Biomass fractionation is important for the further conversion of the cellulosic fraction and the effective utilization of the lignin fraction for the production of biofuels and value-added products. Solvent properties play a crucial role on the fractionation efficiency of lignocellulosics using an organosolv fractionation process catalyzed by acidic ionic liquids (AILs). Herein, 12 organic solvents were selected as co-solvents with water based on their solubility parameters for lignin dissolution, including alcohols, alcohol ethers, lactones, a...