Phase Eqequilibrium And Separation Process Optimization Of Three Azeotropic Systems Containing Alkanes By Imidazole Ionic Liquids

Chemical separation technology is becoming more and more mature,but looking for green and efficient separation solvent is still the focus of research.Ionic liquids are widely used in the extraction and separation of azeotropes because of their designability and difficult volatility.In this work,the liquid-liquid equilibrium and extraction mechanism for ionic liquids separation of n-heptane-tert-butanol,n-heptane-dimethyl carbonate and n-octane-n-butanol azeotropic system were studied,and the process of ionic liquids extraction and separation of azeotropes were design and optimized.The main research contents and results are as follows:Firstly,based on COSMO-SAC model,ionic liquids with infinite dilution partition coefficient and high selectivity were selected as the extractant.[Omim][OTf],[Hmim][OTf]and[Bmim][OTf]were selected from 100 kinds of ionic liquids for n-heptane-tert-butanol system,[Omim][OTf],[Omim][PF₆]and[Omim][NTf₂]were selected from 280 kinds of ionic liquids for n-heptane-dimethyl carbonate system;[Bmim][HSO₄],[Bmim][NO₃]and[Bmim][OTf]were selected from 418 kinds of ionic liquids for octane-n-butanol system.Based on quantum chemical calculation,the interaction between azeotrope and ionic liquids were explored on the molecular scale.By calculating the charge density,bond energy and bond length between tert-butanol,dimethyl carbonate,n-butanol and the selected ionic liquids molecules,it was determined that there was hydrogen bond interaction between azeotrope and ionic liquids,and the interaction between[Hmim][OTf]and tert-butanol,[Omim][NTf₂]and dimethyl carbonate,[Bmim][NO₃]and n-butanol were the strongest,and the bond energy were-104.3264 k J/mol,-96.5253 k J/mol and-65.1188 k J/mol respectively.Secondly,the experimental data of liquid-liquid equilibrium between three alkane containing azeotropic systems and the above selected ionic liquids at 298.15 K and atmospheric pressure were measured.The thermodynamic consistency of the data was tested according to Othmer-Tobias equation,and the correlation accuracy was close to1.The NRTL model was used to analyze the correlation of the experimental data,and the root mean square error were less than 0.02.According to the experimental data of liquid-liquid equilibrium,the separation coefficient and distribution coefficient were calculated.The optimal extractants for the three systems were[Hmim][OTf],[Omim][NTf₂]and[Bmim][NO₃],and the distribution coefficients of the three ionic liquids for n-heptane-tert-butanol,n-heptane-dimethyl carbonate and n-octane-n-butanol systems were 6.7368,6.3270 and 3.2859,and the separation coefficients were63.8061,134.8467 and 111.7199,respectively.And finally,the process of separating alkane containing system by ionic liquids were designed and optimized.The process of[Hmim][OTf]separating n-heptane-tert-butanol system,[Omim][NTf₂]separating n-heptane-dimethyl carbonate and[Bmim][NO₃]separating n-octane-n-butanol were designed.The optimal number of trays were 3,3,and 2,respectively.The feed ratios were 0.06,0.05 and 0.015,respectively.The minimum annual total costs were 9.2343×10~5$/y,6.4657×10~5$/y and8.6489×10~5$/y,respectively.This study provides a theoretical basis for screening green and clean separation solvents and practical application of ionic liquids.