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Pretreatment is an important step to reduce the recalcitrance factors in biomass for effective biomass utilization. In particular, the choice of processing solvents in the pretreatment influences the quantity and quality of the final products. Although conventional organosolv pretreatments are effective, they are typically performed under harsh conditions. Compared to those approaches, recent studies have shown that the use of Deep Eutectic Solvents (DES) made up of a hydrogen bond donor and acceptor at the eutectic point can be a promising alternative as biomass processing solvents because of their good thermal stability and compatibility with natural components. In this study, DES pretreatment was applied to corn stover, which is the largest agricultural residue in the United States. The performance of the pretreatments was assessed by measuring the removal of xylan and lignin from the corn stover, as well as the production of glucose and xylose by subsequent enzymatic hydrolysis. The results indicated that the DES pretreatment resulted in significantly higher delignification rates (75%) than an organosolv pretreatment (35%) at the same processing temperature. The DES pretreatment also resulted in a more effective conversion of glucan (81%) and xylan (56%) than the organosolv pretreatment. The results indicated that DES pretreatment is a promising processing strategy for biomass utilization. 

Hydrotropic solvents are a promising solvent in biomass processing due to their unique amphiphilic structure. This review summarizes recent advances in hydrotropic solvent systems with their chemical structure, amphiphilicity, roles, and mechanism. 

Abstract Biomass‐derived deep eutectic solvents (DESs) have been introduced as promising pretreatment and fractionation solvents because of their mild processing conditions, easy synthesis, and green solvent components from biomass. In recent DES studies, solvent‐based third constituents like water, ethanol, and others improve the processibility of typical binary DESs. However, the impacts of these components are not well understood. Here, two solvent‐based constituents, including water and ethylene glycol, were applied to 3,4‐dihydroxybenzoic acid (DHBA)‐based DES system for improving the conversion efficiency of cellulose‐rich fraction and the properties of lignin fraction. Chemical composition, enzymatic digestibility, degree of polymerization of cellulose and physicochemical properties of lignin were used to evaluate the impact of each third constituent on biomass processing. Ternary ChCl‐DHBA DESs exhibited better performances in delignification, fermentable sugar production, and preservation of β‐O‐4 ether linkage in lignin compared with binary ChCl‐DHBA DES.