WO2008138785A1 - Selective hydrogenation catalyst - Google Patents

Abstract

A supported catalyst, made from aluminium oxide, containing a) palladium as hydrogenation active metal, b) silver and scandium as additional promoters and a method for selective hydrogenation of unsaturated bonds in hydrocarbon streams using said catalysts are disclosed.

Description

 selective hydrogenation catalyst

description

The present invention relates to supported catalysts based on alumina, comprising a) palladium as the hydrogenation-active metal and b) silver and scandium as additional promoters and processes for the selective hydrogenation of unsaturated compounds in hydrocarbon streams using these catalysts.

In refineries and petrochemical plants, hydrocarbon streams are produced, stored and processed on a large scale. In these hydrocarbon streams, unsaturated compounds are frequently present whose presence, in particular during processing and / or storage, leads to problems or which are not the desired product of value and are therefore undesirable components of the corresponding hydrocarbon streams.

Acetylene is technically disadvantageous in the so-called C2 streams from steam crackers. Because of its tendency to polymerize and inactivate transition metal catalysts for various engineering reactions, acetylene is an undesirable constituent of feedstocks. These streams essentially contain ethylene and ethane as well as small amounts of acetylene. For use of these streams for the production of polyethylene, the acetylene content must be lowered to less than 1 ppm. At catalysts suitable for the hydrogenation of acetylene, high demands are made with regard to their selectivity and activity, since the hydrogenation should take place without loss of ethylene.

Components to be hydrogenated in C3 streams are usually propyne (methylacetylene, MA) and propadiene (Allen, PD).

In C4 streams, 1,3-butadiene can be the desired product. In this case, 1,3-butadiene is extracted and the remaining C4 cut, raffinate I, must be freed by a selective hydrogenation of butadiene traces by selectively hydrogenating the butadiene to butenes.

However, there is no use for pure butadiene, but a high demand for butenes, the high proportion of 1, 3-butadiene from the crude C4 stream of the steam crackers can be selectively hydrogenated to butenes. Furthermore, from this crude C4 cut 1, 2-butadiene, butenine (vinyl acetylene), butyne (ethyl acetylene) and traces of non-separated by distillation propadiene can be hydrogenated.

For some subsequent processes (eg metathesis with ethene to propene) a high content of 2-butenes is required. Since the 2-butenes at the reaction temperatures thermally are dynamically distinctly preferred over 1-butene, these are generally obtained in excess in the hydrogenation. However, if 1-butene is the desired product, special catalysts are required to obtain predominantly 1-butene.

In general, hydrocarbon streams are therefore generally unsaturated compounds having triple bonds (alkynes) and / or diunsaturated compounds (dienes) and / or diunsaturated or polyunsaturated compounds (polyenes, alkenes, alkynenes) and / or aromatic compounds having one or more unsaturated substituents (phenylalkenes and phenylalkynes) to obtain the desired products, such as ethylene, propylene, 1-butene, isobutene, 1, 3-butadiene, aromatics or gasoline fuel in the required quality. However, not every unsaturated compound is always an undesirable component to be removed from the hydrocarbon stream in question. For example, 1, 3-butadiene, as mentioned above, depending on the application, an undesirable secondary component or the desired value product.

The removal of undesired unsaturated compounds from hydrocarbon streams containing them often takes place by selective hydrogenation of some or all of the undesired unsaturated compounds in the corresponding hydrocarbon stream, preferably by selective hydrogenation to non-interfering, higher saturated compounds and particularly preferably to the products of value representing components of the hydrocarbon stream. For example, in C3 streams propyne and propadiene are hydrogenated to propene and in C4 streams butyne to butenes, vinyl acetylene to 1,3-butadiene and / or 1,3-butadiene to butenes.

Typically, such unwanted compounds are to be removed except for residual contents of a few ppm by weight. However, the ("over") hydrogenation to compounds which are more highly saturated than the desired desired product, and / or the parallel hydrogenation of a value product containing one or more multiple bonds to the corresponding higher or fully saturated compound should, as far as possible, be avoided The selectivity of the hydrogenation of the undesired unsaturated compounds must therefore be as high as possible, In addition, a sufficiently high activity of the catalyst and a long service life are generally desired, while at the same time the catalyst should as far as possible cause no other undesirable side reactions to avoid the double bond isomerization of 1-butene to 2-butene, if 1-butene is the desired product.

Usually, noble metal supported catalysts are used for the hydrogenation, in which the noble metal is deposited on a catalyst support. Often, palladium is used as a noble metal, the support generally comprising a porous inorganic oxide, for example, silica, aluminosilicate, titania, zirconia, Zinc aluminate, zinc titanate and / or a mixture of such carriers. In most cases, alumina is used as the carrier material.

EP 0 992 284 A2 describes catalysts for the selective hydrogenation of unsaturated compounds in hydrocarbon streams consisting of noble metal or noble metal compounds on a specific AbC 2 support, wherein the catalyst is defined by a specific X-ray diffraction pattern. This X-ray diffraction pattern is predominantly determined by the carrier.

DE 31 19 850 A1 describes a process for the selective hydrogenation of a diolefin in a hydrocarbon mixture having at least four carbon atoms, which contains an α-olefin, using a catalyst which simultaneously contains palladium or a palladium compound and silver or a silver compound and the palladium content of the catalyst is 0.05-0.5% by weight and the silver content is 0.05-1% by weight.

