Preparation of dialkyl esters of 2,5-furandicarboxylic acid

1. A process for the preparation of dialkyl esters of 2,5-furandicarboxylic acid from a 2,5-furandicarboxylic acid-containing starting material, which process comprises:

contacting a vaporous stream of an alkanol countercurrently with the at least partially liquid starting material comprising the 2,5-furandicarboxylic acid in a reaction zone to conduct an esterification reaction to the dialkyl ester of 2,5-furandicarboxylic acid and water;

withdrawing a reaction vapor comprising the alkanol and water from the reaction zone, wherein water is removed via the reaction vapor, while the esters of 2,5-furandicarboxylic acid and the 2,5-furandicarboxylic acid remain in the liquid in the reaction zone; and

discharging a liquid phase comprising at least the dialkyl ester of 2,5-furandicarboxylic acid, from the bottom part of the reaction zone, to obtain the dialkyl ester of 2,5-furandicarboxylic acid.

2. The process according to claim 1 , wherein the alkanol has 1 to 4 carbon atoms.

3. The process according to claim 1 , wherein the reaction zone comprises a reactive stripping column.

4. The process according to claim 1 , wherein the reaction zone comprises reactor internals and/or a packing.

5. The process according to claim 1 , wherein the liquid starting material comprises 2,5-furandicarboxylic acid and the monoester thereof.

6. The process according to claim 1 , wherein the starting material comprises the oxidation product of a compound selected from 5-hydroxymethylfurfural, an ether thereof, an ester thereof and mixtures of any such compounds, with an oxidizing agent.

7. The process according to claim 1 , wherein the reaction vapor, comprising the alkanol and water, is separated into an alkanol fraction and a water fraction.

8. The process according to claim 7 , wherein the reaction vapor is separated by means of distillation.

9. The process according to claim 7 , wherein the alkanol fraction is recycled to the reaction zone.

10. The process according to claim 1 , wherein a portion of the liquid phase is recycled to the reaction zone.

11. The process according to claim 10 , wherein another part of the liquid phase is discharged as a bleed stream.

12. The process according to claim 1 , wherein the liquid phase is separated into a first fraction enriched in the monoester of 2,5-furandicarboxylic acid and a second fraction rich in the diester of 2,5-furandicarboxylic acid.

13. The process according to claim 12 , wherein at least a portion of the first fraction is recycled to the reaction zone.

14. The process according to claim 13 , wherein another part of the first fraction is discharged as a bleed stream.

15. The process according to claim 12 , wherein the liquid phase is separated into the first and second fraction by means of cooling crystallization, evaporative crystallization, melt crystallization, evaporation or a combination thereof.

16. The process according to claim 1 , wherein the reaction conditions in the reaction zone include a reaction temperature in the range of 150 to 300° C., and a pressure of 5 to 25 bar.

17. The process according to claim 1 , which process is conducted as a continuous process.

18. The process according to claim 2 , wherein the alkanol is methanol.

19. The process according to claim 4 , wherein the reaction zone comprises sieve plates.

20. The process according to claim 6 , wherein the oxidizing agent is an oxygen-containing gas.