Microwave Catalytic Depolymerization of Polyethylene Terephthalate Plastic to the Monomers

Plastic waste management has emerged as a critical environmental issue due to the exponential increase in plastic consumption worldwide. Polyethylene terephthalate (PET) is extensively used in the production of water bottles, which constitutes a significant fraction of the plastic waste. PET recycling is a challenging task due to the lack of efficient and cost-effective depolymerization methods. In this study, we developed a microwave (MW) catalytic depolymerization method for PET recycling using modified zinc oxide loaded with manganese oxide as a cocatalyst. The modified Mn3O4/ZnO catalyst presents high efficiency in depolymerizing PET into its monomers with only 0.4 wt % ratio of the catalyst to PET at 175 °C for 5 min, resulting in 100% conversion of PET and 88% selectivity toward bis-hydroxyethyl terephthalate monomers. It is believed that Mn3O4 provides additional Lewis acid sites, promoting the dissociation of glycol from PET, and the MW irradiation plays a crucial role in rapidly heating the ethylene glycol and the catalyst, thereby accelerating the PET depolymerization process. In addition, the heterogeneous nature of the catalyst facilitates its easy separation from the reaction mixture for reuse, simplifying the catalyst recovery process and enabling cost-effective and sustainable PET recycling. Thus, this study provides an innovative and sustainable solution for PET recycling, contributing toward the circular economy and mitigating the environmental impact of plastic waste.