Unveiling the role of lignin feature on bio-ethanol and xylose derived from poplar during combined alkali/ethanol synergistic pretreatment.

This study adopted a mixed experimental research design to investigate the effects of alkali and alkali-catalyzed ethanol pretreatment of poplar wood under different NaOH loadings on the pretreatment liquid, pretreatment solids, and polysaccharide conversion, with a particular emphasis on the utility of the lignin for subsequent conversion. Specifically, NaOH catalyzed ethanol pretreatment at 10% NaOH loading resulted in the removal of more than 80% lignin with >80% carbohydrates remaining in the residual solids. Simultaneous saccharification fermentation of this pretreated residue resulted in 29.09 g/L (72.84%) and 14.86 g/L (69.26%) of ethanol and xylose, respectively, following a fermentation period of 72 h. Then, an integrated evaluation of the lignin characterization in raw and pretreated residues was carried out to emphasize their influence on ethanol and xylose yield by two-dimensional heteronuclear single quantum coherence (2D-HSQC) NMR and gel permeation chromatography (GPC) analysis. The results showed that most of the side-chain structures were oxidized and the aryl-ether bond was dissociated with the synergistic influence of NaOH and ethanol treatment, accompanied by low molecular weight lignin obtained in the solid fraction. Overall, NaOH catalyzed ethanol pretreatment offered a strategy for selective biomass fractionation into carbohydrates conversion and lignin valorization with a high yield. • NaOH-catalyzed ethanol pretreatment is effective to bioethanol and xylose production. • >80% lignin removal with more than 80% cellulose/hemicellulose recovery was obtained. • The linear correlation between lignin inhibition and sugars conversion was analyzed. • Lignin inhibition positively related to its Mw, S/G units and β-O-4 linkages. [ABSTRACT FROM AUTHOR]