2-Naphthol Modification Alleviated the Inhibition of Ethanol Organosolv Lignin on Enzymatic Hydrolysis

It has been reported that the lignins deposited on surfaces of pretreated biomass directly affected the enzyme adsorption, thus impeding enzymatic hydrolysis of lignocellulose. Alleviating the surface lignin inhibition is urgently needed for establishing an efficient lignocellulose biorefinery process. In this study, ethanol organosolv lignins (EOLs) from masson pine and poplar were employed as representatives of surface lignins. Aiming to mitigate the EOLs inhibition on enzymatic hydrolysis, 2-naphthol as a carbocation scavenger was added in the organosolv pretreatment. The function of 2-naphthol for suppressing lignin condensation was verified by investigating the lignin structural changes with NMR analysis. Moreover, it was verified that 2-naphthol modification remarkably eliminated the negative effects of EOLs from both two wood species, leading to a 6.8–34.4% increase in hydrolysis yields. The effects of 2-napthol modified lignins were even reversed to slightly promote the enzymatic hydrolysis of pure cellulose. The mechanism of 2-naphthol modification for relieving lignin inhibition was revealed by evaluating the relationship between lignin structural features and hydrolysis performance with Pearson's correlation heatmap. Results enrich our understanding of surface lignin inhibition, thereby providing ideas for promoting enzymatic hydrolysis by alleviating the surface lignin inhibition.