DE10149353A1 - Continuous process for the purification of (meth) acrylic acid - Google Patents

Abstract

The invention relates to a method for the purification of (meth)acrylic acid comprising a stage which consists of the following steps a) (meth) acrylic acid is crystallized from a mother liquor; b) crystallized (meth) acrylic acid is separated from the mother liquor; c) at least one part of the separated (meth)acrylic acid crystals is melted; d) the melted part is at least partially returned to step a) or b). The inventive method, the device suitable for carrying out said method and the use of the inventive device for the production of (meth) acrylic acid are characterized by the high purity of the (meth) acrylic acid thus obtained, and high efficiency with regard to the desired yield and amount of energy required.

Description

The present invention is directed to a method for Production of very pure (meth) acrylic acid directed. In particular, this method consists of two Process steps that detail the crystallization and washing the crystallized (meth) acrylic acid.

The processing of (meth) acrylic acid to purities of <99.9% by weight is common for their use in polymers indispensable. For example, in the hygiene area in the Trap of superabsorbents based on polyacrylates required that certain by-products only below the Detection limit may be present.

As an alternative to producing high purity organic substances are crystallization. Technically, two methods are used in particular Application, the suspension crystallization and the Layer crystallization (Wintermantel et al., Chem. Ing. Tech. 1991, 63, 881-891; Steiner et al. Chem. Ing. Tech. 1985, 57, 91-102).

However, crystallization alone is often not enough out to by-products sufficiently well from or from the Remove crystals because of micro inclusions of Mother liquors or installation of impurities Crystal defects etc. among finite Crystal growth conditions cannot be excluded. The sticking of mother liquor on the crystal can also Purity of the products deteriorate.

For this reason, the crystals produced are often re- separation from the mother liquor with washing liquids washed and / or the crystals are a sweating process subjected to any kind of contamination can be depleted.  

Such a process can continuously in so-called Wash columns are carried out. Offers an overview here the dissertation by Poschmann (Zur Suspension crystallization of organic melts and After-treatment of the crystals by sweating and washing, Diss. Uni. Bremen, Shaker Verlag, Aachen 1996).

EP0616998 discloses a method for producing <99.9% by weight acrylic acid starting from pre-cleaned Product with an acrylic acid content of 97.771% by weight. The Cleaning effect is achieved through the interaction of dynamic and static crystallization processes reached. The final crystallization organ takes place here a so-called falling film crystallization application. The Operation of such a system is only discontinuous possible and due to the many process cycles that lead to Obtaining the appropriate purities are necessary high equipment and logistical effort.

From WO99 / 14181 it is known to use crude (meth) acrylic acid Cleaning in a first step to crystallize and in a second step, if necessary, using washing columns work up. The method disclosed there goes directly of the condensation products of the catalytic Gas phase oxidation to produce (meth) acrylic acid. This method describes that the after Washing and separating the crystals of mother liquor is returned to the condensation stage. through this process was obtained from 90.972% by weight Acrylic acid a product with a purity of 98.8816 wt .-%. However, this is for some technical applications unsatisfactory. This is how the salary forms Inhibitors and aldehydes in pure (meth) acrylic acid a critical size that z. Tie downstream polymerization process for disadvantages provides.  

By Nienrood et al. it has been described that acrylic acid can be purified well by suspension crystallization and subsequent treatment in a hydraulic washing column (so-called TNO process; Proc. Bremer International Workshop on Industrial Crystallization, Bremen, 1994, ed .: J. Ulrich, pp. 4-11; Purification Potential of Suspension Growth Melt Crystallization, Proc. 4 ^th International Workshop an Crystal Growth of Organic Materials, Bremen, 1997, ed .: J. Ulrich, Aachen Shaker Verlag, pp. 139-145). The acrylic acid used in these tests was obtained from Aldrich and had a purity of 99.75% by weight. It could be purified to a purity of 99.97% by weight using this method. However, the use of acrylic acid with lower purities has not been disclosed.

