Q ≤ 2,5 beträgt.
• 15. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 11, dadurch gekennzeichnet, dass der Quotient Q ≤ 2 beträgt.
• 16. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 15, dadurch gekennzeichnet, dass der Abstand L ≥ 0,5 m beträgt.
• 17. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 15, dadurch gekennzeichnet, dass der Abstand L ≥ 0,8 m beträgt.
• 18. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 15, dadurch gekennzeichnet, dass der Abstand L ≥ 1 m beträgt.
• 19. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 8, dadurch gekennzeichnet, dass der Abstand L ≤ 5 m beträgt.
• 20. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 8, dadurch gekennzeichnet, dass der Abstand L ≤ 4 m beträgt.
• 21. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 8, dadurch gekennzeichnet, dass der Abstand L ≤ 3 m beträgt.
• 22. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 21, dadurch gekennzeichnet, dass die Beziehung T^KB ≤ T^S + 10°C erfüllt ist.
• 23. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 21, dadurch gekennzeichnet, dass die Beziehung T^KB ≤ T^S + 5°C erfüllt ist.
• 24. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 23, dadurch gekennzeichnet, dass T^KB nicht mehr als 20°C unterhalb von T^S liegt.
• 25. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 23, dadurch gekennzeichnet, dass T^KB nicht mehr als 10°C unterhalb von T^S liegt.
• 26. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 23, dadurch gekennzeichnet, dass T^KB nicht mehr als 5°C unterhalb von T^S liegt.
• 27. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 26, dadurch gekennzeichnet, dass die Anfahrflüssigkeit AT von der Suspension S abgetrennte Mutterlauge ist.
• 28. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 26, dadurch gekennzeichnet, dass die Anfahrflüssigkeit AT die Schmelze von aus der Suspension S abgetrennten Kristallen ist.
• 29. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 26, dadurch gekennzeichnet, dass die Anfahrflüssigkeit AT aufgeschmolzene Suspension S ist.
• 30. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 26, dadurch gekennzeichnet, dass die Anfahrflüssigkeit AT diejenige Flüssigkeit ist, aus der durch Abkühlen die Suspension S erzeugt wird.
• 31. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 26, dadurch gekennzeichnet, dass die Anfahrflüssigkeit AT eine Mischung aus wenigstens zwei der in den Ansprüchen 27 bis 30 genannten Anfahrflüssigkeiten AT ist.
• 32. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 50% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 80 m³/(m²·h) beträgt.
• 33. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 50% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 70 m³/(m²·h) beträgt.
• 34. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 50% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 60 m³/(m²·h) beträgt.
• 35. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 75% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 80 m³/(m²·h) beträgt.
• 36. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 75% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 70 m³/(m²·h) beträgt.
• 37. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass wenigstens während 75% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 60 m³/(m^{2 .}h) beträgt.
• 38. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zu fuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 80 m³/(m²·h) beträgt.
• 39. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 70 m³/(m²·h) beträgt.
• 40. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 31, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F nicht mehr als 60 m³/(m²·h) beträgt.
• 41. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 40, dadurch gekennzeichnet, dass wenigstens während 50% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F wenigstens 5 m³/(m²·h) oder wenigstens 10 m³/(m²·h) beträgt.
• 42. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 40, dadurch gekennzeichnet, dass wenigstens während 75% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F wenigstens 5 m³/(m²·h) oder wenigstens 10 m³/(m²·h) beträgt.
• 43. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 40, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, die zum jeweiligen Zeitpunkt bestehende Flächenbelastung der Filter F wenigstens 5 m³/(m²·h) oder wenigstens 10 m³/(m²·h) beträgt.
• 44. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 43, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, der arithmetische Mittelwert M des dem Prozessraum der Waschkolonne insgesamt zugeführten Stroms an Flüssigkeit, geteilt durch die freie Querschnittsfläche des Prozessraums 1 bis 30 m³/(m²·h) beträgt.
• 45. Ein Verfahren gemäß Ausführungsform 44, dadurch gekennzeichnet, dass der arithmetische Mittelwert M geteilt durch die freie Querschnittsfläche des Prozessraums 5 bis 25 m³/(m²·h) beträgt.
• 46. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 45, dadurch gekennzeichnet, dass wenigstens während 50% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, der dem Prozessraum der Waschkolonne zum jeweiligen Zeitpunkt insgesamt zugeführte Strom an Flüssigkeit, geteilt durch die freie Querschnittsfläche des Prozessraums 1 bis 30 m³/(m²·h) oder 5 bis 25 m³/(m²·h) beträgt.
• 47. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 45, dadurch gekennzeichnet, dass wenigstens während 75% des Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, der dem Prozessraum der Waschkolonne zum jeweiligen Zeitpunkt insgesamt zugeführte Strom an Flüssigkeit, geteilt durch die freie Querschnittsfläche des Prozessraums 1 bis 30 m³/(m²·h) oder 5 bis 25 m³/(m²·h) beträgt.
• 48. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 45, dadurch gekennzeichnet, dass während des gesamten Zeitraums, gerechnet vom Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunkts t_S, der dem Prozessraum der Waschkolonne zum jeweiligen Zeitpunkt insgesamt zugeführte Strom an Flüssigkeit, geteilt durch die freie Querschnittsfläche des Prozessraums 1 bis 30 m³/(m²·h) oder 5 bis 25 m³/(m²·h) beträgt.
• 49. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 48, dadurch gekennzeichnet, dass der Gehalt der Suspension S an Acrylsäure ≥ 70 Gew.-% beträgt.
• 50. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 48, dadurch gekennzeichnet, dass der Gehalt der Suspension S an Acrylsäure ≥ 80 Gew.-% beträgt.
• 51. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 48, dadurch gekennzeichnet, dass der Gehalt der Suspension S an Acrylsäure ≥ 90 Gew.-% beträgt.
• 52. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 51, dadurch gekennzeichnet, dass der Gehalt der Suspension S an Acrylsäure ≤ 99 Gew.-% beträgt.
• 53. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 52, dadurch gekennzeichnet, dass der Kristallisationsgrad der Suspension S ≥ 0,10 beträgt.
• 54. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 52, dadurch gekennzeichnet, dass der Kristallisationsgrad der Suspension S ≥ 0,20 beträgt.
• 55. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 52, dadurch gekennzeichnet, dass der Kristallisationsgrad der Suspension S ≥ 0,25 beträgt.
• 56. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 55, dadurch gekennzeichnet, dass der Kristallisationsgrad der Suspension S ≤ 0,60 beträgt.
• 57. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 55, dadurch gekennzeichnet, dass der Kristallisationsgrad der Suspension S ≤ 0,50 beträgt.
• 58. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 57, dadurch gekennzeichnet, dass die Längstausdehnung der in der Suspension S enthaltenen Acrylsäurekristalle mehrheitlich 50 bis 1600 μm beträgt.
• 59. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 57, dadurch gekennzeichnet, dass die Längstausdehnung der in der Suspension S enthaltenen Acrylsäurekristalle mehrheitlich 200 bis 900 μm beträgt.
• 60. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 59, dadurch gekennzeichnet, dass das Öffnungsverhältnis OV der Abtrageinrichtung ≥ 0,01 beträgt.
• 61. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 59, dadurch gekennzeichnet, dass das Öffnungsverhältnis OV der Abtrageinrichtung ≥ 0,03 beträgt.
• 62. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 59, dadurch gekennzeichnet, dass das Öffnungsverhältnis OV der Abtrageinrichtung ≤ 0,9 beträgt.
• 63. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 62, dadurch gekennzeichnet, dass die Abtrageinrichtung eine Durchgangsöffnungen aufweisende Messerscheibe ist.
• 64. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 63, dadurch gekennzeichnet, dass, bezogen auf das Gesamtvolumen des Kristallschmelzkreises, 30 bis 60 Vol.-% auf das Volumen des Kristallschmelzeraums entfallen.
• 65. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 64, dadurch gekennzeichnet, dass man den Kristallschmelzekreis und den Prozessraum der zuvor unbefüllten Waschkolonne mit einer Acrylsäure enthaltenden Anfahrflüssigkeit AT zunächst so befüllt, dass die Füllhöhe der Anfahrflüssigkeit AT im Prozessraum wenigstens die Filter F überragt.
• 66. Ein Verfahren gemäß Ausführungsform 65, dadurch gekennzeichnet, dass die Füllhöhe der Anfahrflüssigkeit AT wenigstens bis zur Mitte des Abstands L vom unteren bis zum oberen Ende des Prozessraums ragt.
• 67. Ein Verfahren gemäß Ausführungsform 65, dadurch gekennzeichnet, dass die Füllhöhe der Anfahrflüssigkeit AT wenigstens bis zum letzten Viertel des Abstands L vom unteren bis zum oberen Ende des Prozessraums ragt.
• 68. Ein Verfahren gemäß Ausführungsform 65, dadurch gekennzeichnet, dass die Füllhöhe der Anfahrflüssigkeit AT wenigstens bis zum oberen Ende des Prozessraums ragt.
• 69. Ein Verfahren gemäß Ausführungsform 65, dadurch gekennzeichnet, dass die Füllhöhe der Anfahrflüssigkeit AT über den Prozessraum hinaus bis in den Verteilerraum hineinragt und das Volumen desselben bis wenigstens zur Hälfte ausfüllt.
• 70. Ein Verfahren gemäß Ausführungsform 65, dadurch gekennzeichnet, dass die Füllhöhe der Anfahrflüssigkeit AT über den Prozessraum hinaus bis in den Verteilerraum hineinragt und das Volumen desselben vollständig ausfüllt.
• 71. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 70, dadurch gekennzeichnet, dass der Wärmeübertrager W ein Rohrbündelwärmeübertrager ist.
• 72. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 71, dadurch gekennzeichnet, dass die Temperatur der Suspension S –25 bis +14°C beträgt.
• 73. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 71, dadurch gekennzeichnet, dass die Temperatur der Suspension S –5 bis +12°C beträgt.
• 74. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 71, dadurch gekennzeichnet, dass die Temperatur der Suspension S +4 bis +9°C beträgt.
• 75. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 74, dadurch gekennzeichnet, dass die in der Suspension S enthaltene Mutterlauge ≥ 70 Gew.-%, oder ≥ 80 Gew.-% an Acrylsäure enthält.
• 76. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 75, dadurch gekennzeichnet, dass die in der Suspension S enthaltene Mutterlauge ≤ 99 Gew.-% an Acrylsäure enthält.
• 77. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 76, dadurch gekennzeichnet, dass von dem durch die Filterrohre aus der Waschkolonne herausgeführten Ablaugestrom SM* als Quelle QT* mit der Pumpe P3 ein Teilstrom als Steuerlaugestrom SL* durch die Förderverbindungen C1, C2 über den Verteilerraum und durch die Durchgänge U hindurch in den Prozessraum der Waschkolonne geführt wird.
• 78. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 77, dadurch gekennzeichnet, dass die Förderverbindungen E2 und C2 vor dem Zuführraum der hydraulischen Waschkolonne als koaxiale Rohrleitungen ausgeführt sind, wobei die innen geführte Rohrleitung in Strömungsrichtung vor dem Zuführraum ausläuft, und nur die äußere Rohrleitung als gemeinsame Förderverbindung E2, 02 bis zum Verteilerraum weitergeführt wird.
• 79. Ein Verfahren gemäß Ausführungsform 78, dadurch gekennzeichnet, dass sich der Querschnitt der innen geführten Rohrleitung zu ihrem Auslauf hin verjüngt.
• 80. Ein Verfahren gemäß Ausführungsform 78 oder 79, dadurch gekennzeichnet, dass in der innen geführten Rohrleitung die Suspension S strömt.
• 81. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 80, dadurch gekennzeichnet, dass während der Inbetriebnahme sowohl der Druck P_K als auch der Druck P_V gemessen wird.
• 82. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 81, dadurch gekennzeichnet, dass der Differenzdruck P_D mit einem Differenzdruckmanometer bestimmt wird.
• 83. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 82, dadurch gekennzeichnet, dass ab Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunktes t_S, der Wärmeaustauscher W außer Betrieb ist.
• 84. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 83, dadurch gekennzeichnet, dass ab Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunktes t_S die Förderpumpe P1 außer Betrieb ist.
• 85. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 84, dadurch gekennzeichnet, dass ab Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunktes t_S die rotationsfähige Abtrageinrichtung nicht in Betrieb genommen ist.
• 86. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 85, dadurch gekennzeichnet, dass ab Beginn der Zufuhr des Stroms ST* der Suspension S bis zum Erreichen des Zeitpunktes t_S der Durchfluss des Auslasses A gesperrt ist.
• 87. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 86, dadurch gekennzeichnet, dass nach dem Zeitpunkt t_S der Schmelzkreis und die Abtrageinrichtung in Betrieb genommen und der Durchfluss des Auslasses A geöffnet wird, sowie dem Schmelzkreis ein molekularen Sauerstoff enthaltendes Gas zudosiert wird, in dem in einen Teilstrom des Schmelzkreises das molekularen Sauerstoff enthaltende Gas eingebracht, und anschließend der den molekularen Sauerstoff enthaltende Teilstrom wieder dem Schmelzkreis zugeführt wird.
• 88. Ein Verfahren gemäß Ausführungsform 87, dadurch gekennzeichnet, dass bevor der den molekularen Sauerstoff enthaltende Teilstrom wieder dem Schmelzkreis zugeführt wird, im Teilstrom nicht gelöstes Gas in einem Gasabscheider abgetrennt wird.
• 89. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 88, dadurch gekennzeichnet, dass der Prozessraum der hydraulischen Waschkolonne einen zentralen Verdrängerkörper aufweist.
• 90. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 89, dadurch gekennzeichnet, dass die Höhe der Durchgänge U 200 bis 1000 mm beträgt.
• 91. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 90, dadurch gekennzeichnet, dass die Öffnungen der Durchgänge U, die in den Prozessraum oder in den Verteilerraum führen, eine Querschnittsfläche aufweisen, die, bezogen auf eine kreisrunde Form der Öffnung, einem Durchmesser von 15 bis 300 mm entsprechen.
• 92. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 92, dadurch gekennzeichnet, dass das Verhältnis der Gesamtfläche aller dem Prozessraum zugewandten Öffnungen der Durchgänge U zur Gesamtfläche des Prozessraumquerschnitts 0,10 bis 0,60 beträgt.
• 93. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 92, dadurch gekennzeichnet, dass die Anzahl der Filterrohre in der hydraulischen Waschkolonne 3 bis 200 beträgt.
• 94. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 93, dadurch gekennzeichnet, dass der Innendurchmesser der Filterrohre 5 bis 200 mm beträgt.
• 95. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 93, dadurch gekennzeichnet, dass der Innendurchmesser der Filterrohre 20 bis 80 mm beträgt.
• 96. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 95, dadurch gekennzeichnet, dass die Suspension S nachfolgende Gehalte aufweist. ≥ 70 Gew.-% Acrylsäure, bis zu 15 Gew.-% Essigsäure, bis zu 5 Gew.-% Propionsäure, bis zu 5 Gew.-% niedermolekulare Aldehyde, bis zu 3 Gew.-% Diacrylsäure, und bis zu 25 Gew.-% Wasser.
• 97. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 96, dadurch gekennzeichnet, dass die Suspension S wenigstens 0,1 Gew.-% Wasser enthält.
• 98. Ein Verfahren gemäß einer der Ausführungsformen 1 bis 97, dadurch gekennzeichnet, dass sich an das Verfahren der Inbetriebnahme ein Trennverfahren der reinigenden Abtrennung von Acrylsäurekristallen aus der Suspension S ihrer Kristalle in Mutterlauge in der in Betrieb genommen hydraulischen Waschkolonne anschließt.
• 99. Ein Trennverfahren zur reinigenden Abtrennung von Acrylsäurekristallen aus einer Suspension S ihrer Kristalle in Mutterlauge mit einer Vorrichtung, die eine hydraulische Waschkolonne umfasst, dadurch gekennzeichnet, dass das Trennverfahren gemäß einem Verfahren der Ausführungsformen 1 bis 97 in Betrieb genommen worden ist.
• 100. Ein Verfahren gemäß Ausführungsform 98 oder 99, dadurch gekennzeichnet, dass sich ein weiteres Verfahren anschließt, bei dem abgetrenntes und aufgeschmolzenes Acrylsäurekristallisat einer Polymerisation mit sich oder anderen wenigstens einfach ethylenisch ungesättigten Verbindungen unterworfen wird.

