A cyclic process for full enzymatic saccharification of pretreated cellulose with full recovery and reuse of the ionic liquid 1-butyl-3-methylimidazolium chloride

Abstract

A sustainable cyclic process for the enzymatic saccharification of ionic liquid (IL)-pretreated cellulose, in which the IL is recovered and recycled, has been developed. Homogeneous cellulose solutions in the IL 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) were used to prepare amorphous cellulose by antisolvent precipitation with water, ethanol or equimolar water–ethanol mixtures as green molecular solvents. Several operation parameters (e.g., solvent, temperature, ultrasounds, etc.) for both cellulose precipitation and the washing steps were tested to achieve full desorption of the IL from the cellulose backbone. In the best conditions, up to 99.7% IL was recovered, which was then successfully reused in further cellulose dissolution/precipitation cyclic processes. Furthermore, the cellulose regenerated in each cycle was an excellent substrate for enzymatic hydrolysis, permitting full hydrolysis (i.e., up to 97.7% hydrolysis after 4 h at 50 °C) by the combined action of both cellulase and cellobiase enzymes, that provides a clear glucose solution. The excellent suitability of this glucose solution for growing aerobic Saccharomyces cerevisiae was demonstrated.