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.