Separation Of Benzene And Cyclohexane By Extractive Distillation With Mixed Solvent Containing Ionic Liquid

Both benzene and cyclohexane are important petrochemical raw materials,and there is a great demand for separating them in industry.Due to similar structures and properties,benzene and cyclohexane are extremely easy to form azeotrope,which makes it a tough problem to separate them by ordinary separation technology.Extractive distillation is one of the most effective special distillation method for separating azeotropic systems in industry,and the key is to select a suitable entrainer.In view of the disadvantages of large solvent dosage and high volatility in the industrial organic solvents,the idea of adding a little ionic liquid in organic solvent was put forward in this thesis to fully take the advantages of the two solvents.The experiments and simulation were carried out to study the effects of different ratios of mixed solvents on separation performances,and those were analyzed and explained on the molecular level.Solubility and selectivity were calculated by COSMO-RS model to screen a proper additive in 48 common ionic liquids.After considering solubility,selectivity,stability,corrosiveness and price of ionic liquids,the thermal stability and corrosivity were analyzed and verified to select the mixture of[EMIM]+[BF4]-and organic solvents as the entrainer at last.The vapor liquid equilibrium data were measured in the full range of concentration.The conclusions are as follow:four kinds of entrainer all can improve the relative volatility of cyclohexane and benzene and break azeotropic point;Compared with the pure solvent,on one hand adding IL can slightly promote the relative volatility of key components in the system,and on the other hand,it can effectively reduce the traditional solvent content in the gas phase.Comprehensively considering the separation effect and energy consumption of solvent recovery,NMP +[EMIM]+[BF4]-mixed entrainer was selected as the best entrainer.Meanwhile,the experimental data were correlated by the UNIFAC-Lei model,and the relative average deviations are all within the acceptable range,which shows the reliability of extending interaction parameters to other systems in the future.Based on the conclusions and parameters above,the separation process of benzene and cyclohexane was simulated by Aspen software.The optimized process parameters were determined by sensitivity analysis,and the separation effect and energy consumption of using pure NMP and NMP+IL mixed solvents were analyzed and compared.The results show that the addition of IL can reduce the content of NMP in the products,save the amount of entrainer in the process and decrease the reflux ratio under the premise of acquiring products with the same purity.In addition,the heat duty of the condenser is reduced by 7.60%,and that of the reboiler is reduced by 5.51%.In this thesis,the excess enthalpy and binding energy in the system were calculated by COSMO-RS model and Gaussian software respectively to analyze and explain the experimental conclusions from the molecular level.Both the results indicate that the interaction force between NMP+IL mixed entrainer and benzene is stronger than that between entrainer and cyclohexane.In addition,the binding energy results also indicate that the interaction force between entrainer and benzene is stronger than that between cyclohexane and benzene.The results above confirmed its practical potential to separate benzene and cyclohexane using NMP+IL mixed solvent by extractive distillation.