Catalyst for the synthesis of methylmercaptan and method thereof

 

(57) Abstract:

The invention relates to a catalyst used for the synthesis of mercaptan from methanol and hydrogen sulfide, as well as to a method for producing this catalyst. Describes the catalyst used for the synthesis of mercaptan from hydrogen sulfide and methanol, as well as the method of obtaining this catalyst. The catalyst consists of active alumina, on which deposition is applied 15-40 wt.% of caesium tungstate as a promoter. Compared to the predominantly used in the prior art by tungstate, potassium promoter is cesium tungstate provides an unexpected increase in catalytic activity and selectivity. 2 S. and 1 C.p. f-crystals, 2 tab.

The present invention relates to a catalyst used for the synthesis of mercaptan from methanol and hydrogen sulfide, as well as to a method for producing this catalyst.

The mercaptan is an industrially important intermediate product for the synthesis of methionine, as well as for obtaining dimethyl sulfoxide and dimethyl sulfone. Currently, it is mainly obtained from methanol and hydrogen sulfide in the presence of a catalyst based on aluminum oxide. Synthesis of metal the P CLASS="ptx2">

The reaction gas mixture contains, along with the mercaptan formed unreacted educt and by-products, such in particular as dimethylsulfide simple and dimethyl ether, as well as inert to the reaction gases, such as methane, carbon monoxide, hydrogen and nitrogen. From this reaction mixture allocate the resulting mercaptan.

If the interaction between hydrogen sulfide and methanol in the presence of a catalyst is carried out at increased pressure and thus in the process of obtaining mercaptan product is formed at high pressure (>7 bar), as described in the application DE Germany 1768826, the mercaptan can be selected, for example, by washing with methanol at a temperature in the head part of the scrubber 25oC. If the product is under normal pressure, for subsequent processing in order to obtain the mercaptan in the liquid form it is necessary to work at temperatures down to -60o(Cf. paved the application of Japan JP-OS 45-10728). Unreacted hydrogen sulfide, as described in the aforementioned application DE 1768826 again to return to the reactor.

The efficiency of the method includes the highest selectivity by kataliticheskogo reduce logistical costs in the allocation of the resulting mercaptan from the reaction mixture to a minimum. It is primarily about such a significant factor, as the high energy intensity of the process of cooling the reaction gas mixture for separation of condensate methylmercaptan.

To improve the activity and selectivity aluminiumoxide catalyst latter usually promotirovat the potassium tungstate. The promoter when it is used usually in an amount up to 15 wt.% in terms of the total weight of the catalyst. Increased activity and selectivity reached also by increasing the molar ratio between hydrogen sulfide and methanol. In most cases, this molar ratio is 1-10. At the same time, a high molar ratio means the presence in the reaction gas mixture a large excess of hydrogen sulfide and thus the need to introduce into the circuit a significant amount of gas. Therefore, to reduce required for these purposes, energy molar ratio between hydrogen sulfide and methanol ought to choose a little more than 1. Further, to reduce heat loss in the reactor, it is desirable to carry out the reaction at the lowest possible temperatures.

In U.S. patent 2820062 described a method of obtaining organic thiols, in which used catalyst based on Akti is telesfora. Using this catalyst to achieve high activity and selectivity at a temperature of 400oC and a molar ratio equal to 2. According to the above U.S. patent are various possibilities for the introduction of potassium tungstate in the aluminum oxide. Thus, in particular, can use the methods of impregnation, coprecipitation and clean mix. Actually getting the same catalyst as an important indicator of the efficiency of the method of synthesis of methylmercaptan in the publication is given only a small place.

The present invention was based on the task to obtain the catalyst and to develop a method thereof, and the catalyst had to be different at low molar ratios between hydrogen sulfide and methanol higher activity and selectivity compared with the known catalysts and to provide thereby increasing the efficiency of the method.

This problem is solved thanks to the molded catalyst based on aluminum oxide containing an alkali metal tungstate as a promoter. The catalyst is characterized by the fact that, as the promoter used cesium tungstate, which is injected in an amount of from 15 to 40, preferably from 20 to 35 wt.%in predominantly used in the prior art by potassium tungstate gives a catalyst of higher activity with simultaneous increase its selectivity. These improved characteristics reach only at much higher concentrations used according to the invention promoter compared with the traditional promoter potassium tungstate. At concentrations of less than 15 wt.% the cesium tungstate no advantages in comparison with potassium tungstate. However, while the potassium tungstate increasing its concentration does not improve the above characteristics of the catalyst, the use of caesium tungstate unexpectedly provides improved activity and selectivity of the catalyst at a concentration higher than 25 wt.%. When exceeding the upper limit of concentration of 40 wt.% significant improvement in these catalytic characteristics no longer reach.