Thus, the present application comprises in particular the following embodiments according to the invention:

• 1. A method of commissioning a separation process for the purifying separation of acrylic acid crystals from a suspension S of their crystals in mother liquor with a device comprising a hydraulic wash column having a rotationally symmetric to its top-to-bottom longitudinal axis process space, of a cylindrical shell wall and two ends opposite to each other on the symmetry axis, wherein
• - extending from the upper end of the process space parallel to the longitudinal axis of one or more filter tubes through the process space, which run towards the upper end of the opposite end of the process space, and in the lower end of the process space facing half of the process space at least one filter F, which forms the only direct connection between the respective filter tube interior and the process space, and are led out of the wash column outside the process space,
• The quotient Q = LID from the distance L between the upper and the lower end of the process space and the diameter D of the process space is 0.3 to 4,
• - Directed at the bottom of the process chamber down the crystal melt space of the wash column, wherein between the two spaces integrated a rotatable Abtrageinrichtung and through the crystal melt space a crystal melt cycle is passed, which except the crystal melt space
• A conveying pump P1 located outside the washing column and having a suction and a pressure side,
• A first conveying connection G1, which leads from the crystal melt space of the washing column to the suction side of the feed pump P1,
• A second conveying connection G2, which leads back from the pressure side of the feed pump P1 into the crystal melt space of the washing column and has an outlet A from the controlled-flow crystal melt circuit, and
• A heat exchanger W, via which either the conveying connection G1 is guided from the crystal melt space to the suction side of the feed pump P1, or the feed connection G2 is guided from the pressure side of the feed pump P1 to the crystal melt space,
• - Upstream of the upper end of the process space, a distribution space is upstream, which is separated from the process space at least by a bottom B, which has passages U, which on the process space facing side of the bottom B in the process room and on the side facing away from the process space lead the floor B into the distributor room,
• - Be outside the wash column, a feed pump P2, which has a suction and a pressure side, and a source QS of the suspension S, wherein
• A first delivery connection E1 from the source QS to the suction side of the delivery pump P2, and
• A second conveying connection E 2 leads from the pressure side of the feed pump P 2 into the distributor space,
• - Outside the scrubbing column optionally a delivery pump P3, which has a suction and a pressure side, and a source QT of a control liquor, wherein
• A first delivery connection C1 from the suction side of the pump P3 to the source QT, and
• A second conveying connection C2 leads from the pressure side of the pump P3 into the distributor space and / or into the longitudinal section of the process space located between its upper end and the filters F of the filter tubes, and in the steady-state operation of the separation process
• - With the pump P2 continuously a stream ST of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and through the passages U passes into the process space of the wash column,
• Optionally with the pump P3, a flow SL of the control liquor from the source QT through the feed connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column,
• Via the filter F of the filter tubes a total of a stream SM comprising mother liquor and optionally control liquor as Ablaugestrom in the filter tube inside and leads out via the filter tubes from the wash column, and this led out of the wash column Ablaugestrom SM used as the source QT for the control liquor
• - Maintains the formation of a crystal bed of acrylic acid crystals by the mother and optionally Steuerlaugeführung in the process chamber of the wash column, which has a the upper end of the process space facing the mounting front, at which continuously accumulate crystals of the supplied stream ST of the suspension S to the crystal bed,
• - Promotes the crystal bed by the force resulting from the hydraulic flow pressure loss of the parent and possibly Steuerlaugeführung in the process space from top to bottom on the filters F on the rotating Abtragageinrichtung
• - removes acrylic acid crystals from the crystal bed impinging on them with the rotating removal device,
• - Promotes the flow of ablated acrylic acid crystals through the rotating Abtragageinrichtung and / or past the rotating Abtrageinrichtung in the direction of conveyance of the crystal bed to the process space subsequent crystal melt space, and in the guided through the crystal melt space Kristallschmelzekreis by entry of heat with the heat exchanger W to melts a crystal melt stream, and
• - Regulates the flow of the outlet A so that, based on the strength of the aforementioned crystalline melt stream, starting from the crystal melt a partial stream of crystal melt as a wash melt stream through the rotating removal device and / or past the rotating removal device against the direction of movement of the crystal bed back into the process space , where it rises in the downwardly conveyed crystal bed and thereby washes off the crystals remaining in the crystal bed and with this under the filter F funded mother liquor and pushed back, wherein extending from the filters F to the lower end of the process space extending longitudinal section of the process chamber in the crystal bed Washing front forms, which divides the crystal bed from top to bottom in a mother liquor zone and in a wash melt zone, and the remaining part stream of the aforementioned crystal melt stream leaves the crystal melt through the outlet A, characterized gekennze ichnet, that you at the start of the separation process for the initial training of the crystal bed in the process room
• - the crystalline melt zone comprising the crystal melt space and the process space of the previously unfilled wash column are initially filled with a start-up liquid AT containing acrylic acid such that the filling level of the start-up liquid AT in the process space exceeds at least the removal device,
• - Subsequently, the filling of the scrubbing column continues by passing with the pump P2 a flow ST * of the suspension S from the source QS through the conveyor connections E1, E2 through the distributor space and through the passages U in the process space of the wash column and of the case the filter tubes from the wash column led out Ablaugestrom SM * as a source QT * optionally with the pump P3 a partial flow as Steuerlaugestrom SL * through the conveyor connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column leads, and this at least until the time t _{S is} reached, at which the differential pressure P _D = P _K - P _V , where P _K of at any selected point in the crystal melt space at a given time of supply of the current ST * each existing pressure and P _V of each at the same time at any selected point in the distribution space existing Dru ck is, depending on the duration of the supply of the current ST * no longer increases or remains constant, but suddenly decreases, and this with the proviso that
• - Until the time t _S, the average surface load of the filter F, calculated as the arithmetic mean of the during the supply of the current ST * through the filter F of the filter tubes at the time in total flowing Ablaugestroms SM *, divided by the total area of all filters F, not is more than 80 m ³ / (m ² · h),
• The starting liquid AT containing acrylic acid is one from which, on cooling to onset of crystallization, the crystals forming on crystallization are acrylic acid crystals, and
• - Between the specified in degrees Celsius crystal formation temperature T ^{KB of} acrylic acid crystals in the start-up liquid AT and the specified in degrees Celsius temperature T ^{S of} the suspension S of the stream ST * the relationship T KB ≤ T S + 15 ° C is satisfied.
• 2. A method according to embodiment 1, characterized in that until the time t _S, the average surface load of the filter F is not more than 75 m ³ / (m ² · h).
• 3. A method according to embodiment 1, characterized in that until the time t _S, the average surface load of the filter F is not more than 70 m ³ / (m ² · h).
• 4. A method according to any one of embodiments 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 5 m ³ / (m ² · h).
• 5. A method according to any one of embodiments 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 10 m ³ / (m ² · h).
• 6. A method according to any one of embodiments 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 15 m ³ / (m ² · h).
• 7. A method according to any one of embodiments 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 20 m ³ / (m ² · h).
• 8. A method according to any one of embodiments 1 to 7, characterized in that until the time t _S, the average surface load of the filter F is not more than 60 m ³ / (m ² · h).
• 9. A method according to any one of embodiments 1 to 7, characterized in that until at the time t _S, the average surface load of the filter F is not more than 50 m ³ / (m ² · h).
• 10. A method according to any one of embodiments 1 to 9, characterized in that the quotient Q ≥ 0.5.
• 11. A method according to any one of embodiments 1 to 9, characterized in that the quotient Q ≥ 0.7.
• 12. A method according to any one of embodiments 1 to 11, characterized in that the quotient Q ≤ 3.5.
• 13. A method according to any one of embodiments 1 to 11, characterized in that the quotient Q ≤ 3.
• 14. A method according to any one of embodiments 1 to 11, characterized in that the quotient Q ≤ 2.5.
• 15. A method according to any one of embodiments 1 to 11, characterized in that the quotient Q ≤ 2.
• 16. A method according to any one of embodiments 1 to 15, characterized in that the distance L ≥ 0.5 m.
• 17. A method according to any one of embodiments 1 to 15, characterized in that the distance L ≥ 0.8 m.
• 18. A method according to any one of embodiments 1 to 15, characterized in that the distance L ≥ 1 m.
• 19. A method according to any one of embodiments 1 to 8, characterized in that the distance L ≤ 5 m.
• 20. A method according to any one of embodiments 1 to 8, characterized in that the distance L ≤ 4 m.
• 21. A method according to any one of embodiments 1 to 8, characterized in that the distance L ≤ 3 m.
• 22. A method according to any of embodiments 1 to 21, characterized in that the relationship T ^KB ≤ T ^S + 10 ° C is satisfied.
• 23. A method according to any one of embodiments 1 to 21, characterized in that the relationship T ^KB ≤ T ^S + 5 ° C is satisfied.
• 24. A method according to any one of embodiments 1 to 23, characterized in that T ^{KB is} not more than 20 ° C below T ^S.
• 25. A method according to any of embodiments 1 to 23, characterized in that T ^{KB is} not more than 10 ° C below T ^S.
• 26. A method according to any one of embodiments 1 to 23, characterized in that T ^{KB is} not more than 5 ° C below T ^S.
• 27. A method according to any one of embodiments 1 to 26, characterized in that the starting liquid AT is separated from the suspension S mother liquor.
• 28. A method according to any one of embodiments 1 to 26, characterized in that the starting liquid AT is the melt of crystals separated from the suspension S.
• 29. A method according to any one of embodiments 1 to 26, characterized in that the starting liquid AT molten suspension S is.
• 30. A method according to any one of embodiments 1 to 26, characterized in that the starting liquid AT is that liquid from which the suspension S is produced by cooling.
• 31. A method according to any one of embodiments 1 to 26, characterized in that the starting liquid AT is a mixture of at least two of the starting liquids AT mentioned in claims 27 to 30.
• 32. A method according to one of the embodiments 1 to 31, characterized in that at least during 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is not more than 80 m ³ / (m ² · h).
• 33. A method according to any one of embodiments 1 to 31, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is not more than 70 m ³ / (m ² · h).
• 34. A method according to one of the embodiments 1 to 31, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is not more than 60 m ³ / (m ² · h).
• 35. A method according to one of the embodiments 1 to 31, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the current ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is not more than 80 m ³ / (m ² · h).
• 36. A method according to one of the embodiments 1 to 31, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is not more than 70 m ³ / (m ² · h).
