LAUSR

Abstract A high-calorific-value oil with a high amount of oxygen-free aromatics was produced from highly recalcitrant concentrated-sulfuric-acid-hydrolysis lignin (CSAHL) using a two-step approach. In the first step, lignin-derived bio-oil (LBO) was produced by the liquefaction of CSAHL in a mixture of supercritical ethanol and formic acid. In the second step, hydrodeoxygenation (HDO) of the LBO over sulfided CoMo/γ-Al2O3 (CoMoSx/γ-Al2O3), Pd/Al2O3, and Ru/γ-Al2O3 catalysts was performed to produce upgraded LBO. Although the yield of the LBO was high (70 wt%), its calorific value and the yield of monoaromatics (mainly oxygenated guaiacol- and syringol-type molecules) were low (27.2 MJ kg−1 and 4 wt% (based on CSAHL), respectively). The LBO was separated from the ethanol and used as a feed for HDO in formic acid, which acts as an in-situ hydrogen donating agent. HDO of the LBO over CoMoSx/γ-Al2O3 at 350 °C for 4 h produced oxygen-free aromatics, such as alkylated benzenes, indanes, and tetralins, with the high yield of 6.8 wt% (based on CSAHL). The degree of deoxygenation was high (>90%) and the upgraded LBO exhibited a high calorific value (>40 MJ kg−1). The effects of different HDO parameters, including catalyst loading, amount of formic acid, reaction time, catalyst type, and solvent type were assessed to gain insight into the LBO deoxygenation mechanisms.