Vapor-Liquid Phase Equilibrium Separation For The Binary Azeotrope Using Ionic Liquids As The Solvent

As the excellent solvents,acetonitrile,n-propanol and tert-butanol(TBA)were usually using in chemical engineering.Acetonitrile and n-propanol were exsited in the production of chemicals and drugs,or existed as the mobile-phase using in high performance liquid chromatography(HPLC);TBA and water were exsits in the production of isobutene based on the dehydration of TBA,or exsited in the commercial production of TBA using the isobutene.Therefore,as the liquid waste,the two binary azeotropic systems of acetonitrile-n-propanol and TBA-water were the common system in chemical separated process.Generally,extractive distillation was adopted to separate azeotrope.As the new solvent with green and eco-friendly,ionic liquids(ILs)as the extraction solvents(solvent)was proposed to separate azeotrope for the reason of low volatility,stable physicochemical property and adjustable structure.In this paper,the alkyl imidazolium phosphate-based ILs:1,3-dimethyl imidazolium dimethyl phosphate([MMIM][DMP])and 1-ethyl-3-methyl imidazolium diethyl phosphate([EMIM][DEP])were chosen as the solvent to separate the two binary azeotropic systems of acetonitrile-n-propanol and TBA-water with merits of no halogen element,high stability,low corrosivity and simple synthetic;method,and the binary and ternary isobaric vapor-liquid equilibrium(VLE)experiments data was measured and compared with results from references until now.Then,the activity coefficient models and the COSMO-RS were adopted to do the modelling study,and the calculated results of the optimized geometries,the bonding energies?E,?-profiles,?-potentials,a-surfaces,bond lengths and bond angles between moleculars,which were got base on the quantum chemical methods,were used to do the theoretical analyses.The major works accomplished in this paper were given as followed:One-step reaction was used to synthesize the two ILs:[MMIM][DMP]and[EMIM][DEP],purification process and characterization process were done after that.For the ILs:[MMIM][DMP]and[EMIM][DEP],the yields of them were nearly 90%;the purities(without water,wt%)of them were 98.63%and 98.22%,respectively;the water contents of them were all less than 500 mg/kg.The synthesized ILs could be used in experiments of VLE due to the results of purities and water contents were satisfied.The modified Othmer still was used to measure the five binary and two ternary VLE data for the system of acetonitrile-n-propanol-[MMIM][DMP]/[EMIM][DEP]and TBA-water-[MMIM][DMP]/[EMIM][DEP].The result showed that:after[MMIM][DMP]or[EMIM][DEP]adding into,the mole fractions of acetonitrile or TBA in vapor-phase were changed and the crossover effect between salting-in and salting-out was appeared for the system of acetonitrile-n-propanol and TBA-water;the the minimum mole fractions of acetonitrile-n-propanol for making the azeotropic point disappeared were x3,min([MMIM][DMP])?0.0235 and x3,min([EMIM][DEP])?0.0211,respectively;and the minimum mole fractions of TBA-water for making the azeotropic point disappeared were x3,min([MMEM][DMP])?0.0600 and x3,min([EMIM][DEP])?0.0750;compared with the separated results using organic solvent,inorganic salts and other ILs as the solvents,the separated effect of[MMIM][DMP]and[EMIM][DEP]was better than salts,organic solvent(EG,NMP,DMF and DMSO)and other ILs([BzMIM][Cl],[BzMIM][Br]and[HMIM][Br])for the system of acetonitrile-n-propanol,and[EMIM][DEP]was the best one;the separated effect of[MMIM][DMP]and[EMIM][DEP]was better than salts(LiCl),organic solvent(EG and TEG),mixed solvents([EMIM][DCA]+[EMIM][Ac]and Propane-1,3-Diol+[EMIM][Cl])and other ILs([EMIM][DCA],[EMIM][Br]and[TEA][Lc])for the system of TBA-water,and[MMIM][DMP]was the best one.The activity coefficient models(NRTL.UNIQUAC and Wilson model)and COSMO-RS were adpoted to do the modelling study for the systems of acetonitrilc-n-propanol[MMIM][DMP]/[EMIM][DEP]and TBA-water-[MMIM][DMP]/[EMIM][DEP].First,the NRTL model,UNIQUAC model and Wilson model were adopted to correlate the binary enperimental VLE data and the binary interaction parameters between components were got,then the predict the ternary VLE data were got based on them.Compared the predicted data with experimental data,the results were ARDNRTL(T)<ARDwilson(T)<ARDUNIQUAC(T),ARDNRTL(y1)<ARDWilson(y1)<ARDUNIQUAC(y1).Second,COSMO-RS was adopted to predict the ternary VLE data for the systems of acetonitrile-n-propanol-[MMIM][DMP]/[EMIM][DEP]and TBA-water-[MMIM][DMP]/[EMIM][DEP].Compared the predicted data with experimental data,the ARD for the mole fractions of vapor-phase y1 and the relative volatilities ?12 were ARDNRTL(Y1)<ARDCOSMO-RS(y1),ARDNRTL(T)<ARDCOSMO-RS(T),ARDNRTL(?12)<ARDCOSMO-RS(?12).The calculated results of optimized geometries for acetonitrile,n-propanol,TBA,water,[MMIM]+,[EMIM]+,[DMP]-and[DEP]-,the bonding energies ?E,?-profiles,?-potentials,?-surfaces,bond lengths and bond angles between moleculars were got base on the quantum chemical methods.Compared the results of ?E:for the system of acetonitrile-n-propanol[MMIM][DMP]/[EMIM][DEP],the affinity between n-propanol and[EMIM][DEP]was the strongest,the affinity between n-propanol and[MMIM][DMP]was the second one,and the the affinity between acetonitrile and n-propanol was the weakest;for the system of TBAwater-[MMIM][DMP]/[EMIM][DEP],the affinity between water and[MMIM][DMP]was the strongest,the affinity between water and[EMIM][DEP]was the second one,and the the affinity between TBA and water was the weakest.Compared the results of ?-profiles,?-potentials,?-surfaces,bond lengths and bond angles between molecular,the hydrogen bond,which exsited between the O atom of[DMP]-or[DEP]-and the the H atom of hydroxyl of n-propanol,was more stable than the hydrogen bond which exsited between the H atom of hydroxyl of n-propanol and or the N atom of acetonitrile;the hydrogen bond,which exsited between the O atom of[DMP]-or[DEP]-and the H atom of water,was more stable than the hydrogen bond which exsited between the H atom of hydroxyl of TBA and the O atom of water.Therefore the azeotropoic point of acetonitrile-n-propanol or TBA-water was disappeared with the addition of[MMIM][DMP]or[EMIM][DEP],and the separation of them was come true with the acetonitrile and TBA became light component in extractive distillation.