Effect of ethanol organosolv pretreatment factors on enzymatic digestibility and ethanol organosolv lignin structure from Liriodendron tulipifera in specific combined severity factors

In this study, various ethanol organosolv pretreatment factors including reaction temperature, time, and concentration of acid catalyst were evaluated for effective decomposition of lignocellulosic biomass. The different pretreatment conditions had the same combined severity factor (1.16). With an increase in reaction temperature and pH, the water-insoluble residue recovery and amount of lignin in the solid residue decreased from 52.6% to 42.4% and from 10.4% to 5.5%, respectively, whereas enzymatic digestibility increased up to 97.9%. After pretreatment, ethanol organosolv lignin (EOL) recovered from the liquid hydrolyzate was subjected to nitrobenzene oxidation, gel permeation chromatography, and supercritical ethanol treatment for evaluation of the lignin structural properties. At a higher reaction temperature and pH, the proportion of ether linkages and the polydispersity of EOL decreased from 15.7% to 10.9% and from 3.1 to 1.9, respectively, while the amount of phenolic monomers ranged from 16.7 mg/g to 27.9 mg/g.