Catalytic glycolysis of poly(ethylene terephthalate) using zinc and cobalt oxides recycled from spent batteries

Abstract

The chemical recycling of polyethylene terephthalate (PET) to bis(2-hydroxyethyl) terephthalate (BHET) was studied using recycled metal oxides. Recovered zinc (RZnO) and cobalt (RCoO) oxides were obtained after a biohydrometallurgical process to recycle spent alkaline and lithium-ion batteries (LIBs), respectively. Besides, a mixed oxide (Co/RZnO) was prepared by mechanical milling of 2.5 wt% of RCoO on RZnO. The structural, textural, and acidity properties of the catalysts were analyzed by XRD, XANES, SEM, TEM, FT-IR, SBET and pyridine-TPD. The depolymerization of PET (from soft-drink bottles) was carried out with ethylene glycol (EG) at 196 °C for 2 h, using PET/catalyst and PET/EG ratios of 100:1 and 1:8, respectively. The yields of the BHET monomer in the presence of RZnO, RCoO and Co/RZnO as catalysts were 50%, 10% and 80%, respectively. The highest catalytic activity of Co/RZnO could be attributed to the presence of weak and strong acid sites, its overall higher concentration of acid sites and a synergetic efect between Co3O4 and ZnO. The obtained BHET was characterized by DSC, FT-IR, 1 H NMR and 13C NMR analyses, which confrmed the purity and structure of the monomer. Metal oxides obtained using spent alkaline and lithium-ion batteries as raw materials could be used as catalysts for waste PET treatment and pure BHET monomer synthesis.