As aluminum oxide for the proposed catalyst is used the so-called active alumina. This material has a high specific surface area of from 10 to 400 m2/g and represents mainly the oxides of the transition modification (patterns) crystallographic phases of aluminum oxide (see , for example, Ullmann's Enzyclopedia of Industrial Chemistry, 1985, vol A1, S. 561-562). These crystalline modifications are as follows -, -, -, -, - and-aluminum oxide. Everything its thermally stable form. Active alumina is commercially available and is proposed for use in catalytic reactions with different qualities and different for deliveries. Particularly suitable for the purposes of the invention granulated or extruded aluminum oxide with a diameter of grains from 1 to 5 mm, a specific surface area of 180-400 2/g, a total pore volume of 0.3 to 1.0 ml/g and a bulk density of 300 to 900 g/L. For the purposes of the invention are used preferably aluminum oxide with a specific surface area of more than 200 m2/g, because the catalytic activity of the finished catalyst to increase the surface of the aluminum oxide increases slightly.

Aqueous impregnating solution of caesium tungstate can be easily obtained from commercially available tungsten acid (H2WO4) and cesium hydroxide (CsOHH2O). With this purpose, tungsten acid is suspended in water and adding a base and heating, dissolve. The cesium hydroxide also dissolve in water, but separately from tungsten acid. Then two solutions are combined. For the stability of the finished impregnating solution, it is desirable pH value in the alkaline range to choose in the range from 8 to 14. Otherwise, it is impossible poluchit organic bases. Preferably use such grounds that when the final heat treatment of the catalyst can be completely removed. Such bases include ammonium hydroxide and organic bases, particularly amines.

Before the introduction of the impregnating solution, it is advisable from a molded mass of aluminum oxide by calcination at temperatures in the range from 250 to 600oC for 1-10 hours, preferably within 2-6 h to remove adsorbed water and other volatile impurities. However, such pre-processing is not required.

For the introduction of cesium tungstate may be used various technology of impregnation, as, for example, impregnation, dipping, impregnation, spraying, impregnation of the pore volume, which is carried by single-stage or multi-stage mechanism. The main condition of the choice of the method of impregnation is to provide the opportunity for optimal uniform distribution of the required large number of caesium tungstate throughout the cross section of the molded aluminum oxide. This uniformity of impregnation can be increased due to the additional pre-drying the impregnated alumina, the cesium tungstate applied to particles of aluminum oxide by impregnation of pore volume, carried out in one stage. After pre-drying for 2 to 20 h at room temperature can be almost completely equalize the initial unevenness of concentration throughout the cross section of the catalyst particles. In conclusion, cooked described in the preliminary stages of a catalyst for 1-10 h, annealed at temperatures in the range from 300 to 600oC. the Result of this treatment: the cesium tungstate is firmly fixed on the aluminum oxide and the base, available in the impregnating solution, decomposed and removed.

In order to avoid damage to the catalyst, which may be due to too rapid removal of residual moisture, temperature after pre-drying is slowly increased from room temperature to the final, required for calcination. An alternative to this it is possible to also carry out the corresponding intermediate drying at 100-200oC for 0.5-4 hours

In the examples presented here have used two different types of aluminum oxide. Their properties are listed in the following table.1.

Comparative example 1.

1 kg of alumina I was soaked 8 wt.% the potassium tungstate method of impregnation of the pore volume. If this worked is For preparation of a solution of potassium tungstate 66.6 g tungstic acid are suspended in 500 ml of water and 29.9 g of potassium hydroxide was dissolved in 450 ml of water. Then both components were combined and with stirring, they were heated to 95oWith; this formed a clear solution, which is sprayed over the mix in the apparatus for drazhirovanija granulate. The volume of the impregnating solution corresponded to about 110% of a defined experimental by water absorption of the entire weight of the loaded granules. Further impregnated granulate was kept for 16 h in air, then in order to remove residual moisture was dried at a temperature of 160oC for 2 h and Then for 4 h granulate was progulivali at 455oWith on the air.

Comparative example 2.

Worked similarly to comparative example 1 with that, however, the difference is that for promotion granulate used 16 wt.% the potassium tungstate. To this end, the number of used tungsten acid and potassium hydroxide, respectively, increased.

Comparative example 3.

1 kg of aluminum oxide II was promotional similarly to comparative example 18 wt. % of potassium tungstate, calculated on the total weight of impregnowanego of aluminum oxide. To this end 66.6 g tungstic acid are suspended in 400 ml of water, and 29.9 g of potassium hydroxide was dissolved in 170 ml of water, Polsa clear solution. Due to the fact that the pore volume of alumina II was smaller volume of impregnating solution corresponded to about 110% of a defined experimental by water absorption of the entire weight of the loaded granules.

Comparative example 4.

Worked similarly to comparative example 3 with that, however, the difference is that for impregnation of the granules used 16 wt.% the potassium tungstate. To this end, the number of used tungsten acid and potassium hydroxide, respectively, increased.

Comparative example 5.

Worked similarly to comparative example 4, however, the amount of potassium tungstate was increased to 20 wt.%.

Comparative example 6.

