Mechanochemical AlCl3-Catalyzed Cracking of Waste Polyolefins and Synthetic Rubbers into Liquid Fuel

Abstract

Conventional recycling of polyolefins and rubbers is hindered by high energy consumption, complex processing, and limited substrate compatibility—fundamental barriers that have long impeded practical waste valorization. Here, we overcome these limitations with a mechanochemical strategy that leverages AlCl3, a classic Lewis acid historically central to petroleum cracking, to catalytically degrade these recalcitrant polymers under ambient, solvent-free conditions. The process achieves near-quantitative conversion of polyethylene (>99%) and polypropylene (97%) within 30 minutes, yielding liquid hydrocarbons with exceptionally narrow carbon number distributions (C8–C14) and polydispersity indices as low as 1.14—highly competitive uniformity for waste-derived oils. This efficiency extends readily to butadiene rubber and ethylene-propylene copolymer, and the catalyst maintains high activity during 11 successive feeding experiments, effectively processing real-world post-consumer waste with minimal pretreatment. Combining model-substrate experiments, selective poisoning studies, and DFT calculations, we propose a carbocationic pathway initiated by in situ Brønsted acid formation, involving selective C–C bond scission and intramolecular cyclization/aromatization. This work establishes a scalable, energy-efficient route that transforms plastic waste into high-quality hydrocarbon feedstocks, offering a transformative alternative to energy-intensive conventional methods.