8-07: Pretreatment of lignocellulose biomass by dialkylphosphate-based ionic liquids and fermentation by Clostridium sp

Lignocellulosic biomass is a potential source of biofuels and biochemicals. Lignocellulose is naturally recalcitrant to enzymatic hydrolysis and microbial fermentation and therefore pretreatment is necessary to improve its digestibility and to obtain simple sugars for fermentation. Current pretreatment methods such as dilute acid method are corrosive, energy intensive and produce inhibitory chemicals for fermentation. A greener and better approach of pretreatment is to use ionic liquids. The overall goal is to develop a comprehensive process for bioconversion of lignocelluloses to ethanol and butanol using ionic liquids as a pretreatment and fermentation by Clostridia.

We investigated the effect of dialkylphosphate based ionic liquids (ILs) with different cations and/or functional groups for their ability to dissolve cellulose and lignocellulosic biomass. The ILs 1,3-dimethylimidazolium dimethylphosphate [MMIM][DMP], 1-ethyl-3- methylimidazolium diethylphosphate [EMIM][DEP], and 1-butyl-3-methylimidazolium dibutylphosphate [BMIM][DBP] can be easily synthesized, are less viscous, and are cheaper than currently used ILs such as 1-ethyl-3-methylimidazolium acetate [EMIM][Ac] and 1-butyl-3-methylimidazolium chloride [BMIM][Cl] for dissolution of lignocellulose. Of the imidazolium based ILs examined, [EMIM][DEP] showed the highest dissolution of hardwood flour. FTIR and SEM analysis of recovered cellulose showed reduction in lignin content and amorphous nature. Cellulase and β-glucosidase enzyme activities were not significantly affected in the presence of lower concentrations (<5%) of ILs. Similarly, growth of Clostridium sp and glucose fermentation was not affected in the presence of <2.5 g/L [EMIM][Ac], [EMIM][DEP] and [MMIM][DMP]. The fermentability of various ILs pretreated lignocellulosic biomass by Clostridium sp. will be discussed in this presentation.