Process for recycling polyester materials
View Patent ↗The present invention is a process for recycling colored polyester. More specifically, colored polyester for recycling is depolymerized by the addition of glycol to form the monomer BHET. The BHET is contacted with activated carbon to remove some colorant. The remaining colorant is extracted with water, alcohol, or glycol to produce white, purified BHET. The white, purified BHET is separated from the extraction solvent (water, alcohol, or glycol) by filtering, decanting, or centrifuging, for example. The purified BHET monomer can be polymerized to polyethylene terephthalate meeting food contact specifications, using known polymerization processes.
1. A method for removing colorants from colored polyester waste wherein the method comprises the following sequential steps:
a. depolymerizing said colored polyester by adding a glycol to said polyester at a temperature in the range of from 180° C. to 280° C. for a period of from one to five hours to produce a glycolyzed monomer;
b. optionally filtering specific contaminants from said glycolyzed monomer;
c. feeding said glycolyzed monomer through a bed of activated carbon to remove some colorant;
d. extracting the remaining colorant from said glycolyzed monomer by introducing said glycolyzed monomer to a stirred reactor along with an extraction solvent at a temperature that is below the temperature of the glycolyzed monomer, said extraction solvent being selected from water, methanol, or a glycol whereby the glycolyzed monomer precipitates out and the remaining colorant transfers to the extraction solvent; and
e. separating said glycolyzed monomer from the extraction solvent.
2. The method of claim 1 , wherein said glycol of step (a) is ethylene glycol.
3. The method of claim 1 , wherein said polyester includes polymer contaminants that swell in glycol, and said glycolyzed monomer of step (a) is filtered to remove said swellable polymer contaminants.
4. The method of claim 3 , wherein said filtering occurs within about 3 hours of adding glycol to said polyester.
5. The method of claim 1 , wherein said bed of activated carbon is maintained at a temperature that is greater than about 170° C.
6. The method of claim 1 , wherein the weight of said activated carbon in step (c) is at least about the same weight of said glycolyzed monomer.
7. The method of claim 1 , wherein said glycolyzed monomer is filtered after step c, to remove any impurities.
8. The method of claim 1 , wherein the weight of said extraction solvent in step (d) is at least twice the weight of said glycolyzed monomer.
9. The method of claim 8 , wherein the extraction solvent in step (d) is methanol and the glycolyzed monomer is decanted from said methanol.
10. The method of claim 1 , wherein said separated glycolyzed monomer is polymerized to produce clear polyester polymer.
11. The method of claim 1 , wherein said colored polyester is green.
12. The method of claim 1 , wherein separating said glycolyzed monomer from the extraction solvent is accomplished by at least one of filtering, centrifuging, and decanting.
13. The method of claim 1 , wherein said glycolyzed monomer is bis-hydroxyethyl terephthalate.