EP3397381A1

EP3397381A1 - Process for producing a catalyst comprising an alkali metal and a transition metal in oxidised form

Info

Publication number: EP3397381A1
Application number: EP16819581.6A
Authority: EP
Inventors: Benjamin FONFÉ; Nadine Dürr; Harald Jakob; Anastasia PASHIGREVA; Oliver GUTIERREZ; Johannes A. Lercher
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2015-12-30
Filing date: 2016-12-28
Publication date: 2018-11-07
Also published as: JP6926092B2; WO2017114858A1; JP2019501769A; CN108430620A; EP3187261A1

Abstract

The present invention relates to a process for producing a catalyst which comprises at least one alkali metal and at least one transition metal in oxidised form, comprising the steps of a) providing a solution comprising at least one compound comprising an alkali metal and at least one compound comprising a transition metal in oxidised form, wherein the alkali metal and the transition metal may be constituents of the same compound, b) applying the solution from step a) onto a pulverulent support material having a particle diameter of less than 1000 µm, and c) shaping the laden support material obtained from step b), to a catalyst obtained or obtainable by the process according to the invention and to the use of a catalyst according to the invention and/or a catalystobtained or obtainable by the process according to the invention in the production of an alkyl mercaptan.

Description

Process for producing a catalyst comprising an alkali metal and a transition metal in oxidised form

The present invention relates to a process for producing a catalyst which comprises at least one alkali metal and at least one transition metal in oxidised form, to a catalyst obtained or obtainable by the process according to the invention and to the use thereof in the production of an alkyl mercaptan.

AlkyI mercaptans, which are also used synonymously with the term alkanethiol in the context of the present invention, are organic chemical compounds having as a functional group at least one aliphatically bonded thiol group (-SH). Alkyl mercaptans may thus be formally regarded as alcohols where the oxygen atom has been replaced by a sulfur atom. In addition to their diverse direct application potential the importance of alkyl mercaptans in organic chemistry derives especially from their status as important intermediates in the synthesis of other organic compounds with corresponding added value. Examples thereof are the production of methionine and of dimethyl disulfide and dimethyl sulfone by conversion of methyl mercaptan which is the alkyl mercaptan of greatest industrial importance.

Industrial production of alkyl mercaptans typically proceeds by reaction of alkyl alcohols with hydrogen sulfide in the presence of an aluminium-oxide-based heterogeneous catalyst. This reaction is usually performed as a gas phase reaction at a temperature between 300°C and 500°C and a pressure between 1 and 25 bar. The product mixture obtained from this reaction comprises not only the desired alkyl mercaptan but also unconverted starting compounds and byproducts, such as dialkyl sulfides and dialkyl ethers. The unconverted starting compounds, in particular the toxic hydrogen sulfide, are typically recycled back into the reaction immediately after their removal from the product mixture in order to increase the overall yield based on the respective starting compound.

The desired alkyl mercaptan is generally removed by condensing it out of the product mixture. This separation and in particular the energy requirements associated with the cooling of the product mixture represent a large cost factor. To keep the energy requirements for the removal of the alkyl mercaptan from the product mixture as low as possible the highest possible yield and selectivity for the formation of the alkyl mercaptan are thus sought.

Yield and selectivity for the formation of the relevant alkyl mercaptan can in principle be improved both by an increase in the molar ratio of alkyl alcohol to hydrogen sulfide and by the choice of the catalyst employed.

To achieve the highest possible alkyl mercaptan yields the reactants hydrogen sulfide and alkyl mercaptan are in practice reacted in an at least equimolar ratio, but preferably with a molar excess of hydrogen sulfide. Thus for example in the production of methyl mercaptan, hydrogen sulfide and methanol are reacted with one another in molar ratios of 1 : 1 to 10:1 . However, a high molar ratio of hydrogen sulfide to methanol also means a high excess of hydrogen sulfide in the product mixture. Yet, recycling of large amounts of unconverted hydrogen sulfide into the process is associated with high capital and energy costs. To reduce the energy requirements required therefor the ratio of hydrogen sulfide to methanol should thus deviate from 1 only slightly. There are thus corresponding limits to the option of increasing the yield and selectivity in the production of alkyl mercaptans by increasing the molar ratio of hydrogen sulfide to alkyl alcohol. The only remaining option for optimizing alkyl mercaptan yield and selectivity therefore resides in the choice of suitable catalysts. High yields and selectivities for the formation of alkyl mercaptans are generally achieved with catalysts where the catalytically active aluminium oxide is admixed with an alkali metal tungstate promoter. Aluminium oxide alone is too active in the reaction of alkyl alcohols with hydrogen sulphide to igve alkyl mercpatans and therefore also catalyses the further reaction of alkyl mercaptans with alkyl alcohol to give dialkyl sulphide. The addition of alkali metal tungstate promoters to aluminium oxide is believed to reduce the activity of the aluminium oxide and therefore improves the selectivity for the formation of the desired alkyl mercaptans The tungstate is typically employed in amounts of up to 25 weight percent based on the total weight of the catalyst in order to achieve a minimum activity for the employed catalyst.

