Evaluation of organosolv pretreatment on the structural characteristics of lignin polymers and follow-up enzymatic hydrolysis of the substrates from Eucalyptus wood

In the present study, Eucalyptus was subjected to organosolv pretreatment processes with aqueous 2-propanol at 200-220 °C to obtain lignin with benign characters for its valorization and digestible substrates for bioethanol production. Results showed that different delignification ratios (64.00%-81.26%) and molecular weights (Mw = 610-2680 g/mol) of lignin fractions were dissociated from various pretreatment conditions, and the glucose yields of all the pretreated substrates significantly increased to 54.65-88.59% as compared to that of raw material (9.20%). Additionally, the amounts of β-O-4, β-β, and β-5 substructures were regularly decreased with the increased temperature and time. By contrast, the structural characteristics of the lignin fractions obtained with 70% 2-PrOH/water were less-altered than those with 50% 2-PrOH/water pretreatment. Remarkably, lignin with the lowest molecular weight (Mw = 610 g/mol) and less-altered chemical structure was achieved at 200 °C for 120 min, which is beneficial to subsequent catalytic degradation of lignin.