In-situ modification of lignin in alkaline-pretreated sugarcane bagasse by sulfomethylation and carboxymethylation to improve the enzymatic hydrolysis efficiency

Although sulfomethylation (SM) and carboxymethylation (CM) have been used in the pretreatments of lignocelluloses, their effects on lignin structure of biomass and the interaction between lignin and cellulase remain unclear. In this work, alkaline pretreatment firstly removed 52.5% of lignin in sugarcane bagasse (SCB). The sequential SM and CM further increased the delignification capacities by 43.1% and 34.3%, respectively. Results of nuclear magnetic resonance, Fourier transform infrared spectroscopy and adsorption experiments show that the unites of ferulic acid and p-coumaric acid in residual lignin in alkaline-pretreated SCB (AP-SCB) were dissociated, and the -SO3- and carboxyl groups were introduced into the residual lignin in AP-SCB by SM and CM. The structural modification of residual lignin by SM and CM decreased the adsorption capacity of cellulase toward residual lignin in AP-SCB by 25.6% and 21.7%, resulting in the increase of glucose yield of AP-SCB from 52.2% to 83.8% and 73.6%, respectively. This work provides an efficient strategy to enhance sugars yields of alkaline-pretreated SCB through the mitigated nonproductive adsorption of residual lignin by SM and CM.