Phase-Exchange Solvent Pretreatment Improves the Enzymatic Digestibility of Cellulose and Total Sugar Recovery from Energy Sorghum

Traditional liquid hot water pretreatment (LHWP) has a high water consumption, a high reaction temperature, and low lignin removal, making it unsuitable for industrial applications of biomass conversion. In this study, we developed a new phase-exchange solvent pretreatment (PESP) based on the varied phase composition of furfural (FF)-water at different temperatures. Substitution of water with FF had no significant influence on xylan hydrolysis, but it improved the mass transfer performance. At the optimum conditions of 180 °C, an FF:water ratio of 30:70 (v/v), a solid:liquid ratio of 1:8 (w/v), and 0.2 wt % sulfuric acid for 30 min, the PESP of energy sorghum achieved a 74.98% total xylose yield and removed 85.08% of the lignin, while there was a selective distribution of sugar and lignin in the aqueous and organic phases, respectively. Moreover, 99.58% of the cellulase enzyme digestibility and 94.02% of the total sugar recovery were achieved after 72 h. This unusually high enzymatic digestibility could be attributed to the physicochemical changes in the substrate after the pretreatment. When compared with a traditional LHWP (5% solid loading), the water consumption decreased by approximately 72% and the lignin removal increased by 60.74%. These results demonstrate that PESP is a promising technology for biorefining lignocellulosic biomass with high efficiency and low energy consumption.