Conversion of Lignin into Phenolic Monomer and Low Molecular Weight Bio-oil in Different Supercritical Solvent System

High-value utilization of lignin is crucial in further developing biomass refining processes and producing biofuels. In this work, lignin depolymerization was examined in different supercritical systems. The effects of reaction temperature and reaction time on various lignin depolymerization products were investigated in detail. Among them, in the supercritical ethanol/water system (50% ethanol), the beta-o-4 aryl ether bonds of lignin were depolymerized into phenolic hydroxyl groups, alcoholic hydroxyl groups and alkyl groups through hydrogenation and hydrolysis reactions. The lignin intermediate fragments produced by depolymerization undergo further hydrocracking to form more low molecular weight products such as 4-alkylguaiacols. In addition, low molecular weight lignin intermediates also produced lignin oligomers and carbon solid residues (SR) through repolymerization reactions. When the reaction temperature was higher than 360 degrees C, the repolymerization reaction between the highly active lignin depolymerization intermediates could be promoted to form more SR products. All in all, when the reaction temperature was 300 degrees C, lignin was more suitable for depolymerization into phenolic monomer products during the supercritical ethanol/water system (1/1, v/v). [GRAPHICS] .