EP 780 155 A1 describes a selective hydrogenation catalyst in which aluminum oxide in the α-modification is used as carrier material. The supported catalyst is coated with the metals palladium and silver, the content of palladium being 0.01-0.5% by weight and the content of silver being 0.001-0.1% by weight. At least 30% of the metal particles of the catalyst are palladium and / or silver. The ratio of palladium to silver is 0.33-2.50. Further, 80% of the palladium and the silver are in the profile of the thickness of 0.2 r maximum.

EP 0 686 615 A1 relates to a supported catalyst which comprises α-aluminum oxide as carrier material and palladium and silver as metals. The content of palladium is 0.01-0.5% by weight and the content of silver is 0.001-0.02% by weight. 80% of the palladium and silver are in the profile of a thickness of 0.2 r, with the ratio of palladium to silver being 2.50-20.

US 4,404,124 relates to a supported catalyst with the carrier material α-alumina and the metals palladium and silver. The palladium content is 0.01-0.25% by weight, while the silver content is 0.02-0.05% by weight. This results in a ratio of palladium to silver of not more than 0.5. Further, the palladium is present in the shell of the catalyst material to 300 microns, while the silver in the entire cross-section of the catalyst material is present in at least 90% of the catalyst pellets.

US 2002/0165092 A1 relates to a supported catalyst of aluminum oxide, which contains palladium and silver as the hydrogenation metal. The palladium content is 0.002-1.0% by weight. This results in a ratio of palladium to silver of 1-20. The silver and the palladium are uniformly present in the profile, the penetration depth in the Profile is more than 300 microns. In preferred embodiments, the penetration depth of the palladium and the silver is between 500 and 1000 microns.

No. 6,822,127 B2 describes a selective hydrogenation catalyst in which u. a. Aluminum oxide is used as a carrier material. The supported catalyst disclosed in the examples is coated with the hydrogenation-active metal palladium and contains as further active components silver, bismuth and optionally potassium or a lanthanide.

The known catalysts generally have the disadvantage of too low olefin selectivity and pronounced green oil formation, the olefin selectivity being understood to mean the ratio ΔOlefine / ΔAlkine.

The demands on catalysts and processes for the selective hydrogenation of undesired unsaturated compounds in hydrocarbon streams containing them with a view to reducing the residual content of undesired unsaturated compounds after hydrogenation and increasing the selectivity are constantly increasing. Although the known methods and catalysts already operate at a very high technical level, they are still unsatisfactory in view of the increasing demands. It is therefore an object to find an improved catalyst and an improved process for the selective hydrogenation of unsaturated compounds in hydrocarbon streams containing them, the focus being on providing catalysts having high hydrogenation activity, high olefin selectivity, and low green oil formation and associated long lifetime is directed.

The solution to this problem is based on a supported catalyst based on alumina, containing a) palladium as the hydrogenation-active metal and b) silver and scan dium as additional promoters.

A preferred embodiment of the catalyst according to the invention is characterized in that at least 80% of the palladium in a layer between the surface of the catalyst and a penetration depth corresponding to a maximum of 80% of the radius of the catalyst, calculated from the surface of the catalyst, substantially homogeneous and the promoters are substantially homogeneously distributed over the entire cross-section of the catalyst.

In a particularly preferred embodiment, the catalyst has a diameter of 2.0 to 10 mm, most preferably 2.5 to 5 mm, in particular 2.5 to 3.5 mm, wherein at least 80%, preferably at least 90%, especially preferably at least 95%, in particular at least 98%, especially 100% of the palladium in a layer between the surface of the catalyst and a penetration depth of at most 1000 μm, calculated from the surface of the catalyst, in the considerably homogenous and the promoters are distributed substantially homogeneously over the entire cross section.

According to the invention, a catalyst is thus provided in which the palladium forms a shell structure in the catalyst, while the promoters silver and scandium are impregnated.

A further preferred embodiment of the catalyst according to the invention is characterized in that the palladium and the promoters are substantially homogeneously distributed over the entire cross section of the catalyst.

Particularly preferred is an embodiment in which the catalyst has a diameter of 2.0 to 10 mm, most preferably 2.5 to 5 mm, in particular 2.5 to 3.5 mm, and the metals palladium silver and scandium over the entire cross-section is substantially homogeneously distributed.

The catalyst according to the invention may have any shapes, for example strands, hollow strands, tablets, rings, spherical particles or spheres. It is preferred if the catalyst according to the invention is formed as a strand.

The metals can be present in pure metallic form, but also in the form of compounds, for example in the form of metal oxides. Under the operating conditions of a hydrogenation process, palladium and silver are generally in the form of metals. The conversion of any oxides into metals can be carried out in a manner known to those skilled in the art prior to use of the catalyst in a hydrogenation in or outside a hydrogenation reactor, for example by prereduction and, if necessary or advantageous for manipulations with the prereduced catalyst, subsequent surface passivation.

The content of palladium in the catalyst, based on the total weight of the supported catalyst, is generally at least 0.001% by weight, preferably at least 0.005% by weight, particularly preferably at least 0.01% by weight. In general, this content is at most 2.0 wt .-%, preferably at most 1, 5 wt .-%, particularly preferably at most 0.08 wt .-%.

The content of silver in the catalyst, based on the total weight of the supported catalyst, is generally at least 0.001% by weight, preferably at least 0.05% by weight, more preferably at least 0.1% by weight. In general, this content is at most 2 wt .-%, preferably at most 1, 5 wt .-%, particularly preferably at most 0.8 wt .-%. The content of scandium in the catalyst, based on the total weight of the supported catalyst, is generally at least 0.001% by weight, preferably at least 0.05% by weight, more preferably at least 0.1% by weight. In general, this content is at most 2.0 wt .-%, preferably at most 1, 5 wt .-%, most preferably at most 0.8 wt .-%.

