Upgrading polyolefin plastics: experiences from petroleum refining and distinct characteristics

The upgrading of polyolefins poses a significant challenge in polymer recycling due to their abundance and chemical inertness. While petroleum refining technologies could be transformed into polyolefins’ upgrading due to their similarities in atomic composition, there are essential differences. Current research aims to develop a better understanding of polyolefins’ “refinery”, but there is a lack of systematic comparison with traditional refinery methods. This review provides a comprehensive overview of the most recent reactions employed in polyolefin upgrading, establishing parallels with recognized petroleum refining technologies. It starts with a comparison of physicochemical properties between feedstocks from plastics and from petroleum-based origin. Below major classes of reactions are then discussed, i.e., (1) C–C bond cleavage over solid acid catalysts and/or metallic catalysts, with their conventional refining analogues of fluidized catalytic cracking, hydrocracking and hydrogenolysis; (2) C–C bond rearrangement, mainly aromatization, with petroleum analogue of catalytic reforming; (3) heteroatom removal from impurities, with petroleum analogue of hydrotreating. The review emphasizes the scenario-dependent challenges and corresponding advancements associated with these reactions. Furthermore, we draw a conclusion by identifying key areas that are inadequately addressed in existing literature, highlighting the technological requirements necessary to progress from laboratory-scale chemistry to pilot demonstrations, and providing insight into future directions and opportunities for advancing polyolefin upgrading technologies.