Mechanism of azeotrope elimination in the ethyl propionate–ethanol system using ionic liquid HMIMOAc as an entrainer: experimental and theoretical insights

Ionic liquids (ILs) are highly effective entrainers for extractive distillation of azeotropes, owing to their unique physicochemical properties. However, the intrinsic molecular mechanisms underlying the role of ILs in the azeotropic separation process remain insufficiently understood. To investigate the intrinsic causes of azeotrope elimination by ILs, the study focused on the v(O–D) region of ethanol employing both experimental and theoretical methods to investigate the microstructural properties of the ethyl propionate (EP)–ethanol azeotrope before and after separation by 1-hexyl-3-methylimidazole acetate (HMIMOAc). The key findings are as follows: (1) the interaction between HMIMOAc and ethanol is significantly stronger than that between EP and ethanol. (2) The interaction between [OAc]⁻ in HMIMOAc and ethanol plays a critical role in eliminating the azeotrope. (3) Ethanol self-aggregates, EP–ethanol interaction complexes, and HMIMOAc–ethanol interaction complexes were identified and characterized using excess spectroscopy and quantum chemical calculations.