Although lower and higher levels of palladium, silver and / or scandium are possible, they are normally unsatisfactory because of too low activity or too high raw material costs.

The ratio of the amounts of palladium and additives or dopants is an individual parameter to be optimized. Generally, the atomic ratio of palladium to silver is in the range of 0.01 to 10, preferably in the range of 0.05 to 7, more preferably in the range of 0.08 to 5 and in scandium in the range of 0.0001 to 10, preferably in the range of 0.001 to 1, particularly preferably in the range of 0.01 to 0.5.

The alumina used as support material for the catalyst according to the invention is preferably present in a mixture of δ-, θ- and α-alumina. The carrier may contain, in addition to unavoidable impurities, other additives to some extent. For example, other inorganic oxides such as oxides of IIA., HIB., IVB., INA. and IVA. Group of the Periodic Table of the Elements, in particular silica, titania, zirconia, zinc oxide, magnesium oxide, sodium oxide and calcium oxide. The maximum content of the support in such oxides other than alumina is dependent on the actual oxide present, but to be determined in the individual case on the basis of the X-ray diffraction pattern of the hydrogenation catalyst, since a change in the structure is accompanied by a significant change in the X-ray diffraction pattern. In general, the content of such, other than alumina oxides, below 50 wt .-%, preferably below 30 wt .-%, more preferably below 10 wt .-%, most preferably below 5 wt .-% , The purity of the alumina is preferably higher than 99%.

The designation of the groups of the periodic system of the elements takes place according to the CAS nomenclature (chemical abstracts service).

To prepare the support, a suitable aluminum-containing raw material, preferably boehmite, is peptized with a peptizer such as water, dilute acid or dilute base. As the acid, for example, a mineral acid such as nitric acid or an organic acid such as formic acid is used. As the base, an inorganic base such as ammonia is preferably used. The acid or base is generally dissolved in water. Preferably, as Peptizer used water or dilute aqueous nitric acid. The concentration of the non-aqueous fraction in the peptizer is generally 0 to 10% by weight, preferably 0 to 7% by weight, particularly preferably 0 to 5% by weight. Following peptization, the support is deformed dried and calcined.

Boehmite (γ-AIO (OH)) is a common commercial product, but can also in a known manner immediately prior to the actual carrier preparation by precipitation from a solution of an aluminum salt, such as aluminum nitrate, with a base, separating, washing, drying and calcination of precipitated solid can be produced. Advantageously, boehmite is used in the form of a powder. A suitable commercial boehmite powder is, for example Versal ^® 250, available from UOP. The boehmite is treated with the peptizer by moistening it with the peptizer and mixing it intensively, for example in a kneader, mixer or pug mill. The peptization is continued until the mass is well malleable. Subsequently, the mass is deformed by conventional methods to the desired carrier moldings, for example by extrusion, extrusion, tableting or agglomeration. For deformation, any known method is suitable. If necessary or advantageous conventional additives can be used. Examples of such additives are extruding or tableting aids, such as polyglycols or graphite.

It is also possible to admix the carrier raw material prior to deformation additives which influence the pore structure of the carrier after KaI- cation in a known manner as Ausbrennstoffe, for example polymers, fibers, natural fuels, such as nutshell flours, or other conventional additives. Preference is given to the use of boehmite in a particle size distribution and the addition of burnout materials, which leads to a pore radius distribution of the finished carrier at which 50 to 90% by volume of the total pore volume in the form of pores having an average diameter in the range of 0 , 01 to 0.1 microns and 10 to 50 vol .-% of the total pore volume in the form of pores having a mean diameter in the range of 0.1 to 1 microns are present. The measures necessary for this purpose are known to those skilled in the art.

Following the deformation, the shaped bodies are dried in a customary manner, generally at a temperature above 60 ^° C., preferably above

80 ⁰ C, more preferably above 100 ⁰ C, most preferably at a temperature in the range of 120 to 300 ⁰ C. The drying is continued until water present in moldings has escaped substantially completely from the moldings, which is generally after a few hours is the case. Typical drying times are in the range of 1 to 30 hours and depend on the set drying temperature, with a higher temperature being the drying time shortened. The drying can be further accelerated by applying a negative pressure.

After drying, the shaped bodies are converted by calcination into a finished carrier. The calcination temperature is generally in the range 900-1150 ⁰ C, preferably in the range from 1000 to 1120 ⁰ C, more preferably in the range of 1050-1100 ⁰ C. The calcination time is generally between 0.5 and 5 hours, preferably between 1 and 4 hours, more preferably between 1, 5 and 3 hours. The calcination is carried out in a conventional furnace, for example in a rotary kiln, in a tunnel kiln, in a belt calciner or in a chamber kiln. The calcination can be followed directly by the drying without intermediate cooling of the moldings.

The supports thus obtained have a specific surface area (BET, Brunauer - Emmet plate, determined in accordance with DIN 66131 by nitrogen adsorption at 77 K) of 20 to 250 m ² / g, preferably 50 to 150 m ² / g, in particular 60 to 90 m ² / g, up. The surface can be varied by known methods, in particular using finely divided or coarser starting materials, calcination time and calcination temperature. Like the BET surface area, the pore volume can also be varied in a known manner; in general, it is determined by means of mercury porosimetry in a range from 0.3 to 1.0 ml / g, preferably in a range from 0.4 to 0.9 ml / g, more preferably in a range of 0.5 to 0.8 ml / g.