The object of the present invention was therefore to provide another method for producing high purity (Meth) acrylic acid from a contaminated raw (Meth) acrylic acid stream from a manufacturing process of (meth) acrylic acid. This procedure should technical scale well applicable and therefore from economic and ecological point of view the process of Be superior to the state of the art. In particular, in this context an excellent one Purification ability, sufficient process stability and especially the possibility of a continuous Procedure to name.

These and other unspecified ones, however, derive from the State of the art tasks are solved by a process with the characteristic features of the Claim 1 solved. Further preferred embodiments this method are dependent on claim 1 Subclaims listed. Claim 8 protects preferred Uses.  

The fact that in a continuous process for the purification of (meth) acrylic acid

• a) Crystallization of (meth) acrylic acid from a contaminated crude (meth) acrylic acid stream from one Process for the production of (meth) acrylic acid,
• b) separating the (meth) acrylic acid crystals from the Mother liquor by means of a washing column, the mother liquor from step b) at least partially in the Step a) leads back, the crude (meth) acrylic acid stream a purity of <99.5% by weight of (meth) acrylic acid has, you get in a surprising way, but for it no less advantageous, too pure products that are also suitable for use in polymers, e.g. B. for the Hygiene area.

It is essential for the successful operation of a washing column essential that the crystals to be washed are hard enough and have a certain narrow size distribution to a appropriate porosity and stability of the resulting to ensure packed or unpacked filter bed. That (meth) acrylic acid even with technical qualities of <99.5% by weight to form the required Crystal properties was not possible before known. It is therefore this property of (Meth) acrylic acid, which allows the inventive Operate process with a wash column and at the same time, the resulting mother liquor, if necessary, directly at least partly due to the crystallization, without the crystal quality by accumulating the To influence by-products so negatively that the The method according to the invention is no longer successful can be executed. This is due to the state of the art Technology in no way suggested.

As mentioned, the method according to the invention can also be used contaminated crude (meth) acrylic acid operated, the <99.5% by weight (meth) acrylic acid. Has preferred crude (meth) acrylic acid used a purity of 50% by weight  up to 95% by weight, preferably 75% by weight to 90% by weight on (meth) acrylic acid.

The condensed mixture can be very particularly preferred a catalytic gas phase oxidation for the production of Use (meth) acrylic acid directly in step a).

As crystallization agents, those are to be used allow the purification process according to the invention to design continuously. Preferably comes Suspension crystallization used. This can advantageously in a stirred tank crystallizer, Scratch crystallizer, cooling disc crystallizer, Crystallization screw, drum crystallizer, Tube bundle crystallizer can be performed. In particular can those mentioned in WO99 / 14181 Crystallization variants for the stated purpose be used. Are of particular advantage here in turn those crystallizers that are continuous can be operated. These are preferably the Cooling disc crystallizers or the scratch cooler (Diss. Poschmann, p. 14). Is very particularly preferred Crystallization used a scratch cooler.

In principle, anyone can do this for the method in question Wash column are used, the continuous Permits operation of the cleaning process according to the invention. In a conventional embodiment, the suspension is in a hydraulic washing column in the upper part of the column given up; the liquid phase (mother liquor) is over a Filter removed from the column, causing a tightly packed crystal bed. The crystal bed will from the liquid phase towards the bottom of the column flows through and through the flow resistance down pressed. At the bottom of the column there is a moving preferably rotating scratching device, which from the densely packed crystal bed and the one at the bottom of the Wash column introduced a melt  Suspension created. This suspension is preferred pumped through a heat exchanger and melted. On Part of the melt can e.g. B. serve as a wash; this is then pumped back into the column and washes the in crystal bed migrating in the opposite direction. The Washing melt on the one hand causes the crystals to be washed, on the other hand, the melt crystallizes on the crystals out. The enthalpy of crystallization released heats up the crystal bed in the washing area of the column. This will a cleaning effect analogous to sweating the crystals achieved. This allows the high-purity production of the (Meth) acrylic acid.

Also comes into question for the invention and primarily a mechanically operated washing column (Diss. Poschmann, P. 18).

