Enzymatic hydrolysis of lignocellulosic polysaccharides in the presence of ionic liquids

Biofuels and -chemicals can be produced from carbohydrates in lignocellulosic biomass. For an efficient total enzymatic hydrolysis of the plant cell wall polysaccharides, a pretreatment step is required. Ionic liquids (ILs) have recently gained considerable interest as solvents for cellulose and lignocellulosic biomass and pretreatment of lignocellulose with ILs is currently an extensively studied concept. However, the applicability of ILs in an integrated process, in which enzymatic hydrolysis is done in the same vessel as the IL pretreatment without IL removal and substrate washing between the process steps, suffers from the fact that cellulose-dissolving ILs severely inactivate the cellulases used to catalyse the polysaccharide hydrolysis. This article reviews research on cellulase activity, stability and action in hydrolysis in cellulose-dissolving ILs, and different routes to increase the cellulase performance in these reaction systems. Impressive advances have recently been made in discovering and developing cellulases and other glycosyl hydrolases with increased IL-tolerance. Different cellulase stabilisation techniques and the design of enzyme-friendly cellulose-dissolving ILs are also discussed. In light of the recent developments, the integrated enzymatic hydrolysis of polysaccharides in the presence of ILs may well prove to be a potential route for utilizing lignocellulosic biomass as feedstock in biofuel and -chemical production.