Efficient enzymatic hydrolysis of cellulose treated by mixed ionic liquids

In recent years, ionic liquids (ILs) have been confirmed to be efficient and green solvent for treatment of cellulosic biomass toward subsequent bioprocess. However, few attempts have been made to use mixed ILs as solvent to treat cellulose. In order to expand the scope of IL and mixed ILs used for cellulose treatment, we developed mixed ionic liquids as reagent to treat cellulose. Subsequently, the treated cellulose and treatment process were assessed by measuring the indexes of cellulose in and after treatment process. As a result, mixed ILs combination 1-methyl-3-methylimidazolium dimethylphosphate ([DMIM][DMP]) and 1-ethyl-3-ethylimidazoliumbisulfate ([EMIM][HSO4]) were selected as a candidate reagent for cellulose treatment. Unlike some other studies, not only outermost surface of cellulose was changed, but structure of cellulose was destroyed and converted into 3–6 μm particles, resulting in almost complete enzymatic hydrolysis of treated cellulose within 12 h. In addition, the initial rate of enzymatic hydrolysis of cellulose treated by candidate mixed ILs was 56.3 times that of water-treated cellulose (control). It was demonstrated that intact structure of cellulose was destroyed by mixed ionic liquids treatment and resulted in a new framework that greatly improved enzymatic hydrolysis, which opened a new way for efficient enzyme conversion of cellulosic biomass.