Liquid–Liquid Equilibrium Behavior and Intermolecular Interactions of Water, Propylene Glycol Methyl Ether, and Alkyl Alcohols

This work focuses on exploring feasible strategies for the efficient separation of propylene glycol methyl ether (PGME) from aqueous solutions using a series of alkyl alcohols (1-hexanol, 1-heptanol, 1-octanol, 1-nonanol) as extractants, in which liquid–liquid equilibrium (LLE) experiments and separation mechanism analyses were performed for water + PGME + alkyl alcohol at 303 K and 101.3 kPa. The extraction performance of alkyl alcohols was evaluated by calculating distribution coefficients ( D ) and separation factors ( S ), correlating liquid–liquid extraction data with NRTL and UNIQUAC thermodynamic models to regress binary interaction parameters, and validating the reliability of model parameters by verifying thermodynamic consistency; furthermore, the intrinsic extraction mechanisms at the molecular level were revealed by combining σ-Profile analysis, deformation charge density analysis, intermolecular interaction energy calculations, and reduced density gradient (RDG) analysis. This work provides a theoretical basis for the screening and application of alkyl alcohol extractants.