Chemical recycling of polyolefin waste: from the perspective of efficient pyrolysis reactors

Polyolefins, widely used for packaging, construction, and electronics, facilitate daily life but cause severe environmental pollution when discarded after usage. Chemical recycling of polyolefins has received widespread attention for eliminating polyolefin pollution, as it is promising to convert polyolefin wastes to high-value chemicals (e.g., fuels, light olefins, aromatic hydrocarbons). However, the chemical recycling of polyolefins typically involves high-viscosity, high-temperature and high-pressure, and its efficiency depends on the catalytic materials, reaction conditions, and more essentially, on the reactors which are overlooked in previous studies. Herein, this review first introduces the mechanisms and influencing factors of polyolefin waste upcycling, followed by a brief overview of in situ and ex situ processes. Emphatically, the review focuses on the various reactors used in polyolefin recycling (i.e., batch/semi-batch reactor, fixed bed reactor, fluidized bed reactor, conical spouted bed reactor, screw reactor, molten metal bed reactor, vertical falling film reactor, rotary kiln reactor and microwave-assisted reactor) and their respective merits and demerits. Nevertheless, challenges remain in developing highly efficient reacting techniques to realize the practical application. In light of this, the review is concluded with recommendations and prospects to enlighten the future of polyolefin upcycling.