Co-Producing Xylo-Oligosaccharides, 5-HMF, Furfural, Organic Acids, and Reducing Sugars from Waste Poplar Debris by Clean Hydrothermal Pretreatment

The sustainable valorization of lignocellulosic biomass into value-added biobased chemicals has gained more and more attention on a large industrial scale. To efficiently utilize the abundant, inexpensive, and renewable biomass, it is necessary to employ an effective biomass pretreatment technology for breaking down hemicellulose and lignin. Hydrothermal pretreatment is an effective way to change the structure of lignocellulose and improve its enzymatic hydrolysis efficiency. The hydrothermal cleaning of waste poplar debris (PD) was conducted when the severity factor (LogR0) score was 5.49. At 220 °C and a solid–liquid ratio of 1:10 for 90 min, the pretreatment liquor contained 4.90 g/L of xylo-oligosaccharides, 1.23 g/L of furfural, 0.41 g/L of formic acid, 2.42 g/L of acetic acid, and 0.57 g/L of 5-HMF. Additionally, 74.9% xylan and 82.4% lignin were removed. After 72 h of enzymatic saccharification, a high enzymolysis efficiency of PD was obtained. A series of characterizations (such as chemical composition analysis, hydrophobicity, lignin surface area, and cellulase accessibility) indicated that hydrothermal pretreatment destroyed the surface structure of PD, improved cellulose accessibility, decreased lignin surface area and weakened lignin hydrophobicity. In general, hydrothermal pretreatment is a simple, green, and environmentally friendly approach for sustainable pretreatment of PD using water as a solvent. It can efficiently break the surface structure of PD and remove lignin and xylan, acquiring high enzymolysis efficiency and realizing the co-production of 5-HMF, furfural, xylo-oligosaccharides, and organic acids. It provides an innovative idea for the value-added utilization of wood-based and straw-based biomass in a sustainable and cost-effective way, showing high potential in industrial application.