Enzymatic saccharification and structural properties of industrial wood sawdust: Recycled ionic liquids pretreatments

Abstract : Wood residues constitute a promising challenge for biochemical processing into bioethanol and chemicals with competitive costs. Here, we report the impacts of pretreatments in a hydrophilic ionic liquid ([C2mim][OAc]), onto the physicochemical properties and enzymatic saccharification of softwood (spruce) and hardwood (oak) sawdust. Enzymatic saccharification of IL-pretreated sawdust is significantly increased (up to 7 times) when compared to untreated ones. Methanol, ethanol or water can be used as polar anti-solvent for the recovery of a cellulose rich fraction after dissolution in IL (i.e regener-ation step) without any effect on enzymatic saccharification. Chemical, textural and structural modifications possibly induced by the IL pretreatments have been investigated through various means (Infra-red spectroscopy, NMR, X-ray diffraction) in order to correlate the observed modifications in enzymatic sac-charification. This mild pretreatment seemed to mainly act in a breakdown of lignocellulosic organization leading to better cellulase accessibility to cellulose thanks to the expansion of the powder and the creation of a large porous volume (5 times more apparent porous volume). Partial removal of lignin and extractives may also contribute to the best enzymatic performances. The recyclability and reuse up to 7 times of [C2mim][OAc] is shown without the need of strictly anhydrous conditions and any alteration of the pretreatment.