Liquid–Liquid Equilibrium Measurement for the Separation of n-Propanol + n-Propyl Acetate Using Imidazolium-Based Ionic Liquids with Different Anions at T = 303.15 K

Abstract

Separating the mixture of the target product n-propyl acetate (NPAC) and the unreacted reactant n-propanol (NPA) is necessary during the production of NPAC. NPA and NPAC cannot be separated by simple distillation because the two could form an azeotrope under atmospheric pressure. Liquid–liquid extraction is an energy-saving and environment-friendly method for separating azeotropic mixtures. Ionic liquids (ILs) are promising alternatives to conventional extractants for separating azeotropes due to the advantages of designability and negligible vapor pressure. In this study, the liquid–liquid equilibrium (LLE) data for the ternary systems of NPAC + NPA + 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM][H2PO4]) or 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) were determined at 303.15 K and 101.3 kPa. The accuracy of the experimental LLE data was checked by the Bachman, Hand, and Othmer–Tobias equations. The selectivity and partition coefficient were calculated to evaluate the extraction capability of the selected extractants. The experimental LLE data were correlated with the nonrandom two-liquid model, and the binary interaction parameters were regressed. Finally, the separation mechanism of the three ILs was explored through σ-profile analysis.