Methods and materials for depolymerizing polyesters
Provided is a method of depolymerizing polyesters from post-consumer products, such as beverage bottles, to produce a high purity reaction product. For the depolymerization reaction, the polyesters are reacted with an alcohol and an amine organocatalyst at a temperature of about 150° C. to about 250° C. In one application, the use of an organocatalyst with a boiling point significantly lower than the boiling point of the reactant alcohol allows for the ready recycling of the amine organocatalyst. In another application, performing the depolymerization reaction under pressure at a temperature above the boiling point of the alcohol allows for accelerated depolymerization rates and the recovery of the organocatalyst with no further heat input. In a further application, glycolytic depolymerization of poly(ethylene terephthalate) (PET) produces a reaction product of bis(2-hydroxyethyl)terephthalate (BHET), which may in turn be used to produce high purity beverage bottle grade PET, in a closed loop process with minimal waste.
1. A method comprising:
depolymerizing a polyester with (i) an alcohol and (ii) an amine organocatalyst and/or carboxylic acid salt of same according to Structure 1,
wherein,
R1, R2, and R3 are independently selected from the group consisting of C 1 -C 10 alkyl, branched alkyl, cycloalkyl, and dialkylaminoalkyl, wherein R2 and R3 may form a saturated or unsaturated alicyclic ring;
carbon spacing between any two nitrogen atoms in Structure 1 is greater than one; and
the amine organocatalyst has a boiling point lower than the boiling point of the alcohol.
2. The method of claim 1 , wherein the amine organocatalyst of Structure 1 is selected from the group consisting of tetramethylethylenediamine (TMEDA); pentamethyldiethylenetriamine (PMDETA); triethylamine (TEA); and combinations thereof.
3. The method of claim 1 , wherein the polyester is selected from the group consisting of poly(ethylene terephthalate) (PET); poly(butylene terephthalate) (PBT); polytrimethylene terephthalate (PTT); polyethylene naphthalate (PEN); polyethylene furanoate (PEF), and combinations thereof.
4. The method of claim 1 , wherein the alcohol is selected from the group consisting of 1,2-ethanediol (ethylene glycol); 1,3-propanediol (trimethylene glycol); 1,4-butanediol (tetramethylene glycol); and 1,5-pentanediol (pentylene glycol).
5. The method of claim 1 , wherein the amine organocatalyst and/or carboxylic salt of same has a boiling point at least about 50° C. lower than the boiling point of the alcohol.
6. The method of claim 1 , wherein the amine organocatalyst is a tertiary amine, the alcohol is ethylene glycol, and the depolymerization is carried out at a temperature of about 150° C. to about 198° C.
7. The method of claim 1 , wherein the amine organocatalyst is a tertiary amine, the alcohol is ethylene glycol, and the depolymerization is carried out at a temperature of about 200° C. to about 250° C.
8. The method of claim 1 , wherein the depolymerization produces a reaction product comprising a monomeric and/or oligomeric diester, the alcohol, and the amine organocatalyst.
9. The method of claim 8 wherein the amine organocatalyst is recycled as a distillate from the reaction product.
10. The method of claim 1 , wherein the depolymerization reaction and one or more optional purification steps are run as a continuous flow process.
11. A method according to claim 1 comprising:
depolymerizing a polyester with (i) an alcohol and (ii) an amine organocatalyst and/or carboxylic acid salt of same in a pressure reactor at a temperature higher than the boiling point of the alcohol, wherein the amine organocatalyst has a boiling point at least about 50° C. lower than the boiling point of the alcohol.
12. The method of claim 11 , wherein the pressure reactor has a pressure of about 10 psi to about 20 psi and the temperature is about 10° C. to about 30° C. higher than the boiling point of the alcohol.
13. The method of claim 11 , wherein the amine organocatalyst has a boiling point of at least about 100° C. lower than the boiling point of the alcohol.
14. The method of claim 11 , wherein the amine organocatalyst comprises triethylamine (TEA).
15. The method of claim 11 , wherein the polyester is poly(ethylene terephthalate) (PET), the alcohol is ethylene glycol (EG), the amine organocatalyst is triethylamine (TEA), and the depolymerization reaction produces a reaction product comprising bis(2-hydroxyethyl)terephthalate (BHET) and EG.
16. The method of claim 15 , wherein the BHET reaction product is purified by a method selected from the group consisting of filtration, ion exchange treatment, decolorization, distillation, and combinations thereof.
17. The method of claim 11 , wherein the depolymerization reaction is run as a continuous flow process in the pressure reactor.
18. A method according to claim 1 comprising:
depolymerizing a polyester in a reaction mixture comprising (i) an alcohol of 2 to 5 carbon atoms and (ii) an amine organocatalyst and/or carboxylic acid salt of same, wherein,
(a) the depolymerization is carried out at a pressure in the range of 0 to about 50 psi and at a temperature of about 150° C. to about 250° C.;
(b) the alcohol acts as the only solvent in the reaction mixture;
(c) the amine organocatalyst and/or carboxylic salt of same has a boiling point at least about 50° C. lower than the boiling point of the alcohol; and
(d) the amine organocatalyst is present in the reaction mixture in the range of about 0.1 mol% to about 10 mol% relative to total moles of the polyester in the reaction mixture.
19. The method of claims 18 , wherein the depolymerization reaction and one or more optional purification steps are run as a continuous flow process.
20. The method of claim 1 , wherein the depolymerization is carried out under pressure in the range of 0 to about 50 psi and at a temperature of about 150° C. to about 250° C.
21. The method of claim 1 , wherein the depolymerization is carried out under pressure in the range of about 0 to about 50 psi and at a temperature of about 200° C. to about 250° C.
22. The method of claim 1 , wherein the amine organocatalyst and/or carboxylic salt of same has a boiling point of at least about 100° C. lower than the boiling point of the alcohol.
23. The method of claim 1 , wherein the polyester is poly(ethylene terephthalate) (PET), the alcohol is ethylene glycol (EG), the amine organocatalyst is triethylamine (TEA), and the depolymerization is carried out at a temperature of about 200° C. to about 250° C., wherein the depolymerization produces a reaction product comprising bis(2-hydroxyethyl)terephthalate (BHET) and EG.
24. The method of claim 7 , wherein the depolymerization and one or more optional purification steps are run as a continuous flow process.
25. The method of claim 8 , wherein the reaction product is purified by a method selected from the group consisting of filtration, ion exchange treatment, decolorization, distillation, and combinations thereof.
26. The method of claim 10 , wherein the continuous flow process is run in a pressure reactor.
27. The method of claim 19 , wherein the continuous flow process is run in a pressure reactor.
28. The method of claim 8 , wherein the reaction product is washed with a solvent.
29. The method of claim 28 , wherein the solvent is ethylene glycol.
30. The method of claim 15 , wherein the BHET reaction product is washed with a solvent.
31. The method of claim 30 , wherein the solvent is ethylene glycol.