• 37. A method according to any of embodiments 1 to 31, characterized in that at least during 75% of the period from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S, the existing from time to time the filter surface load F not more than 60 m ³ / (m ^2. h) is.
• 38. A method according to any one of embodiments 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply current ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F is not more than 80 m ³ / (m ² · h).
• 39. A method according to any one of embodiments 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply of the current ST * of the suspension S until reaching the time t _S, the current surface loading of the filter F is not is more than 70 m ³ / (m ² · h).
• 40. A method according to any one of embodiments 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F not more than 60 m ³ / (m ² · h).
• 41. A method according to any one of embodiments 1 to 40, characterized in that at least during 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at that time surface load of Filter F is at least 5 m ³ / (m ² · h) or at least 10 m ³ / (m ² · h).
• 42. A method according to one of the embodiments 1 to 40, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of Filter F is at least 5 m ³ / (m ² · h) or at least 10 m ³ / (m ² · h).
• 43. A method according to any one of embodiments 1 to 40, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at that time surface loading of the filter F at least 5 m ³ / (m ² .h) or at least 10 m ³ / (m ² .h).
• 44. A method according to any one of embodiments 1 to 43, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the arithmetic mean M of the process space of the wash column total supplied stream of liquid, divided by the free cross-sectional area of the process space is 1 to 30 m ³ / (m ² · h).
• 45. A method according to embodiment 44, characterized in that the arithmetic mean M divided by the free cross-sectional area of the process space is 5 to 25 m ³ / (m ² · h).
• 46. A method according to any of embodiments 1 to 45, characterized in that at least during 50% of the period from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the process space of the wash column to the respective Time total supplied stream of liquid, divided by the free cross-sectional area of the process space 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h).
• 47. A method according to any one of embodiments 1 to 45, characterized in that at least during 75% of the period from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the process space of the wash column to the respective Time total supplied stream of liquid, divided by the free cross-sectional area of the process space 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h).
• 48. A method according to any one of embodiments 1 to 45, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the process space of the washing column at the respective time in total supplied stream of liquid, divided by the free cross-sectional area of the process space 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h).
• 49. A method according to any one of embodiments 1 to 48, characterized in that the content of the suspension S of acrylic acid ≥ 70 wt .-% is.
• 50. A method according to any one of embodiments 1 to 48, characterized in that the content of the suspension S of acrylic acid is ≥ 80 wt .-%.
• 51. A method according to any one of embodiments 1 to 48, characterized in that the content of the suspension S of acrylic acid is ≥ 90 wt .-%.
• 52. A method according to any of embodiments 1 to 51, characterized in that the content of the suspension S of acrylic acid is ≦ 99% by weight.
• 53. A method according to any one of embodiments 1 to 52, characterized in that the degree of crystallinity of the suspension S ≥ 0.10.
• 54. A method according to any one of embodiments 1 to 52, characterized in that the degree of crystallinity of the suspension S ≥ 0.20.
• 55. A method according to one of the embodiments Forms 1 to 52, characterized in that the degree of crystallinity of the suspension S ≥ 0.25.
• 56. A method according to any one of embodiments 1 to 55, characterized in that the degree of crystallinity of the suspension S ≤ 0.60.
• 57. A method according to any of embodiments 1 to 55, characterized in that the degree of crystallization of the suspension S ≤ 0.50.
• 58. A method according to any one of embodiments 1 to 57, characterized in that the longest dimension of the acrylic acid crystals contained in the suspension S is mostly 50 to 1600 microns.
• 59. A method according to any one of embodiments 1 to 57, characterized in that the longest dimension of the acrylic acid crystals contained in the suspension S is mostly 200 to 900 microns.
• 60. A method according to any one of embodiments 1 to 59, characterized in that the opening ratio OV of the removal device is ≥ 0.01.
• 61. A method according to any one of embodiments 1 to 59, characterized in that the opening ratio OV of the removal device is ≥ 0.03.
• 62. A method according to any one of embodiments 1 to 59, characterized in that the opening ratio OV of the removal device is ≤ 0.9.
• 63. A method according to any one of embodiments 1 to 62, characterized in that the removal device is a through-hole having cutting disc.
• 64. A method according to any of embodiments 1 to 63, characterized in that, based on the total volume of the crystal melt, accounts for 30 to 60 vol .-% on the volume of the crystal melt space.
• 65. A process according to one of the embodiments 1 to 64, characterized in that the crystal melt cycle and the process space of the previously unfilled wash column are initially filled with a start-up liquid AT containing acrylic acid so that the filling level of the start-up liquid AT projects beyond at least the filters F in the process space.
• 66. A method according to embodiment 65, characterized in that the filling level of the starting liquid AT projects at least to the middle of the distance L from the lower to the upper end of the process space.
• 67. A method according to embodiment 65, characterized in that the filling level of the starting liquid AT protrudes at least until the last quarter of the distance L from the bottom to the top of the process space.
• 68. A method according to embodiment 65, characterized in that the filling level of the starting liquid AT projects at least to the upper end of the process space.
• 69. A method according to embodiment 65, characterized in that the filling level of the starting liquid AT projects beyond the process space into the distributor space and fills the volume thereof to at least half.
• 70. A method according to embodiment 65, characterized in that the filling level of the starting liquid AT projects beyond the process space into the distributor space and completely fills the volume thereof.
• 71. A method according to any one of embodiments 1 to 70, characterized in that the heat exchanger W is a tube bundle heat exchanger.
• 72. A method according to any one of embodiments 1 to 71, characterized in that the temperature of the suspension S is -25 to + 14 ° C.
• 73. A method according to any of embodiments 1 to 71, characterized in that the temperature of the suspension S is -5 to + 12 ° C.
• 74. A method according to any one of embodiments 1 to 71, characterized in that the temperature of the suspension is S +4 to + 9 ° C.
• 75. A method according to any one of embodiments 1 to 74, characterized in that the mother liquor contained in the suspension S contains ≥ 70 wt .-%, or ≥ 80 wt .-% of acrylic acid.
• 76. A method according to any one of embodiments 1 to 75, characterized in that the mother liquor contained in the suspension S contains ≤ 99 wt .-% of acrylic acid.
• 77. A method according to any of embodiments 1 to 76, characterized in that of the led out through the filter tubes from the wash column Ablaugestrom SM * as the source QT * with the pump P3 a partial flow as Steuerlaugestrom SL * through the conveyor connections C1, C2 via the Manifold and is passed through the passages U through into the process space of the wash column.
• 78. A method according to any one of embodiments 1 to 77, characterized in that the conveyor connections E2 and C2 are designed as coaxial piping in front of the feed space of the hydraulic scrubbing column, wherein the internally guided pipe runs in the flow direction in front of the feed space, and only the outer pipe is continued as a common conveyor connection E2, 02 to the distribution room.
• 79. A method according to embodiment 78, characterized in that the transverse cut the internally routed pipe tapers to its outlet.
• 80. A method according to embodiment 78 or 79, characterized in that in the internally guided pipe, the suspension S flows.
• 81. A method according to any one of embodiments 1 to 80, characterized in that during the commissioning of both the pressure P _K and the pressure P _{V is} measured.
• 82. A method according to any one of embodiments 1 to 81, characterized in that the differential pressure P _{D is determined} with a differential pressure gauge.
• 83. A method according to any one of embodiments 1 to 82, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the heat exchanger W is out of operation.
• 84. A method according to any one of embodiments 1 to 83, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S, the feed pump P1 is out of operation.
• 85. A method according to any one of embodiments 1 to 84, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S, the rotatable removal device is not put into operation.
• 86. A method according to any one of embodiments 1 to 85, characterized in that from the beginning of the supply of the stream ST * of the suspension S until the time t _S, the flow of the outlet A is blocked.
• 87. A method according to any one of embodiments 1 to 86, characterized in that after the time t _S, the melt circuit and the removal device is put into operation and the flow of the outlet A is opened, and the molten cycle is a molecular oxygen-containing gas is added, in the gas containing the molecular oxygen is introduced into a partial stream of the melt circuit, and then the partial stream containing the molecular oxygen is returned to the melt circuit.
• 88. A process according to embodiment 87, characterized in that, before the partial stream containing the molecular oxygen is returned to the melt circuit, gas not dissolved in the partial flow is separated off in a gas separator.
• 89. A method according to any of embodiments 1 to 88, characterized in that the process space of the hydraulic wash column has a central displacement body.
• 90. A method according to any of embodiments 1 to 89, characterized in that the height of the passages U is 200 to 1000 mm.
• 91. A method according to one of the embodiments 1 to 90, characterized in that the openings of the passages U, which lead into the process space or in the distribution chamber, have a cross-sectional area, based on a circular shape of the opening, a diameter of 15 up to 300 mm.
• 92. A method according to any one of embodiments 1 to 92, characterized in that the ratio of the total area of all the process space facing openings of the passages U to the total area of the process space cross section is 0.10 to 0.60.
• 93. A method according to any of embodiments 1 to 92, characterized in that the number of filter tubes in the hydraulic scrubbing column is 3 to 200.
• 94. A method according to any one of embodiments 1 to 93, characterized in that the inner diameter of the filter tubes is 5 to 200 mm.
• 95. A method according to any one of embodiments 1 to 93, characterized in that the inner diameter of the filter tubes is 20 to 80 mm.
• 96. A method according to any one of embodiments 1 to 95, characterized in that the suspension S has subsequent contents. ≥ 70 wt .-% acrylic acid, up to 15 wt .-% acetic acid, up to 5 wt .-% propionic acid, up to 5 wt .-% low molecular weight aldehydes, up to 3 wt .-% diacrylic acid, and up to 25 wt .-% Water.
• 97. A method according to any of embodiments 1 to 96, characterized in that the suspension S contains at least 0.1% by weight of water.
• 98. A method according to any one of embodiments 1 to 97, characterized in that adjoining the method of commissioning a separation process of the cleaning separation of acrylic acid crystals from the suspension S of their crystals in mother liquor in the put into operation hydraulic scrubbing column.
• 99. A separation process for purifying separation of acrylic acid crystals from a suspension S of their crystals in mother liquor with a device comprising a hydraulic wash column, characterized in that the separation process has been put into operation according to a method of embodiments 1 to 97.
• 100. A process according to embodiment 98 or 99, characterized in that it is followed by a further process in which separated and melted acrylic acid crystals of a polymerization with one another or at least one other ethylenically unsaturated Compounds is subjected.

