Effects of hydrogen bond acceptor with benzyl group in deep eutectic solvents on pretreatment performance of bamboo residue

Nine benzylammonium chloride-based deep eutectic solvents (DESs) were prepared and used to disrupt the natural recalcitrance of bamboo cell walls, to simultaneously produce fermentable sugars and lignin by-products. Under pretreatment conditions of 130 °C and 6 h, nearly 90 % of lignin was removed during the tributyl benzyl ammonium chloride/oxalic acid (TBBAC/OA) pretreatment of Dendrocalamus giganteus Munro bamboo (DG), accompanied by a satisfactory recovery of cellulose (∼84 %). The enzymatic digestibility of TBBAC/OA-DG released 83.72 % of fermentable sugars, which is about twice as high as tetrabutylammonium chloride/oxalic acid pretreated DG (TBAC/OA-DG) without benzyl groups as the hydrogen bond acceptor in the DES system. The structural characteristics of hydrogen bond acceptors (HBA) in DESs remarkably influenced the removal of lignin and xylan, which resulted in a loose structure after DES pretreatment, then increased the enzymatic accessibility of bamboo. Furthermore, the obtained regenerated lignin has a narrow molecular weight distribution and excellent solubility in organic solvents, which demonstrated potential industrial applications. These findings not only explain the relationship between HBA structure and bamboo fractionation, but also provide new insights for the selection and design of DES in biomass pretreatment.