In the case of a mechanical washing column - is an example EP 0 193 226 B and NL 1007687 A - is a dense crystal bed within the column by means of a piston permeable to the melt. The piston can be at the top or bottom of the column; in the first case, the suspension is fed in at the top Area of the column, in the second case in the middle or lower area. The piston is for the melt permeable, so that when compressing the melt at the Back of the piston emerges and is pulled off there. Analogous to a hydraulic washing column, this also contains mechanical washing column a device for scraping, for example a moving, preferably rotating Scraper organ to scrape crystals from the crystal bed and to convert it into a suspension with the wash melt. The wash melt moves in countercurrent to Crystal bed. From the side opposite the piston the washing column is withdrawn suspension, and after Part of the melt can melt as a wash melt returned and the other part as a pure product from the Circuit be subtracted.  

Embodiments for suspension crystallization with downstream washing of the crystals in one Hydraulic or mechanical washing columns are the book "Melt Crystallization Technology" by G.F. Arkenbout, Technomic Publishing Co. Inc., Lancaster-Basel (1995), p. 265-288 as well as on the stainless steel freeze concentration article on chemical preconcentration Engineering engineer (72) (10/2000), 1231-1233.

Depending on the intended use, the washing liquid can be one of the Washing liquid familiar to a specialist can be used (at aqueous solutions e.g. B. water). Very particularly preferred are used to wash the crystallized (meth) acrylic acid as already indicated, a subset of the melted Crystals of the same.

This measure ensures on the one hand that Production of high purity products no other substance in that System must be introduced, the other serve the melted crystals but also to push back the Mother liquor front in the wash column and practice at the same time a cleaning effect on the crystals analogous to sweating. A product loss takes place not instead, as the washing liquid is to be washed Crystals crystallized out again and so in Product found (brochure of the company Niro Process Technology B.V., Crystallization and wash column separation set new standards in purity of chemical compounds).

The subject method continues to offer the Possibility of the mother liquor from step b) before the Return to step a) at least once with one treat further purification processes. such Methods are well known to the person skilled in the art.

As such, methods preferably come in detail the following to apply:

1. Simple distillation

Separation into low boilers (acetic acid, water, etc.),  Medium boilers (meth (acrylic acid)) and high boilers (MSA, PTA etc.). Cleaning contaminated (Meth) acrylic acid (especially water and acetic acid) is used in a large part of the cases Azeotropic rectification performed. For use come, for example, entraining agents such as toluene or MIBK (EP 0 695 736 B1).

2. Extraction of acrylic acid

The (meth) acrylic acid can be extractive with n-butanol be won. What remains is an aqueous phase, in the secondary components are solved. The extraction of (meth) acrylic acid from contaminated solutions State of the art such as distillation.

For example, (meth) acrylic acid can be extracted also from aqueous solutions with liquid Ion exchangers, mixtures of tri-n-alkylamines and aliphatic alcohols or n-butanol (Vogel et al .: Chem.Eng.Technol. 23 (2000) 1, pp. 70-74; Tamada et al .: in Solvent Extraction 1990, Ed .: T. Sekine, Elsevier Science Publishers B.V., pp. 1791-1796; JP 57 095 938; WO 98/40342; Information brochure of the SULZER Chemtech company for fractional extraction of (METH) ACRYLIC ACID with n-butanol).

3. Drainage of (meth) acrylic acid by pervaporation DE 44 01 405 A1

Advantageously, the mother liquor from step b) can be treated at least once with a method comprising steps a) and b) before being returned to step a) and the respective purer branched partial stream can be returned in step a) of the original or a previous method, in order to generate maximum purity with a minimal loss of yield. Fig. 2 explains this fact. The mother liquor from the crystal separation in the washing column can also be treated in a next crystallization vessel. The resulting suspension can then be worked up again in a washing column as before. The mother liquor that has now formed can be treated analogously in the following stages. One has the choice of returning the purer partial streams obtained in this procedure to the crystallization of the first purification process or to the crystallization of a previous process. In this way, a maximum of purity with a minimum of waste can be achieved with relatively little expenditure on equipment.

In a further embodiment, the Invention with the use of the invention prepared (meth) acrylic acid in a process for Production of polymers, preferably super absorbers, Detergents or special polymers for the areas: Wastewater treatment, emulsion paints, cosmetics, Textiles, leather finishing, paper production.