Repeated impregnation of a support material with a solution comprising cesium and tungsten in ratios of less than 2: 1 , as is described in WO 2005/021491 A1 and in EP 0832878 A2, allows the loading of the catalyst with cesium tungstate to be enhanced to up to 25 weight percent or more based on the total weight of the catalyst. While an increase in the loading of the catalyst with cesium tungstate to above 25 weight percent based on the total weight of the catalyst does result in an enhancement in the selectivity for the formation of the alkyl mercaptan, this is coupled with a reduction in the activity of the catalyst. When the loadings of the catalyst with cesium tungstate are increased to 35 weight percent or more based on the total weight of the catalyst both the selectivity and the activity of the catalyst are reduced. Comparable effects are also observed for the halide-containing catalysts of WO 2006/015668 A1 and the halide-free catalysts of WO 2006/063669 A1 , each of which are produced by repeated impregnation. A further disadvantage of the production of catalysts by repeated impregnation is that cesium and tungsten cannot be uniformly distributed over the cross section of the shaped bodies customarily employed in industry as catalyst supports. However, a uniform distribution of the catalytically active components over the cross section of the catalyst support is regarded as a necessary criterion for catalysts having a high activity and selectivity for the production of alkyl mercaptans. In WO 2013/092129 A1 catalysts having a uniform distribution of alkali metal and tungsten over the entire shaped body cross section are obtained not by impregnating the support material but rather by mixing it with an oxidic tungsten compound and at least one separate, i.e. not present in the tungsten compound, alkali metal compound and then shaping the thus-obtained catalyst mass. The catalysts obtained by this process have a loading with alkali metal tungstate of over 45 weight percent based on the total weight of the catalyst. This allows yield and selectivity for the catalyzed formation of methyl mercaptan to be further enhanced. In comparison thereto, no positive effects on yield and selectivity are observed for catalysts produced by impregnation having a loading with alkali metal tungstate of 45 weight percent or more based on the total weight of the catalyst. However, the high yields and selectivities in the production of methyl mercaptan achieved with the catalysts of WO 2013/092129 A1 do not last long. On the contrary a rapid reduction in the methanol conversion and the methyl mercaptan selectivity is observed, accompanied by an increase in the formation of the byproduct dimethyl ether.

There was accordingly a need for a process for producing catalysts which achieve a high selectivity for the formation of alkyl mercaptans from alkyl alcohols and hydrogen sulfide over a prolonged period.

This object is achieved in accordance with the invention by producing a supported catalyst by a combination of applying a solution comprising at least one alkali metal and at least one transition metal in oxidised form onto a pulverulent support body having a particle diameter of less than 1000 μιη and subsequent shaping.

The present invention accordingly provides a process for producing a supported catalyst comprising at least one alkali metal and at least one transition metal in oxidised form, comprising the steps of a) providing a solution comprising at least one compound comprising an alkali metal and at least one compound comprising a transition metal in oxidised form, wherein the alkali metal and the transition metal may be constituents of the same compound,

b) applying the thus obtained solution onto a pulverulent support material having a particle diameter of less than 1000 μιτι to give a laden support material, and

c) shaping the laden support material.

