(154m) Polyethylene Terephthalate Depolymerization: Controlled Glycolysis to Oligomers Via Microwave Irradiation Using Antimony (III) Oxide

The production of oligomers from the glycolysis of polyethylene terephthalate (PET), instead of its fully glycolyzed product, bis-(hydroxyethyl) terephthalate (BHET) can be done under microwave using a suitable catalyst. We show that zinc acetate catalysts can generate BHET as the ultimate glycolysis product and the antimony (III) oxide (Sb₂O₃) catalyst can promote the production of higher oligomers of PET under microwave irradiation. Waste PET from drinking water bottles was glycolyzed by antimony (III) oxide (Sb₂O₃) with a loading of 0.25 wt% as the catalyst at 240°C in a Mars 6 microwave from CEM corporation, resulting in an oligomer yield of 96.7%. The conversion of PET to oligomers reached 100% in only 5 min at 240°C (with a 10 min ramping time) and a PET to ethylene glycol weight ratio of 2.5. In comparison, 0.025 wt% of zinc acetate, a well-known catalyst for PET glycolysis, produces only BHET monomer with a 96.3% yield, under the same reaction conditions. The reaction mixture and isolated products were characterized by FTIR, NMR, DSC, TGA, and HPLC. Our results demonstrated that by using Sb₂O₃ as a catalyst under microwave irradiation, the PET glycolysis can be controlled to produce higher PET oligomers as an alternative for a complete chemical depolymerization to BHET monomer. These oligomers can have potential applications as functional monomers and additives for other polymer products and also to produce high-quality second-generation products, including regenerated PET.