Novel self-pretreatment of biomass by in-situ preparation of acid-assisted carbohydrate-derived DES

Deep eutectic solvents (DES) can greenly and efficiently fractionate biomass, but their utilization efficiency is severely limited by the high ratio of DES required and the wasted hemicelluloses released during the pretreatment. Herein, this work first developed a novel self-pretreatment of biomass by in-situ preparation of acid-assisted carbohydrate-derived DES with the aid of ball milling to facilitate enzymatic hydrolysis. The effect of hydrogen bond acceptor types, water content, acid content, and ball-milling time on enzymatic hydrolysis was studied systematically. Under the optimal condition (tetrabutylammonium chloride (TBAC), 1000 wt% H2O, 100 wt% acids, ball milling for 2 h), the yields of glucose and xylose produced from the pretreated substrates after enzymatic hydrolysis were >99.9 % and 88 %, respectively. Furthermore, the structural integrity of the residual lignin was well-preserved, making it suitable for positional structural characterization and ideal substrates for lignin degradation. Characterization suggested that the hemicelluloses fragments via in-situ acid hydrolysis acted as hydrogen bond donors and combined in situ with TBAC to form DES. This strategy avoided the use of high dosages of DES and the wastage of hemicelluloses, and promoted the sustainability of the entire biorefinery process. [Display omitted] •Self-pretreatment by in situ forming carbohydrate-derived DES was first developed.•Hemicelluloses fragments and tetrabutylammonium chloride formed the DES in situ.•Yields of glucose and xylose reached >99 % and 88 %, respectively.•The structural integrity of the residual lignin was well-preserved.