It is thought that a high dispersion of the phase catalytically active for the formation of alkyl mercaptans favors a high selectivity for the formation of the alkyl mercaptan. The compounds applied to the support material in step b) of the process according to the invention are either already present as oxides/in oxidised form or are converted into the corresponding oxide or into the corresponding oxidic form by a subsequent treatment, preferably by calcination. A high dispersion of the catalytically active phase is optimally achieved by a highest possible dispersion of the corresponding precursor of the oxide of the catalytically active phase. It is thought that this dispersion is a mixing of alkali metal and transition metal on an ionic level. It is further thought that an improved distribution of the applied alkali metal and transition metal is achieved by the subsequent shaping of the support material laden in step c). In order to bring about the best possible distribution through this mechanical treatment a pulverulent support material having the smallest possible particle diameter is employed. The pulverulent support material preferably has a particle diameter of less than 500 μιτι, particularly preferably of less than 250 μιτι or even less than 100 μιτι, for example 15 μιτι or less. In one embodiment of the process according to the invention the pulverulent support material has a particle diameter of less than 250 μιτι.

Particularly good results are obtained with a pulverulent support material made of aluminium oxide, preferably gamma-aluminium oxide. This is because aluminium oxide, and in particular gamma- aluminium oxide, itself exhibits catalytic activity for the reaction of alkyl alcohols with hydrogen sulfide to afford alkyl mercaptans.

Accordingly, in one embodiment of the process according to the invention the pulverulent support material is aluminium oxide.

The process according to the invention is not subject to any restrictions in terms of the solution provided in step a). Accordingly, the process according to the invention may employ either a single solution comprising a single compound which comprises both the alkali metal and the transition metal or a solution comprising a plurality of compounds which comprise an alkali metal or a plurality of alkali metals and a transition metal in oxidised form or a plurality of transition metals in oxidised form. When a plurality of solutions are employed then these may comprise the same alkali metal/transition metal in oxidised form or the same alkali metals/transition metals in oxidised form or different alkali metals/transition metals in oxidised form. The provision of a solution in step a) is effected by dissolving alkali metal compounds such as hydroxides, carbonates, oxalates, acetates or the like of, for example, sodium, potassium or cesium and dissolving compounds comprising a transition metal in oxidised form such as tungstic acid, tungsten trioxide, alkali metal tungstate or ammonium tungstate in protic media, such as water, ethanol or also ammonia or aqueous solutions of ammonia. When the alkali metal and the transition metal present in oxidised form are constituents of the same compound this compound is preferably an alkali metal tungstate, in particular sodium, potassium or cesium tungstate.

The process according to the invention is not subject to any restrictions in terms of the application of the solution provided in step a) either. The application of the solution provided in step a) is preferably effected by impregnation of the pulverulent support material with the solution. This is because this is an option for application of the solution to the pulverulent support material that is particularly easy to perform. The application of the solution to the pulverulent support material is also referred to in the context of the present invention as loading of the support material with the solution, the alkali metal, the transition metal, the catalytically active elements or similar.

Accordingly, in one embodiment of the process according to the invention in step b) the solution is applied to the pulverulent support material by impregnation.

A multistage impregnation with one or more identical or different impregnation solutions allows either different alkali metals and/or transition metals or a higher loading of the same alkali metal and/or of the same transition metal to be applied to the pulverulent support material. The impregnation may thus be effected as a two-stage or three-stage procedure.

Accordingly, in a preferred embodiment of the process according to the invention in step b) the solution is applied to the pulverulent support material by multistage impregnation.

Supported catalysts, in particular comprising aluminium oxide and in particular gamma-aluminium oxide as support material, based on tungsten in oxidised form are particularly suitable for the production of alkyl mercaptans from alkyl alcohols and hydrogen sulfide. Supported catalysts of the type described hereinabove where the alkali metal is sodium, potassium or cesium are particularly suitable for the production of alkyl mercaptans from alkyl alcohols and hydrogen sulfide. It is particularly preferable in the process according to the invention when the alkali metal is cesium.

Accordingly, in one embodiment of the process according to the invention the transition metal is tungsten.

In a further embodiment of the process according to the invention the alkali metal is sodium, potassium or cesium. In contrast to the processes known from the prior art, for example the process of WO 2006/063669 A1 , in the process according to the invention preference is given to employing only those alkali-metal- and transition-metal-comprising compounds which do not comprise halogens. This is because it has been found that in the production of alkyl mercaptans halogen-comprising catalysts result in sometimes severe corrosion of the reactor tubes.

