Redeposition of lignin derivatives in AlCl3-ethanol-glycerol pretreated pine wood: Impacts on cellulose structure and enzymatic hydrolysis efficiency

Glycerol-based pretreatment enhanced the enzymatic hydrolysis efficiency of biomass. Post-reaction addition of a dilution solvent facilitated filtration of the pretreated slurry. The dilution solvent also affected the cellulose structure of the pretreated samples and the behavior/structure of lignin derivatives, which influenced the enzymatic hydrolysis efficiency of cellulose. When H2O was employed as the dilution solvent, the cellulose conversion of pretreated pine (with redeposited lignin derivatives) reached 76.9 % in enzymatic hydrolysis, surpassing values obtained with ethanol-diluting (29.7 %) and acetone-diluting (42.3 %) pretreated pines (without redeposited lignin derivatives). The study revealed that 1) lignin deposited during aqueous dilution acts as a steric hindrance agent, effectively preventing cellulose microfibril re-aggregation. The resultant cellulose exhibited lower crystallinity (72.2 % vs 81.7–87.9 %) and smaller crystallite size (2.48 nm vs 2.76–3.10 nm) compared to organic solvent (ethanol or acetone)-diluted pretreated pine. 2) Among the lignin derivatives derived from this system, those exhibiting higher aliphatic hydroxyl content, lower phenolic hydroxyl content, and higher molecular weight showed no inhibitory effect on the enzymatic hydrolysis of α-cellulose, with conversion hovering over 52.4–54.1 % upon the addition of lignin derivatives obtained from both ethanol/acetone-diluted H2O-washed processes to α-cellulose.