Reviving Pretreatment Effectiveness of Deep Eutectic Solvents on Lignocellulosic Date Palm Residues by Prior Recalcitrance Reduction

Deep eutectic solvents (DESs), featured as promising green solvents, have increasingly drawn attention in the processing of a wide spectrum of lignocellulosic biomass (e.g., corn stover, wheat straw, and rice straw). However, the ineffectiveness of enhancing enzymatic digestibility of lignocellulosic date palm residues by pretreatment using DESs (choline chloride/glycerol) only was observed in this study. Inspired by the different observation with counterparts, it was hypothesized that the recalcitrance of date palm residues caused the ineffectiveness. A novel approach of reducing recalcitrance of biomass through hydrothermal pretreatment prior to DESs treatment was proposed to revive the effectiveness of DESs on enhancing cellulose digestibility. The results showed that hydrothermal treatment effectively triggered the functioning of choline chloride/glycerol to boost enzymatic digestibility (1.7 times increase) of date palm residues. In addition, this study indicated that the significant increases of both xylan (25%) and lignin (22%) removals rather than the modification of cellulose crystallinity by choline chloride/glycerol were responsible for the enhancement of enzymatic digestibility.