The support of the catalyst according to the invention is preferably characterized by the following X-ray diffraction diagram:

Lattice plane spacing angle relative intensity

Angstrom [λ] 2-theta [°] l / lo d = 4,552 19,483 0.05 to 0.15 d = 2.857 31, 278 0.35 to 0.50 d = 2.730 32.775 0.65 to 0.80 d 2,449 36,671 0.45 to 0.55 d = 2.317 38.842 0.35 to 0.45 d = 2.259 39.861 0.35 to 0.45 d = 2.022 44.790 0.45 to 0.65 d = 1, 910 47.570 0, 30 to 0.40 d = 1, 798 50.720 0.10 to 0.25 d = 1, 543 59.915 0.25 to 0.35 d = 1, 51 1 61, 307 0 to 0.35 d = 1, 489 62.289 0.20 to 0.30 d = 1, 455 63.926 0.25 to 0.35 d = 1, 387 67.446 1 This X-ray diffraction pattern is determined as described in EP 0 992 284 A2 on page 9, lines 6 to 9.

X-ray diffraction patterns are characteristic of the specific structure of the investigated material. The structure of the catalyst according to the invention is sufficiently defined by the occurrence of the above-mentioned reflexes. In addition to the characteristic reflections given above, in the X-ray diffraction pattern one or more reflections of any intensity for the interplanar spacings 3,48; 2.55; 2.38; 2.09; 1, 78; 1, 74; 1, 62; 1, 60; 1, 57; 1, 42; 1, 40 and / or 1, 37 all in unit [A].

Furthermore, any further reflections can occur in the X-ray diffraction diagram of the catalyst according to the invention.

On the thus obtained support of the catalyst according to the invention, the active composition and optionally further additives can be deposited.

The metals, additives and / or dopants to be deposited on the carrier can be applied to the carrier by any known method, for example by coating from the gas phase (chemical or physical vapor deposition) or impregnation of the carrier material with a solution containing the substances to be separated off and / or contains compounds.

The preferred method is the impregnation with a solution of the metals to be deposited in the form of their salts or mixtures of their salts, which convert in the course of further catalyst production in the substances to be deposited. These metal salts can be deposited individually and / or in partial quantities in several process steps or together and completely in one process step.

The metal salts are, above all, those salts which can easily be converted into the corresponding oxides in the calcination, for example hydroxides, carbonates, chlorides, nitrates, nitrites, acetates and formates. Some of these metal salt solutions are acidic due to the anions used. Neutral solutions are acidified in a preferred embodiment prior to impregnation by, for example, mineral acids.

A preferred embodiment of the process for preparing the catalyst according to the invention is first the joint deposition of one or more salts of the metals palladium and silver in a impregnation step and subsequent impregnation of the support with a solution of one or more salts of scandium. A likewise preferred embodiment of the process for the preparation of the catalyst according to the invention is first the deposition of one or more salts of scandium in a impregnation stage and subsequent impregnation of the support with a solution of one or more salts of palladium and silver.

A further preferred embodiment of the process for preparing the catalyst according to the invention is the co-deposition of one or more salts of the metals palladium, silver and scandium in a impregnation step.

In general, when the carrier is impregnated with a solution of salts of the components to be separated, the volume of the solution is dimensioned such that the solution is absorbed almost completely by the pore volume of the carrier ("incipient wetness" method) The solution is so dimensioned that after impregnation and conversion of the supported catalyst to the finished catalyst, the components to be deposited are present in the desired concentration on the catalyst The salts are chosen so as not to leave any residue in the preparation of the catalyst or its subsequent use Nitrates or ammonium salts are used.

In a particularly preferred embodiment, impregnation solutions are used which contain palladium nitrate and nitrite as well as silver nitrate and scandium nitrate individually or as mixtures.

In general, the pH of the impregnation solution is at most 5, preferably at most 3, particularly preferably at most 2.5. The lower limit of the pH is generally 0.2, preferably 0.3, more preferably 0.5.

Following the impregnation of the impregnation steps or after the individual geträger- te catalyst is dried, generally at a temperature above 60 ⁰ C, preferably above 80 ⁰ C, more preferably above 100 ⁰ C, in particular at a temperature in the range from 120 to 300 ^° C. Drying is continued until substantially all of the water present in the impregnated catalyst has escaped, which is generally the case after a few hours. Typical drying times are in the range of 1 to 30 hours and depend on the set drying temperature, with a higher drying temperature shortens the drying time. The drying can be further accelerated by applying a negative pressure.

In a particularly preferred embodiment of the process according to the invention, the drying of the impregnated catalyst takes place with simultaneous movement of the impregnated carrier material, for example in a rotary kiln oven. In a particular embodiment of the present invention, the air stream used for drying is passed in countercurrent through the rotary tube.

After drying, the catalyst is prepared in the usual way by calcination. This calcination essentially serves to convert the impregnated salts into the components or precursors of such components to be deposited and differs from the previously described calcination, which serves for the preparation of the support material and the support structure. In the case of impregnation of metal nitrates, in this calcination, substantially the nitrates are decomposed into metals and / or metal oxides remaining in the catalyst and nitrous gases which escape.

The calcination temperature is generally from 200 to 900 ⁰ C, preferably from 280 to 800 ⁰ C, particularly preferably 300 to 700 ⁰ C. The calcination time is generally between 0.5 and 20 hours, preferably between 0.5 and 10 hours , more preferably between 0.5 and 5 hours. The calcination is carried out in a conventional oven, for example in a rotary kiln, in a belt calciner or in a chamber furnace. The calcination may be followed directly by the drying without intermediate cooling of the supported and dried support.