Examples and Comparative Examples

Comparative Example 1 (Method of starting up a hydraulic wash column with LID = 4.7 at a mean filter surface loading of 119 m ³ / (m ² · h)

Like in the WO 08/090190 described fractional fractional condensation of the product gas mixture of a two-stage heterogeneously catalyzed gas phase partial oxidation of propylene of purity "chemical grade" were separated on the side of the condensation column per hour 1.5 t of a crude acrylic acid, which had the following contents:
96.1% by weight of acrylic acid,
446 weight cppm acrolein,
20 wt. Ppm allyl acrylate,
3764 ppm by weight of diacrylic acid,
7460 ppm by weight of acetic acid,
6719 wt. Ppm furfural,
7131 ppm by weight of benzaldehyde,
751 ppm by weight of propionic acid,
91 wt. Ppm phenothiazine,
247 wt ppm MEHQ, and
0.83 wt ppm of water.

By continuous addition of 31 kg / h of water to the crude acrylic acid their water content was increased to 2.8 wt .-%. This "watery" raw Acrylic acid was then heated at a temperature fed from 20 ° C a suspension crystallizer. As a suspension crystallizer, a cooling disk crystallizer was used the company GMF (Netherlands) with a capacity used by 2500 l. The crystallizer contained an equidistant spaced arrangement of 7 wiped cooling disks, the one uniform diameter of 1.25 m.

By the cooling disks was used as a coolant a stream of a mixture of 70% by volume of water and 30% by volume of glycol guided, wherein the feed temperature 0.5 to 1 ° C. amounted to. The aqueous crude acrylic acid and the brine were countercurrently viewed over the crystallizer guided by the same. The from the suspension crystallizer led out suspension of acrylic acid crystals in mother liquor had a degree of crystallinity of 0.24 and a temperature from 6.9 to 7.0 ° C.

The thus produced Kristallisatsuspension poured over an overflow weir out of the suspension crystallizer in a stirred heatable container. In selbigem the crystals of the suspension were melted again and the resulting "aqueous" crude Acrylic acid returned to the fractionating condensation (above the side take-off).

On this was a stream of acrylic acid crystal suspension available for commissioning the following hydraulic scrubbing column was used. Furthermore, stood in the collection container re-melted crystal suspension as starting liquid AT available (it had a temperature of 17 ° C on).

The hydraulic wash column was essentially the design according to 1 this writing on. The inner diameter D of the circular cylindrical process chamber (B) was 263 mm. The thickness of the shell wall was 5 mm. Production material was stainless steel ( DIN material 1.4571 ). The length L of the process space (B) was 1230 mm (measured from the upper edge of the Abtragage ( 16 ) inserted cutting disc). The process space (B) had only one filter tube ( 6 ), which was made of the same stainless steel and ran in the center of the process space cross-section from top to bottom. The wall thickness of the circular cylindrical filter tube ( 6 ) was 2 mm. Its outer diameter was 48 mm. The total length of the filter tube ( 6 ) (including displacer ( 38 )) was 1225 mm. The active filter length (height) was 60 mm. The top edge of the filter F ( 7 ) was on a filter tube length of 965 mm (measured from top to bottom). The process space (B) was preceded by a distributor space (A) whose height was 250 mm. Process room (B) and distribution room (A) were separated by a floor B ( 32 ) of thickness 250 mm apart (in the interior of the bottom was the Ablaugesammelraum ( 27 )). Over the ground B ( 32 ) were evenly distributed 3 passes U ( 26 ), which connected the two spaces with circular openings of diameter 26 mm and over the passage section of constant cross-section.

First, the hydraulic wash column ( 0 ) completely filled with the 17 ° C warm starting liquid AT from the collecting container (melt circle ( 31 ) + Process room (B) + distribution room (A) + the conveyor connections E2 ( 34 ), C2 ( 36 ), C1 ( 35 ) + the feed pump P3 ( 13 )). The filling took place through a T-piece on the crystal melt circle.

