Novel compatible system of [C2OHmim][OAc]-cellulases for the in situhydrolysis of lignocellulosic biomass

Abstract

The ionic liquid (IL) 1-(2-hydroxyethyl)-3-methylimidazolium acetate ([C₂OHmim][OAc]) was designed and used to provide a compatible IL-cellulase system in which lignocellulosic biomass can be effectively solubilized and activated, while maintaining the high stability and activity of the cellulase. In this study, we investigated the stability and activity of a commercially available cellulase (optimum pH 4.8) in the presence of different concentrations of a [C₂OHmim][OAc]/buffer solution, using CMC (carboxy-methylcellulose) as substrate. The cellulase retained 87% and 79% of its original activity after being pre-incubated in 15% (pH = 5.79) and 20% (pH = 6.0) (w/v) IL solutions at 50 °C for 1.5 h, respectively. Similar results obtained for both the IL and traditional buffer solutions led us to conclude that the reduction in the enzymatic activity may have been caused by the deviation of the solutions' pH from the optimum pH for cellulase; the IL showed improved enzymatic hydrolysis of cellulose compared with the traditional buffer solution. The cellulases also retained high activity in [C₂OHmim][OAc] (15%) to hydrolyze MCC (microcrystalline cellulose), a model substrate for cellulase analysis, with a conversion efficiency of approximately 99.67%. Using this IL-cellulase system, the saccharification of straw, cotton and filter paper, which have different compositions of cellulose, hemicellulose and ligin, was also significantly improved during the first hour of enzymatic hydrolysis. The IL can be separated from the reducing sugar using affinity solvent extraction, and can then be reused. Together, these findings provide compelling evidence that [C₂OHmim][OAc] was compatible with the cellulase, and this compatible IL-cellulase system is promising for the efficient activation and hydrolysis of native biomass to produce biofuels.