One-pot enzymatic depolymerization of cellulose in [BMIm][Cl]

Lignocellulosic biomass is a renewable, low cost, non-food and abundant feedstock for biofuel production and a source of C atoms for chemistry alternative to fossil resources. The most important factor hampering massive exploitation of cellulose, the main component of plant biomass, is its well known low reactivity and recalcitrance to chemical processing. The usual steps in producing biofuels from cellulosic sources are: pretreatment followed by cellulose precipitation, enzymatic hydrolysis and fermentation. Pretreatment of cellulose is a necessary step in the production of ethanol from cellulosic material since it makes the recalcitrant cellulosic biomass more accessible to enzymatic hydrolysis. A possible greener alternative for the activation of cellulose fibrilles towards facile hydrolysis and/or derivatization passes through an emerging chemical pretreatment step using ionic liquids (ILs). Unlikely, cellulases have been reported to be inactivated by ILs. In the present work we present a study on a single-batch, homogeneous phase enzymatic hydrolysis of cellulose using a commercial IL, 1-butyl-3-methylimidazolium chloride ([BMIm][Cl]), which is a well known good solvent for celluloses. We have tested two native proteins from Trichoderma reesei and Humicola insolens and two engineered proteins from T. reesei and Streptomyces sp.. The [BMIm][Cl] does not denature the cellulases used, increases their operational stability (at 75°C) as compared to standard buffer solutions and facilitates the dissolution of cellulose. Interestingly, the stability of the four cellulases in the presence of the IL allows to set-up a procedure lacking of the cellulose pretreatment step. We believe that this strategy could be amenable of scale-up and innovative industrial applications for the efficient one-batch conversion of inexpensive cellulosic materials into derivatives (biofuels, derivatized cellulose, monosaccharides for fine chemicals, etc.) with high potential commercial interest and in the framework of environmentally friendly chemistry