Fe-assisted hydrothermal liquefaction of cellulose: Effects of hydrogenation catalyst addition on properties of water-soluble fraction

Abstract Hydrothermal liquefaction (HTL) is an effective way of converting biomass into fuels and chemicals. Recently, the addition of catalysts in the HTL has been investigated to improve the yield and quality of bio-oil. We previously reported that metallic-Fe-promoted HTL of lignocellulosic biomass affords a water-soluble (WS) fraction that furnishes light olefins and aromatic hydrocarbons upon catalytic cracking over a solid acid catalyst. We demonstrated that the Fe-assisted HTL of cellulose in the presence of a hydrogenation catalyst results in a superior yield and quality of the WS fraction, thereby enhancing the hydrocarbon yield in the catalytic cracking of the WS fraction. When the HTL of cellulose was performed in the presence of Fe and Pd/Al2O3 at 250 °C for 1 h, the WS fraction yield reached 73%. The addition of hydrogenation catalysts led to higher hydrogen-to-effective-carbon ratios (up to 1.33) and proportions of the volatile light WS fraction (up to 63%) than those obtained by Fe-assisted HTL. This improved performance was attributed to the synergistic acceleration by metallic Fe and the hydrogenation catalyst, which particularly hydrogenates ketones to alcohols. Finally, a plausible mechanism that explains the effect of the hydrogenation catalyst was proposed.