In a particularly preferred embodiment of the process according to the invention, the drying and the calcination of the catalyst are combined in a rotary kiln.

After calcination, the catalyst is in principle ready for use. If required or desired, it is activated by pre-reduction in a known manner prior to incorporation into the hydrogenation reactor and, if appropriate, also passivated on the surface again.

In general, however, the reduction of the hydrogenation catalyst usually takes place only in the hydrogenation reactor itself. This is done by a manner known to those skilled in the art by initial inertization with nitrogen or another inert gas. The reduction is carried out with a hydrogen-containing gas as pure gas phase or under inert circulation. The temperature at which this prereduction is carried out is generally from 5 to 200 ⁰ C, preferably 20 to 150 ⁰ C.

A regeneration of the catalyst according to the invention is possible outside or within the hydrogenation reactor at temperatures of 15 to 500 ⁰ C.

A further subject of the present invention are the hydrogenation catalysts obtainable by this process. The present invention moreover relates to the use of the catalysts according to the invention for the hydrogenation of unsaturated compounds and to corresponding hydrogenation processes.

The selective hydrogenation processes according to the invention are distinguished by the use of the catalyst according to the invention. The hydrogenation processes according to the invention are generally carried out in the same way as the known, heterogeneously catalyzed hydrogenation processes which serve the same purpose. They can be used as heterogeneously catalyzed gas-phase processes in which both the hydrocarbon stream and the hydrogenating hydrogen are in the gas phase, or as heterogeneously catalyzed gas / liquid phase processes in which the hydrocarbon stream is at least partially in liquid phase and hydrogen in the gas phase and / or be present in dissolved form in the liquid phase, carried out. The parameters to be set, such as throughput of hydrocarbon stream, expressed in space velocity in the unit [Nm ³ / m ³ (kat) -h] or mass velocity [t / m ³ (cat) h], based on the catalyst volume, temperature and pressure are chosen analogously to those of known methods. The inlet temperature is usually in the range of 0 to 250 ⁰ C and the pressure in the range of 0.01 to 50 bar. The hydrogenation can be carried out in one or more reaction stages, wherein a catalyst according to the invention is used in at least one reaction stage.

The amount of hydrogen used, based on the amount of the hydrocarbon stream supplied, is dependent on the content of the hydrocarbon stream of undesirable unsaturated compounds and their nature. In general, the amount of hydrogen in an amount of 0.4 to 5 times stoichiometrically full hydrogen conversion during the reactor passage required amount. The hydrogenation of triple bonds usually proceeds faster than that of conjugated double bonds, which in turn are faster than those of unconjugated double bonds. This allows a corresponding control of the process based on the added amount of hydrogen. In special cases, for example, if a high isomerization of 1-butene to cis- or trans-2-butene is desired, a higher hydrogen excess, for example a 10-fold excess of hydrogen, can also be used. The hydrogen may contain inert gases, for example noble gases such as helium, neon or argon, nitrogen, carbon dioxide and / or lower alkanes such as methane, ethane, propane and / or butane. Such inert gases in hydrogen are preferably present in a concentration of less than 30% by volume. Most preferably, the hydrogen is substantially free of carbon monoxide.

The processes can be carried out in one or more reactors connected in parallel or in series, in each case in a single pass or in circulation mode. When carrying out the processes in the gas / liquid phase, the hydrocarbon stream after passing through a reactor is usually Freed from a separator of gases and recycled a portion of the liquid obtained in the reactor. The ratio between recirculated and first fed into the reactor hydrocarbon stream, the so-called reflux ratio is adjusted so that under the other reaction conditions, such as pressure, inlet temperature, flow rate and amount of hydrogen, the adiabatic temperature increase is not too large.

The purposes of the process according to the invention are, for example, the hydrogenation of alkynes to alkadienes, of alkynes, alkynes and alkadienes to alkenes, of phenyllalkynes to phenylalkenes and / or of phenylalkenes to phenylalkanes.

Examples of methods according to the invention are:

For the selective hydrogenation of acetylene in C2 streams to ethylene with minimal formation of ethane (hereinafter referred to as "process A" for simplicity)

For the selective hydrogenation of propyne and / or propadiene in C3 streams to propylene with minimal formation of propane ("process B"),

For the selective hydrogenation of 1-butyne, 2-butyne, 1, 2-butadiene and / or vinylacetylene in C4 streams to give 1,3-butadiene, 1-butene, cis- and / or trans-2-butene ( "Method C"),

For the selective hydrogenation of 1-butyne, 2-butyne, 1, 2-butadiene, 1, 3-butadiene and / or vinyl acetylene in C4 streams to 1-butene, cis- and / or trans-2-butene, butadiene-rich C4 streams ("crude C4 cut") or low butadiene C4 streams ("raffinate I") ("process D"), and

For the selective hydrogenation of unsaturated compounds and / or unsaturated

Substituents of aromatic compounds in C5 + streams to higher saturated compounds and / or aromatic compounds having higher saturated substituents with minimal hydrogenation of the aromatic nuclei ("Process E"),

each using the catalyst of the invention.

Method A: The catalysts according to the invention can preferably be used for the selective hydrogenation of acetylene in hydrocarbon streams. Of particular interest are streams of steam crackers which, in addition to the main constituents ethylene and ethane, contain acetylene in quantities of from 0.01 to 5% by volume. Acetylene-containing hydrocarbon streams are in the gas phase at hydrogen pressures of 0.01 bar to 50 bar, preferably 10 to 30 bar, with a space velocity of the gaseous C2 stream of 500 Nm ³ / m ^{3 *} h, based on the catalyst volume, to 10000 Nm ³ / m ^{3 *} h hydrogenated. Depending on the amount of acetylene to be hydrogenated, the hydrogenation can take place in one or more stages, it being possible to use intermediate cooling and hydrogen feeds in each individual reactor in a manner known per se. An adiabatic procedure is preferred and can be easily realized for acetylene contents of less than 1% by volume.

