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

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

3. The catalyst of claim 2, 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.

4. The catalyst of claim 3, wherein the molybdenum- and potassium-based active component is obtained from a precursor having the formula K.sub.2MOS.sub.4.

5. The catalyst of claim 4, 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.

6. The catalyst of claim 3, wherein the molybdenum- and potassium-based active component is obtained from a precursor having structure K.sub.2MoO.sub.4.

7. The catalyst of claim 6, 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.4/Ca.sub.10(PO.sub.4).sub.6(OH).sub.2=50.7/100.

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

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

10. The catalyst of claim 1, wherein the hydroxyapatite-based support has a specific area greater than 25 m.sup.2/g.

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

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

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

14. The catalyst of claim 1, wherein the catalyst further comprises a promoter.

15. The catalyst of claim 14, wherein the promoter comprises at least one of tellurium oxide, nickel oxide or iron oxide.

16. The catalyst of claim 1, wherein the hydroxyapatite-based support has a specific area of 40 m.sup.2/g to 300 m.sup.2/g.

17. The catalyst of claim 1, 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.

18. A process for preparing the catalyst of claim 1, 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.

(8) Evaluating the Catalysts

(9) The catalysts are evaluated in a reaction to produce methyl mercaptan in a fixed-bed reactor in the following conditions: Temperature: 280 C., Pressure: 10 bars, Composition of CO/H.sub.2/H.sub.2S=1/2/1 feed gas (v/v), GHSV (Gas Hourly Space Velocity)=1333 h.sup.1

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

(11) 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.

(12) The results are in table 2 below.

(13) 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

(14) 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).

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

(16) 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.

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

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

(19) 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.