Investigation on the molecular interaction mechanisms of ionic liquid-organic mixed entrainers for azeotrope separation in extractive distillation

The limited selectivity of single organic solvents and the high viscosity of single ionic liquids present considerable challenges to the efficient separation of azeotropic mixtures within the extractive distillation system. To address the constraints of single solvents application, a mixed solvent comprising ionic liquid and organic entrainer was investigated for azeotropes separation based on the improved extractive distillation scheme, which including the determination of effective entrainers, molecular mechanism analysis, process-scale stochastic optimization, and the heat pump-based improvement. Quantum chemical calculations were utilized to preliminarily select dimethyl sulfoxide (DMSO) and 1-butyl-3-methylimidazolium acetate ([BMIM][AC]) as a mixed solvent for the separation of a binary azeotropic mixture of ethanol and isopropyl acetate. A strong hydrogen bonding interaction between [AC]⁻ and ethanol was observed via the interaction mechanism-based analysis. The pure [BMIM][AC], pure DMSO, and mixed solvent were integrated into the extractive distillation process design. Three conventional schemes and two heat pump-based processes were proposed and optimized using the multi-objective particle swarm optimization (MOPSO) algorithm. The results indicated that the introduction of organic solvents not only effectively mitigates the high viscosity drawback of ionic liquids but also significantly enhances economic performance. Compared to the design using pure DMSO solvent, the intensified extractive distillation with mixed solvents (HP-MEED) reduces the total annual cost by 41.21 %, lowers CO₂ emissions by 58.89 %, and decreases energy consumption by 53.64 %. These results suggest that the ionic liquid-based mixed solvent exhibits significant potential for azeotropic mixture separation, and more combinations of ionic liquid-based mixtures can be expected in future studies.