Deep eutectic solvent as an efficient molecular liquid for lignin solubilization and wood delignification

Abstract Lignin is an abundant heterogeneous aromatic biopolymer in the nature with a complex and an irregular structure and very low solubility in common solvents. Such drawbacks limit lignin isolation from wood and its conversion to value-added products. Here, for the first time we report a very high solubility of lignin in the very economic and green deep eutectic solvents using ultrasound irradiation. We synthesized a series of deep eutectic solvent based on the possible favorable solute-solvent interactions. It was found that lignin can be solubilized in these solvents up to about 50% w/w. To the best of our knowledge, this is the highest amount of any lignocellulosic compound solubility which has been reported to this time. Moreover, due to the low solubility of cellulose in these deep eutectic solvents, lignin can be completely isolated from lignocellulosic biomass in one-pot procedure. We think that this exploration can open new promising window to lignin-based science and technology.