The inlet temperature of the acetylene-containing hydrocarbon streams in the first reactor are generally 10 to 250 ⁰ C, preferably 15 to 120 ⁰ C, more preferably 25 to 95 ⁰ C. When using only one reactor, the molar ratio of hydrogen to acetylene is usually at 1, 1 to 2: 1, preferably at 1, 2 to 1, 6: 1. By contrast, when using multiple reactors in series with hydrogen supplied to each reactor, it may be 0.6 to 1.2: 1.

The catalysts of the invention are very active in the hydrogenation of acetylene and can be used at relatively low temperatures. They are highly selective even with low acetylene contents, without having to meter in carbon monoxide in the hydrogenation stage. It can be achieved Restacetylengehalte of about 1 ppm, which can be compared to known catalysts with low stoichiometric hydrogen excesses.

Process B: The catalysts according to the invention are also suitable, for example, for use in a process for the selective hydrogenation of unsaturated hydrocarbons from alkene- and / or alkadiene-containing liquid hydrocarbon mixtures whose main constituents contain three carbon atoms in the molecule, the catalyst according to the invention containing the hydrocarbon stream, For example, under the conditions described above, is brought into contact.

Hydrogenation processes for such C3 streams are already known from the prior art. Thus, DE 37 09 328 A1 describes a trickle phase process for the selective hydrogenation of strongly unsaturated hydrocarbons. The process serves for the most extensive and selective removal of highly unsaturated components from alkene-, alkadiene- and / or aromatic-containing liquid hydrocarbon mixtures whose

Main constituents contain at least three carbon atoms in the molecule. The hydrogenation is carried out on a fixed palladium-supported catalyst or a fixed catalyst system consisting of two to four supported palladium catalysts.

A disadvantage of this process using pure palladium catalysts is that the use of pure palladium catalysts can easily lead to an overhydration. tion and green oil production. This has a fast coking result and thus requires short lifetimes of the catalyst used.

In order to prevent this, the palladium-, silver- and scandium-containing catalyst according to the invention is used in a hydrogenation process for the hydrogenation of C3 streams. As a result, the overhydration and green oil formation is reduced. In addition, the palladium used must be located in a certain peripheral zone of the catalyst in order to have sufficient hydrogenation activity of the C3 streams. This is fulfilled by the catalysts of the invention, which have a penetration depth of palladium of up to 1000 microns.

The silver used is also distributed substantially homogeneously over the entire profile of the catalyst. As a result, a green oil formation is reduced or avoided by the catalyst.

The process according to the invention for the hydrogenation of the C3 streams essentially serves for the selective hydrogenation of propylene and / or propadiene contained in these hydrocarbon mixtures to give propene with minimal formation of propane.

In a particularly preferred embodiment, the hydrogenation takes place in one stage.

Alternatively, the hydrogenation can also be carried out in two process stages. The C3 stream thus obtained then has, for example, the following contents, before the respective hydrogenation stages:

The C3 hydrogenation is preferably carried out with a predominantly liquid C3 phase and a hydrogen gas phase.

The pressure is preferably 9 to 30 bar, more preferably 10 to 25 bar, in particular 10 to 16 bar. The inlet temperature is preferably 0 to 50 ⁰ C, more preferably 0 to 40 ⁰ C, in particular 20 to 30 ⁰ C. The temperature increase is preferably 0 to 60 ⁰ C, more preferably 0 to 40 ⁰ C, in particular 0 to 5 ⁰ C. The load (whsv) is preferably 3 to 30 kg / lh, more preferably 5 to 25 kg / lh, in particular 8 to 15 kg / lh. The void space velocity is preferably 0.2 to 20 cm / s, particularly preferably 0.5 to 10 cm / s, in particular 1 to 5 cm / s. The ratio of hydrogen to methylacetylene and propadiene is preferably 0.9 to 2, more preferably 1, 01 to 2.

The reaction is carried out in a manner known to those skilled in the art, for example adiabatic, with boiling or isothermic, preferably isothermal and particularly preferred in the isothermal reaction, the use of a coolant, for. B. ammonia.

Methods C and D: Methods for the hydrogenation of C4 streams are known in the art. Thus, EP 0 523 482 B1 describes a process for the selective hydrogenation of butadiene to butenes in the liquid or trickle phase on fixed noble metal supported catalysts. In this case, a butadiene-rich C4 stream, with butadiene contents of 20-80 wt .-%, based on the C4 stream, hydrogenated in two successive reaction zones so that the hydrogenation product of the first reaction zone 0.1 to 20 wt .-% and the hydrogenation product of the second reaction zone 0.005 to 1 wt .-% residual butadiene, based on the C4 stream containing.

The C4 hydrocarbon mixtures to be used in the present hydrogenation according to the invention are produced mainly in the steam cracking of mineral oil-derived hydrocarbons, eg. Eg naphtha. In addition to the main component 1, 3-butadiene, these hydrocarbon mixtures may also contain small amounts of compounds on cumulated double bonds and / or acetylenic triple bonds. The composition of the crude C4 cut from the steam cracker can vary widely (see Table 1).