Accordingly, in one embodiment of the process according to the invention the at least one compound comprising an alkali metal and the at least one compound comprising a transition metal in oxidised form are halogen-free. The shaping performed in accordance with the invention brings about an improved distribution of the alkali metal applied to the support material and of the transition metal. Any conceivable shaping of the pulverulent support material laden in the preceding steps is in principle suitable for this purpose provided it is ensured that the respective shaping achieves an improved distribution of the alkali metal applied to the support material and of the transition metal. Easily performable options that meet this requirement are extrusion and tableting, these steps being performable according to the typical procedures for an extrusion or tableting of catalyst particles.

In one embodiment of the process according to the invention the shaping in step c) is effected by extrusion or tableting. A particularly good distribution of the alkali metal applied to the support material and of the transition metal is achieved when, before the shaping, the laden support material is subjected to the steps of drying and/or calcining and of commixing of the laden support material. If the applying in step b) of the process according to the invention is effected by impregnation the laden support material is initially separated from the impregnation solution, preferably by filtration. Since the laden support material separated from the impregnation solution still contains residual moisture it is then preferably subjected to a drying and/or calcining. The drying is effected at a temperature above the boiling point of the medium used to provide the impregnation solution/the impregnation solutions, preferably water. In most cases the drying is accordingly effected at temperatures of more than 100°C. The drying is preferably effected by increasing the temperature to about 120°C at a heating rate of about 1 °C/ min. This temperature is then maintained for several hours, preferably for up to three or more hours. Optionally the drying may also be preceded by a predrying at a temperature of less than 100°C, preferably at about 60°C, in order to remove volatile components of the medium used to produce the impregnation solution, preferably ammonia. To convert the alkali metal and the transition metal into an oxidic form/to ensure that the alkali metal and the transition metal have been converted into the oxidic form the drying is followed by a calcining. The calcining is preferably carried out at temperatures of 400°C or more. The calcining is preferably performed such that the temperature is increased from the value during the drying to the final calcining temperature at a heating rate of about 5°C/min. This temperature is then maintained for several hours, preferably for up to three or more hours.

In one embodiment the process according to the present invention further comprises the step, preceding the shaping, of b') drying and/or calcining of the laden support material.

The laden support material is then preferably commixed, particularly when it is baked together, for example after the removal of the impregnation liquid by filtration. If a filtercake is present after a filtration for example then this filtercake is broken up and ground after the calcining. In the context of the process according to the invention the commixing or grinding serves primarily to commix the laden support material in order to achieve the most uniform possible distribution of the elements applied to the support material. In any case the commixing or grinding gives a pulverulent laden support material with a particle diameter of less than 1000 μιτι, which can be subjected to a shaping or to a repeated application of the solution of step a) onto said material. It is accordingly not necessary in the context of the present invention for a further comminution of the laden particles to be achieved with the commixing or grinding procedure.

In another embodiment the process according to the present invention therefore further comprises the step, preceding the shaping, of b") commixing the laden support material. In a preferred embodiment of the process according to the invention the commixing is effected by grinding.

Alternatively or in addition the filtercake may also be commixed prior to the drying and/or calcining, preferably using a kneader, for example a laboratory batch kneader. The process according to the invention is accordingly not subject to any restriction in terms of the sequence of the steps b') drying and/or calcining and b") commixing the laden support material, and the number of times these steps are performed.

In one embodiment the process according to the invention further comprises the steps, preceding the shaping, of b') drying and/or calcining of the laden support material and

b") commixing of the laden support material,

Alternatively, the sequence of the steps b') and b") can be changed.

In the following, the thus obtained laden support material is finally subjected to shaping in step c). Thus, in one embodiment the process according to the invention comprises the steps of providing a solution comprising at least one compound comprising an alkali metal and at least one compound comprising a transition metal in oxidised form, wherein the alkali metal and the transition metal may be constituents of the same compound,

applying the thus obtained solution onto a pulverulent support material having a particle diameter of less than 1000 μιτι to give a laden support material,

drying and/or calcining of the laden support material,

commixing of the laden support material, and

shaping the support material.

In an alternative embodiment of said process the sequence of the steps b') and b") is changed. The steps a) to c), preferably in combination with the steps b') and b"), of the process according to the invention result in the formation of a catalytic active mass on the support material. To increase the loading of the support material with the catalytic active mass or to load different layers of catalytic active masses onto the support material, the laden support material obtained from steps b), b') and/or b") is preferably resubjected to the steps a) to b) and optionally to the steps b') and/or b") of the process according to the invention.

