Catalyst for the synthesis of methyl mercaptan and process for producing methyl mercaptan from synthesis gas and hydrogen sulphide

Abstract

The invention relates to a catalyst comprising an active component based on molybdenum and on potassium and a support based on hydroxyapatite, and also to a process for preparing said catalyst and a process for producing methyl mercaptan in a catalytic process by reaction of carbon monoxide, sulphur and/or hydrogen sulphide and hydrogen, comprising the use of said catalyst.

Claims

1. A process for producing methyl mercaptan in a catalytic process by reacting carbon oxide, sulfur and/or hydrogen sulfide and hydrogen, comprising using a catalyst comprising a molybdenum- and potassium-based active component and a hydroxyapatite-based support.

2. The process of claim 1, wherein the hydroxyapatite of the hydroxyapatite-based support has a Ca/P molar ratio ranging from 1.5 to 2.1.

3. The process of claim 1, wherein the hydroxyapatite of the hydroxyapatite-based support has, a Ca/P molar ratio of 1.67.

4. The process of claim 1, wherein the hydroxyapatite-based support specific area greater than 25 m.sup.2/g.

5. The process of claim 1, wherein the hydroxyapatite-based support has a specific area greater than 40 m.sup.2/g.

6. The process of claim 1, wherein h catalyst support is hydroxyapatite having stoichiometric formula Ca.sub.10(PO.sub.4).sub.6(OH).sub.2.

7. The process of claim 6, wherein the molybdenum- and potassium-based active component is selected from the group consisting of compounds based on MoSK, compounds based on MoOK, and their mixtures.

8. The process of claim 7, wherein the molybdenum- and potassium- sed active component has been obtained from a precursor having structure K.sub.2MoS.sub.4.

9. The process of claim 8, wherein the weight ratio of K.sub.2MoS.sub.4 and Ca.sub.10(PO.sub.4).sub.6(OH).sub.2 used to obtain the catalyst is:
K.sub.2MoS.sub.4/Ca.sub.10(PO.sub.4).sub.6(OH).sub.2=31.3/100.

10. The process of claim 7, wherein the molybdenum and potassium-based active component has been obtained from a precursor having structure K.sub.2MoS.sub.4.

11. The process of claim 10, wherein the weight ratio of K.sub.2MoS.sub.4 and Ca.sub.10(PO.sub.4).sub.6(OH).sub.2 used to obtain the catalyst is:
K.sub.2MoO.sub.4/Ca.sub.10(PO.sub.4).sub.6(OH).sub.2=50.7/100.

12. The process of claim 1, wherein the hydroxyapatite is a stoichiometric hydroxyapatite.

13. The process of claim 1, wherein the catalyst does not include a promoter.

14. The process of claim 1, wherein the catalyst includes a promoter.

15. The process of claim 1, wherein the carbon oxide is CO or CO.sub.2.

16. The process of claim 15, wherein the CO or CO.sub.2/H.sub.2S/H.sub.2 molar ratios range from 1/1/0 to 1/8/8.

17. The process of claim 15, wherein the molar ratios of CO or CO.sub.2/H.sub.2S/H.sub.2/S reagents range from 1/1/0/1 to 1/8/8/8.

18. The process of claim 15, wherein the CO or CO.sub.2/H.sub.2S/H.sub.2 molar ratios range from 1/2/1 to 1/4/4.

19. The process of claim 15, wherein the molar ratios of CO or CO.sub.2/H.sub.2S/H.sub.2/S reagents range from 1/2/2/1 to 1/4/4/4.

20. The process of claim 1, wherein the catalyst is prepared by a process comprising: preparing a precursor for the molybdenum- and potassium-based active component; preparing the hydroxyapatite-based support; and, dry impregnating the hydroxyapatite-based support with the precursor for the molybdenum- and potassium-based active component.

Description

EXAMPLES

Example 1

(1) The catalyst according to the invention is prepared according to the dry impregnation method, as defined above.

(2) The resulting catalyst has the following characteristics:

(3) TABLE-US-00001 TABLE 1 Elemental analysis of the catalyst Catalyst Chemical composition (% by weight) Mo K S N K.sub.2MoS.sub.4/Hap 9.9 8.1 13.3 <0.10

Example 2

(4) The catalyst used is K.sub.2MoO.sub.4 on hydroxyapatite

Example 3

(5) The catalyst tested is K.sub.2MoO.sub.4 on SiO.sub.2

Example 4

(6) The catalyst tested is K.sub.2MoS.sub.4 on Al.sub.2O.sub.3

Example 5

(7) The catalyst tested is K.sub.2MoO.sub.4 on Al.sub.2O.sub.3.

Evaluating the Catalysts

(8) The catalysts are evaluated in a reaction to produce methyl mercaptan in a fixed-bed reactor in the following conditions:

(9) Temperature: 280 C.,

(10) Pressure: 10 bars,

(11) Composition of CO/H.sub.2/H.sub.2S=1/2/1 feed gas (v/v),

(12) GHSV (Gas Hourly Space Velocity)=1333 h.sup.1

(13) The reagents and products were analyzed in-line by gas chromatography.

(14) Before the test, the catalysts were activated in situ with a first procedure consisting in a first step of drying in nitrogen at 250 C., followed by sulfidation with hydrogen sulfide at the same temperature for 1 hour, then a step of reduction/sulfidation with H.sub.2/H.sub.2S at 350 C. for 1 hour.

(15) The results are in table 2 below.

(16) TABLE-US-00002 TABLE 2 Results of catalytic tests Molar selectivities (%) Examples Catalyst CH.sub.3SH COS CO.sub.2 CO.sub.2/CH.sub.3SH ratio 1 (inv) K.sub.2MoS.sub.4/Hap 44.1 23.3 32.6 0.74 2 (inv) K.sub.2MoO.sub.4/Hap 43.3 23.6 31.9 0.74 3 (comp) K.sub.2MoO.sub.4/SiO.sub.2 48.8 5.3 45.3 0.93 4 (comp) K.sub.2MoS.sub.4/Al.sub.2O.sub.3 45.0 7.3 46.6 1.04 5 (comp) K.sub.2MoO.sub.4/Al.sub.2O.sub.3 47.0 3.4 49.6 1.06

(17) The results presented in table 2 show that the catalysts according to the invention (examples 1 and 2) give much lower CO.sub.2 (undesired product) selectivities than catalysts on the supports in the prior art (silica: example 3 or alumina: examples 4 and 5).

(18) The selectivities are compared using carbon monoxide isoconversion, where this conversion is expressed by m.sup.2 of specific air in the catalyst.

(19) By comparing the results obtained with catalysts 1 and 4, we observe a 30% improvement in ratio, and this improvement is linked to choosing hydroxyapatite as support.

(20) The same observation is seen when comparing example 2 according to the invention and examples 3 and 5.

(21) We observe increased methyl mercaptan selectivity compared to the carbon dioxide produced according to a side reaction.

(22) It should be noted that this selectivity is obtained without aid from the promoter such as tellurium oxide, nickel oxide or iron oxide as described in the prior art.