Figs. 1 shows a process scheme in which the process (in one step) will be described in summary:

step 1

1

reservoir

2

Intake

1

in

3

3

Suspension generator (e.g. cooling disc crystallizer, scratch cooler)

4

Intake

3

in

5

5

Washing column, hydraulic or mechanical

6

Product cycle

7

Product circulation pump

8th

Product circuit heat exchanger

9

product container

10

Product return for countercurrent washing in the washing column

5

11

Return of mother liquor (optional)

12

Mother liquor container (repeller)

The melt to be separated is fed from the storage container 1 in the liquid state, that is to say at a temperature slightly above equilibrium, via the feed 2 into the suspension generator 3 . By cooling below the equilibrium temperature of the melt, crystals with a suspension density of between 5 and 50% (preferably 20 to 30%) are formed continuously in the suspension generator 3 . The suspension is continuously fed into the washing column 5 via the inlet 4 and separated into a liquid and a solid phase there using moving filters (hydraulic or mechanical, see above). The filtrate leaves the washing column 5 and is continuously fed to the mother liquor container 12 . To increase the yield, it is optionally possible to also return at least part of the filtrate to the suspension generator 3 via the mother liquor return 11 .

The crystals in the washing column 5 are compacted into a crystal bed and, depending on the type of washing column, scraped off at the top or bottom with rotating knives. The scraped-off product crystals are pumped around as a suspension in the product circuit 6 with the circulation pump 7 and melt by introducing the enthalpy of fusion with the heat exchanger 8 .

A part is returned as washing liquid for countercurrent washing in the washing column through the product return 10 . The other part leaves the system as a product in the container 9 .

Is at a minimum with this one-step driving style Not being able to achieve product loss through repulsion the mother liquor from the first crystallization stage optionally in one or more others Crystallization stages or with other cleaning agents be worked up.  

Fig. 2 shows an example of the implementation in several crystallization stages

Level 2/3 etc.

13

1st stage mother liquor container (= 12)

14

Inlet from

13

in

15

15

Level 2 suspension generator (e.g. Cooling disc crystallizer, scratch cooler)

16

Inlet from

15

in

17

17

Washing column, hydraulic or mechanical

18

2nd stage product cycle

19

Product circulation pump

20

Product circuit heat exchanger

22

Product return in

17

23

Return of mother liquor to the 2nd stage crystallizer (optional)

24

2nd stage mother liquor container (repulsion)

25

Mother liquor supply from the 2nd stage in

26

26

Suspension generator level 3 (e.g. cooling disc crystallizer, scratch cooler)

27

Supply of the product

26

in

28

28

Washing column, hydraulic or mechanical

29

3rd stage product cycle

30

Product circulation pump

31

Product circuit heat exchanger

32

Product return in

28

33

Mother liquor return to the 3rd stage crystallizer (optional)

34

Inlet from

28

in

35

35

3rd stage mother liquor container (repulsion)

36

if necessary, feed to further cleaning stages

The mother liquor (12/13) from the 1st stage is fed partly or completely into the suspension generator of the 2nd stage 15th By cooling below the equilibrium temperature of the melt, crystals with a suspension density between 5 and 50% (preferably 20 to 30%) are formed continuously in the suspension generator 15 . The suspension is fed continuously via the feed 16 into the washing column of the second stage ( 17 ), where it is separated into a liquid and a solid phase using moving filters (hydraulic or mechanical, see above).

The crystals are compacted into a crystal bed, depending on the type of washing column 17, scraped off at the top or bottom with rotating knives. The scraped off product crystals are optionally pumped around (as in the 1st stage) as a suspension in the product circuit 18 with the circulation pump 19 and melt by introducing the melting enthalpy with the heat exchanger 20 .

A part can be returned to the washing column as a washing liquid for countercurrent washing ( 22 ). The other part can be returned as a melted product in the suspension generator of the first stage ( 3 ).

The filtrate leaves the washing column 17 and is continuously fed to the mother liquor container 24 . To further increase the yield, it is optionally possible to return at least some of the filtrate to the suspension generator 15 via the mother liquor return 23 and / or to further process it in a third stage.

