Acid-assisted pretreatment for sweet elephant grass in choline chloride/glycerol DES: Experimental and mechanism study

Abstract

Sweet elephant grass (SEG), a promising bioenergy grass, possesses considerable potential for bioenergy production. However, research on its pretreatment and utilization remains limited. In this study, small quantities of Brønsted acids were introduced to a deep eutectic solvent (DES) comprising choline chloride (ChCl) and glycerol (Gly) for SEG pretreatment. Under mild conditions (110 °C, 2 h), a maximum lignin removal rate of 90.08 % and a complete hemicellulose removal could be accomplished in the presence of Brønsted acid. Cellulose retention rates consistently above 70 % were obtained in all the cases, and a desirable glucose yield up to 94.07 % was achieved from the resulting cellulose after further enzymatic hydrolysis. The pretreatment mechanism was elucidated through a combination of characterizations and theoretical calculations, which demonstrated effective disruption of lignin and lignin-carbohydrate complex occurred by the CH···π, HO···H, and Cl···H bond interactions between lignin and DES. Furthermore, the scission of β-O-4 bond was promoted by Brønsted acids in DES. This systematic investigation paves the way for unraveling the mechanism of the efficient pretreatment of lignocellulose in acidic DES.