Separation of m-Cresol from Coal Tar Model Oil Using Propylamine-Based Ionic Liquids: Extraction and Interaction Mechanism Exploration

m-Cresol is an important chemical material, which is mainly derived from low-temperature coal tar. In this work, for separating m-cresol from coal tar model oil, two propylamine-based ionic liquids (ILs) propylamine formate ([PA][FA]) and propylamine acetate ([PA][Ac]) were selected as extractants. The selected ILs were synthesized and characterized by Fourier transform infrared (FT-IR) and H-1 nuclear magnetic resonance (NMR) spectroscopy. The effects of temperature, mass ratio of IL to model oil, and separation time on the separation efficiency of m-cresol were explored. The separation efficiency (SE) and distribution coefficient (D) were calculated from the experimental data to assess the separation performance of [PA][FA] and [PA][Ac]. The results showed that propylamine formate was a promising extractant with the separation efficiency of 97.8% and distribution coefficient of 27.59 at 298.15 K and m(IL)/m(oil) = 0.2. In the meantime, molecular dynamics (MD) simulations were employed to comprehend the interaction mechanism, from which the noncovalent interaction energy (IE), radial distribution function (RDF), spatial distribution function (SDF), and averaged noncovalent interaction (aNCI) were calculated. The results showed that both cation and anion formed hydrogen bonds with m-cresol and the anions played a leading role with electrostatic interaction energy in separating m-cresol. In addition, the regeneration and reuse of the ionic liquids were explored.