Wood Liquefaction: Role of Solvent

The liquefaction of lignocellulose is strongly affected by the choice of the liquefaction solvent. This effect was studied by processing pinewood at 310 °C in various organic solvents, including some refinery streams. The impact on yields of char, biocrude, and gas was determined. The resulting biocrude was analyzed with GPC and GC-MS, the solid residue with FTIR and HR-SEM, and the gas with GC. The solvents appeared to influence the liquefaction through interaction with early carbohydrate degradation products rather than interaction with the final biocrude. Indeed, biocrude is soluble in all solvents, and char is not formed by degradation of biocrude but rather by degradation of early carbohydrate intermediates. Effective solvents show a good affinity with the biomass, e.g., as expressed by Hildebrand values of 25–40 MPa^1/2 or small Hansen distances (Ra) to cellulose and lignin. Protic solvents further slowed the liquefaction reaction