Insight into liquefaction process of sawdust with hydrogen donor solvents

As a zero-carbon energy source, biomass will play an important role in achieving the goal of carbon neutrality. The efficient conversion and utilization of biomass energy remains a great challenge. Thermochemical liquefaction is one of the most efficient ways to convert biomass into liquid fuels. In this study, five different solvents were used to liquefy sawdust. The results showed that cyclohexanol had the highest conversion of 90.5% with a liquid yield of 79.1%, followed by tetralin (81.7% and 72.0%), ethanol (70.2% and 57.0%), isopropanol (64.5% and 47.7%), and cyclohexane (57.0% and 44.5%). The better performance of cyclohexanol and tetrahydrofuran is due to their greater mass and heat transfer capacity, which is determined by the comparative solvent properties. The liquefied gas, liquid and solid products were characterized by GC, GC-MS and FT-IR, respectively. The results demonstrated that the composition of hydrogen and hydrocarbons in the gas was influenced by the hydrogen donor of the solvent; the distribution of bio-oil was strongly influenced by the hydrogen donor and side reactions of the solvent; the solid residue was mainly from lignin in the wood chip composition. In addition, microcrystalline cellulose and lignin were used as models to further investigate solvent effects and liquefaction mechanisms. The formation pathways of some special chemicals, including acid intermediates, ketones, and phenols, were proposed based on the structural units of cellulose and lignin.