Subsequently, the feed pump P3 ( 13 ) and set their speed so that they have a flow of 400 kg / h of the starting liquid AT via the conveyor connection C1 (FIG. 35 ) sucked in and in the circle "suction side of the feed pump P3 - pressure side of the feed pump P3 - conveyor connection C2 ( 36 ) - Distribution Room (A) - Process Room (B) - Filter F ( 7 ) - Filter tube ( 16 ) - conveying connection C1 ( 35 ) "(Outlet A ( 3 ) was locked).

Then (with outlet A still blocked, 3 ) and non-operating removal device ( 16 ) (Knife disc) and not in operation located melt circuit ( 31 )) the feed pump P2 ( 8th ) and taken with this the suspension crystallizer via a withdrawal nozzle 1000 kg / h of the suspension S of acrylic acid crystals in mother liquor and via the delivery compound E2 ( 34 ) in addition to the above-mentioned flow of 400 kg / h into the distribution space (A) of the hydraulic scrubbing column ( 0 ) pumped. For pump P2 operating in service ( 8th ) and P3 ( 13 ), the formation of the crystal bed in the process space (B) of the hydraulic scrubbing column ( 0 ) (760 kg / h waste liquor flowed out of the outlet ( 2 ) the wash column device). This was accompanied by an initially parallel increase in the pressures measured with the membrane manometers M1 (pressure in the distributor chamber (A)) and M2 (pressure in the crystal melt chamber (C)).

The filter F ( 7 ) flowing leach flow was 1080 l / h, which corresponds to a (mean) filter surface load of 119 m ³ / (m ² · h). After t _S = 14 min (calculated from the start of operation of the feed pump P2 ( 8th )) Suddenly began to fall, the detected with the M2 membrane manometer pressure P _K, while the detected with the membrane manometer M1 pressure P _V continued to rise, corresponding to a first falling differential pressure P _D = _K P - P _V corresponded.

Immediately after the jump in pressure, the feed pumps P2 ( 8th ) and P3 ( 13 ) (in this order) and the feed pump P1 ( 11 ) as well as the rotation of the cutting disc ( 16 ) (in this order). Subsequently, the feed pumps P2 ( 8th ) (with a capacity of 1000 kg / l) and the feed pump P3 ( 13 ) (with a capacity of 800 kg / h) put back into operation, with the crystal bed set together with the construction front down.

Then the heat exchanger W ( 9 ) and the addition of inhibiting air and 1.5 wt .-% MEHQ having pure melt solution (solution of MEHQ in previously correspondingly separated pure product) in the melt into it. By subsequent partial opening of the flow of the outlet A ( 3 ), Commissioning of the control of the temperature of the melt circuit (the associated temperature sensor was located in the flow direction just after the output of the heat exchanger W), commissioning the control of the position of the mounting front ( 25 ) (the level of the crystal bed) according to WO 2006/111565 and start-up of the control of the wash front ( 37 ) (the associated set temperature was 11.0 ° C), as described in the description, the operating separation process is brought into a steady-state operating state, in which the construction front ( 25 ) 690 to 790 mm above the cutting disc ( 16 ) and the wash front ( 37 ) about 80 mm below the lower edge of the filter F ( 7 ) was. The supplied stream of suspension S was 800 to 1400 kg / h and the Steuerlaugestrom was 400 to 1600 kg / h. Over a period of 14 days, the separation process could be continued substantially trouble-free.

Comparative Example 2 (Method of starting up a hydraulic scrubbing column with L / D = 4.7 at a mean filter surface loading of 67 m ³ / (m ² · h)

It was the same hydraulic wash column as in Comparative Example 1 used. The preparation of the suspension S and the production the starting liquid AT was also carried out as in the comparative example 1 described.

The method of commissioning differed from the commissioning method in Comparative Example 1 only in that the feed pump P3 ( 13 ) up to the time t _S to a delivery rate of 200 kg / h and the feed pump P2 ( 8th ) was set to a capacity of 600 kg / h. The filter F ( 7 ) flowing Ablaugestrom was 610 l / h. This corresponds to a (mean) filter surface load of 67 m ³ / (m ² · h). After t _S = 27 min (calculated from the start of operation of the feed pump P2 ( 8th )) Suddenly began to fall, the detected with the M2 membrane manometer pressure P _K, while the detected with the membrane manometer M1 pressure P _V continued to rise, corresponding to a first falling differential pressure P _D = _K P - P _V corresponded.

Subsequently, the procedure was as in Comparative Example 1. When recommissioning the pump P2 ( 8th ) whose output was 1000 kg / h and the feed pump P3 ( 13 ) adjusted to a capacity of 800 kg / h. The commissioned separation process was smoothly transferred to a stationary operating state, in which the construction front ( 25 ) 690 to 790 mm above the cutting disc ( 16 ) and the wash front ( 37 ) about 80 mm below the lower edge of the filter F ( 7 ) was. The associated stream of suspension S was 800 to 1400 kg / h and the Steuerlaugestrom was 400 to 1600 kg / h. Over a period of 14 days, the separation process could be continued substantially trouble-free.

Comparative Example 3 (Method of starting up a hydraulic scrubbing column with L / D = 1.07 at a mean filter surface load of 92 m ³ / (m ² · h)

Like in the WO 08/090190 described fractional condensation of the product gas mixture of a two-stage heterogeneously catalyzed gas phase partial oxidation of propylene of purity "chemical grade" were the Sei 75 t of a crude acrylic acid which had the following contents per hour:
96.7716% by weight of acrylic acid,
0.8253% by weight of acetic acid,
1.6640% by weight of water,
0.0213% by weight of formic acid,
0.0018% by weight of formaldehyde,
0.0070% by weight of acrolein,
0.0681% by weight of propionic acid,
0.1642% by weight furfurale,
0.0027% by weight of allyl acrylate,
0.0012 wt% allyl formate,
0.0164% by weight of benzaldehyde,
0.1052% by weight of maleic anhydride,
0.3278% by weight of diacrylic acid,
0.0050% by weight of phenothiazine,
0.0180 wt% MEHQ, and
0.0002 wt% molecular oxygen.

The crude acrylic acid led out via the side draw from the condensation column was cooled in several stages by indirect heat exchange (inter alia heat-insulated against mother liquor (waste liquor) which had been recycled to the condensation column and previously carried out as described in Comparative Example 3, to a temperature of 17 ° C. 1230 kg / h of water, which had a temperature of 22 ° C. The resulting "aqueous" crude acrylic acid was then divided into three equally strong substreams and each of the three partial streams was fed into one of three identically constructed, parallel operated cooling disk suspension crystallisers ( see. WO 2006/111565 ).

at These crystallizers were each a trough a capacity of 65000 l, in which 24 wiped circular cooling disks in the equidistant Spaced from each other by 30 ± 1 cm in a row were. Their diameter was uniformly 3.3 m. Through the cooling disks was used as a refrigerant in each case a stream of Mixture of 65 wt .-% water and 35 wt .-% glycol led. The aqueous crude acrylic acid and the brine were considered over the respective suspension crystallizer passed in countercurrent by selbigen. The refrigerant was divided into two equally strong partial flows, each of which is only half of the cooling disks of the respective crystallizer flowed. This was the procedure that the respective partial flow of the flowed through him Cooling disk to the next but one cooling disk was passed on. A partial flow led through the "even" figured Cooling disks, while the other partial flow through the "odd" numbered cooling disks flowed (each in the sense of a series connection, the numbering the cooling disks in the direction of flow of the refrigerant first cooling plate with "1" starting). The strength of the respective partial flow was (based on a Crystallizer) 95 to 105 t / h. The temperature of the refrigerant amounted to entry in the direction of flow respectively front cooling disc 2.5 ° C. The wall thickness of made of stainless steel cooling surfaces of the cooling disks was 4 mm. By wiping the cooling disks was the Formation of crystalline deposits on the cooling surfaces suppressed.

The each led out of the three suspension crystallizers Suspension of acrylic acid crystals in mother liquor pointed a temperature of 7.0 to 7.1 ° C and a degree of crystallization from 0.25 to. The speed of the cooling disk wiper was 5 revolutions per minute. The wipers were in the radial direction segmented (4 segments). The wiper material was Ultra High Molecular Weight polyethylene used.

In the conveying direction of the crystal suspension forming the rearmost part of the respective suspension crystallizer (behind the last cooling disk), the crystal suspension formed in each case via an overflow weir in a stirred buffer tank common to all three crystallizers (see. DE-A 10 2007 043759 ). 33 to 37 t per hour of suspension S at a temperature of 7.4 ° C. were pumped out of this buffer vessel into the distributor space of a first hydraulic washing column already in stationary operating state, in order to subject it to a cleaning separation process.

A corresponding residual stream of suspension S flowed into a heated and circulated collecting container. This collecting container was also fed the separated in the first hydraulic wash column mother liquor. Furthermore, in the collecting container, the acrylic acid crystals of the suspension S supplied to it were melted again by appropriate supply of heat so that a starting liquid AT, whose temperature was 18 ° C., could be taken from the collecting container. This was first recycled in its total amount of flow above the side offtake of the crude acrylic acid in the condensation column. In this way, both a start-up liquid AT and a suspension S was available with which a second hydraulic wash column could be put into operation whose design, except for the differential pressure gauge M3, which was not installed, that in 2 this font corresponded.

The inner diameter D of the circular cylindrical process chamber (B) was 1400 mm. The thickness of the jacket wall was 10 mm. Production material was stainless steel ( DIN material 1.4571 ). The length L of the process space (B) was 1500 mm (measured from the upper edge of the as a removal device ( 16 ) inserted cutting disc).

