Screening Solvents Based on Hansen Solubility Parameter Theory To Depolymerize Lignocellulosic Biomass Efficiently under Low Temperature

Ten solvents including water-soluble and water-insoluble solvents were first used to pretreat rice straw under facile conditions (110 °C, 60 min). The results showed that most of the hemicellulose was removed, and much of the cellulose was held in solid residue. On the basis of the Hansen solubility parameter (HSP) theory, the correlation between the relative energy difference of the solvent-system–lignin interactions and the lignin removal was explored. Taking efficient enzymatic hydrolysis and ease fractionation of lignocellulosic biomass into account, biphase solvent 2-phenoxyethanol (KL-EPH) was selected for further study. After that, the effects of temperature, retention time, sulfuric acid loading, and KL-EPH concentration on the degradation of rice straw were studied, and the results indicated that the conditions of temperature 120 °C, retention time 3 h, sulfuric acid loading 0.1 M, and KL-EPH concentration 50% were optimal. Under these conditions, 90.17% of hemicellulose and 53.17% of lignin were removed from rice straw, resulting in the residue enzymatic hydrolysis rate of 88%, and 66% of hemicellulose as xylose was present in the aqueous phase. Moreover, 33.55% of the precipitated solid (lignin rich) was collected from the organic phase. The componential analysis suggested the lignin-rich residue mainly consisted of 78.68% lignin, 8.26% glucan, and 1.65% xylan. The raw materials and residues were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the results showed that the remarkable removal of hemicellulose and lignin primarily contributed to the improved enzymatic hydrolysis of the residue based on these results.