Catalytic depolymerization of waste polyethylene terephthalate plastic in supercritical ethanol by ZnO/γ-Al2O3 catalyst

In order to minimize the environmental impact from polyethylene terephthalate (PET) plastic waste, catalytic depolymerization was employed to break down PET into useful diethyl terephthalate (DET) monomers. This research investigated the depolymerization of waste PET in supercritical ethanol (SCE) catalyzed by ZnO/γ-Al2O3 catalysts. The effect of the types of γ-Al2O3 (neutral and acidic) support, ZnO loading and catalyst dosage were studied. The catalytic efficiency of the catalysts was evaluated by the yield of DET obtained from the catalytic depolymerization of waste PET in SCE at 270 °C and 60 min reaction time. The results revealed that the highest DET yield of 92.2% could be obtained with 7.5 wt% ZnO supported on acidic γ-Al2O3 with catalyst dosage of 5% by weight of waste PET. NMR analysis indicated that the catalytic depolymerization process was complete since there were no PET polymer residues in the liquid. In addition, the ZnO/γ-Al2O3 catalyst also had good stability after five cycles of reuse, its catalytic activity was still satisfactory. The findings suggested that catalytic depolymerization in SCE is a promising alternative for converting waste PET into valuable materials.