Recovery of Monoethanolammonium Acetate from Ionosolv Liquors Using a γ-Valerolactone-Based Aqueous Two-Phase System

Ionic liquids (ILs) enable efficient lignin extraction in the Ionosolv process, but their sustainable implementation requires effective lignin recovery from IL extract to allow IL recycling. Conventional water-based precipitation of lignin is energy intensive due to the high enthalpy of vaporization of water. In this work, we propose a γ-valerolactone (GVL)-based aqueous two-phase system (ATPS) as a more energy-efficient separation strategy. The phase behavior of the ternary ATPS water + GVL + monoethanolammonium acetate ([MEA][OAc]) was experimentally determined and correlated using the thermodynamic non-random two-liquid model. Then, lignin was extracted from Eucalyptus wood using the IL [MEA][OAc]. Application of this ATPS to the Ionosolv liquor enabled selective partitioning of lignin into the GVL-rich phase, followed by its isolation using low-enthalpy organic antisolvents (acetone, tert-butanol, 2-propanol, or 1-butanol). The GVL-rich phases were examined for suspended lignin particles. Structural characterization by 2D-NMR confirmed precipitated lignins exhibit high syringyl content and low degrees of recondensation, resulting in materials with enhanced depolymerizability. These findings show that GVL-based ATPSs are a promising lower-energy downstream option for lignin recovery from Ionosolv liquors. Relative to conventional water precipitation, the proposed route lowers solvent-regeneration energy demand by up to 44% while preserving favorable lignin structural features.