The microstructure characteristics of the 1-ethyl-3-methylimidazolium thiocyanate–methyl acetate−methanol systems

Abstract

The ionic liquid (IL) has demonstrated promising potential as an entrainer in efficiently separating the methyl acetate−methanol azeotropic mixture using extractive distillation. However, comprehending the fundamental mechanism responsible for azeotropism vanished by an IL entrainer is crucial for its large-scale applications. This study aims to explore the microstructure characteristics of the 1-ethyl-3-metfighylimidazolium thiocyanate ([EMIM][SCN])–methyl acetate−methanol systems using FTIR and DFT calculations. The focus is on understanding the fundamental reasons behind azeotrope breaking facilitated by the IL entrainer. Initially, the v(aromatic C–H) region of the imidazolium cation was analyzed to evaluate the interaction strength between the entrainer and methyl acetate/methanol. The results indicated stronger interactions between [EMIM][SCN] and methanol. As a consequence of this variation in interaction strength, the relative vapor pressure of the two constituents was impacted, ultimately resulting in the disturbance of the azeotrope. Subsequently, the v(C=O) region of methyl acetate was utilized to detect interaction complexes in various systems, assisted by excess spectra. Various interaction species, including methyl acetate–methanol/2methanol and methyl acetate–ion cluster/ion pair/cation were found. Notably, when the mole fraction of IL exceeded 0.087, the IL effectively disrupted the interaction complex between methyl acetate and methanol, thereby eliminating azeotropy in the methyl acetate–methanol system.