Pyrolysis oil upgrading via hydrotreatment to produce alternative fuel using ZrO2-supported catalysts and isopropanol as a solvent

Abstract

Biomass pyrolysis is a promising approach for sustainable bioenergy production, primarily due to its ability to produce a high amount of liquid. However, the high oxygen content in pyrolysis oil limits its applicability in transportation fuels, necessitating deoxygenation for upgrading. Conventional two-step upgrading processes, involving stabilization and hydrotreatment, can be complex and costly. This study investigates a one-step hydrotreatment of fast pyrolysis bio-oil from pine wood using isopropanol (IPA) as a hydrogen-donating solvent to upgrade pyrolysis oil properties. A comprehensive evaluation was conducted to assess the influence of solvent type (IPA vs. glycerol), hydrogen pressure (500 vs. 1000 psi), and catalyst types (NiMo/ZrO₂, CoMo/ZrO₂, NiMo/Al₂O₃, CoMo/Al₂O₃, Ni/SiO₂-Al₂O₃) on the physicochemical characteristics of the upgraded oil. IPA demonstrated superior performance in increasing carbon content of upgraded oil (from 43.9 % to 68.5 %) and higher heating value (from 17.4 to 31.2 MJ/kg), whereas glycerol promoted greater oxygen removal (up to 89.6 %) under moderate pressure (500 psi) with NiMo/ZrO₂. The effect of hydrogen pressure depends on the catalyst type. Among the evaluated catalysts, NiMo/ZrO₂ demonstrated superior performance for pyrolysis oil upgrading. Thermogravimetric analysis indicated minimal coke formation on NiMo-based catalysts, particularly with ZrO₂ support. Simulated distillation results further emphasized the role of reaction time in maximizing jet fuel-range product yields. Catalyst regeneration experiments confirmed that NiMo/ZrO₂ maintains robust deoxygenation activity over three cycles, with only slight deactivation attributed to coke accumulation. This study offers a practical route for efficient one-step pyrolysis oil upgrading using a non-noble catalyst and IPA.