For this purpose, the mother liquor is passed via 25 into a further suspension generator 26 . The suspension obtained as above is passed via 27 into the washing column 28 , compacted there to form a crystal bed and, depending on the type of the washing column 28, scraped off at the top or bottom with rotating knives. The scraped-off product crystals are optionally pumped around (as in the 1st stage) as a suspension in the product circuit 29 with the circulation pump 30 and melt by introducing the melting enthalpy with the heat exchanger 31 .

Part of it can be returned to the wash column as a washing liquid for countercurrent washing ( 32 ). The other part can be returned as a melted product in the suspension generator of the first stage 3 or the second stage 15 .

Fig. 3 shows a further preferred interconnection of the work-up method of the invention.

41 storage containers
42 suspension generators (e.g. cooling disc crystallizer, scratch cooler)
43 inlet 42 in 44
44 washing column, hydraulic or mechanical
45 Product cycle
46 Product circulation pump
47 Product circuit heat exchanger
48 product containers
49 Product return for countercurrent washing in the washing column 44
50 feed of the second stage = mother liquor from stage 1 (from the washing column 44 )
51 Suspension generator stage 2 (e.g. cooling disc crystallizer, scratch cooler)
52 inlet 51 in 53
53 washing column, hydraulic or mechanical
54 Product from the 2nd stage (suspension, mixed with the original from 41 , which is not carried out in stage 1 but in stage 2), which is fed into the scratch cooler of the 1st stage ( 42 )
55 Product feed pump
56 feed from the first stage ( 41 ) directly into the top of the washing column 53 of the second stage
57 mother liquor return to the crystallizer of the second stage ( 51 ) (optional)
58 second stage mother liquor container (kick)

A particularly preferred variant of a two-stage or multi-stage embodiment leads the melt to be separated from the first stage 41 via the feed 56 and the pump 55 into the top of the washing column of the second stage 53 , where the scraped-off product crystals from the second stage are suspended as 54 Lead suspension generator of the 1st stage 42 . This variant has the energetic advantage of being able to dispense with melting in the second stage and not having to freeze out the crystals now present in the first stage again.

Countercurrent washing in the washing column of the second stage 53 is achieved here by the melt from 41 via inlet 56 of the first stage, which is very pure in comparison to the impurity concentration in the second stage and therefore has a similarly effective washing as a washing with Product enables.

Although a combination of a scratch cooler and one Washing column for the production of organic substances with high purity, it was not foreseeable that this procedure also for concentrating (Meth) acrylic acid with starting purities of <99.5% by weight is very suitable. With regard to the unknown Crystallization properties of (meth) acrylic acid less purity was not expected in a Level of more than 14% can. It was also surprising that the content of Impurities, such as other organic Carbon compounds, by the invention Procedure reduced to values below the detection limit can be. In this way critical sizes can be used such as fufural, inhibitors, acetic acid or maleic acid uncritical values are depleted. This is so The prior art has not been or will not be apparent not suggested by this either.  

Examples of acrylic and methacrylic acid crystallization

In a device according to FIG. 1 with a scratch crystallizer for the production of a suspension and a mechanical washing column with a piston arranged at the bottom and a discharge of the cleaned melt arranged at the top, acrylic acid with the following composition (Table 1) was placed in the scratch cooler.

Table 1

To increase the impurity concentration in the At the beginning, the scratch cooler was additionally approx. 8% water added. Acrylic acid was used as a feed in Table 2 shown composition used.  

Table 2

The scratch cooler was cooled, leaving it in the scratch cooler at about 5 ° C a crystal layer was formed, which through the all-round scrapers in the scratch cooler for formation a suspension was scraped off.

The filtered mother liquor was always completely in the Scratch cooler returned. This concentrated everyone Secondary components in the circuit so that during the Attempts to decrease the acrylic acid content in the scratch cooler steadily. This has been with a continual drop in Scratch cooler temperature compensated to about 2 ° C constant crystal formation due to the lowering of the Allow equilibrium temperature. After about 24 hours of operation showed the liquid phase in the crystallizer (= Filtrate from the wash column) according to the composition Table 3.  

