From Microscopic Mechanisms to Process Intensification: Regulation Strategy and Multiscale Investigation of Ionic Liquid Extractive Distillation for Benzene/Methanol Separation

Benzene (BEN) and methanol (MeOH) form an azeotrope that severely hinders efficient separation in coal chemical production. This study investigates the separation performance of three ionic liquids (ILs), [C2C1im][Gly], [C2C1im][DEP], and [C4C1im][DBP], for the BEN-MeOH azeotropic system through thermodynamic characterization and molecular simulation, and further optimizes the process based on the selected IL. Vapor–liquid equilibrium (VLE) experiments demonstrate that all three ILs eliminate the azeotrope, with selectivity ranking as [C2C1im][Gly] > [C2C1im][DEP] > [C4C1im][DBP]. However, the first two ILs exhibit poor miscibility with BEN and are prone to liquid–liquid phase separation, whereas [C4C1im][DBP] balances selectivity and complete miscibility, making it the optimal homogeneous entrainer. Molecular simulations reveal that hydrogen bonding between the anions and MeOH is the core mechanism for azeotrope breaking. Based on [C4C1im][DBP], four extractive distillation processes (EDPs), namely, dimethyl sulfoxide (DMSO) EDP, IL EDP, IL(85%) EDP, and heat pump-assisted IL (HP-IL) EDP, were further evaluated. The IL EDP exhibits better economic and environmental performance than the conventional DMSO EDP. Although MeOH dilution reduces the viscosity of the IL entrainer, it increases energy consumption and pollutant emissions. Compared with the IL EDP, the HP-IL EDP reduces total annual cost by 13.70%, energy consumption by 27.45%, and gas emissions by 27.00%. This work provides a reliable route for the green and efficient separation of azeotropic mixtures.