Preparation of dialkyl esters of 2,5-furandicarboxylic acid

1. A process for the preparation of the dialkyl esters of 2,5-furandicarboxylic acid which process comprises:

contacting an acid starting composition comprising 2,5-furandicarboxylic acid with an excess of alkanol to form an esterification product comprising the dialkyl ester of 2,5-furan dicarboxylic acid, water and unreacted alkanol;

separating at least part of the unreacted alkanol and water from the esterification product to yield a solid crude product composition comprising the dialkyl ester of 2,5-furandicarboxylic acid; and

subjecting at least part of the solid crude product composition to an evaporation step, wherein the dialkyl ester of 2,5-furandicarboxylic acid is evaporated and subsequently condensed to yield purified dialkyl ester of 2,5-furandicarboxylic acid,

wherein the solid crude product composition comprising the dialkyl ester of 2,5-furandicarboxylic acid is pre-purified in a concentration zone before being subjected to the evaporation step; and

wherein the evaporation step is conducted in one or more of the equipment selected from a stirrer evaporator, rising film evaporator, circulation evaporator, falling film evaporator and wiped film evaporator.

2. The process according to claim 1 , wherein the evaporation is carried out at a temperature in the range of 120 to 250° C.

3. The process according to claim 1 , wherein the evaporation is carried out at a pressure below 100 mbar.

4. The process according to claim 1 , wherein the contact of 2,5-furandicarboxylic acid with an excess of alkanol is conducted at a temperature of 150 to 300° C., and a pressure of 5 to 25 bar.

5. The process according to claim 1 , wherein the contact of 2,5-furandicarboxylic acid with an excess of alkanol is conducted at a contact time of 0.1 to 3 hr.

6. The process according to claim 1 , wherein the alkanol comprises 1 to 4 carbon atoms.

7. The process according to claim 1 , wherein the 2,5-furandicarboxylic acid and alkanol are contacted in the absence of an esterification catalyst.

8. The process according to claim 1 , wherein the 2,5-furandicarboxylic acid and alkanol are contacted in an esterification zone from which alkanol is continuously withdrawn.

9. The process according to claim 1 , wherein unreacted alkanol from the esterification product is removed by means of distillation, flash distillation or evaporation.

10. The process according to claim 1 , wherein the solid crude product composition is subjected to one or more of the treatments selected from washing, crystallization, re-crystallization and melt crystallization.

11. The process according to claim 1 , wherein the solid crude product composition comprising the dialkyl ester of 2,5-furandicarboxylic acid is washed in a washing zone to yield washed composition comprising the dialkyl ester of 2,5-furan dicarboxylic acid, and the washed composition is crystallized in a crystallization zone to yield crystallized composition that is being subjected to the evaporation step.

12. The process according to claim 1 , which is carried out at as a continuous process.

13. An ester composition comprising dialkyl ester of 2,5-furandicarboxylic acid wherein the composition comprises 99 to 99.9% wt of dialkyl ester of 2,5-furandicarboxylic acid and 1 to 0.1% wt of monoalkyl ester of 2,5-furandicarboxylic acid, the percentages being based on the composition, and which composition has a color of at most 0.005, as measured by absorbance of a 30 mg/L solution in DMSO at a wavelength of 400 nm.

14. The process according to claim 6 , wherein the alkanol is methanol.