Separation Study Of Benzene And Acetonitrile Azeotropic Mixture With Ionic Liquid As Entrainers

Benzene and acetonitrile are important solvents in chemical process production.In the process of producing 2-methylpyridine,acetonitrile and acetylene,were used as raw materials and organic cobalt dissolved in benzene as catalyst agent.the azeotrope composed with benzene and acetonitrile at atomspheric pressure will reduce the yield of 2-methylpyridine.Due to the weak interaction between benzene and acetonitrile,the traditional distillation methods cannot separate that azeotrope.Extractive distillation has become a common distillation process owing to its merits of low energy consumption,easy operation and superior separation performance.In recent years,the green chemical industry was advocated in our country,ionic liquids?ILs?have become the outstanding alternative to conventional organic solvents due to their merits of low toxicity,high thermal stability,negligible vapor pressure and chemical stability,as a extractant in extractive distillation.In order to select a suitable IL to separate benzeneacetonitrile azeotrope,the works of this paper are listed as follows:?1?In this study,the 22 cations and 22 anions were given in literature,and composed 484 ILs to select the suitable ILs using the COSMOtherm X software based on COSMO-RS model,the high selectivity was used as a index to evaluate the ILs.The results illustrate that the ILs with [BF₄]-and [PF₆]-have superior separation performance compared with other anions;Although the ILs with imidazolium-have lower selectivity,the lower viscosity of which make their further industry application,simultaneously,considering the mutual solubility between ILs and azeotrope components,1-octyl-3-mentylimidazolium Hexafluorophosphate [OMIM][PF₆],1-octyl-3-methylimidazolium Tetrafluoroborate [OMIM][BF₄] and 1-decyl-3-methylimidaolium Hexafluorophosphate [OMIM][BF₄] were selected as entrainers to separate the benzene-acetonitrile mixture.?2?The viscosity of the selected ionic liquid was measured from 338.15 K to 368.15 K at atmospheric pressure,and the experimental data was fitted using the VFT equation.Under the same conditions,the viscosity of the three ILs follow the order: [DMIM][PF₆] > [OMIM][PF₆] > [OMIM][BF₄].At the same time,the heat capacity?Cp?of ILs was measured from 338.15 K to 368.15 K at atmospheric pressure,and the measured heat capacity data were correlated with T.The correlation deviation is ± 0.06%.Under the same conditions,the heat capacity of the three ILs follow the order: [OMIM][BF₄] > [DMIM][PF₆] > [OMIM][PF₆].The thermodynamic properties?viscosity and heat capacity?of ionic liquids can provide physical data for the industrial applications.?3?The vapor liquid equilibrium?VLE?data of benzene and acetonitrile binary system,ternary system containing ILs?benzene + acetonitrile + [OMIM][PF₆]/ [OMIM][BF₄]/ [OMIM][BF₄]?were determined at 101.3 k Pa.The results indicate that the dramatic salting-out effect on benzene due to the addition of ILs,which leads to an increase in the content of benzene in the vapor phase and the relative volatility of benzene to acetonitrile.Moreover,the phenomenon become particularly obvious with increasing the content of ILs,eventually eliminate the azeotropic point of benzene and acetonitrile mixture.Otherwise,the NRTL and UNIQUAC activity coefficient models were employed to correlate the VLE data,NRTL model characterize the lowest value of deviation between calculate and experimental data.Based on NRTL model,the minimum mole fraction of three ILs used to separate benzene and acetonitrile mixture are [OMIM][PF₆]=0.061,[OMIM][BF₄]=0.112,[DMIM][PF₆]=0.12.[OMIM][PF₆] represents the superior separation performance.