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The present report focuses on the solvent effect on furfural production from xylose in biphasic systems with methods including combined experiments, molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Six most effective and commonly used biphasic solvents for furfural production were comparatively analyzed and discussed based on the kinetic study, partition coefficient, degradation behavior of furfural in organic solvents, distribution of solvent molecules around xylose/furfural molecules, hydrogen bonding, moving trajectories of xylose/furfural, and the solvation free energy. During the hydrothermal reaction of xylose to furfural in biphasic systems, it was found that the conversion efficiency of biphasic systems can be ordered as DCM/H2O > 2-MTHF/H2O > 2-butanol/H2O ≈ MIBK/H2O > CPME/H2O > toluene/H2O according to the xylose conversion and furfural yield, which are dominated by the solvation free energy (ΔGsol) of furfural in organic solvents, and also be affected by three other factors, namely, the maximum solubility of furfural in organic solvents, the ΔGsol value of organic solvents in water, and the side reaction of furfural in organic solvents. The degradation rate of furfural in 2-butanol was detected to be the fastest, and molecular dynamics simulation data showed that the hydrogen bonding between furfural and 2-butanol may accelerate the degradation of furfural. DCM has excellent extraction ability for furfural, and the maximum furfural yield in the DCM/H2O system (81.64%) is much higher than that in other systems during the hydrothermal reaction without additional catalysts.

In this study, experiments and molecular dynamics simulations were combined to get insights into the role of solvent during the process of xylose conversion under catalyst-free conditions. Solvents used for furfural production were comparatively discussed, including traditional and emerging biomass-derived solvents – water, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), isopropanol (ISO), γ-butyrolactone (GBL) and γ-valerolactone (GVL). The degradation behavior of solvents, the solubility and α/β ratio of xylose, the distribution of the solvent around xylose/furfural and the hydrogen bonding between them were also studied. The results showed that in pure solvents, the different hydrogen bonding between xylose and the solvent resulted in different products. Water was a favourable solvent for xylose to form furfural among these pure solvents because less formic acid was produced from xylose in water under catalyst-free conditions. Furfural could be produced in mixed solvents if there was more water around xylose, which was similar to the case in pure water. Otherwise, the situation in mixed solvents was similar to that in the corresponding pure organic solvents. GBL and GVL, as green solvents, had weaker affinities with xylose than DMSO, DMF and ISO, but were intensively attracted by furfural, thus they could provide protective shells for furfural, which played a positive role during the production of furfural. The highest furfural yield of 46.4% was achieved in GBL–H2O at 180 °C – 150 min in the absence of catalysts.