Lignin extraction and upgrading using deep eutectic solvents

Deep eutectic solvents (DESs) are a class of green solvents exhibiting low vapor pressure, high thermal stability, low toxicity, and biodegradability. These features make them attractive solvents for lignocellulosic biomass processing, especially for lignin valorization. DESs not only solubilize lignin from lignocellulose biomass, but also confer extracted lignin with properties favorable to its further upgrading. This review summarizes recent advances in biomass fractionation using DESs for lignin extraction. It also covers lignin upgrading in DESs in terms of depolymerization and functionalization. The challenges of tailoring lignin properties by DESs for different valorization routes are also discussed.