Isobaric phase equilibrium behavior and mechanism analysis for eliminating azeotropic phenomena of n-propanol and water with ionic liquids as entrainers

Abstract

n-Propanol (NPA), extensively utilized in various fields including biomedicine and industrial production, forms an azeotrope with H₂O. The azeotropic behavior impairs the purity of NPA, posing significant obstacles to the separation of the two substances via conventional distillation methods. Extractive distillation (ED), owing to its remarkable advantages, has become the prevalent technique for separating azeotropic mixtures. In the ED process, the entrainer has emerged as a crucial and indispensable component. Ionic liquids (ILs) are novel entrainers that have been developed recently and are employed as environmentally friendly solvents in the ED process. Based on the COSMO-RS theory, three ILs, [N1111][Ac], [EMMIM][Ac], and [BMMIM][Ac], were screened as entrainers according to the selectivity and solubility, and their capacity to influence the phase equilibrium behavior of the NPA–H₂O system at atmospheric pressure was explored. Each of the three ionic liquids was found capable of disrupting the azeotropic behavior of the binary NPA–H₂O system, with the reliability of the experimental results confirmed by the thermodynamic consistency test. Additionally, the vapor–liquid equilibrium (VLE) data were properly fitted through the nonrandom two-liquid (NRTL) model, and interaction parameters were derived that confirm that the three ILs break the azeotropy. Furthermore, through a series of quantum chemical (QC) studies, it was further confirmed at the theoretical level that the original hydrogen bonds (HB) are reorganized when ILs are used as entrainers. These results showed that the abilities of the three ILs to affect the azeotropy are in the order [N1111][Ac] > [EMMIM][Ac] > [BMMIM][Ac]. The experimental results are consistent with the predictions of the COSMO-RS model and QC calculations.