Process for the production of esters of mono-, di- or polycarboxylic acids

1. A process for the diesterification of maleic acid by reaction of maleic acid with methanol in the presence of water of solution comprising the steps of:

(a) providing a feed solution comprising maleic acid and the water of solution;

(b) reacting the feed solution comprising maleic acid in an esterification zone with methanol to form dimethyl maleate and water of esterification; said esterification being conducted at temperatures of from 65 to 150° C. and pressures from 1 to 5 bar in a two-stage process;

(c) removing the water of solution and the water of esterification; and

(d) recovering the dimethyl maleate.

2. A process according to claim 1 wherein the process is a continuous process.

3. A process according to claim 1 wherein the water removed in step (c) is recycled to step (a).

4. A process according to claim 1 wherein the feed solution in step (a) comprises from about 50 to about 70 wt% water.

5. A process according to claim 1 wherein the feed solution is processed prior to its supply to step (a) to reduce the water content.

6. A process according to claim 1 in which the feed solution comprising maleic acid is subjected in the first stage to mono-esterification in parallel with a mono-esterification of a feed of anhydride.

7. A process according to claim 1 in which the reaction of step (b) is carried out in an esterification zone comprising a first reactor in which maleic acid is converted to the mono ester and a second reactor in which the mono ester is converted to the diester.

8. A process according to claim 1 in which one or more heaters is provided in the esterification zone, wherein the esterification zone comprises one or more reactors.

9. A process according to claim 8 in which at least one heater is located close to the feed point of at least one reactor.

10. A process according to claim 1 in which the water of solution and the water of esterification are substantially stripped out.

11. A process according to claim 1 in which the esterification is carried out in the presence of a catalyst.

12. A process according to claim 1 in which the second stage step of the esterification reaction is carried out in the presence of a catalyst.

13. A process according to claim 11 in which the catalyst is a liquid catalyst.

14. A process according to claim 1 wherein the dimethyl maleate recovered in step (d) is contacted with a hydrogen containing stream in a hydrogenation zone containing a charge of a hydrogenation catalyst effective for catalytic hydrogenation to convert at least some of the dimethyl maleate to a desired product.

15. A process according to claim 14 wherein the water of solution and the water of esterification is removed prior to the dimethyl maleate being passed to the hydrogenation zone.

16. A process according to claim 14 wherein hydrogenation is carried out in the vapour phase in the presence of a heterogeneous ester hydrogenation catalyst.

17. A process according to claim 14 wherein methanol is recovered from the hydrogenation zone and recycled to the esterification zone of step (b).

18. A process according to claim 1 in which the feed solution comprising maleic acid to be formed by hydrolysis of the product from a maleic anhydride reactor and a water rich stream recovered from the esterification zone is recycled to an absorber in which hydrolysis of the product from the maleic anhydride reactor is carried out.

19. A process according to claim 12 in which the catalyst is a liquid catalyst.