Multiscale exploration of ionic liquids for the separation of n-butanol/n-butyl acetate azeotrope

Abstract

The development of green and efficient entrainers is critical for the extractive distillation process of alcohol-ester azeotropes. This study proposes a feasible method for separating the n-butanol (NBA) and n-butyl acetate (NBAC) azeotrope using acetate-based ionic liquids (ILs) as entrainers. Thermodynamic properties, including solvent capacity and selectivity, were first computed using the conductor-like screening model for real solvents (COSMO-RS) to identify three potential IL entrainers. A systematic quantum chemistry approach was then employed to explore the structure–activity relationships between azeotropic components and ILs. The results indicated that van der Waals and hydrogen bond (H-bond) interactions are the primary driving forces for separating the azeotropic mixture, with H-bond making a major contribution. Furthermore, phase equilibrium predictions revealed that the addition of ILs significantly impacts the phase behavior of the mixture systems. Among the tested ILs, tetrabutylammonium acetate ([N₄₄₄₄][Ac]) demonstrated the best separation performance. Finally, molecular dynamics simulations were conducted to explore intermolecular interactions in the actual solvent environment and further confirmed the presence of H-bonds between the [Ac]⁻ and NBA. This study provides valuable insights into the development of entrainers and the industrial application of alcohol-ester azeotrope separation.