Current Research in Green and Sustainable Chemistry, Volume 3, June 2020,
The successful conversion of lignocellulose into value-added products depends on overcoming the recalcitrance of its structure towards enzymatic digestion. The highly crosslinked structure of lignin, crystallinity of cellulose, and low digestibility of hemicellulose create the recalcitrance. Many studies have proved that an appropriate pretreatment method could enhance the digestibility of lignocellulosic biomass by weakening the strong network of its chemical bonds among the cellulose, hemicellulose, and lignin. There are several conventional ways to separate the components from each other, but the requirements of high temperature and pressure, use of strong acids and bases, and expensive instrumentation make the pretreatment methods difficult to use. Greener solvents, e.g. supercritical fluid, ionic liquid, and deep eutectic solvent (DES)-based pretreatment techniques can overcome the difficulties. Although a lot of pilot scale and rigorous studies are required to launch the greener technologies commercially, they have already shown a lot of promise in the field of biomass pretreatments. Among the greener solvents, DESs are cheaper, easily recyclable, environmentally benign, and the efficiency of the DES-based pretreatment can be enhanced manifold by applying microwave and ultrasound. Therefore, DES-based pretreatment could be one of the most popular techniques in the future.