The molecular nature of the eliminating azeotropy in water–acetonitrile system by ionic liquid entrainer using FTIR and DFT calculations

Abstract

This study focused on investigating the structure and hydrogen-bonding characteristics of 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc])-water-acetonitrile mixtures aiming at revealing the molecular intrinsic of the azeotropy breaking by ionic liquid entrainer. Our approach combined FTIR with density functional theory (DFT) calculations applying the CN stretching vibration region as the responsive indicator of the microenvironment to discern the structural and hydrogen-bonding properties of the H2O‒CH3CN and [EMIM][OAc]‒CH3CN binary systems and [EMIM][OAc]−H2O−CH3CN ternary systems. Distinct interaction models were observed between [EMIM][OAc] and CH3CN compared to those in water and CH3CN system, leading to different influences on the CN stretching vibration region. Excess peaks associated with H2O−CH3CN, CH3CN self-aggregator, and IL−CH3CN interaction complexes were identified. The interaction strength between [EMIM][OAc] and CH3CN was notably more potent than that between water and CH3CN. Consequently, IL had the ability to disrupt the interaction complex of water-acetonitrile with the formation of the IL−CH3CN complex. This species transformation during the mixing process elucidated the characteristics of phase equilibrium shift in the azeotrope system.