Process for the preparation of methyl mercaptan

Abstract

The invention relates to a process for preparing methyl mercaptan from a mixture of carbon oxide, hydrogen sulfide and hydrogen, in the presence of a catalyst based on molybdenum and potassium supported on zirconia, said catalyst not comprising any promoter.

Claims

1. A process for preparing methyl mercaptan (CH.sub.3SH), comprising: a) reacting a carbon oxide, hydrogen sulphide (H.sub.2S) and hydrogen (H.sub.2) in the presence of a zirconia-supported molybdenum- and potassium containing catalyst, the catalyst not comprising a promoter, to form a carbonyl sulphide; b) hydrogenating the carbonyl sulphide obtained in step a) in the presence of the hydrogen, to form methyl mercaptan and hydrogen sulphide; c) optionally, recycling the hydrogen sulphide formed in step b) to step a); and d) collecting the methyl mercaptan.

2. The process according to claim 1, wherein the zirconia-supported catalyst used in step a) comprises a molybdenum- and potassium containing active phase.

3. The process according to claim 1, wherein the zirconia-supported molybdenum- and potassium-containing catalyst used in step a) is K.sub.2MoO.sub.4/ZrO.sub.2.

4. The process according to claim 1, wherein the molybdenum- and potassium-containing catalyst is K.sub.2MoO.sub.4, where the catalyst comprises between 1% and 50% by weight, relative to the total weight of the catalyst and the zirconia support.

5. The process according to claim 1, wherein the zirconia catalyst support has a specific surface area greater than 30 m.sup.2.g.sup.−1.

6. The process according to claim 1, wherein the carbon oxide is carbon monoxide (CO).

7. The process according to claim 1, wherein the hydrogen sulphide formed in step b) is recycled in step a).

8. The process according to claim 1, wherein the reaction temperature in step a) is between 100° C. and 500° C.

Description

(1) The following examples illustrate the invention, however without limiting the scope as defined by the claims accompanying the description of the present invention.

EXAMPLE 1

Preparation of the zirconia-supported K.SUB.2.MoO.SUB.4 .catalyst

(2) The catalyst was prepared using the dry impregnation method. For this purpose, a quantity of potassium tetraoxomolybdate (K.sub.2MoO.sub.4) was dissolved in water and this solution was then impregnated on the zirconia. The Mo content in the catalyst depends on the solubility of K.sub.2MoO.sub.4 and on the pore volume of the support.

EXAMPLE 2

Preparation of the silica-supported K.SUB.2.MoO.SUB.4 .catalyst

(3) The catalyst was prepared using the dry impregnation method. For this purpose, a quantity of potassium tetraoxomolybdate (K.sub.2MoO.sub.4) was dissolved in water and this solution was then impregnated on the silica. The Mo content in the catalyst depends on the solubility of K.sub.2MoO.sub.4 and on the pore volume of the support.

EXAMPLE 3

Preparation of the titanium dioxide-supported K.SUB.2.MoO.SUB.4 .catalyst

(4) The catalyst was prepared using the dry impregnation method. For this purpose, a quantity of potassium tetraoxomolybdate (K.sub.2MoO.sub.4) was dissolved in water and this solution was then impregnated on the titanium dioxide. The Mo content in the catalyst depends on the solubility of K.sub.2MoO.sub.4 and on the pore volume of the support.

EXAMPLE 4

Preparation of the alumina-supported K.SUB.2.MoO.SUB.4 .catalyst

(5) The catalyst was prepared using the dry impregnation method. For this purpose, a quantity of potassium tetraoxomolybdate (K.sub.2MoO.sub.4) was dissolved in water and this solution was then impregnated on the alumina. The Mo content in the catalyst depends on the solubility of K.sub.2MoO.sub.4 and on the pore volume of the support.

EXAMPLE 5

Catalytic Test

(6) Before the test, the catalysts were activated in situ by a procedure consisting of a first step of drying in a nitrogen stream at 250° C., following by sulphidation with H.sub.2S at the same temperature for 1 hour and ending with a reduction/sulphidation step with H.sub.2/H.sub.2S at 350° C. for 1 hour.

(7) The performance of the catalysts is then assessed for the methyl mercaptan production reaction in a fixed-bed reactor with a catalyst volume of 3 mL, a temperature of 320° C., at a pressure of 10 bar (1 Mpa), with a volume composition of CO/H.sub.2/H.sub.2S feed gas equal to 1/2/1 and a GHSV (Gas Hourly Space Velocity) equal to 1333 h.sup.−1. The reagents and the products are analysed in line by gas chromatography.

(8) The results obtained for these 4 catalysts are grouped together in Table 1. For these 4 tests, the molybdenum content on the support is 8 wt %, i.e. 19.9% in K.sub.2MoO.sub.4.

(9) TABLE-US-00001 TABLE 1 CO con- Molar CH.sub.3SH yield Ex- version selectivity (%) capacity ample Catalyst (%) CH.sub.3SH COS CO.sub.2 (g .Math. h.sup.−1 .Math. L.sub.cat.sup.−1) 1 K.sub.2MoO.sub.4/ZrO.sub.2 77 53 1 44 290 2 K.sub.2MoO.sub.4/SiO.sub.2 45 49 2 48 158 3 K.sub.2MoO.sub.4/TiO.sub.2 40 50 4 46 141 4 K.sub.2MoO.sub.4/Al.sub.2O.sub.3 55 42 3 47 164

(10) The results shown in Table 1 above show that the catalyst according to the invention (Example 1) procures a clearly improved conversion of the carbon monoxide and clearly improved yield capacity for CH.sub.3SH compared to the catalysts on supports of the prior art (silica, titanium or alumina, examples 2, 3 and 4).

(11) The catalyst of the invention allows methyl mercaptan to be synthesised from carbon oxide, hydrogen and hydrogen sulphide with improved CO conversion, good selectivity and an increased yield capacity for MeSH, combined with an improved conversion of the COS. These enhanced performance levels are obtained on a simple catalyst, without the use of promoters, such as tellurium oxide, nickel oxide, iron oxide and other promoters, as described in the prior art.