Table 3

The crystal suspension withdrawn from the crystallizer was in the washing column to a compact crystal bed compacted. This was at the top of the crystal bed scraped by means of a rotating scraper as Pumped crystal suspension in the product circuit and through melted the heat exchanger. Part became Countercurrent wash returned to the crystal bed. The other part was continuously won as a product. An example of the product qualities achieved is in Table 4 shows the product analysis of that acrylic acid called which is about 1 hour later than the sample from table 3 was taken, i.e. about 25 hours after the start of the test.  

Table 4

As can be seen from Table 4, this enables Process according to the invention the production of high purity Acrylic acid. An average of 6 kg / h was produced.

Instead of acrylic acid was in the scratch cooler Methacrylic acid with a composition according to Table 5 submitted and additionally added about 2.5% of water.

Table 5

Methacrylic acid with the same composition as in Table 5 was used as a feed for the experiments.

The scratch cooler was cooled, leaving it in the scratch cooler at about 9 ° C a crystal layer was formed, which through the all-round scrapers in the scratch cooler for formation a suspension were scraped off.

The filtered mother liquor was always completely in the Scratch cooler returned. This concentrated everyone Secondary components in the circuit so that during the Tries the methacrylic acid content in the scratch cooler steadily decreased. This has been with a continual drop in Scratch cooler temperature compensated to about 6 ° C constant crystal formation due to the lowering of the Allow equilibrium temperature. After about 4 hours of operation showed the liquid phase in the crystallizer (= Filtrate from the wash column) according to the composition Table 6.

Table 6

The crystal suspension withdrawn from the crystallizer was in the washing column to a compact crystal bed compacted. This was at the top of the crystal bed scraped by means of a rotating scraper as  Pumped crystal suspension in the product circuit and through melted the heat exchanger. Part became Countercurrent wash returned to the crystal bed. The other part was continuously won as a product. An example of the product qualities achieved is in Table 7 shows the product analysis of that methacrylic acid called which is about 1 hour later than the sample from table 6 was taken, i.e. about 5 hours after the start of the experiment.

Table 7

As can be seen from Table 4, this enables Process according to the invention the production of high purity Methacrylic acid. There was an average of 6.5 kg / h produced.

The concentration data were determined by GC. The Color number according to the DIN-ISO 6271 method ASTM D 1364 and the inhibitors (MEHQ) according to ASTM D 3125 certainly.

Claims (8)

1. Continuous process for the purification of (meth) acrylic acid by

• a) crystallization of (meth) acrylic acid from a contaminated crude (meth) acrylic acid stream from a process for the preparation of (meth) acrylic acid,
• b) separating the (meth) acrylic acid crystals from the mother liquor by means of a washing column,

characterized in that the mother liquor from step b) is at least partially returned to step a), the crude (meth) acrylic acid stream having a purity of <99.5% by weight of (meth) acrylic acid. 2. The method according to claim 1, characterized in that the contaminated crude (meth) acrylic acid stream 50% by weight up to 95% by weight, preferably 75% by weight to 90% by weight Has (meth) acrylic acid. 3. Method according to one or more of the preceding Expectations, characterized in that the condensed mixture of a catalytic Gas phase oxidation for the production of (Meth) acrylic acid used directly in step a). 4. Method according to one or more of the preceding Expectations, characterized in that a scratch cooler is used for crystallization. 5. Method according to one or more of the preceding Expectations, characterized in that a mechanically operated washing column Wash column begins.   6. Method according to one or more of the preceding Expectations, characterized in that for washing the crystallized (meth) acrylic acid melted crystals of the same can be used. 7. Method according to one or more of the preceding Expectations, characterized in that the mother liquor from step b) before Return to step a) at least once a method comprising steps a) and b) treated and the more pure branched Partial stream in step a) of the output or Predecessor proceedings. 8. Use of the manufactured according to claim 1 (Meth) acrylic acid for the production of polymers, preferably superabsorbents, detergents or Special polymers for areas such as Wastewater treatment, emulsion paints, cosmetics, Textiles, leather finishing, paper production.