Efficient Depolymerization of Polyethylene Terephthalate Waste via Mechanocatalytic Methanolysis Using the K2CO3 Catalyst

Abstract

Tackling plastic waste has garnered growing attention in recent years, spurring intensified research into plastic depolymerization. Among various plastics, polyethylene terephthalate (PET) stands out as the most widely recycled. Although several depolymerization methods have been reported, many still rely on high temperatures and/or excessive amounts of toxic reagents. Herein, we study the depolymerization of PET derived from post-consumer waste bottles via mechanocatalytic methanolysis at room temperature, without any chlorinated solvents or excessive solvents/reactants. Under optimized conditions, 76% yield, 82% PET conversion, and 96% selectivity to the desired dimethyl terephthalate (DMT) were achieved within one hour of milling. Our results demonstrate a critical role of potassium carbonate (K2CO3)—used as a cost-effective, earth-abundant, and environmentally benign catalyst—in generating methoxide nucleophiles, which accelerates the mechanochemical process. To elucidate the underlying mechanism, density functional theory (DFT) calculations were performed. These simulations reveal that the formation of free methoxide anions in the solution is the primary driver of catalytic PET methanolysis under mechanochemical conditions. This work opens new avenues for sustainable plastic waste processing. The key advantage of the method is that it uses 12 times less methanol and is 24 times faster than conventional thermochemical methanolysis, while leading to nearly double the yield, offering a greener and more efficient alternative.