The process room comprised 54 identical filter tubes ( 6 ) (made of the same material as the shell wall). The wall thickness of the circular cylindrical filter tubes ( 6 ) was 5 mm. The Filterrohraußendurchmesser was 48 mm. The total length of a filter tube ( 6 ) was 1497 mm (including displacement ( 38 )). Of this, 60 mm accounted for the height of the filter F ( 6 ), which extended over the entire Filterrohrumfang. The top edge of a filter F ( 7 ) was on a filter tube length of 1182 mm (measured from top to bottom). The length of the filter tube displacer ( 38 ) extended to 250 mm. The central cylindrical displacement body ( 43 ) in the process space (B) had an outer diameter of 350 mm. He was with the ground B ( 32 ) and thereby standing (ie not rotating) executed. The arrangement (distribution) of the filter tubes ( 6 ) in the soil B ( 32 ) and the passages U ( 26 ) corresponded to the doctrine of EP-A 1 448 282 , The number of passes U ( 26 ) was 78, its length (from the distribution room to the process room) was 600 mm. They have a constant over their length circular cross-section, the diameter was uniformly 83 mm. The height of the distributor space (A) was 1700 mm.

First, the hydraulic wash column ( 0 ) completely filled with the start-up liquid AT having 18 ° C from the collecting container (melt circle ( 31 ) + Process room (B) + distribution room (A) + the conveyor connections E2 ( 34 ), C2 ( 36 ), C1 ( 35 ) + the feed pump P3 ( 13 )). The filling took place via the rinsing liquid feed space ( 40 ) through the rinsing tubes ( 42 ) through.

Subsequently, the feed pump P3 (13) was put into operation and its speed adjusted so that it has a flow of 30,000 kg / h of the starting liquid AT via the conveyor connection C1 (FIG. 35 ) sucked in and in the circle "suction side of the feed pump P3 - pressure side of the feed pump P3 - conveyor connection C2 ( 36 ) - Distribution Room (A) - Process Room (B) - Filter F ( 7 ) - Filter tubes ( 6 ) - conveying connection C1 ( 35 ) "(Outlet A ( 3 ) was locked).

Then (with the outlet A (3) still in the locked state and the removal device not in operation ( 16 ) (Knife disc) and non-operating melt circuit ( 31 )) the feed pump P2 ( 8th ) and taken with this the buffer tank via a withdrawal nozzle 25000 kg / h of the suspension S of acrylic acid crystals in mother liquor and at a temperature of 7.4 ° C and via the conveyor connections E1 ( 33 ), E2 ( 34 ) in addition to the above-mentioned stream of 30000 kg / h in the distribution chamber (A) of the hydraulic scrubbing column ( 0 ) pumped. For pump P2 operating in service ( 8th ) and P3 ( 13 ) the formation of the crystal bed in the process space of the hydraulic scrubbing column took place ( 0 ) (18,750 kg / h waste liquor flowed out of the outlet ( 2 ) the wash column device). This was accompanied by an initially parallel increase in the pressures measured with the membrane manometers M1 (pressure in the distributor chamber (A)) and M2 (pressure in the crystal melt chamber (C)). The filter F ( 7 ) total flowing Ablaugestrom was 45200 l / h, which corresponded to a (mean) filter surface load of 92 m ³ / (m ² · h).

After t _S = 24 min (calculated from the start of operation of the feed pump P2 ( 8th )) Suddenly began to fall, the detected with the M2 membrane manometer pressure P _K, while the detected with the membrane manometer M1 pressure P _V continued to rise, corresponding to a first falling differential pressure P _D = _K P - P _V corresponded.

Immediately after the jump in pressure, the feed pumps P2 ( 8th ) and P3 ( 13 ) (in this order) and the feed pump P1 ( 11 ) as well as the rotation of the cutting disc ( 16 ) (in this order). Subsequently, the feed pumps P2 ( 8th ) with a capacity of 25000 kg / h and the feed pump P3 ( 13 ) with a capacity of 30000 kg / h put back into operation, with the crystal bed set up together with the construction front down.

Then the heat exchanger W ( 9 ) and the addition of inhibiting air and 3 wt .-% MEHQ having pure melt solution in the melt circle into it. By subsequent partial opening of the flow of the outlet A ( 3 ), Commissioning of the control of the temperature of the melt circuit ( 31 ) (the associated temperature sensor was located in the flow direction just after the output of the heat exchanger W), commissioning of the control of the position of the mounting front according to WO 2006/111565 (the state of the crystal bed) and start-up of the regulation of the wash front (the associated target temperature was 11.2 ° C), as described in the description, the separation process in a stationary state operating condition of wash front and mounting front transferred, in which the construction front 700th up to 1200 mm above the cutting disc ( 16 ) and the wash front about 100 mm below the lower edge of the filter F ( 7 ) was.

Of the associated flow of suspension S was 30,000 to 32,000 kg / h and the Steuerlaugestrom was 0 (pump off 3) up to 8000 kg / h.

This operating condition could only ei over period of 6.5 hours. Then the rupture disc inserted for pressure protection broke ( 48 ), which was designed for a set pressure of 10 bar. The pressure measurement M1 up to that point showed increasing pressures, but well below the aforementioned response pressure of 10 bar, in the range <4.5 bar.

A Analysis of the pressure conditions present at the time of rupture of the bursting disk put as a cause of the break a lock in the system of feeder the suspension S in the wash column close.

Comparative Example 4 (Method of starting up a hydraulic scrubbing column with L / D = 1.07 at an average filter surface loading of 115 m ³ / (m ² · h)).

It was the same hydraulic wash column as in Comparative Example 3 used, with the difference that these now additionally equipped with the differential pressure gauge M3. The production the suspension S and the generation of the starting liquid AT was also carried out as described in Comparative Example 3.

The method of commissioning differed from the commissioning method in Comparative Example 3 only in that the feed pump P3 (FIG. 13 ) up to the time t _S to a flow rate of 40000 kg / h and the feed pump P2 ( 8th ) was set to a capacity of 28000 kg / h. The filter F ( 7 ) total flowing Ablaugestrom was 56600 l / h. This corresponds to a (mean) filter surface load of 115 m ³ / (m ² · h).

After 19 minutes (calculated from the start of operation of the feed pump P2 ( 8th )), the differential pressure gauge M3 began to indicate an increasing and decreasing pressure difference. After another 4 minutes, the time t _{S was} reached. The detected with the membrane manometer M2 pressure P _K suddenly began to fall, while the detected with the membrane manometer M1 pressure P _V continued to rise, representing a first falling differential pressure P _D = P _K - corresponded P _V.

Subsequently, the procedure was as in Comparative Example 3. When recommissioning the pump P2 ( 8th ) whose output was 28000 kg / h and the delivery rate of the feed pump P3 ( 13 ) set to 30000 kg / h, with the crystal bed set in motion with its construction front.

The separation process, which was put into operation as described, was transferred, as in Comparative Example 3, to a stationary-state operating state of the wash front and the construction front, in which the construction front was located 700 to 1200 mm above the cutter disk (US Pat. 16 ) and the wash front about 100 mm below the lower edge of the filter F ( 7 ) was. The corresponding stream of suspension S was 30,000 to 33,000 kg / h and the Steuerlaugestrom was 0 to 8000 kg / h. This operating condition could only be maintained for a period of 5 hours. Within this period, the differential pressure gauge M3 showed an increasing increase of the differential pressure. Then the rupture disc inserted for pressure protection broke ( 4 ), which was designed for a set pressure of 10 bar. The diaphragm pressure gauge M1 up to then had shown increasing, but well below the above set pressure of 10 bar pressure in the range <6 bar.

The time course of the pressure differential tracked with the differential pressure gauge M3 shows that in the construction of the crystal bed the same is grown into the distributor space (A) before reaching the time t _S. The steady increase in the aforementioned differential pressure suggests a progressive transfer of the distribution space (A) and a concomitant increasing compression of the in the same Kristallhaufwerks.

example

(Commissioning of a hydraulic scrubbing column according to the invention with L / D = 1.07 at an average filter surface load of 39 m ³ / (m ² · h)).

It was the same hydraulic wash column as in Comparative Example 4 used. The preparation of the suspension S and the production the starting liquid AT was carried out as in the comparative example 3 described.

The method of commissioning differed from the commissioning method in Comparative Example 3 only in that the feed pump P3 (FIG. 13 ) remained out of operation until time t _S and the feed pump P2 ( 8th ) was set to a capacity of 28000 kg / h. The overall through the filter F flowing Ablaugestrom was so 19000 l / h. This corresponds to a (mean) filter surface load of 39 m ³ / (m ² · h). When the feed pump P2 was running on its own, the crystal bed was now set up in the process room. As in the case of the start-up methods of the comparative examples, this was evident from the initially parallel increase in the pressures measured with the manometers M1 and M2.

After 16 minutes (calculated from the start-up of the feed pump P2 ( 8th )) there was an increasing pressure difference in the differential pressure membrane manometer M3. After another 3 minutes, the time t _{S was} reached. The one with the Membrane pressure gauge M2 detected pressure P _K began to fall suddenly, while the detected with the diaphragm manometer M1 pressure P _V further increased, which corresponded to a first falling differential pressure P _D = P _K - P _V.

Subsequently, the procedure was as in Comparative Example 3. When recommissioning the pump P2 ( 8th ) whose delivery rate was set to 30,000 kg / h. In addition to restarting the feed pump P2 ( 8th ) immediately afterwards the pump P3 ( 13 ) with a capacity of 20000 kg / h put into operation, with the crystal bed set in motion with its construction front.

The separation process, which was put into operation as described, was subsequently transferred, with the measures described in Comparative Example 3, to an operating state with a stationary position of the wash front and the construction front, in which the construction front extends 700 to 1200 mm above the cutter disk (FIG. 16 ) and the wash front about 100 mm below the filter F ( 7 ) was. The corresponding stream of suspension S was 30,000 to 35,000 kg / h and the Steuerlaugestrom was 0 to 12,000 kg / h.

about a period of 21 days, the separation process was essentially without interference.

With the restart of the pump P2 ( 8th ) as well as the commissioning of the control lift pump P3 ( 18 ), the differential pressure recorded with the differential pressure gauge M3 began to decrease again. In the further course, the differential pressure increase observed up to time t _S with the differential pressure manometer M3 was completely reduced.

