Production of low-aromatic oil from catalytic pyrolysis of waste plastics-derived wax

Chemical recycling of waste plastics into diesel fuel and other precursors that can be used to generate new plastics reduces reliance on conventional fossil energy sources and ensures a circular economy. In this study, we investigated the catalytic pyrolysis of waste plastics-derived pyrolysis wax (PW) into low-aromatic oil, focusing on naphtha (C₅-C₁₂)- and diesel (C₁₃-C₂₂)-range hydrocarbons, by examining the effects of commercial catalysts (i.e., Al₂O₃, HZSM-5 (SiO₂/Al₂O₃: 50, 80), and HY (SiO₂/Al₂O₃: 60, 80)) and mixed catalysts (i.e., 1CaO/1HY (80), 1MgO/1HY (80), 1CeO₂/1HY (80)) on product distribution. The use of catalysts significantly enhanced wax conversion compared to non-catalytic test by facilitating the cracking of long-chain polymers. HY (80) achieved the highest performance with 92.2 wt% wax conversion and 57.2 wt% oil yield, producing oil with the lowest aromatic content (38.6 %) and significant naphtha (45.4 %) and diesel-range (14.7 %) hydrocarbons. This can be attributed to its moderate acidity and well-developed structure among zeolite catalysts. Mixed catalysts, especially 1CeO₂/1HY (80), showed improved performance by reducing aromatic selectivity to 20.4 % and increasing the diesel fraction to 23.6 %, while maintaining comparable wax conversion, oil yield, and naphtha production to HY (80). This improvement is attributed to the alkaline and redox properties of CeO₂. The enhanced wax conversion and oil yield compared to the theoretical values obtained using binary catalysts, especially 1CeO₂/1HY (80), confirmed the synergistic effect of combining metal oxides with HY (80) in producing low-aromatic oil. Examining of various CeO₂-to-HY ratios identified 2/1 as the optimal ratio to produce low-aromatic oil. The use of inexpensive and readily available metal oxides with zeolites as mixed catalysts for PW pyrolysis to produce low-aromatic oils provides a commercially viable solution for PW management.