On alumina II two-stage application inflicted a total of 16 wt.% the potassium tungstate. At the first stage of impregnation worked with excess impregnating solution. In the second stage used the method of impregnating the pore volume. Specifically worked in the following way:

1 kg of aluminum oxide II for 4 h was progulivali at 455oWith on the air. On placed in a container of granular poured pre-prepared solution of 8.7 wt.% the potassium tungstate in water, had ten min excess water was decanted, wet catalyst particles for 16 h were subjected to preliminary drying in air at room temperature, and then dried for 2 h at 120oC. the result of this treatment, the catalyst particles were deposited 7 wt.% the potassium tungstate, i.e. 75,

For carrying out the impregnation of the pore volume 115,2 g of potassium tungstate was dissolved in 520 ml of water, which corresponded to 100% of the measured capacity of the catalytic material at a temperature of 95oWith, and this solution was poured stir in the apparatus for drazhirovanija granulate. Then re-spent 16-hour pre-drying air being finalized two-hour drying at 110oC. At the end of the catalyst particles was progulivali for 4 h at 455oC.

Comparative example 7.

1 kg of aluminum oxide II was impregnable 8 wt.% the cesium tungstate, similarly to that described in comparative example 3. This purpose of 42.3 g of tungstic acid are suspended in 400 ml of water and 56,9 g CsOHH2O was dissolved in 170 ml of water. After mixing both solutions were heated with stirring to 65oWith and formed slightly turbid solution. Further heating the solution to 95oWith, as in the case of wills is the key, staging and calcination was carried out similarly as described in the last two of the above comparative examples.

Example 1.

1 kg of aluminum oxide II was promotional 20 wt.% of caesium tungstate. With this purpose to 121.6 g of tungstic acid are suspended in 140 ml of water and by the addition of 260 ml of 25% ammonia solution and heated to 50oWith a fully dissolved. Then 163,5 g CsOHH2O was dissolved in 170 ml of water and mixed with the first solution.

Processes pre-calcination, impregnation, drying and the final calcination was carried out similarly as described in the previous examples.

Examples 2 and 3.

Worked similarly to example 1, with that, however, the difference is that the aluminum oxide was promotionally the cesium tungstate in the amount of 25 wt.%, 30 wt.%.

The example application.

The catalysts were pilot-tested on their effectiveness in the synthesis of mercaptan from hydrogen sulfide and methanol. The synthesis process was carried out in the tube of the noble metal with an inner diameter of 14 mm and a length of 500 mm Loaded portion of the catalyst according to 32.4 ml, respectively recorded in Rea is tricastin by was heated to the desired reaction temperature of about 350oC. Products - mercaptan, dimethyl sulfide, dimethyl ether and unreacted methanol after cooling to 25oWith washed from the gas stream with methanol and subjected to further processing by distillation.

Conditions of the experiments presented below: hourly average gas flow rate - 1280 h-1(in terms of standard conditions); average hourly feed rate of the liquid - 0,56 h-1(in terms of liquid Meon); the reaction temperature is 300 to 400oC; molar ratio of H2S/MeOH and 1.5; the pressure is 9 bar.

The measurement results obtained by gas chromatography of the reaction mixture in the flow and composition of past experimental verification of the catalysts are presented in table. 2. A measure of the activity of the catalysts was determined by the reaction temperature T90%required for 90% conversion of methanol. In table. 2 presents, in addition, determined in the course of the above experimental test of selectivity. As shown in the results table. 2, due to the use of aluminum oxide with a higher specific surface area, increased activity of the catalyst, and, to a lesser extent, its selectivity. Input increase the number of tungstate KGO selectivity. Further increase in the number of input promoter to 20 wt.% leads to a further decline in activity. Selectivity increases only slightly and, thus, the catalysts promoted with more than 16 wt. % of potassium tungstate, do not provide the efficiency of the production of methylmercaptan.

A similar trend could also be expected with the introduction of cesium tungstate. However, unexpectedly, the catalysts promoted with cesium tungstate, show significantly higher activity in both good selectivity. Selectivity can be increased even up to 92% due to the introduction of the promoter in the amount of more than 20 wt.%, without sacrificing any significant activity.

The above justification of technical solutions of the invention are to simplify limited by the problems of synthesis of methylmercaptan. To a person skilled in the art, however, it is clear that the proposed catalyst can also be applied to the total synthesis of mercaptans, carried out by the catalytic interaction of olefinic hydrocarbons with hydrogen sulfide.

1. Molded catalyst based on aluminum oxide for synthesis of NetPromoter catalyst contains cesium tungstate in an amount of from more than 15 to 40 wt.% in terms of the total weight of the finished catalyst.

2. The catalyst p. 1, characterized in that it contains aluminum oxide with a specific surface area of 180 to 400 m2/,

3. A method of producing a catalyst for the synthesis of methylmercaptan, comprising impregnating a molded mass of aluminum oxide with an aqueous solution of an alkali metal tungstate, drying and calcination, wherein the impregnation is carried out aqueous alkaline solution of caesium tungstate and calcination is carried out in a period of 2-10 hours at a temperature of from 300 to 500oWith obtaining catalyst under item 1.

 

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