The time course of the differential pressure tracked with the differential pressure gauge M3 proves that during the construction of the crystal bed, the same has grown into the distributor space (A) before reaching the time t _S. The subsequent regression of the differential pressure rise proves that when commissioning according to the invention, however, this obviously unavoidable installation of the distributor space (A) with crystallizate is a reversible one.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

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• - WO 2006/111565 [0017, 0025, 0059, 0107, 0108, 0108, 0113, 0113, 0113, 0140, 0191, 0196, 0208]
• - EP 1448282 A [0017, 0058, 0077, 0082, 0147, 0150, 0151, 0155, 0155, 0155, 0155, 0155, 0158, 0163, 0163, 0202]
• - US 2009/018347 A [0017, 0075, 0113]
• WO 03/041832 [0017, 0074, 0113]
• - WO 01/77056 [0017, 0033, 0036, 0108, 0142, 0169]
• WO 04/35514 [0017]
• WO 03/41833 [0017, 0108]
• WO 02/9839 [0017]
• - DE 10036881 A [0017, 0139]
• WO 02/55469 [0017]
• WO 03/78378 [0017]
• - DE 10228859 A [0056]
• - DE 102008054587 [0056, 0056]
• - DE 102007028333 A [0081]
• - DE 102007028332 A [0081]
• EP 1079194A [0095]
• US 6382313 [0095]
• EP 1232004A [0095]
• WO 01/32301 [0095]
• WO 03/41832 [0108]
• - DE 102006045089 A [0112, 0131]
• - DE 10211290 A [0113]
• - EP 492400 A [0133]
• WO 02/09839 [0139]
• WO 08/090190 [0142, 0180, 0195]
• WO 2004/035514 [0168]
• - DE 10243625 A [0168]
• - DE 10323758 A [0168]

Cited non-patent literature

• - DIN material no. 1.4571 [0074]
• - 1.4539 [0074]
• - 1.4462 [0074]
• - 1.4541 [0074]
• - DIN type 1.4571 [0098]
• - 1.4541 [0098]
• - 1.4306 [0098]
• - 1.0425 [0098]
• - 1.4541 [0098]
• - 1.4571 [0098]
• - 1.4306 [0098]
• - DIN material 1.4571 [0185]
• - DIN material 1.4571 [0201]

Claims (100)