In a further embodiment of the process according to the invention the steps a) to b), a) to b') or a) to b"), are accordingly repeated with the laden support material obtained from step b), b') or b"). Preferably, the steps a) to b") are repeated with the laden support material obtained from step b"). In that case the support material in the step b) to be repeated is the laden support material obtained from the step b") which was performed prior to the step b) to be repeated.

In a preferred embodiment the process according to the invention therefore comprises the steps of providing a solution comprising at least one compound comprising an alkali metal and at least one compound comprising a transition metal in oxidised form, wherein the alkali metal and the transition metal may be constituents of the same compound,

drying and/or calcining of the laden support material,

commixing of the laden support material, and

shaping the support material, wherein the steps a) to b") are performed at least once, preferably twice or more.

The catalyst actually present in the production of alkyl mercaptans from alkyl alcohols and hydrogen sulfide is of a sulfidic nature. It is therefore preferable when the catalyst obtained or obtainable by the process according to the invention is subjected to a sulfidation step after the shaping. In the simplest case the sulfidation step is undertaken with the catalyst charged into a reactor. The sulfidation is preferably performed by treatment of the catalyst obtained or obtainable by the process according to the invention with hydrogen sulfide.

The catalysts produced or obtainable by the process according to the invention and the catalyst according to the invention are suitable for the production of alkyl mercaptans from alkyl alcohols and hydrogen sulfide.

The present invention further provides a catalyst obtained or obtainable by the process according to the invention.

In addition, the present invention also further provides for the use of a catalyst obtained or obtainable by the process according to the invention and/or a catalyst according to the invention in the production of an alkyl mercaptan by reaction of an alkyl alcohol with hydrogen sulfide. In the context of the present invention the term alkyl alcohol is used synonymously with alkanol and refers to an alcohol where the hydroxyl group is directly bonded to an aliphatic carbon atom.

The process according to the invention is not subject to any restrictions in terms of the alkyl alcohol to be reacted provided that it is ensured that the employed alkyl alcohols do not undergo side reactions under the reaction conditions typically employed in the production of alkyl mercaptans. This is generally ensured by using alkyl alcohols having 1 to 4 carbon atoms, in particular linear alkyl alcohols having 1 to 4 carbon atoms.

Accordingly, in one embodiment of the process according to the invention the alkyl alcohol has 1 to 4 carbon atoms.

It is preferable when the alkyl alcohol employed is methanol.

Examples:

Example 1 (comparative example):

As described in example 2 (comparative example) on page 17 of WO 2013/092129 A1 , 200 g of spherical aluminium oxide having a particle diameter of 2 to 5 mm (Spheralite 501 A from Axens having a specific surface area of 303 m²/g, a pore volume of 45 ml/100 g and a bulk density of 815 kg/m³) were impregnated in a three-stage impregnation with 17.8 wt% of WO3 and 17.3 wt% of CS2O based on the total mass of the catalyst. The procedure employed therefor was as follows: 62.2 g of tungstic acid were suspended in 130.4 g of ammonia solution and dissolved by stirring for approximately 30 minutes. 89.3 g of a solution of cesium hydroxide in water (70%) were added to this solution and the resulting solution was stirred for approximately 23 to 24 hours. The aluminium oxide was initially charged into a glass vessel that was evacuated to 150 mbar. By opening the tap the impregnation solution was suctioned off until a supernatant of impregnation solution of approximately 4.5 cm was present over the entire aluminium oxide. The glass vessel was vented and the support was then incubated in the solution for approximately 15 minutes. The solution was then discharged and the catalyst obtained was predried for 1 hour by passing through an air stream of 200 standard l/h (volume flow under standard conditions at 0°C and 1.013 bar absolute as per DIN 1343) to flush any still adherent impregnation solution into the receiver. The catalyst was subsequently heated to 120°C under an air stream of 60 m³/h at a heating rate of 1 °C/min and dried at this temperature for 3 hours. The temperature was then increased to 455°C at a heating rate of 5°C/min and the catalyst was calcined at this temperature for 3 hours. To perform the second impregnation, an impregnation solution as previously described for the first step was made up and applied in the same way by vacuum impregnation to the already laden catalyst obtained from the first impregnation. The predrying at room temperature of the catalyst obtained from the second impregnation followed by the three-hour drying at 120°C and the subsequent calcination at 455°C for 3 hours were effected as described previously. The third impregnation was performed in the same way.

