Pyrolysis of waste plastics in the rotary-kiln reactor

Chemical recycling of end-of-life plastics contributes to the circular economy, and pyrolysis in rotary kilns is a commercially available technology for this purpose. This study examines the pyrolysis of real-world waste plastics, including polypropylene (PP), polyethylene (PE), and polystyrene (PS), in a simulated rotary-kiln-type reactor at three pyrolysis temperatures (450, 500, and 550 °C). Particular attention is given on effects of heating rate (6 °C min -1 , 32 °C min -1 , and 100 °C min -1 ), which correspond to three representative operating modes of rotary kilns. Although the pyrolysis oil yield remained within narrow ranges, the quality of the pyrolysis oil varied significantly with the heating rate. Fast heating induced a transition from a waxy oil to a flowable oil during pyrolysis of waste PE and PP (accompanied by reductions in average molecular weight), and increased styrene selectivity during pyrolysis of waste PS. The results are explained by a dual-pathway model in which the fate of plastic pyrolysis vapor is governed by competition between wall-induced secondary cracking and rapid vapor removal. These findings show that pyrolysis effectiveness in rotating kilns depends strongly on both heat parameters (temperature and heating rate) and polymer structure, offering crucial insights for optimizing pyrolysis processes to recover high-value chemicals from waste plastics.