Lignin derived hydrophobic deep eutectic solvents as sustainable extractants

Solvent innovation has become a central task for improving the sustainability of chemical processes1. Deep eutectic solvents (DESs) emerge as environmentally friendly alternatives to toxic and volatile organic solvents. One appealing aspect for DESs is that they can be synthesized using naturally occurring compounds from biomass. Herein, we prepared novel hydrophobic DESs based on lignin derivatives and characterized their physicochemical properties including density, viscosity, and thermal behavior. The results showed that five lignin-derived hydrophobic DESs made from menthol, thymol, and 2,6-dimethoxyphenol were promising as green solvents due to their low viscosities and environmentally friendly constituents. To evaluate the potential application of these DESs, liquid-liquid extraction was performed to recover the typical biofuel fermentation products including acetone, ethanol, n-butanol, and isopentanol from aqueous solutions. High distribution coefficients, selectivity, and recovery rates for acetone, n-butanol, and isopentanol were achieved with the thymol: 2,6-dimethoxyphenol DESs. Moreover, molecular dynamic simulations were conducted to investigate the DES molecular interactions and formation mechanism. This work demonstrates the potential of lignin derived hydrophobic DESs for applications as sustainable extraction media.