Mechanism Analysis for Separation of Cyclohexane and tert-Butanol System via Ionic Liquids as Extractants and Process Optimization

Ionic liquids (ILs) are used in separation of organic substances in industry. In order to screen suitable ILs for industrial separation, the interaction between molecules is studied based on the extraction mechanism. The result is verified by experiments. The binary interaction parameters obtained from experiments are applied to process simulation. In this work, the liquid–liquid extraction of cyclohexane and tert-butanol azeotropic mixture with different ILs {1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl), 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium hydrogen sulfate} is studied. The extraction mechanism is discussed based on the molecular scale. The relationship of the hydrogen bond donor and acceptor between ILs and TBA is analyzed by COSMO-SAC. Then the hydrogen-bonding interaction between ILs and TBA is determined by using quantum chemical calculation, including bond length, total charge density, deformation charge density, and interaction energy. The experimental results are verified. The liquid–liquid equilibrium experiment is carried out at 298.15 K. The NRTL and UNIQUAC models are adopted to correlate the liquid–liquid equilibrium data, and results could well correlate the experiments. Then NRTL binary interaction parameters obtained from the experiment are used to simulate the extraction process. Minimum total annual cost is calculated.