A method of starting up a separation process for the purification separation of acrylic acid crystals from a suspension S of their crystals in mother liquor with a device comprising a hydraulic wash column having a rotationally symmetric to its top-to-bottom longitudinal axis process space, of a cylindrical shell wall and two on the symmetry axis is limited to opposite ends, wherein - extend from the upper end of the process chamber parallel to the longitudinal axis of one or more filter tubes through the process space, which run towards the upper end opposite lower end of the process space, and in the lower end of At least one filter F, which forms the only direct connection between the respective filter tube interior and the process space, and have to be led out of the wash column outside the process space, the quota ient Q = LID from the distance L between the upper and the lower end of the process space and the diameter D of the process space is 0.3 to 4, - at the lower end of the process space directed down the crystal melt space of the wash column connects, wherein between the two A rotatable Abtragageinrichtung integrated and through the crystal melt space a crystal melt cycle is passed, in addition to the crystal melt space - located outside the scrubber feed pump P1, which has a suction and a pressure side, - a first conveying connection G1, from the crystal melt space of the scrubbing column to the suction side of Feed pump P1 leads, - a second feed connection G2, which leads back from the pressure side of the feed pump P1 in the crystal melt space of the wash column and an outlet A from the Kristallschmelzekreis with controllable flow, and - a heat exchanger W, via which either the Förderv compound G1 is guided from the crystal melt space to the suction side of the feed pumps P1, or the feed connection G2 from the pressure side of the feed pump P1 to the crystal melt space, - upstream of the upper end of the process space, a distributor space which is separated from the process space by at least one bottom B. is, which passages U, which lead on the side facing the process space of the bottom B in the process space and on the side facing away from the process space side of the bottom B in the distribution space, - outside the wash column, a feed pump P2, a suction and a suction Pressure side, and a source QS of the suspension S are, wherein - a first conveying connection E1 from the source QS to the suction side of the feed pump P2, and - a second conveying connection E2 from the pressure side of the feed pump P2 leads into the distribution chamber, - outside the wash column optionally a feed pump P3, which has a suction and a D and a source QT of a control liquor, wherein - a first conveying connection C1 from the suction side of the pump P3 to the source QT, and - a second conveying connection C2 from the pressure side of the pump P3 into the distributor space and / or between its upper End and the filters F of the filter tubes longitudinal section of the process space leads, and which is carried out when performing the separation process in its steady operation - with the pump P2 continuously a stream ST of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and passes through the passages U into the process space of the scrubbing column, optionally with the pump P3, a flow SL of the control liquor from the source QT through the feed connections C1, C2 through the distributor space and passages U and / or directly into the process space Washing column leads, - on the filter F of the filter tubes total include a stream SM end mother liquor and optionally control liquor as Ablaugestrom in the filter tube inside and leads out through the filter tubes from the wash column, and this led out of the wash column Ablaugestrom SM used as the source QT for the control liquor, - by the mother and optionally Steuerlaugeführung in the process chamber of the wash column maintains the formation of a crystal bed of acrylic acid crystals, which has a the upper end of the process space facing mounting front at which continuously crystals of the supplied stream ST of the suspension S attached to the crystal bed, - the crystal bed by the hydraulic flow pressure loss of the mother and optionally Steuerlaugeführung to convey the force resulting from the process space from top to bottom past the filters F to the rotating removal device, - to remove acrylic acid crystals from the crystal bed impinging on them with the rotating removal device, - to remove the St ration of the ablated acrylic acid crystals through the rotating removal device and / or past the rotating removal device into the crystal melt space adjoining the process space in the conveying direction of the crystal bed, and in the crystal melt zone guided through the crystal melt space by introducing heat with the heat transferer W into a crystal melt stream melts, and - regulates the flow of the outlet A so that Based on the strength of the aforementioned crystal melt stream, starting from the crystal melt space, a partial stream of crystal melt as a wash melt stream through the rotating removal device and / or flows past the rotating removal device against the direction of movement of the crystal bed in the process space, where it rises in the downwardly conveyed crystal bed and thereby the crystals in the crystal bed and washed with this funded under the filter F mother liquor and pushed back, wherein forms a wash front in the crystal bed from the filters F to the lower end of the process space extending longitudinal portion of the process space in the crystal bed, the crystal bed from top to bottom in a mother liquor zone and divides into a wash melt zone, and the remaining partial stream of the aforementioned crystal melt stream leaves the crystal melt circuit through the outlet A, characterized in that at the start of the Trennve For the first-time formation of the crystal bed in the process space, the crystalline melt zone comprising the crystal melt space and the process space of the previously unfilled wash column are initially filled with starting liquid AT containing acrylic acid so that the filling level of the starting liquid AT in the process space exceeds at least the removal device, followed by the filling of the wash column continues, with the pump P2 a stream ST * of the suspension S from the source QS through the conveyor connections E1, E2 via the distributor space and through the passages U through into the process space of the wash column and thereby led out through the filter tubes from the wash column Ablaugestrom SM * as a source QT * optionally with the pump P3 a partial flow as Steuerlaugestrom SL * through the conveyor connections C1, C2 through the distributor space and the passages U and / or directly into the process space of the wash column leads, and the least ens until the time t _{S is} reached, at which the differential pressure P _D = P _K - P _V , where P _K of each selected at any point in the crystal melt space at a given time of supply of the current ST * existing pressure and P _{V is} the pressure existing at the same time at an arbitrarily selected point in the distributor space, no longer increases or remains constant as a function of the duration of the supply of the current ST *, but suddenly decreases, with the proviso that - to at time t _S, the mean surface loading of the filters F calculated as the arithmetic mean of the total bleed current SM * flowing during the supply of the stream ST * through the filters F of the filter tubes at the respective time, divided by the total area of all the filters F, not more than 80 m ³ / (m ² · h), - the starting liquid AT containing acrylic acid is one from which, on cooling, until it starts crystallization crystallized crystals forming are acrylic acid crystals, and - between the specified in degrees Celsius crystal formation temperature T ^{KB of} acrylic acid crystals in the start-up liquid AT and the temperature specified in degrees Celsius T ^{S of} the suspension S of the stream ST * the relationship T KB ≤ T S + 15 ° C is satisfied. A method according to claim 1, characterized in that until the time t _S, the average surface load of the filter F is not more than 75 m ³ / (m ² · h). A method according to claim 1, characterized in that until the time t _S, the average surface load of the filter F is not more than 70 m ³ / (m ² · h). Method according to one of claims 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 5 m ³ / (m ² · h). Method according to one of claims 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 10 m ³ / (m ² · h). Method according to one of claims 1 to 3, characterized in that until the time t _S, the mean surface load of the filter F is at least 15 m ³ / (m ² · h). Method according to one of claims 1 to 3, characterized in that until the time t _S, the average surface load of the filter F is at least 20 m ³ / (m ² · h). Method according to one of claims 1 to 7, characterized in that until the time t _S, the average surface load of the filter F is not more than 60 m ³ / (m ² · h). Method according to one of claims 1 to 7, characterized in that until the time t _S, the average surface load of the filter F is not more than 50 m ³ / (m ² · h). Method according to one of claims 1 to 9, characterized in that the quotient Q ≥ 0.5. Method according to one of claims 1 to 9, characterized in that the quotient Q ≥ 0.7. Method according to one of claims 1 to 11, characterized in that the quotient Q ≤ 3.5. Method according to one of claims 1 to 11, characterized in that the quotient Q ≤ 3. Method according to one of claims 1 to 11, characterized in that the quotient Q ≤ 2.5. Method according to one of claims 1 to 11, characterized in that the quotient Q ≤ 2. Method according to one of claims 1 to 15, characterized in that the distance L ≥ 0.5 m. Method according to one of claims 1 to 15, characterized in that the distance L ≥ 0.8 m. Method according to one of claims 1 to 15, characterized in that the distance L ≥ 1 m. Method according to one of claims 1 to 8, characterized in that the distance L ≤ 5 m. Method according to one of claims 1 to 8, characterized in that the distance L ≤ 4 m. Method according to one of claims 1 to 8, characterized in that the distance L ≤ 3 m. Method according to one of claims 1 to 21, characterized in that the relationship T ^KB ≤ T ^S + 10 ° C is satisfied. Method according to one of claims 1 to 21, characterized in that the relationship T ^KB ≤ T ^S + 5 ° C is satisfied. Method according to one of claims 1 to 23, characterized in that T ^{KB is} not more than 20 ° C below T ^S. Method according to one of claims 1 to 23, characterized in that T ^{KB is} not more than 10 ° C below T ^S. Method according to one of claims 1 to 23, characterized in that T ^{KB is} not more than 5 ° C below T ^S. Method according to one of claims 1 to 26, characterized in that the starting liquid AT of the suspension S separated mother liquor. Method according to one of claims 1 to 26, characterized in that the starting liquid AT the Melt of crystals separated from the suspension S is. Method according to one of claims 1 to 26, characterized in that the starting liquid AT melted Suspension S is. Method according to one of claims 1 to 26, characterized in that the starting liquid AT the one Liquid is from which by cooling the suspension S is generated. Method according to one of claims 1 to 26, characterized in that the starting liquid AT a Mixture of at least two of those in claims 27 to 30 starting liquids AT is. Method according to one of claims 1 to 31, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F not is more than 80 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F not is more than 70 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F not is more than 60 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the respective time point loading of the filter F not more than 80 m ³ / (m ² .h). Method according to one of claims 1 to 31, characterized in that at least during 75% of the period, calculated from the beginning of Supply of the current ST * of the suspension S until reaching the time t _S , the present at each time existing surface load of the filter F is not more than 70 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the time point surface load of the filter F not is more than 60 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the time surface loading of the filter F no more than 80 m3 / (m ² · h). Method according to one of claims 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the time surface loading of the filter F no more than 70 m ³ / (m ² · h). Method according to one of claims 1 to 31, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the time surface loading of the filter F no more than 60 m ³ / (m ² .h). Method according to one of claims 1 to 40, characterized in that at least for 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the present at the time existing surface load of the filter F at least 5 m ³ / (m ² .h) or at least 10 m ³ / (m ² .h). Method according to one of claims 1 to 40, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the respective time point loading of the filter F at least 5 m ³ / (m ² .h) or at least 10 m ³ / (m ² .h). Method according to one of claims 1 to 40, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the existing at the time surface load of the filter F at least 5 m ³ / (m ² .h) or at least 10 m ³ / (m ² .h). Method according to one of claims 1 to 43, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the arithmetic mean M of the process chamber of the washing column total supplied current in liquid, divided by the free cross-sectional area of the process space is 1 to 30 m ³ / (m ² · h). A method according to claim 44, characterized in that the arithmetic mean M divided by the free cross-sectional area of the process space is 5 to 25 m ³ / (m ² · h). Method according to one of claims 1 to 45, characterized in that at least during 50% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the total supplied to the process space of the scrubbing column at the respective time Stream of liquid divided by the free cross-sectional area of the process space is 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h). Method according to one of claims 1 to 45, characterized in that at least during 75% of the period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the total supplied to the process space of the wash column at the respective time Stream of liquid divided by the free cross-sectional area of the process space is 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h). Method according to one of claims 1 to 45, characterized in that during the entire period, calculated from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the total power supplied to the process space of the wash column at the respective time Liquid, divided by the free cross-sectional area of the process space 1 to 30 m ³ / (m ² · h) or 5 to 25 m ³ / (m ² · h). Method according to one of claims 1 to 48, characterized in that the content of the suspension S of acrylic acid ≥ 70 Wt .-% is. Method according to one of claims 1 to 48, characterized in that the content of the suspension S of acrylic acid ≥ 80 Wt .-% is. Method according to one of claims 1 to 48, characterized in that the content of the suspension S of acrylic acid ≥ 90 Wt .-% is. Method according to one of claims 1 to 51, characterized in that the content of the suspension S of acrylic acid ≤ 99 Wt .-% is. Method according to one of claims 1 to 52, characterized in that the degree of crystallization of the suspension S ≥ 0.10. Method according to one of claims 1 to 52, characterized in that the degree of crystallization of the suspension S ≥ 0.20. Method according to one of claims 1 to 52, characterized in that the degree of crystallization of the suspension S ≥ 0.25. Method according to one of claims 1 to 55, characterized in that the degree of crystallization of the suspension S ≤ 0.60. Method according to one of claims 1 to 55, characterized in that the degree of crystallization of the suspension S ≤ 0.50. Method according to one of claims 1 to 57, characterized in that the longitudinal extension of the in the suspension S contained acrylic acid crystals in the majority 50 to 1600 microns. Method according to one of claims 1 to 57, characterized in that the longitudinal extension of the in the suspension S contained acrylic acid crystals in the majority 200 to 900 microns. Method according to one of claims 1 to 59, characterized in that the aperture ratio OV of the removal device is ≥ 0.01. Method according to one of claims 1 to 59, characterized in that the aperture ratio OV of the removal device is ≥ 0.03. Method according to one of claims 1 to 59, characterized in that the aperture ratio OV the removal device is ≤ 0.9. Method according to one of claims 1 to 62, characterized in that the removal device has a passage openings having knife blade is. Method according to one of claims 1 to 63, characterized in that, based on the total volume of Kristallschmelzkreises, 30 to 60 vol .-% on the volume of the crystal melt space omitted. Method according to one of claims 1 to 64, characterized in that the crystal melt cycle and the Process room of the previously unfilled washing column with a Acrylic acid-containing starting liquid AT first filled so that the filling level of the starting liquid AT in the process space at least the filter F surmounted. Method according to claim 65, characterized that the filling level of the starting liquid AT at least until the middle of the distance L from the lower to the upper End of the process space protrudes. Method according to claim 65, characterized that the filling level of the starting liquid AT at least until the last quarter of the distance L from the bottom protrudes to the top of the process room. Method according to claim 65, characterized that the filling level of the starting liquid AT protrudes at least to the upper end of the process space. Method according to claim 65, characterized that the filling level of the starting liquid AT beyond the process room to the distribution room protrudes and the volume of the same to at least half fills. Method according to claim 65, characterized that the filling level of the starting liquid AT beyond the process room to the distribution room protrudes and the volume of the same completely fills. Method according to one of claims 1 to 70, characterized in that the heat exchanger W is a tube bundle heat exchanger. Method according to one of claims 1 to 71, characterized in that the temperature of the suspension S -25 to + 14 ° C. Method according to one of claims 1 to 71, characterized in that the temperature of the suspension S -5 to + 12 ° C. Method according to one of claims 1 to 71, characterized in that the temperature of the suspension S +4 to + 9 ° C. Method according to one of claims 1 to 74, characterized in that contained in the suspension S Mother liquor ≥ 70 wt .-%, or ≥ 80 wt .-% of acrylic acid contains. Method according to one of claims 1 to 75, characterized in that contained in the suspension S Mother liquor contains ≤ 99 wt .-% of acrylic acid. Method according to one of claims 1 to 76, characterized in that from the through the filter tubes from the Wash column led out Ablaugestrom SM * as a source QT * with the pump P3 a partial flow as Steuerlaugestrom SL * through the conveyor connections C1, C2 via the distributor space and through the passages U through into the process space the washing column is guided. Method according to one of claims 1 to 77, characterized in that the conveyor connections E2 and C2 in front of the feed space of the hydraulic scrubbing column are designed as coaxial pipes, the inside guided pipeline in the flow direction before runs out of the feed space, and only the outer Pipeline as common conveying connection E2, 02 bis continues to the distribution room. Method according to claim 78, characterized in that that is, the cross section of the internally routed pipeline tapered to its spout. A method according to claim 78 or 79, characterized that in the internally routed pipeline the suspension S is streaming. Method according to one of claims 1 to 80, characterized in that during the commissioning of both the pressure P _K and the pressure P _{V is} measured. Method according to one of claims 1 to 81, characterized in that the differential pressure P _{D is determined} with a differential pressure gauge. Method according to one of claims 1 to 82, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S , the heat exchanger W is out of operation. Method according to one of claims 1 to 83, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S, the feed pump P1 is out of operation. Method according to one of claims 1 to 84, characterized in that from the beginning of the supply of the stream ST * of the suspension S until reaching the time t _S, the rotatable removal device is not put into operation. Method according to one of claims 1 to 85, characterized in that from the beginning of the supply of the stream ST * of the suspension S until the time t _S, the flow of the outlet A is blocked. Method according to one of claims 1 to 86, characterized in that after the time t _S, the melt circuit and the removal device is put into operation and the flow of the outlet A is opened, as well as the melt a molecular oxygen-containing gas is added, in which Partial flow of the melt circuit introduced the molecular oxygen-containing gas, and then the molecular oxygen-containing substream is fed back into the melt circuit. Method according to claim 87, characterized in that that before the partial stream containing the molecular oxygen is returned to the melt, not in the partial flow dissolved gas is separated in a gas separator. Method according to one of claims 1 to 88, characterized in that the process space of the hydraulic wash column having a central displacer. Method according to one of claims 1 to 89, characterized in that the height of the passages U is 200 to 1000 mm. Method according to one of claims 1 to 90, characterized in that the openings of the passages U, which lead into the process room or the distribution room, have a cross-sectional area which, based on a circular shape of the opening, a diameter of 15 to 300 mm. Method according to one of claims 1 to 92, characterized in that the ratio of the total area all of the process space facing openings of the passages U to the total area of the process space cross section 0.10 to 0.60. Method according to one of claims 1 to 92, characterized in that the number of filter tubes in the hydraulic Washing column is 3 to 200. Method according to one of claims 1 to 93, characterized in that the inner diameter of the filter tubes 5 to 200 mm. Method according to one of claims 1 to 93, characterized in that the inner diameter of the filter tubes 20 to 80 mm. Method according to one of claims 1 to 95, characterized in that the suspension S has the following contents. ≥ 70% by weight of acrylic acid, up to 15% by weight of acetic acid, up to 5% by weight of propionic acid, up to 5 wt .-% low molecular weight aldehydes, up to 3 wt .-% diacrylic acid, and up to 25 wt .-% water. Method according to one of claims 1 to 96, characterized in that the suspension S at least 0.1 wt .-% Contains water. Method according to one of claims 1 to 97, characterized in that follows the method of commissioning a separation process of purifying separation of acrylic acid crystals from the suspension S of their crystals in mother liquor in the in operation taken hydraulic washing column connects. Separation process for the purification separation of acrylic acid crystals from a suspension S of its crystals in mother liquor with a Device comprising a hydraulic washing column, characterized that the separation method according to a method of claims 1 to 97 has been put into operation. Method according to claim 98 or 99, characterized that is followed by another method in which separated and molten Acrylsäurekristallisat a polymerization at least one ethylenically unsaturated one with itself or with others Compounds is subjected.