Tuning the Properties of Lignin-derived Deep Eutectic Solvents for Biomass Processing.

Lignin-derived deep eutectic solvents (DESs) have been investigated as sustainable green media for biomass processing. However, the properties and processability of DESs have not been fully understood with the chemical structures of their constituents for biomass fractionation. In this study, the properties of the phenolic DESs were discussed with different numbers of functional groups such as -OCH3 and -CHO in their hydrogen bond donor (HBD) structures. The formation of DES was significantly related to the hydrogen bond between its constituents, identified by 1H nuclear magnetic resonance analysis and density functional theory calculation. Lower viscosity and net basicity of DES were achieved with fewer -OCH3 groups on HBD structures, resulting in enhanced processability and fractionation efficiency. The thermal stability of the DES was also influenced by the -OCH3 and -CHO of HBD based on its onset temperatures. The recyclability of the phenolic DES was confirmed by the fractionation performance of the recycled DES. Understanding the structural impacts of DES constituents on the properties and performance is crucial for designing solvents in biorefinery applications.