Experimental research on the hydrotreatment of waste tire pyrolysis oil upgrading with CoMo/Al2O3 catalyst

Waste tire pyrolysis oil (WTPO) exhibits high calorific value but requires heteroatoms (S/N) and polycyclic aromatic hydrocarbons (PAHs) reduction for fuel applications. Hydrotreatment is an effective method for removing these heteroatoms, enhancing hydrocarbon saturation, and improving oil quality. This study compares unpresulfurised CoMo/Al₂O₃ catalytic versus non-catalytic hydrotreatment to upgrade WTPO. The research systematically explores the transformation of sulfur- and nitrogen-containing compounds, as well as hydrocarbons, under various reaction conditions. The difficulty of hydrogenation desulfurization for four types of sulfur-containing compounds was ranked. C–N bonds in linear compounds and heterocycles in nitrogen-containing compounds can break under the influence of a catalyst or at elevated temperatures and pressures. However, the direct elimination of nitrogen atoms bonded to the benzene ring in aniline-like compounds remains challenging using this catalyst. A representative heterocyclic compound containing both nitrogen and sulfur, benzothiazole, underwent ring-opening conversion to aniline. Even when using unpresulfurized catalysts at higher weight hourly space velocity (WHSV), dehydrogenation side reactions and PAHs formation can be suppressed to a certain extent. Based on these findings, this paper offers useful insights into the catalytic performance of CoMo/Al₂O₃ during WTPO hydrotreatment and provides practical references for catalyst selection and reaction condition optimization.