Table 1: Typical composition of a C4 cut of a steam cracker, expressed in weight%. C ₄ feed

Total C3 traces <1 1, 3-butadiene 35-70

Isobutene 14 - 35

1-Butene 5-22 trans-2-butene 3-7 cis-2-butene 2-6 butane 1-12 i-butane 0-10

Butenine (vinyl acetylene) 0.3-2 1-butyne (ethylacetylene) 0.1-0.5

1, 2-butadiene 0 - 0.5

Total C5 tracks <1

The composition is essentially dependent on the feedstock and the cracking conditions of the steam cracker. Usually in the crude C4 cut between 35 to 50 wt .-% butadiene is included.

In principle, with the processes according to the invention or catalysts according to the invention, all C4 cuts, however obtained, having butadiene contents of up to 80% by weight, can be selectively hydrogenated. Preferably, C4 streams are used which contain from 30 to 60% by weight of butadiene. Vinyl acetylene and butynes are also selectively hydrogenated to butenes. n-butane and i-butane proceed unchanged from the process according to the invention. Depending on the process conditions, i-butene may undesirably be hydrogenated to i-butane with high hydrogenating power.

The process according to the invention is expediently carried out in the liquid or trickle phase, the hydrogen being dispersed in a manner known per se in the liquid C4 stream. The selective hydrogenation of the butadiene in the trickle phase is preferably carried out from top to bottom with fixed hydrogenation catalysts. An implementation from bottom to top is possible.

In preferred embodiments, the process according to the invention for the hydrogenation of C4 streams takes place in two or three stages.

The two reaction zones must be separated from each other so that hydrogen can be metered in between them and finely distributed. Preferably, the reaction zones are in the form of separate hydrogenation reactors. The hydrogen is added in one to two times the stoichiometric amount required for the calculated conversion (based on the overall process (all stages)), preferably the stoichiometrically required amount is added to an excess of hydrogen in a 1.2-fold amount.

The hydrogen used for the hydrogenation can be up to 30% by volume of inert gas, for. As methane, without thereby hydrogenation is significantly impaired. The hydrogen used for the process according to the invention should preferably be CO-free; however, small amounts of CO (<5 ppm) do not disturb.

The reaction conditions in each of the reactors can be varied within wide limits. Thus, the inventive method runs at reactor inlet temperature of 20 to 100 ⁰ C, preferably 30 to 90 ⁰ C, wherein the temperature increase is preferably 10 to 60 ⁰ C. The pressure is preferably 5 to 50 bar, especially preferably 5 to 30 bar. The liquid hourly space velocity (Ihsv) based on the C4 feed is preferably from 1 to 30 Ir ¹ , preferably from 2 to 15 h " ^1. The fresh feed load (whsv) is preferably from 0.5 to 15 kg The ratio of circulation stream to fresh feed is preferably from 2 to 20 and the ratio of hydrogen to butadiene is preferably from 1 to 1.5.

Under these conditions, the maximum possible content of 1-butene is achieved with a low leaving content of 1,3-butadiene of preferably 10 to 1000 ppm, whereby a high 1-butene selectivity is achieved. Thus, the 1-butene content in the hydrogenated C4 stream is preferably 30%, particularly preferably 40%, in particular 50% (after isobutene removal, the remainder isobutene: preferably 0.5 to 4%, particularly preferably 1 to 3%), while the ratio of 1-butene to 2-butene is preferably 1.2 to 2.0, more preferably 1.3 to 1.6.

If the hydrogenation of the C4 stream takes place in two stages, then the catalyst according to the invention is preferably used in the first reaction stage, whereby a 1- butene selectivity of preferably greater than 60% is achieved.

The inventive method has a number of advantages. The butadiene contained in the starting material is hydrogenated virtually quantitatively with very high selectivity. Despite the very high butadiene conversion, a butene selectivity S of at least 96% is achieved.

Hydrogenation is selective over a very wide range up to extremely high butadiene conversions. The isomerization of butene-1 to butene-2 is significantly lower by the choice of the catalyst according to the invention in the first stage than in the standard method and isobutene is essentially not converted to isobutane. No special purity requirements are imposed on hydrogen unless irreversible catalyst poisons such as lead or arsenic are included. The hydrogen dosing can be regulated with automatic analysis methods.

Since the selectivity is maintained even at higher reaction temperature, no expensive cooling devices or systems for cooling are needed. The heat removal is simply controlled by a sufficient amount of liquid recycle of hydrogenated product. The circulation stream contains a heat exchanger.

Furthermore, no appreciable amounts of oligomerization products are formed in the process according to the invention.

Process E is preferably used as a gas / liquid phase process with a space velocity of the liquid C5 + stream of 0.5 m ³ / m ^{3 *} h, based on the catalyst volume, to 30 m ³ / m ^{3 *} h at a temperature of 0 ⁰ C to 180 ⁰ C and a pressure from 2 bar to 50 bar, wherein per mole of hydrogenation bond in the C5 + stream one to two moles of hydrogen are added. Process E can be used, for example, as selective pyrolysis gasoline hydrogenation, as selective hydrogenation of olefins in reformate streams or coke oven condensates, for the hydrogenation of phenylacetylene to styrene or for the hydrogenation of styrene to ethylbenzene.

The present invention will be explained in more detail with reference to the examples described below.

The preparation of the catalysts was carried out according to the known in the art "in- cipient wetness" method

Example 1: Preparation of the catalyst according to the invention

Al 2 O 3 strands having a surface area of 60 to 90 m ² / g were impregnated with an impregnation solution containing PdNO 3, AgNCh and Sc (NOs) 3, which was acidified with HNO 3 to give a clear solution. The wet strands were dried at 200 ⁰ C and calcined at 600 ⁰ C. A catalyst containing 0.03% by weight of palladium, 0.2% by weight of silver and 0.45% by weight of scandium was obtained.