Example 2 (comparative example): As described in example 6 on pages 18 and 19 of WO 2013/092129 A1 , 1.05 kg of pulverulent aluminium oxide having a particle diameter of 7 to 15 μιτι (Spheralite 509 A from Axens having a specific surface area of 335 m²/g, a pore volume of 56 ml/100 g and a bulk density of 840 kg/m³) were first mixed with solid tungstic acid and the thus obtained mixture was subsequently mixed with an aqueous calcium hydroxide solution. The procedure employed therefor was as follows: 1.05 kg of Spheralite 509 A and 537.9 g of solid tungstic acid were mixed in a laboratory batch kneader (Coperion LUK 2.5, Weinheim. Stuttgart, Germany) at 40 revolutions per minute of the kneading hook and 1 1 revolutions per minute of the discharge screw (backward-directed), the barrel of the kneader being cooled to 10°C with of a cryostat. 740.5 g of a 70 wt% aqueous caesium hydroxide solution were then added over a period of 1 min with constant mixing, the temperature rising briefly by 30-40°C. 10 minutes after addition was complete, 127.5 g of deionized water and then 175 g of a colloidal silica dispersion (Lithosol 1530, Zschimmer & Schwarz GmbH & Co. KG, Lahnstein, Germany) were added. The mixture obtained was mixed for a further 10 minutes before a mixture of 30 g of a highly-polymeric polysaccharide (Zusoplast PS 1 , Zschimmer & Schwarz GmbH & Co. KG, Lahnstein, Germany) and 30 g of hydroxyethylcellulose (Tylose H 10000 P2 ShinEtsu, Tokyo, Japan) were added. The binders were allowed to swell for 120 minutes with constant kneading of the mass. 15 g of a nonionic wax dispersion (Zusoplast WE8, Zschimmer & Schwarz GmbH & Co. KG, Lahnstein, Germany) were then added. After a total kneading time of 190 minutes extrusion was commenced by changing the rotation sense of the screw over to conveying and increasing the rotation speed of the screw to 13 revolutions per minute while keeping the kneader rotation speed constant. As the compression mold an attachment with four horizontal bores having respective diameters of 3.2 mm was employed. Two horizontal-cutting cutting wires were operated at 400 revolutions per minute to obtain extrudates of about 3.2 mm in length. The die pressure was 12.7 bar. The chopped extrudates were allowed to fall onto a drying belt and predried at 60°C before being heated to 120°C at a heating rate of 1 °C/min in a muffle furnace and dried at this temperature for 3 hours. The dried extrudates were calcined immediately afterwards by increasing the temperature to 455°C at a heating rate of 5°C/min and maintaining this temperature for 3 hours.

Example 3 (inventive):

150 g of a pulverulent aluminium oxide having a particle diameter of 7 to 15 μιτι (Spheralite 509 A from Axens having a specific surface area of 335 m²/g, a pore volume of 56 ml/100 g and a bulk density of 840 kg/m³) were impregnated with 17.8 wt% of WO3 and 17.3 wt% of CS2O based on the total mass of the catalyst. The procedure employed therefor was as follows: 63.8 g of tungstic acid were dissolved in 127.7 g of a 25% ammonia solution. To this solution were added 121.3 g of a solution of cesium hydroxide in water (50.48%) and the solution was then stirred for 24 hours. The solution was then made up to a volume of 243 ml by addition of water. The thus obtained solution was referred to as impregnation solution. The impregnation solution was initially charged into a glass vessel and the aluminium oxide was added with constant stirring. 15 minutes after addition was complete the suspension was filtered-off through a blue ribbon filter in a Nutsche filter. The filtercake was then dried at 120°C for three hours to remove residual moisture. The temperature was then increased to 455°C at a heating rate of 5°C/min and the filtercake was calcined at this temperature for 3 hours. After the calcining the filtercake was broken up and ground. The thus-obtained powder was reimpregnated as described hereinabove using an impregnation solution produced in the same way. Drying and calcination likewise effected as described hereinabove. After the calcining the filtercake was broken up and ground. The thus-produced catalyst powder was then pressed into tablets in a tablet press.

