Ionic Liquids for Separation of n-Heptane and Acetone: Liquid–Liquid Equilibrium Experiment and Mechanistic Analysis

Ionic liquids (ILs) exhibited enhanced extraction performance compared with traditional organic solvents in azeotropic separation processes. In this paper, three kinds of ILs: 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]), 1-butyl-3-methylimidazolium diethylphosphate ([BMIM][DEP]), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF₆]) were considered as extractants for separate n-heptane and acetone. The effect of temperature (298.15, 303.15, and 308.15 K) on the selectivity and distribution coefficients was then investigated. Liquid–liquid equilibrium (LLE) experiments demonstrated that three ILs proved the separation efficiency for acetone. The experimental data were then regressed and validated using the Othmer–Tobias equation and the Hand equation. In addition, the NRTL (nonrandom two liquids) model was used to correlate the LLE experimental data, and the NRTL parameters are verified through the “GMcal_TieLinesLL” tool. Finally, molecular interaction mechanisms were further elucidated through surface electrostatic potential mapping (ESP) and an independent gradient model based on Hirshfeld partition analysis (IGMH) analysis. This research establishes a theoretical framework for industrial-scale separation of ketone/alkane mixtures while providing valuable insights into structure–property relationships of ILs in separation processes.