Catalytic pyrolysis of different plastics using low-cost catalysts: wax characteristics and oil stability

The marketing of pyrolysis oil derived from plastic waste is impeded by oil instability, influenced by the wax formation. It is essential to identify the wax source and determine the fuel types produced from various plastic waste. This research aims to investigate the outcomes of pyrolysis conducted at 450 °C using bentonite catalyst. Wax formation and pyrolysis oil stability were analyzed across different storage temperatures (16–42 °C). The result revealed that each type of plastic waste has its own characteristics. Pyrolysis of PS and PP without catalyst produced almost wax free oil and completely wax free oil using catalyst. HDPE and LDPE non-catalytic pyrolysis produced entirely waxy pyrolysis oil (melting point at 38 °C). The utilization of a catalyst does not significantly alter the melting point. PC and PVC plastics are not advisable for large-scale pyrolysis oil conversion due to their low yields, high char, and substantial energy requirements. The highest oil yield was achieved in PS pyrolysis (97.62 wt%), followed by LDPE (77.66 wt%), PP (74.98 wt%), and HDPE (65.82 wt%). The application of catalyst reduces the liquid yield and increases the gas yield for PS, PP, and LDPE pyrolysis. The highest gasoline fraction was predominantly obtained from PS pyrolysis without catalyst (56.43 wt%), while the highest diesel from PS with catalyst (37.09 wt%). PS, PP, HDPE, and LDPE are recommended for conversion into pyrolysis oil. Further research on catalysts is required to prevent and process the waxy pyrolysis oil into marketable fuels in the second stage of catalytic cracking.