Complete conversion of cellulose to water soluble substances by pretreatment with ionic liquids

Pretreatment of cellulose to water soluble substances (WSS) can enhance its efficient conversion in water solvent, such as ethanol fermentation. In this work, we found ionic liquid (IL), 1-methyl-3-methylimidazolium dimethylphosphate (Mmim]DMP]), could convert efficiently cellulose to obtain WSS, and the product WSS and IL mixture could be separated by ethanol anti-solvent way. Effects of ILs, time, temperature and water on cellulose conversion were investigated. NMR, FTIR, XRD and SEM were employed to study the mechanism of cellulose conversion with ILs. The results indicate that Mmim]DMP] has a greater ability to interact with cellulose than Bmim]Cl] under the same conditions. Cellulose can be completely converted into WSS in Mmim]DMP] under all the investigated temperatures from 140 to 160 °C. Increasing temperature is beneficial to the conversion rate of cellulose. But the presence of water can decrease the conversion rate of cellulose. During the treatment by Mmim]DMP], the hydroxyls of cellulose can form hydrogen bonds with both anion and cation of Mmim]DMP], and after the treatment the inter- and intramolecular hydrogen bonds of cellulose and the compact structure of cellulose are collapsed.