Hybrid process for the depolymerization of polyethylene terephthalate (PET) from post-consumer mixed textile wastes

Abstract

In this study, we developed a new process integrating glycolysis and methanolysis to depolymerize low-quality polyethylene terephthalate (PET) wastes, particularly post-consumer mixed textiles. PET is first depolymerized with ethylene glycol and a catalyst, i.e. Na₂CO₃, to produce bis(2-hydroxyethyl) terephthalate (BHET). This is then extracted from the glycolyzed products and a transesterification with methanol is performed, yielding dimethyl terephthalate (DMT). Finally, DMT is recovered from the solution and purified by distillation. The proposed process allows a very low weight ratio between the fibers containing PET and the ethylene glycol used in the glycolysis reaction, thus avoiding a final step of product concentration. Also, BHET dimers and trimers can be recovered together with the monomer, thus increasing the global process yield. Indeed, a global DMT yield up to 77% can be achieved with this hybrid process, which is higher than that of other chemical recycling processes currently applied to textile wastes.