Research strategy for the separation of toluene/methylcyclohexane azeotropes by ionic liquids

The separation of toluene (TOL) and methylcyclohexane (MCH) is a key step to achieve high-purity aromatic recovery, but traditional distillation processes consume significant energy. In this study, an ionic liquids (ILs)-based extractive distillation strategy was proposed to achieve efficient separation by computational screening, experimental validation, and process simulation. First, 1722 candidate ILs were systematically screened using the COSMO-RS model, selecting three high-performance ILs based on selectivity and viscosity criteria. Experimentally determined vapor–liquid equilibrium data showed that 1,3-dimethylimidazolium bis(fluorosulfonyl)imide salt ([MMIM][FSI]) significantly enhanced the relative volatility of TOL-to-MCH. Quantum chemical analyses revealed the separation mechanism. Based on this, an extractive distillation process was constructed by Aspen Plus process simulation: the use of [MMIM][FSI] as an entraining agent reduced the total annualized cost (TAC) by 55.55% compared with conventional distillation. This study provides an industrially feasible solution for low-carbon separation of aromatic/non-aromatic systems through an innovative pathway of molecular design–experimental validation–process integration.