1-Butyl-3-methylimidazolium halide based ionic liquids as solvents for the pretreatment of bamboo slices: Effect of electronegativity of anions

In-depth understanding the influence of ionic liquid structure on the selective dissolution of the main biopolymers from plant cell walls is necessary for designing ionic liquids that could efficiently pretreat and fractionate lignocellulosic biomass. The current study aimed to investigate the effect of electronegativity of anions of 1-butyl-3-methylimidazolium halide based ionic liquids BmimCl, BmimBr, and BmimI on dissolving bamboo slices. The surface of pretreated bamboo slices and the regenerated carbohydrate-rich fractions were characterized carefully. The results revealed that the ability to damage bamboo cell walls and dissolve bamboo slices followed the order of BmimCl>BmimBr>BmimI, which was consistent with the electronegativity of halogen anions (Cl->Br->I-). The dissolving selectivity for lignin from bamboo cell walls was in the order of BmimBr>BmimI>BmimCl. The ionic liquids performed a greater dissolving selectivity for lignin than carbohydrates (cellulose and hemicellulose). The permeating rate of ionic liquid molecules into bamboo cell walls increased with the enhancement of electronegativity of halogen anions. The regenerated carbohydrate-rich fractions were rich in hemicellulose and cellulose with an amount of lignin. Both temperature and time had also great effect on the dissolution of bamboo slices. On the whole, the electronegativity of halogen anions had a profound impact on the deconstruction of bamboo cell walls and dissolution of bamboo. This study provided important theoretical assistance for designing ionic liquids that could more efficiently pretreat and fractionate lignocellulosic biomass.