Process for the preparation of a polyester
A polyester including ethylene 2,5-furandicarboxylate units is prepared in a process, where in an esterification step a 2,5-furandicarboxylate compound is reacted with ethylene glycol to form an ester composition, including components with 2-hydroxyethyl and 2,5-furandicarboxylate moieties; where in a polycondensation step the ester composition thus obtained is subjected to polycondensation at reduced pressure in the presence of a polycondensation catalyst to obtain a polycondensate; and where during the polycondensation step 2,5-furandicarboxylic acid is added to the ester composition.
1. A process for the preparation of a polyester comprising ethylene 2,5-furandicarboxylate units, wherein in an esterification step a 2,5-furandicarboxylate compound is reacted with ethylene glycol to form an ester composition, comprising components with 2-hydroxyethyl and 2,5-furandicarboxylate moieties; wherein in a polycondensation step the ester composition thus obtained is subjected to polycondensation at reduced pressure in the presence of a polycondensation catalyst to obtain a polycondensate; and wherein during the polycondensation step 2,5-furandicarboxylic acid is added to the ester composition.
2. The process according to claim 1 , wherein the 2,5furandicarboxylate compound is selected from the group consisting of 2,5-furandicarboxylic acid, dialkyl ester of 2,5-furandicarboxylic acid and combinations thereof.
3. The process according to claim 2 , wherein the 2,5furandicarboxylate compound is dimethyl-2,5-furandicarboxylate, diethyl-2,5-furandicarboxylate or a mixture thereof.
4. The process according to claim 1 , wherein the molar ratio of 2,5-furandicarboxylate compound to ethylene glycol is in the range of 1:1.01 to 1:4.
5. The process according to claim 1 , wherein the esterification step is carried out in the presence of an esterification catalyst, preferably a zinc-containing or titanium-containing catalyst.
6. The process according to claim 1 , wherein the esterification step is carried out at a temperature of 160 to 240° C. and a pressure of 0.9 to 5 bar for a period of 0.5 to 5 hr.
7. The process according to claim 1 , wherein in the esterification step ethylene glycol and any volatile compound that is formed during the reaction between the 2,5-furandicarboxylate compound and ethylene glycol, are removed in a distillation system, and wherein ethylene glycol that is removed with the volatile compounds is separated therefrom and at least partly recycled.
8. The process according to claim 1 , wherein the polycondensation step comprises a pre-polycondensation reaction conducted at a pressure of 25 to 700 mbar and a polycondensation reaction conducted at a pressure of 0.05 to 20 mbar.
9. The process according to claim 1 , wherein the polycondensation step takes a period in the range of 1.5 to 4 hours.
10. The process according to claim 1 , wherein during the polycondensation step ethylene glycol that is formed is removed from the ester composition that is subjected to polycondensation.
11. The process according to claim 1 , wherein the polycondensation step is carried out in the presence of a polycondensation catalyst selected from the catalysts comprising one or more elements selected from tin, zinc, titanium, antimony and combinations thereof.
12. Process according to claim 1 , wherein the polycondensation reaction is carried out at a temperature of 205 to 280° C. and a pressure of 0.05 to 20 mbar.
13. The process according to claim 1 , wherein 2,5furandicarboxylic acid is added to the ester composition when the ester composition has been exposed to a pressure in the polycondensation step of at most 20 mbar.
14. The process according to claim 1 , wherein 2,5furandicarboxylic acid is added to the ester composition in the period of 5 to 90 minutes after the reduced pressure in the polycondensation step has been attained.
15. The process according to claim 1 , wherein the amount of 2,5furandicarboxylic acid that is added to the ester composition is in the range of 0.1 to 10 mole %, based on the molar amount of the 2,5-furandicarboxylate compound that is provided in the esterification step.
16. The process according to claim 1 , wherein the polycondensate is crystallized at a temperature in the range of 90 to 200° C. for a period of 2 to 48 hr in a crystallization step to yield a semi-crystalline polyester.
17. The process according to claim 16 , wherein the semicrystalline polyester is subjected to solid state polymerization at a temperature in the range of 180 to 220° C. for a period of at most 120 hr to obtain a solid state polymerized polyester.
18. A polyester comprising ethylene 2,5-furandicarboxylate units, which polyester has a number average molecular weight as determined by gel permeation chromatography (GPC) using polystyrene as standard, of at least 10,000, and which polyester has a hydroxyl end group content in the range of 65 to 120, determined by 1H-NMR in deuterated 1,1,2,2-tetrachloro ethane.
19. The polyester according to claim 18 , further comprising one or more metals selected from the group consisting of zinc, titanium, tin and calcium.