Example 2: Preparation of a Comparative Catalyst I

The preparation of the comparative catalyst I was carried out analogously to Example 1, with the difference that no scandium nitrate was used. The result was a catalyst with 0.03 wt .-% palladium, 0.2 wt .-% silver.

Example 3: Test for determining the deactivation rate of the catalysts

The catalyst was reduced before the experiment in the reactor at a temperature of 120 ⁰ C overnight, in a hydrogen stream, pressureless. After the reduction, a gas mixture consisting of 3 vol.% Hydrogen, 2 vol.% Acetylene and 95 vol.% Ethylene in the reactor filled with the catalyst under a pressure of 20 bar and at a ghsv of 2000 Nm ³ gas / m ³ cat ^* hours passed.

The hydrogenation was carried out isothermally at a temperature of 70 ⁰ C, while the gas mixture was preheated to the temperature of 50 ⁰ C before entering the reactor. The composition of the inlet and outlet gases was determined by means of an on-line gas chromatograph.

The comparison of deactivation of the catalysts was carried out in such a way that the turnover decrease was observed during the course of the experiment. Under the reaction conditions used, there was normally a linear decrease in the conversion. The Catalyst deactivation rate was mathematically determined by the slope of the deposited straight line in the Revenue / Time graph.

The results of the experiments are given in the table

Claims

claims 1. Supported catalyst based on alumina, containing a) palladium as the hydrogenation-active metal and b) silver and scandium as additional promoters. 2. A catalyst according to claim 1, characterized in that the catalyst has a diameter of 2.0 to 10 mm, at least 80% of the palladium contained in a layer between the surface of the catalyst and a penetration depth of at most 1000 microns, calculated from the surface of the catalyst, substantially homogeneous and the promoters throughout Cross section of the catalyst are present substantially homogeneously distributed. 3. A catalyst according to claim 1, characterized in that the catalyst has a diameter of 2.0 to 10 mm and the palladium and the Pro motors over the entire cross section of the catalyst are substantially homogeneously distributed. 4. Catalyst according to one of claims 1 to 3, characterized in that the carrier is present alumina as a mixture of δ-, θ- and α-alumina. 5. Catalyst according to one of claims 1 to 4, characterized in that the palladium in an amount of at least 0.001 wt .-% and at most 2 wt .-%, based on the total weight of the supported catalyst, is included. 6. A catalyst according to any one of claims 1 to 5, characterized in that the silver in an amount of at least 0.001 wt .-% and at most 2% by weight, based on the total weight of the supported catalyst is included. 7. Catalyst according to one of claims 1 to 6, characterized in that the scandium in an amount of at least 0.001 wt .-% and at most 2 Wt .-%, based on the total weight of the supported catalyst, is included. 8. Catalyst according to one of claims 1 to 7, characterized in that the atomic ratio of palladium to silver in the range of 0.01 to 10. 9. Catalyst according to one of claims 1 to 8, characterized in that the atomic ratio of palladium to scandium is in the range of 0.0001 to 10. 10. A process for the preparation of a catalyst, defined according to any one of claims 1 to 9, by a) treating an aluminum-containing raw material with water, dilute acid or dilute base, deformation to form body, drying the shaped body and calcination of the dried shaped bodies, b) impregnation of the calcined shaped bodies with one or more solutions containing salts of palladium, silver or scandium or mixtures thereof and c) completion of the catalyst by calcination of the impregnated and dried shaped bodies. 1 1. A process for the preparation of a catalyst according to claim 10, characterized in that the dried molded article in step b) impregnated with a solution of one or more salts of palladium, silver and scandium, then dried and calcined. 12. A method for producing a catalyst according to claim 10, characterized in that the dried shaped body in step bi) first impregnated with a solution of one or more salts of palladium and silver, then dried and calcined and in step b2) with a Solution of one or more salts of scandium impregnated, then dried and calcined. 13. A process for preparing a catalyst according to claim 10, character- ized in that the dried shaped body in process step bi) first impregnated with a solution of one or more salts of scandium, then dried and calcined and in process step b2) with a solution of a or more salts of palladium and silver, then dried and calcined. 14. The method according to any one of claims 10 to 13, characterized in that the drying of the catalyst takes place with movement in a rotary tube. 15. The method according to any one of claims 10 to 14, characterized in that the drying is carried out with an air flow as a countercurrent. 16. The method according to any one of claims 10 to 15, characterized in that the drying and the calcining takes place in a rotary tube combined. 17. The method according to any one of claims 10 to 16, characterized in that the catalyst outside or within a hydrogenation reactor at temperatures of 5 to 200 ⁰ C is reduced. 18. The method according to any one of claims 10 to 17, characterized in that the catalyst outside or within a hydrogenation reactor at temperatures of 15 to 500 ⁰ C is regenerated. 19. A catalyst obtainable by a process as defined in any one of claims 10 to 18. 20. Use of a catalyst, defined according to any one of claims 1 to 9 or 19 for the hydrogenation of unsaturated compounds. 21. A process for the selective hydrogenation of unsaturated compounds in the gas phase or mixed gas / liquid phase at inlet temperatures of 0 to 250 0C and pressures in the range of 0.01 to 50 bar, characterized in that one carries out the selective hydrogenation in one or more reaction stages and in at least one reaction stage, a catalyst according to any one of claims 1 to 9 or 19 used. 22. The method according to claim 21, characterized in that hydrogenating acetylene in C2 streams selectively to ethylene.