Molecular Mechanism of Ethanol-Acetonitrile Azeotrope Disruption by the Ionic Liquid [BMIM][NTf₂]

Ionic liquids (ILs) have attracted significant attention as green solvents for azeotrope separation via extractive distillation; however, the microscopic mechanism by which ILs eliminate azeotropic phenomena remains inadequately understood. This study employs a combination of spectroscopic methods and theoretical calculations to elucidate the mechanism by which 1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide ([BMIM][NTf₂]) breaks the ethanol-acetonitrile azeotrope. Analysis of the hydroxyl stretching vibration region of ethanol indicates that the ethanol-acetonitrile cross-interaction is weaker than ethanol self-association, which is responsible for the minimum-boiling azeotrope. The addition of IL breaks the ethanol-acetonitrile azeotrope. The underlying mechanism is that the addition of the IL induces the formation of stronger interaction complexes between ethanol and the IL, which enhances the relative volatility of the azeotropic constituents and thereby enables azeotropic separation. This work provides a critical basis for elucidating the molecular mechanism responsible for the disruption of azeotropic phenomena by ILs.