DOI: https://doi.org/10.36347/sjpms.2026.v13i01.005

Pages: 32-48

The sustainable management of used engine oil (UEO) represents a critical environmental and energy challenge due to its complex composition, high toxicity, and improper disposal practices. In this study, thermo-catalytic cracking was employed as an effective route for upgrading UEO into gasoline-range hydrocarbons using Na/K/Ca–promoted Fe3O4 nanoparticle on HZSM-5 support as catalysts. Na–Fe₃O₄/HZSM-5, K–Fe₃O₄/HZSM-5, and Ca–Fe₃O₄/HZSM-5 catalysts were evaluated over a reaction temperature range of 350–450 °C, varying catalyst loadings and reaction times to elucidate the effects of process parameters on product distribution and fuel quality. Process optimization was performed using the Taguchi experimental design coupled with analysis of variance (ANOVA), which revealed reaction temperature as the dominant parameter influencing UEO conversion, gasoline-range (C₄–C₁₂) selectivity, and PONA composition. The highest gasoline-range selectivity of 97.91% was achieved at 450 °C using 5 wt.% Na–Fe₃O₄/HZSM-5, attributed to the optimal balance of Brønsted and Lewis acid sites and improved accessibility of the HZSM-5 pore structure. Higher loadings resulted in reduced selectivity due to nanoparticle aggregation and partial pore blockage. The upgraded liquid products exhibited significant improvements in fuel properties compared to raw UEO, including reduced kinematic viscosity and carbon residue, specific gravity, high research octane numbers, and acceptable flash point and autoignition characteristics. These results confirm the production of gasoline-like fuels with enhanced combustion performance and handling safety. Overall, this work demonstrates the technical viability of Na/K/Ca–promoted Fe₃O₄/HZSM-5 catalysts for efficient conversion of UEO into high-value transportation fuels, offering a promising waste to energy pathway that addresses both environmental remediation and sustainable fuel production.