Catalytic hydrodeoxygenation of crude bio-oil in supercritical methanol using supported nickel catalysts

Pyrolysis oil (bio-oil) consists of high water content and vast variety of oxygenates (acids, alcohols, aldehydes, esters, ketones, sugars and phenols), causing some undesirable properties that prevent the direct use of bio-oil as a transportation fuel. Bio-oil upgrading to decrease its oxygen content provides a sustainable fuel that can be considered a valuable substitution for depleting fossil fuels. Catalytic hydrodeoxygenation (HDO) is an efficient method for bio-oil upgrading. This paper presents the HDO of crude bio-oil in supercritical fluid (ethanol, methanol, and 2-propanol) using a batch high pressure reactor. Supercritical fluids have unique physicochemical properties of liquid-like density and gas-like high diffusivity and low viscosity. The upgrading efficiency was evaluated by measuring the elemental composition (CHNS[sbnd]O), water content, carbon residue, and high heating value (HHV) of the bio-oil upgraded over Ni/HBeta catalyst. Compared to ethanol and 2-propanol, supercritical methanol resulted in a higher decrease in the oxygen content of bio-oil. The activity of Ni/HBeta was examined by varying the Ni loading (5–20 wt%), initial hydrogen pressure (10–30 bar), and reaction time (2–6 h). Meanwhile, effects of support materials (HZSM-5, HBeta, HY, Al-SBA-15, and silylated HBeta) on the performance of nickel catalyst in bio-oil upgrading were investigated using supercritical methanol.