Liquid–Liquid Equilibrium Behavior for Ternary Mixtures Water and 2-Methylpyridine with Hydrophobic Imidazolium-Based Ionic Liquids

To recover 2-methylpyridine from aqueous solution using an extraction process, three hydrophobic imidazolium-based ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim][BF4]), 1-octyl-3-methylimidazolium hexafluorophosphate ([Omim][PF6]), and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Omim][NTf2]), were selected as the extractants. The liquid–liquid equilibrium (LLE) investigation was conducted for ternary mixtures (water + 2-methylpyridine + hydrophobic imidazolium-based ionic liquids) at a temperature of 298.15 K and pressure of 101.3 kPa. Distribution coefficient and selectivity computed with the ascertained LLE tie-line data were employed to evaluate the separation performance of the ILs. The results indicated that [Omim][NTf2] exhibited superior extraction efficiency followed by [Omim][PF6] and [Omim][BF4]. The tie-line data was fitted by the NRTL model with the most root-mean-square deviation value of 0.9995%. Additionally, the intermolecular interactions between the ILs and 2-methylpyridine were explored by quantum chemical calculations. The findings demonstrate that the hydrophobic ILs exhibit significant potential as sustainable extractants in separating 2-methylpyridine from an aqueous solution.