Hydrogenation and esterification to form diesters
A process is disclosed which employs hydrogenation and esterification to form alkyl diesters. The process subjects an unrefined or otherwise not purified composition comprising maleic anhydride production residue to the processes of hydrogenation and esterification and forming diesters at high conversion efficiency.
1. A process for making dialkyl succinate, comprising:
a. providing a mixture comprising about 30 to 90 wt % maleic anhydride and about 5 to 68 wt % fumaric acid;
b. contacting the mixture of (a) with an alkyl alcohol solvent in sufficient amount to form a solution and holding the solution at a temperature of from about 20° C. to about 250° C. for a holding time;
c. hydrogenating the solution of (b), in the absence of an intermediate distillation between (b) and (c), at hydrogenation conditions of temperature from about 50 to 200° C. under hydrogen pressure from about 50 to 1000 psig (about 450 to 7000 kPa) in the presence of a hydrogenation catalyst to form a hydrogenation product;
d. treating the hydrogenation product with alcohol at an esterification temperature of about 100° C. to 140° C. to form crude product containing dialkyl esters, wherein at least 85 percent of maleic anhydride, fumaric acid and their derivatives of (a) have been converted to dialkyl esters in the crude product; and
e. isolating dialkyl succinate from the crude product of (d).
2. The process of claim 1 wherein the mixture of (a) further comprises about 0.4 to 2 wt % maleic acid.
3. The process of claim 2 wherein the mixture of (a) further comprises about 0.1 to 0.5 wt % succinic anhydride.
4. The process of claim 3 wherein the mixture of (a) further comprises about 0.05 to 0.5 wt % succinic acid.
5. The process of claim 4 wherein the mixture of (a) further comprises about 0. 1 to 1 wt % phthalic anhydride.
6. The process of claim 5 wherein the mixture of (a) further comprises about 0.1 to 0.5 wt % fumaric monoaldehyde.
7. The process of claim 6 wherein the mixture of (a) further comprises about 0.1 to 0.5 wt % 5-hydroxy-2-furanone.
8. The process of claim 7 wherein the mixture of (a) further comprises about 0.5 to 1.5 wt % malic acid.
9. The process of claim 8 wherein the mixture of (a) further comprises about 0.1 to 0.3% o-xylene.
10. The process of claim 9 wherein the mixture of (a) further comprises about 0.02 to 0.1 wt % acetic acid.
11. The process of claim 1 wherein the mixture comprising about 30 to 90 wt % maleic anhydride and about 5 to 68 wt % fumaric acid is maleic anhydride production residue.
12. The process of claim 1 wherein the hydrogenation catalyst comprises palladium.
13. The process of claim 1 wherein at least one of the contacting (b) or the esterification (d) is carried out in the presence of an esterification catalyst.
14. The process of claim 13 wherein the esterification catalyst is an acid catalyst.
15. The process of claim 1 , wherein isolating dialkyl succinate from the crude product containing dialkyl esters is conducted by distillation.
16. The process of claim 15 , wherein the distillation comprises:
a. distilling in a first distillation column the crude product containing dialkyl esters to separate a low-boiling overhead stream enriched in dialkyl esters from high-boiling acids and esters;
b. distilling in a second distillation column the low-boiling overhead stream enriched dialkyl esters from the first distillation column to produce a low-boiling overhead stream enriched in dialkyl fumarate, a side-stream enriched in dialkyl succinate, and a bottoms stream containing higher boiling materials; and
c. withdrawing the side-stream enriched in dialkyl succinate as the product.
17. The process of claim 16 wherein at least a portion of the low-boiling overhead stream enriched in dialkyl fumarate is recycled to the hydrogenating step.
18. The process of claim 15 , wherein the distillation comprises:
a. distilling in a distillation column the crude product containing dialkyl esters to produce a low-boiling overhead stream enriched in dialkyl fumarate;
b. cooling the low-boiling overhead stream enriched in dialkyl fumarate to form condensed liquid and solids;
c. separating the solids from the condensed liquid to form a condensed liquid substantially free of solids;
d. returning at least a portion of the condensed liquid substantially free of solids to the distillation column.
19. The process of claim 18 , wherein separating the solids from the condensed liquid to form a condensed liquid substantially free of solids is conducted by filtration.
20. The process of claim 18 , wherein separating the solids from the condensed liquid to form a condensed liquid substantially free of solids is conducted by crystallization.
21. The process of claim 1 wherein at least 95 weight percent of maleic anhydride, fumaric acid and their derivatives of (a) have been converted to dialkyl esters in the crude product.