Waste-derived fuel from tire pyrolysis oil hydrotreating: Insight into the transformation of heavy compounds and heteroatom removal

Pyrolysis offers a promising route for valorization of waste tires. However, waste tire pyrolysis oil (WTPO) contains high concentrations of heteroatoms, limiting its direct use as a fuel. In this study, the transformation of WTPO fractions and representative compound groups during hydrotreating was investigated under a range of operating conditions. Temperature was identified as a key factor controlling the balance between hydrogenation and thermal cracking. At lower temperature hydrogenation was effective, whereas depolymerization and cracking increased substantially at 380 °C and above. The reactivity of gum-forming olefinic compounds depended strongly on molecular structure. Terminal and conjugated olefins were readily hydrogenated, while internal olefins required more hydrogen-rich conditions for effective stabilization. Sulfur speciation analysis showed that hydrodesulfurization (HDS) activity was governed by aromaticity and steric effects, with thiophenic compounds exhibiting higher reactivity than bulkier dibenzothiophenes. Effective upgrading was achieved at 360 °C using a catalyst-to-WTPO ratio of 8:75, providing strong hydrogenation activity while minimizing cracking. Under these conditions, a 96.7 wt% liquid yield, near-complete olefin removal, and 63% HDS were obtained. The catalyst also exhibited stable performance over multiple cycles, with negligible deactivation following recalcination. These findings provide mechanistic insights and practical guidance for efficient WTPO upgrading to high-quality fuel products.