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

• 1-Ethyl-3-metylimidazolium acetate is an effective catalyst for pretreatment of hardwood and softwood sawdust.
• Regeneration of cellulosic fraction from ionic liquid is discussed.
• 1-Ethyl-3-methylimidazolium acetate can be reused at least 7 times without loss of its efficiency.
• Removal of extractives and lignin with slight cellulose and xylan losses were observed.
• Better cellulase accessibility to cellulose thanks to the expansion of the powder and the creation of a large porous volume.

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 regeneration 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 saccharification. 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.

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