Industrial Applications of Ionic Liquids in Acetonitrile–Water Azeotrope Separation: Molecular Dynamics and DFT Insights into Azeotrope Breaking Methods

Abstract

Separating acetonitrile–water azeotropic systems is challenging due to unclear molecular-level interaction mechanisms of ionic liquids (ILs). This study investigated ILs ([Emim]Br, [Bmim]Br, [Emim][BF₄], and [Bmim][BF₄]) as entrainers using experimental and theoretical approaches to elucidate the azeotropic point-breaking mechanism. Molecular dynamics (MD) simulations were employed to analyze binary and ternary solutions, while density functional theory (DFT) at B3LYP/6–311 + G(d) was used to refine the complexation energies and Boltzmann-averaged multiple isomers. Vapor–liquid equilibrium (VLE) data (T, x, and y) for the pseudobinary systems of acetonitrile, water, and ILs at 101.33 kPa were measured and correlated using the nonrandom two-liquid (NRTL) model. The results show that ILs exhibit a stronger salting-out effect than solvation, enhancing the relative volatility of acetonitrile and eliminating the azeotropic point. The salting-out efficacy followed the order [Emim]Br > [Bmim]Br > [Emim][BF₄] > [Bmim][BF₄], with [Emim]⁺ and Br^– being the most effective. These findings highlight the ILs’ potential for efficient, sustainable industrial azeotrope separation.