Hydrogen-free catalytic depolymerization of waste polyolefins at mild temperatures

Abstract

Reductive methods of polyolefin waste deconstruction such as hydrogenolysis/hydrocracking have enabled advances in plastic upcycling at low temperatures. However, these processes require hydrogen gas, presenting economic and environmental tradeoffs. Here, we present an overview of recent developments in low-temperature, hydrogen-free depolymerization of polyolefins. We start by introducing technologies that utilize sacrificial solvents to cleave C-C bonds, followed by progress in solvent-free depolymerization. We then provide an overview of catalytic processes in petroleum and lignin upgrading that may be extended to polyolefin activation and depolymerization, including alkane dehydrogenation/aromatization, transfer hydrogenation, and hydrogen co-generation, as well as opportunities for utilizing the polymer itself as a hydrogen source. Next, we provide an overview of techniques for quantifying reaction progress via hydrogen consumption and for characterizing the degree of unsaturation of polyolefins. We close with an outlook on the role of feedstock treatment, economic analysis, and process optimization in ushering in these new technologies.