Enabling efficient dissolution and fractionation of lignin by renewable and adjustable dimethyl isosorbide-based solvent systems

Efficient dissolution is highly important for upgrading of lignin into useful chemicals, which relays on the development of robust solvent systems. Herein, a novel, green, and robust solvent system for lignin dissolution was developed using biomass-derived dimethyl isosorbide (DMI) and water. Interestingly, the developed DMI-based solvent systems showed good ability to dissolve different types of lignin, i.e., alkali lignin (AL), enzymatic hydrolysis lignin (EHL), kraft lignin (KL) and dealkaline lignin (DAL), by tuning the weight ratio of DMI and water. Systematic investigations revealed that the lignin solubility correlated with Hansen solubility parameters and Kamlet-Taft parameters although the relationship varied with the lignin type. More importantly, lignin (with AL as an example) fractions with controlled molar mass could be obtained via gradient precipitation by gradually increasing the water content in the solvent system. Additionally, DMI had a good recyclability, and the recycled DMI showed no obvious decrease in the ability to dissolve lignin. This work provided an innovative and green solvent system to dissolve lignin, contributing to the realization of a “closed-loop” biorefinery process.