Efficiency of Ionic Liquids in the Dissolution of Rice Husk

Ionic liquids that dissolve cellulose provide an option to pretreat lignocellulosic biomass. In this study, potential application of three ionic liquids in pretreating rice husk and their abilities in dissolving rice husk cellulose were investigated. The ionic liquids applied were 1-butyl-3methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM]DEP). Dissolution of rice husk was conducted by heating 1.5% (w/v) rice husk-ionic liquid mixture at 100C for 20 hours. The dissolved cellulose was subsequently regenerated with deionised water. All the ionic liquids were able to dissolve rice husk cellulose to varying extents, with the highest dissolution (36.7%) given by [EMIM]OAc followed by [BMIM]Cl (31.3%) and [EMIM]DEP (16.0%) at the 10 hour of heating. All the regenerated cellulose were found to be more amorphous as compared to the untreated rice husk. The energy study showed that both [EMIM]OAc and [BMIM]Cl had lower energy requirement compared to [EMIM]DEP. The results of energy requirement complemented the findings of dissolution ability of the ionic liquid. Both [EMIM]OAc and [BMIM]Cl are potential ionic liquids to be used in the pretreatment of rice husk, as they dissolved rice husk equally well.