One-step alcoholysis of lignin into small-molecular aromatics: Influence of temperature, solvent, and catalyst

Lignin valorization is a challenge because of its complex structure and high thermal stability. Supercritical alcoholysis of lignin without external hydrogen in a self-made high-pressure reactor is investigated under different temperatures (450–500 °C) and solvents as well as catalysts by using a reactant suspension mode. Small-molecular arenes and mono-phenols (C(7)-C(12)) are generated under short residence time of 30 min. High temperature (500 °C) favors efficient deoxy-liquefaction of lignin (70%) and formation of small-molecular arenes (C(6)-C(9)). Solvents methanol and ethanol demonstrate much more synergistic effect on efficient deoxy-liquefaction of lignin than propanol. The catalyst Cu-C has the optimal activity and selectivity in methanol (70% of conversion, 83.93% of arenes), whereas Fe-SiC possesses the optimal catalytic deoxygenation in ethanol, resulting in the formation of arenes other than phenols. Further analysis indicates that lignin is converted into arenes by efficient cleavages of C—O ether bonds and C—C bonds under high temperature and pressure.