Highly efficient dissolution of xylan in ionic liquid-based deep eutectic solvents

Abstract

Development of efficient solvents to dissolve lignocellulose and its main components is of significant importance for the utilization/transformation of lignocellulose. Herein, several ionic liquid (IL)-based deep eutectic solvents (DESs) were prepared using four ILs as the hydrogen bond acceptors and four different hydrogen bond donors, including thiourea (TU), N-methylthiourea (NMTU), glycerol (Gly), and ethylene glycol (EG). Using the dissolution of xylan (a typical type of hemicellulose) as the example, it was observed that the synthesized IL-based DESs could efficiently dissolve xylan. Especially in the DES formed from 1-allyl-3-methylimidazolium chloride and EG, the xylan solubility could reach as high as 40.4 wt% at 343.15 K. More importantly, the solubility of xylan in IL-based DESs was much higher than that in the corresponding IL. The enhancement effect might be ascribed to that the formation of DESs could significantly decrease the viscosity and increase the hydrogen bond accepting ability. Additionally, the regeneration of the xylan from the DESs could be easily realized using ethanol as the anti-solvent, and the regenerated xylan kept a high consistency with the original xylan. Ionic liquid-based deep eutectic solvents were designed for highly efficient dissolution of xylan owing to the decreased viscosity and the increased hydrogen-bond accepting ability.