Study On Separation Azeotrope System Of Benzene-cyclohexane-thiophene Vapor Liquid Phase Equilibrium By Extractive Distillation

The separation of the mixture occupies an extremely important position inchemical production departments, which produce variety of chemical materials,such as coal chemical, petroleum chemical and medical industries.the mixturewhich have a similar boiling point or forms azeotropic liquid cannot beseparated by normal distillation, but the extractive distillation sometimes cansolve this problem.This paper takes the separating from benezene-cyclohexane–thiopheneclose boiling system by extractive distillation as the subject and summarizes thecurrent separate situation of benzene-cyclohexane system and benzene-thiophene system firstly. The basis and method of selecting extractant in theextractive distillation was also expounded.And then the Phenol, NMP, DMF,DMSO, NFM,2-bromothiophene,2,5-dibromothiophene were choosed asextractants. and the impact of different kind and content of extractants on thebenzene, cyclohexane, thiophene’s relative volatility and activity coefficent were investigated.The isobaric vapor-liquid equilibrium datas of benzene-thiophene, benzene-phenol, thiophene-phenol and benzene-thiophene-phenol, were measured byusing a modified Rose vapor–liquid equilibrium still. These three binary VLEdata were estimated by Wilson and NRTL model and the binary parameters ofthese two models were obtained. At the same time, the parameters obtained wereused to predict the ternary VLE data of benzene-thiophene-phenol, and thecalculated value was compared with experimental one showing littledifference.additionally, the vapor-liquid equilibrium datas of quaternary systembenzene–cyclohexane-NMP (DMF, DMSO, NFM,2-bromothiophene,2,5–dibromo thiophene) were measured at different temperature and pressure. Andthe relationship between relative volatility and the content of solvents wasinvestigated.Then the VLE data of NMP+benzene+cyclohexane+thiophenesystem were correlated by UNIFAC-Dortmund model firstly so as to verify thereliability and accuracy of the model. The VLE datas of benzene+cyclohexane+thiophene+DMF and benzene+cyclohexane+thiophene+2-bromothiophene were estimated by the UNIFAC-Dortmund model, as a resultthe parameters for two pairs of UNIFAC groups (52ACS-39DMF,52ACS-33Br)were obtained. finally, the values of activity coefficient were calculated by themodel when NMP, DMF,2-bromothiophene were used as solvent respectively,and the combinatorial term and residual term values which comprised theactivity coefficient were also figured out. and the change rule of activity coefficient was discussed, thus to obtain the conclusion as follow:①NMP had little effect on activity coefficient of benzene, while theDMF,2-bromothiophene had a great influence on the activity coefficientsbecause of the interaction between group benzene and solvent.②For cyclohexane, NMP had an effect on values of combinatorial termand residual term with positive deviation, as a result the activity coefficient wasincreased. DMF had no effect on combinatorial term but increased residual term,in other words, the interaction between groups is the main factor for the changeof cyclohexane’s activity coefficient. When2-bromothiophene was used as thesolvent, the combinatorial term was increased but residual term was decreased,so the activity coefficient was kept constant.③NMP, DMF, and2-bromothiophene had little effect on combinatorialterm and residual term of thiophene, so the activity coefficient was kept constant,which indicated that the interaction between thiophene group and solvent groupwas quite weak, and the thiophene’s activity coefficient was independence of thesize of these solvent molecules.