New two-stage pretreatment for the fractionation of lignocellulosic components using hydrothermal pretreatment followed by imidazole delignification: Focus on the polysaccharide valorization.

The combination of hydrothermal pretreatment followed by delignification with imidazole was evaluated for the first time as a potential selective two-stage fractionation for elephant grass, aiming at obtaining pure fractions susceptible to conversion to high value-added products. In addition, the recovery of cellulose and hemicelluloses and enzymatic hydrolysis yield of pretreated elephant grass were evaluated. Hydrothermal pretreatment at 180 °C under non-isothermal conditions allowed obtaining a liquor rich mainly in xylo- and glucooligosaccharides, as well as pentoses. Subsequent treatment of the recovered solid fraction with imidazole at 140 °C for 182.5 min resulted in 83.8 wt% delignification and cellulose enrichment of 97.7 wt%. The solids obtained from the two-stage pretreatment process also permitted high glucan to glucose conversion through enzymatic hydrolysis using Cellic CTec2 (99.0 mol%) or an enzymatic complex of Penicillium echinulatum (96.3 mol%).