Solvent System with Improved Hydroxide Reactivity for Mild and High-Efficiency PET Alkaline Hydrolysis

Abstract

Depolymerization of polyethylene terephthalate (PET) in alkaline mixed solutions can be carried out efficiently. However, the direction of the suitable solvent system selection is unclear, limiting the development of this approach. To address this problem, the effect of solvents on the alkaline hydrolysis of PET is discussed from the perspective of hydroxide reactivity. Dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone (DMI), tetrahydrofuran, dioxane, water, toluene, and CCl4 were used as a cosolvent for the alkaline hydrolysis of PET in ethylene glycol (EG) to regulate the hydroxide reactivity. The results show that a cosolvent that can act as a hydrogen-bond acceptor but not as a hydrogen-bond donor is suitable because this cosolvent can compete with hydroxide for hydrogen-bond formation with EG and improve the hydroxide reactivity. According to this direction, a PET recycling scheme based on a DMI-EG-NaOH system is designed, which is highly efficient and cost-effective.