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:
(a) depolymerizing a polyester in a reaction mixture comprising (i) an alcohol and (ii) an amine organocatalyst and/or carboxylic acid salt of same, wherein the depolymerization produces a reaction product comprising a monomeric and/or oligomeric diester, the alcohol, and the amine organocatalyst;
(b) recycling the amine organocatalyst as a distillate from the reaction product; and
(c) (i) repolymerizing the monomeric and/or oligomeric diester and/or (ii) co-polymerizing the monomeric and/or oligomeric diester with a second diester and/or diacid to reproduce the polyester as a recycled product,
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 and the depolymerization is run at a temperature higher than the boiling point of the alcohol.
2. 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.
3. The method of claim 1 , wherein the repolymerization and/or copolymerization of step (c) further includes one or more additional comonomers selected from the group consisting of terephthalates; diacids; diols; isophthalates, and combinations thereof.
4. The method of claim 3 , wherein the one or more additional comonomers are selected from the group consisting of dimethyl terephthalate; terephthalic acid; cyclohexane dimethanol; and combinations thereof.
5. 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 reaction product comprises bis(2-hydroxyethyl)terephthalate (BHET) and EG.
6. The method of claim 5 , wherein the BHET is purified by a method selected from the group consisting of filtration, ion exchange, decolorization, distillation, solvent wash and combinations thereof.
7. The method of claim 6 , wherein the solvent wash is carried out with a solvent comprising ethylene glycol.
8. The method of claim 6 , wherein the purified BHET reaction product is repolymerized and/or co-polymerized with a second diester and/or diacid to form PET.
9. The method of claim 6 , wherein the purified BHET reaction product is repolymerized and/or co-polymerized to form PET with a second diester and/or diacid and one or more additional comonomers selected from the group consisting of terephthalates; diacids; diols; isophthalates, and combinations thereof.
10. The method of claim 1 , wherein 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.
11. The method of claim 1 , wherein the alcohol acts as—a single solvent in the reaction mixture.
12. The method of claim 1 , wherein the amine organocatalyst and/or carboxylic salt of same 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.
13. The method of claim 1 , wherein the amine organocatalyst and/or carboxylic salt of same 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.
14. The method of claim 1 , wherein the amine organocatalyst and/or carboxylic salt of same is present in the reaction mixture in a range of about 0.1 mol % to about 10 mol % relative to total moles of the polyester in the reaction mixture.
15. The method of claim 1 , wherein the depolymerization reaction and one or more optional purification steps are run as a continuous flow process.
16. The method of claim 15 , wherein the continuous flow process is run in a reaction vessel.
17. The method of claim 16 , wherein the reaction vessel is a pressure reactor.
18. The method of claim 17 , 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.
19. 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 (PTI); polyethylene naphthalate (PEN); polyethylene furanoate (PEF), and combinations thereof.
20. 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).
21. The method of claim 1 , wherein the amine organocatalyst is selected from the group consisting of tetramethylethylenediamine (TMEDA); pentamethyldiethylenetriamine (PMDETA); trimethyl triaza cyclononane (TACN); triethylamine (TEA); 4-(N,N-dimethylamino)pyridine (DMAP); 1,4-diazabicyclo (2,2,2)octane (DABCO); N-methyl imidazole (NMI); and combinations thereof.