Lignin derived hydrophobic deep eutectic solvents as sustainable extractants

Solvent innovation has become a central task for improving the sustainability of chemical processes. Deep eutectic solvents (DESs) emerge as environmentally friendly alternatives to toxic and volatile organic solvents. One appealing aspect for DESs is that they can use 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. Out of the nineteen DESs tested, five lignin-derived hydrophobic DESs made from menthol, thymol, and 2,6-dimethoxyphenol (also known as syringol) showed promise as green solvents due to their low viscosities and environmentally friendly constituents. Molecular dynamic simulations indicated that the inter- and intra- molecular interactions within the DES contribute to the diverse/tunable DES properties. Moreover, these lignin-based hydrophobic DESs showed outstanding performance in liquid-liquid extraction processes, offering high removal rates for nano-plastic pollutants (>95%) and high extraction efficiencies for fermentation products such as bio-butanol (>86%) and bio-isopentanol (>90%). This work demonstrates the potential of lignin derived hydrophobic DESs for applications as sustainable extraction media.