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

1-10. (canceled)

11. A catalyst comprising a molybdenum- and potassium-based active component and a hydroxyapatite-based support.

12. The catalyst of claim 11, wherein the catalyst support is hydroxyapatite having stoichiometric formula Ca.sub.10(PO.sub.4).sub.6(OH).sub.2.

13. The catalyst of claim 12, wherein the molybdenum- and potassium-based active component is selected from the group consisting of compounds based on MoSK, compounds based on MoOK, and mixtures thereof.

14. The catalyst of claim 13, wherein the molybdenum- and potassium-based active component is obtained from a precursor having the formula K.sub.2MoS.sub.4.

15. The catalyst of claim 14, 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.

16. The catalyst of claim 13, wherein the molybdenum- and potassium-based active component is obtained from a precursor having structure K.sub.2MoO.sub.4.

17. The catalyst of claim 16, wherein the weight ratio of K.sub.2MoO.sub.4 and Ca.sub.10(PO.sub.4).sub.6(OH).sub.2 used to obtain the catalyst is:
K.sub.2MoO.sub.4Ca.sub.10(PO.sub.4).sub.6(OH).sub.2=50.7/100.

18. The catalyst of claim 11, wherein the hydroxyapatite of the hydroxyapatite-based support has a Ca/P molar ratio ranging from 1.5 to 2.1.

19. The catalyst of claim 11, wherein the hydroxyapatite of the hydroxyapatite-based support has a Ca/P molar ratio of 1.67.

20. The catalyst of claim 11, wherein the hydroxyapatite-based support has a specific area greater than 25 m.sup.2/g.

21. The catalyst of claim 11, wherein the hydroxyapatite-based support has a specific area greater than 40 m.sup.2/g.

22. The catalyst of claim 11, wherein the hydroxyapatite is a stoichiometric hydroxyapatite.

23. The catalyst of claim 11, wherein the catalyst does not include a promoter.

24. The catalyst of claim 11, wherein the catalyst further comprises a promoter.

25. The catalyst of claim 24, wherein the promoter comprises at least one of tellurium oxide, nickel oxide or iron oxide.

26. The catalyst of claim 11, wherein the hydroxyapatite-based support has a specific area of 40 m.sup.2/g to 300 m.sup.2/g.

27. The catalyst of claim 11, wherein the hydroxyapatite-based support has a specific area of 40 m.sup.2/g to 300 m.sup.2/g and a Ca/P molar ratio of 1.67.

28. A process for preparing the catalyst of claim 11, 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

[0086] The catalyst according to the invention is prepared according to the dry impregnation method, as defined above.

[0087] The resulting catalyst has the following characteristics:

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

[0088] The catalyst used is K.sub.2MoO.sub.4 on hydroxyapatite

Example 3

[0089] The catalyst tested is K.sub.2MoO.sub.4 on SiO.sub.2

Example 4

[0090] The catalyst tested is K.sub.2MoS.sub.4 on Al.sub.2O.sub.3

Example 5

[0091] The catalyst tested is K.sub.2MoO.sub.4 on Al.sub.2O.sub.3.

[0092] Evaluating the Catalysts

[0093] The catalysts are evaluated in a reaction to produce methyl mercaptan in a fixed-bed reactor in the following conditions: [0094] Temperature: 280 C., [0095] Pressure: 10 bars, [0096] Composition of CO/H.sub.2/H.sub.2S=1/2/1 feed gas (v/v),

[0097] GHSV (Gas Hourly Space Velocity)=1333 h.sup.1

[0098] The reagents and products were analyzed in-line by gas chromatography.

[0099] 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.

[0100] The results are in table 2 below.

TABLE-US-00002 TABLE 2 Results of catalytic tests Molar selectivities (%) CO.sub.2/ Examples Catalyst CH.sub.3SH COS 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/SiO2 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

[0101] 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).

[0102] The selectivities are compared using carbon monoxide isoconversion, where this conversion is expressed by m.sup.2 of specific air in the catalyst.

[0103] 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.

[0104] The same observation is seen when comparing example 2 according to the invention and examples 3 and 5.

[0105] We observe increased methyl mercaptan selectivity compared to the carbon dioxide produced according to a side reaction.

[0106] 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.