Hydrogenation-induced selective degradation of PET wastes†

Abstract

Polyethylene terephthalate (PET) is a ubiquitous and versatile thermoplastic polymer that has a wide range of applications in daily life. However, like other synthetic plastics, the large-scale production and accumulation of PET has resulted in a heavy environmental burden. Chemical upcycling is a promising strategy to address the environmental crises posed by PET plastic wastes, yet its practical implementation remains challenging. Herein, we report a novel hydrogenation-induced hydrothermal degradation strategy for upcycling of PET to valuable products. For the first time, a range of highly crystalline post-consumer PET wastes were efficiently converted into high-value 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and ethylene glycol (EG) in excellent yields under simple neutral water conditions. Detailed mechanistic investigations indicated that hydrogenation of aromatic rings in PET chains occurred preferentially relative to hydrolysis of the ester linkages. The hydrogenation process not only eliminated the intermolecular π–π stacking forces, but also disrupted the intramolecular conjugated π-systems, thus increasing the electrophilic and hydrolytic reactivity of ester linkages in PET. This work opens a new cost-effective route for PET upcycling, which may stimulate the development of an economically viable upcycling industry for PET plastics.