Green pretreatment of lignocellulosic biomasses via deep eutectic solvents

Lignocellulose biomass (LCB) is the most abundant and inexpensive natural renewable biomass. The high-value utilization of LCB is an important direction for solving the energy crisis problem in the world today. Pretreatment of LCB is a key step for biomass refining. Appropriate pretreatment methods can effectively remove lignin, reduce the density of hemicellulose, and open hydrogen bonds in cellulose, thereby converting crystalline cellulose into amorphous cellulose and improving the accessibility of cellulase to hemicellulose and cellulose. Pretreatment of LCB by deep eutectic solvents (DES) has many advantages such as low-cost, low-energy consumption, environment-friendly and high delignification efficiency (60–100%). DES can reduce the ineffective adsorption of cellulase by efficiently removing lignin and improve the stability of the enzyme, thereby increasing the enzymatic hydrolysis efficiency of cellulose and increasing the yield of sugar from less than 50% to more than 60%. This article provides a detailed overview of the preparation methods, types, physicochemical properties of DES and their delignification role in pretreatment of LCB to enhance the efficiency of enzyme digestion of polysaccharides. Furthermore, the combination of DES and auxiliary pretreatment techniques for processing of LCB, the recycling of DES, current challenges and future perspectives of DES are also summarized and discussed in the review. These insights about green pretreatment of LCB via DES in this article are helpful and useful for the development of LCB biorefineries.