UNIFAC-Lei Model-Driven Design of Ionic Liquid-Based Liquid-Liquid Extraction for Efficient Benzene Separation from Hexane/Heptane Mixtures

To address the challenge of separating benzene from hexane/heptane mixtures, this study evaluates ionic liquids(ILs) as sustainable solvents via liquid-liquid equilibrium(LLE) modeling and process simulation. The UNIFAC-Lei model was employed to predict LLE behavior in ternary systems of(benzene + hexane/heptane + IL), demonstrating excellent agreement with experimental data(a root-mean-square deviation < 0.216). Aspen Plus simulations were conducted to optimize a conceptual extraction process, focusing on solvent-to-feed ratio(IL/F = 0.5–4.0) and equilibrium stages(NS = 2–6). Results indicate that[EMIM][NTf₂] outperforms other ILs, achieving 83.3 wt% benzene purity in hexane mixtures and 94.7 wt% in heptane mixtures from a 20 wt% benzene feed. The model predicts that shorter alkyl chains in IL cations enhance selectivity(selectivity order:[EMIM][NTf₂] > [BMIM][NTf₂] > [OMIM][NTf₂]), consistent with experimental trends. Industrial feasibility analysis reveals complete immiscibility between[EMIM][NTf₂] and aliphatic hydrocarbons, eliminating the need for raffinate-based IL recovery units and reducing process complexity. This work establishes the UNIFAC-Lei model as a robust tool for IL screening and process design, offering a sustainable alternative to volatile organic solvents for aromatic-aliphatic separation. The optimized process parameters(IL/F = 2.5–3.5, NS = 5) provide a scalable framework for industrial implementation, balancing high benzene recovery(> 94%) and low energy consumption(heat duty: 4.03–4.45 kW).