Enhancement of enzymatic in situ saccharification of cellulose in aqueous-ionic liquid media by ultrasonic intensification

Abstract

A new approach for in situ enzymatic saccharification of cellulose in ionic liquids (ILs)-aqueous media is presented in which ultrasonic pretreatment was used to enhance the conversion of cellulose. For this purpose, the solubility of cellulose and the activity of cellulase were investigated in six alkylphosphate ILs. 1-Methyl-3-methylimidazolium dimethylphosphate ([Mmim][DMP]) giving favorable solubility and biocompatibility was selected to establish aqueous-ILs system for enzymatic in situ saccharification of cellulose. After further optimization of reaction parameters concerning cellulase concentration, temperature and IL concentration, higher conversion (95.48%) of cellulose was obtained in the media of aqueous-[Mmim][DMP] by conducting the pretreatment of cellulose with ultrasonic heating, whereas the conversion of cellulose untreated was 42.77%. Scanning electronic microscopy (SEM) and viscosity analysis indicated that IL-treated cellulose under ultrasonic condition was subjected to depolymerization, which led to more efficient saccharification. The findings of this study would have great implications for developing a continuous process for transformation of biomass such as straw cellulose to ethanol or other hydrocarbons.