Process for the production of trimellitic acid
Trimellitic acid is produced by oxidation of pseudocumene in acetic acid at temperatures between 130 and 240° C. in the presence of a catalyst composition containing cobalt, manganese and bromine. The process comprises the stages of: (i) simultaneously feeding pseudocumene and air or an oxygen-containing gas into a solution containing acetic acid and the catalyst composition, at an addition rate resulting in an oxygen concentration in the off-gas of less than 8 vol %, and at a temperature and a pressure sufficient to result in 5 to 25 mol % of the total amount of oxygen required to oxidize the pseudocumene to trimellitic acid being consumed, and (ii) feeding air or an oxygen-containing gas into the reaction mixture obtained in stage (i) until essentially all of the pseudocumene has been consumed and a molar yield of trimellitic acid of at least 90% has been obtained. There is no supplementation of catalyst after stage (i).
1. A process for the production of trimellitic acid by oxidation of pseudocumene in acetic acid at temperatures between 130 and 240° C. in the presence of a catalyst composition containing cobalt, manganese and bromine, said process comprising the stages of
(i) gradually and simultaneously feeding pseudocumene and air or an oxygen-containing gas into a solution containing acetic acid and said catalyst composition, at an addition rate resulting in an oxygen concentration in the off-gas of less than 8 vol %, and at a temperature and a pressure sufficient to result in 5 to 25 mol % of the total amount of oxygen required to oxidize the pseudocumene to trimellitic acid being consumed, and
(ii) feeding air or an oxygen-containing gas into the reaction mixture obtained in stage (i) until essentially all of the pseudocumene has been consumed and a molar yield of trimellitic acid of at least 90% has been obtained, wherein there is no supplementation of catalyst after the completion of stage (i).
2. The process of claim 1 , wherein the reaction temperature in stage (i) is between 130° C. and 180° C.
3. The process of claim 1 , wherein in the course of stage (ii) the reaction temperature is increased to a final value between 200° C. and 240° C.
4. The process of claim 1 , wherein the pressure is between 5 and 30 bar.
5. The process of claim 1 , wherein the oxygen concentration of the off gases during stage (i) is from 2 to 6 vol %.
6. The process of claim 1 , wherein the catalyst composition further contains cerium and/or titanium.
7. The process of claim 6 , wherein the cerium content of the catalyst composition is 1 to 30 wt % relative to the total metal content.
8. The process of claim 6 , wherein the titanium content of the catalyst composition is 0.5 to 13 wt % relative to the total metal content.
9. The process of claim 1 , wherein the cobalt content of the catalyst composition is 30 to 70 wt % relative to the total metal content.
10. The process of claim 1 , wherein the manganese content of the catalyst composition is 10 to 50 wt % relative to the total metal content.
11. The process of claim 1 , wherein the total metal concentration comprising cobalt, and manganese, is 0.1 to 1.0 wt % relative to the total amount of pseudocumene employed.
12. The process of claim 6 , wherein the total metal concentration comprising cobalt, manganese and cerium and/or titanium is 0.1 to 1.0 wt % relative to the total amount of pseudocumene employed.
13. The process of claim 1 , wherein the bromine concentration is 0.05 to 0.7 wt % relative to the total amount of pseudocumene employed.
14. The process of claim 1 , wherein the weight ratio of acetic acid to total added pseudocumene is 1:1 to 4:1.
15. The process of claim 2 , wherein the reaction temperature in stage (i) is between 140° C. and 160° C.
16. The process of claim 3 , wherein in the course of stage (ii) the reaction temperature is increased to a final value between 215° C. and 230° C.
17. The process of claim 4 , wherein the pressure is between 6 and 25 bar.
18. The process of claim 7 , wherein the cerium content of the catalyst composition is 5 to 20 wt % relative to the total metal content.
19. The process of claim 8 , wherein the titanium content of the catalyst composition is 3 to 10 wt % relative to the total metal content.
20. The process of claim 9 , wherein the cobalt content of the catalyst composition is 40 to 60 wt % relative to the total metal content.
21. The process of claim 10 , wherein the manganese content of the catalyst composition is 20 to 40 wt % relative to the total metal content.
22. The process of claim 11 , wherein the total metal concentration comprising cobalt, and manganese, is 0.20 to 0.55 wt % relative to the total amount of pseudocumene employed.
23. The process of claim 12 , wherein the total metal concentration comprising cobalt, manganese and cerium and/or titanium is 0.20 to 0.55 wt % relative to the total amount of pseudocumene employed.
24. The process of claim 13 , wherein the bromine concentration is 0.1 to 0.3 wt % relative to the total amount of pseudocumene employed.
25. The process of claim 14 , wherein the weight ratio of acetic acid to total added pseudocumene is 1:5 to 3:1.