Example 4 (catalyst testing): The catalysts produced in examples 1 to 3 were analysed in respect of their performance characteristics in the synthesis of methyl mercaptan from hydrogen sulfide and methanol. The reaction of hydrogen sulfide with methanol to afford methyl mercaptan was performed in a stainless steel tube of 18 mm in diameter and 500 mm in length. A catalyst bed having a volume of 76 ml was employed in each case and said catalyst bed was secured in the reaction tube from both sides by inert beds of glass beads in each case. The reaction tube was heated to the various reaction temperatures in the range from 300°C to 360°C indicated in Table 1 below that are required for a methanol conversion of approximately 90% with a thermal oil via a double-wall. The further reaction conditions were: GHSV (gas hourly space velocity) = 1300 h^~ (based on standard conditions at 0°C and 1.013 bar as per DIN 1343), LHSV (liquid hourly space velocity) = 0.4 h \ the mass ratio of hydrogen sulfide to methanol was 1.9 and the pressure was 9 bar. The reaction mixtures obtained in each case comprising the products methyl mercaptan, dimethyl sulfide, dimethyl disulfide and dimethyl ether and also the unconverted reactants methanol and hydrogen sulfide were subjected to online analysis by gas chromatography. The experimental parameters for the reactions with the respective catalysts and the pertinent measured results are summarized in the table below.

Table 1 : Overview of test results The measured results show that the catalyst according to the invention is more active than the catalyst of example 1 (comparative example) and therefore requires a markedly lower reaction temperature than the catalyst of example 1 (comparative example) to achieve a methanol conversion of 90%. Moreover, the catalyst according to the invention additionally achieves a higher selectivity for the formation of methyl mercaptan than the catalyst of example 1 (comparative example).

The measured results further show that the catalyst according to the invention is also more active than the catalyst of example 2 (comparative example). This is even more surprising when it is considered that the catalyst of example 2 has a loading with WO3 and CS2O that is 37% higher than the catalyst according to the invention. The measured values additionally show that in contrast to the catalyst of example 2 the catalyst according to the invention exhibits long-term stability. For the catalyst not only maintains the initially achieved selectivity for the formation of methyl mercaptan almost unabatedly but in fact after a prolonged operating time it even achieves a better methyl mercaptan selectivity than the catalyst of example 2 (comparative example)

Claims

Process for producing a supported catalyst comprising at least one alkali metal and at least one transition metal in oxidised form, comprising the steps of a) providing a solution comprising at least one compound comprising an alkali metal and at least one compound comprising a transition metal in oxidised form, wherein the alkali metal and the transition metal may be constituents of the same compound, b) applying the thus obtained solution onto a pulverulent support material having a particle diameter of less than 1000 μιτι to give a laden support material, and c) shaping the laden support material.

2. Process according to Claim 1 , wherein the pulverulent support material has a particle diameter of less than 250 μιτι.

3. Process according to Claim 1 or 2, wherein the pulverulent support material is aluminium oxide.

4. Process according to any of Claims 1 to 3, wherein the solution in step b) is applied by impregnation onto the pulverulent support material.

5. Process according to Claim 4, wherein the solution in step b) is applied by multi-stage impregnation onto the pulverulent support material.

6. Process according to any of Claims 1 to 5, wherein the transition metal is tungsten.

7. Process according to any of Claims 1 to 6, wherein the alkali metal is sodium, potassium or cesium.

Process according to any of Claims 1 to 7, wherein the at least one compound comprising an alkali metal and the at least one compound comprising a transition metal in oxidised form are halogen-free.

Process according to any of Claims 1 to 8, wherein the shaping in step c) is effected by extrusion or tableting.

Process according to any of Claims 1 to 9, further comprising the steps, preceding the shaping, of b') drying and/or calcining of the laden support material obtained from step b) and b") commixing of the laden support material.

11. Process according to Claim 10, wherein the commixing is effected by grinding.

12. Process according to any of Claims 1 to 11 , wherein the steps a) to b), a) to b') or a) to b") are repeated with the laden support material obtained from step b), b') or b").

13. Catalyst obtained or obtainable by a process according to any of preceding Claims 1 to 12.

14. Use of a catalyst obtained or obtainable by a process according to any of Claims 1 to 12 and/or a catalyst according to Claim 13 in the production of an alkyl mercaptan by reaction of an alkyl alcohol with hydrogen sulfide.

15. Use according to Claim 14, wherein the alkyl alcohol has 1 to 4 carbon atoms.