Process for the preparation of alkyl mercaptans

1. A process for preparing an alkyl mercaptan, the process comprising:

reacting an aliphatic alcohol with hydrogen sulfide in the presence of a heterogeneous catalyst, and

a) starting the preparation of the alkyl mercaptan at a temperature T 1 and preparing the alkyl mercaptan at the temperature T 1 for a time period t 1 , and

b) performing temperature cycles of the number n, comprising

b1) increasing the reaction temperature to a temperature T 2 and preparing the alkyl mercaptan at the temperature T 2 for a time period t 2 , followed by

b2) decreasing the reaction temperature from the temperature T 2 to a temperature T 3 and preparing the alkyl mercaptan at the temperature T 3 for a time period t 3 ,

wherein

the temperature T 2 is always higher than the temperatures T 1 and T 3 ,

and

n is an integer larger than zero.

2. The process according to claim 1 , wherein the temperature T 1 and the temperature T 3 independently from each other range from 250° C.+/−10° C. to 350° C.+/−10° C.

3. The process according to claim 1 , wherein the temperature T 2 is at least 5° C. higher than each of the temperatures T 1 and T 3 .

4. The process according to claim 1 , wherein the temperature T 3 of a temperature cycle of the number n has an equal or a different value compared to the temperature T 3 in the preceding temperature cycle of the number n−1.

5. The process according to claim 1 , wherein the temperature T 2 in a temperature cycle of the number n has the same value as the temperature T 2 in the preceding temperature cycle of the number n−1.

6. The process according to claim 1 , wherein the temperature T 2 in a temperature cycle of the number n has a higher value than the temperature T 2 in the preceding temperature cycle of the number n−1.

7. The process according to claim 1 , wherein the time period t 1 ranges from 1 hour+/−10% to a month.

8. The process according to claim 7 , wherein the time period t 2 ranges from 1 hour+/−10% to 50 hours+/−10%.

9. The process according to claim 1 , wherein the time period t 3 is until the recharging of the reactor with a new catalyst.

10. The process according to claim 9 , wherein the time period t 3 is up to a month.

11. The process according to claim 1 , wherein an aluminum oxide-based catalyst containing an alkali tungstate is used.

12. The process according to claim 11 , wherein the catalyst contains a cesium tungstate.

13. The process according to claim 1 , wherein the catalyst is sulfidized prior to its use in the preparation of alkyl mercaptans.

14. The process according to claim 1 , wherein the aliphatic alcohol is a C 1 -C 3 alcohol.

15. The process according to claim 14 , wherein the aliphatic alcohol is methanol, ethanol, n-propanol, iso-propanol or tert-butanol.

16. The process according to claim 1 , wherein methyl mercaptan is prepared from methanol and hydrogen sulphide over an aluminum oxide-based catalyst containing cesium tungstate as promoter.

17. The process according to claim 2 , wherein the temperature T 2 is at least 5° C. higher than each of the temperatures T 1 and T 3 .

18. The process according to claim 2 , wherein the temperature T 3 of a temperature cycle of the number n has an equal or a different value compared to the temperature T 3 in the preceding temperature cycle of the number n−1.

19. The process according to claim 2 , wherein the temperature T 2 in a temperature cycle of the number n has the same value as the temperature T 2 in the preceding temperature cycle of the number n−1.

20. The process according to claim 2 , wherein the temperature T 2 in a temperature cycle of the number n has a higher value than the temperature T 2 in the preceding temperature cycle of the number n−1.