Measurement Of Vapor-Liquid Equilibria And Simulation Study On Pressure Swing Distillation For Toluene-alcohols Binary System

Ethanol, toluene and isopropanol are very important organic solvents, which arewidely used in chemical, pharmaceutical and dye industry and so on. But the mixtureof these two components from both binary system (Ethanol-toluene,isopropanol-toluene) can not be separated by conventional distillation, because theyform azeotrope at atmospheric pressure. Even worse VLE data of these binarysystems are inadequate, especially in the case of pressurization. This will have a badeffect on the accuracy of distillation simulation to separate and purify these mixtures.Firstly, Vapor-liquid equilibria (VLE) data and azeotropic data for toluene-ethanol, toluene-isopropanol binary systems have been measured at (101.3,121.3,161.3and201.3) kPa using a vapor-liquid equilibrium recirculating still. Theexperimental data were checked with the Herington method, which showedthermodynamic consistency. The experimental VLE data were correlated with Wilson,NRTL and UNIQUAC activity coefficient models. The results show that thecalculated values of vapor phase mole fraction and boiling temperature by the Wilson,NRTL and UNIQUAC models agree well with the experimental data. NRTL modelgives a slightly better result.Furthermore, Aspen Plus software was applied to simulate the pressure swingdistillation process of both binary systems (Ethanol-toluene, isopropanol-toluene).Sensitivity analysis was applied to optimize the separation process in order to get theoptimum process conditions such as operating pressure, theoretical plate number,reflux ratio, feeding position and circulating ratio. The final product was obtainedwith a satisfactory purity and yield which is more than99.9%. We also compared thedouble-effect pressure swing distillation with traditional pressure swing distillation toanalyse the energy consumption. The result shows that the former can save powermore than48percent.Finally, any azeotrope which might appear in alcohol and benzene-based binarysystem was simulated and speculated in the text, with the result that not all binarysystem can form azeotrope at atmospheric pressure. The range and properties ofazeotrope in alcohol-benzene-based binary system were calculated and analysed inour work. The sensitivity of azeotropic composition to pressure was researched in this paper. The conclusion shows that azeotropic composition will change significantly asthe pressure varies a little bit. Alcohol content will increase in the azeotrope as thesystem pressure increase. All of these will be important criterions for the pressureswing distillation design in separating alcohol-benzene-based binary azeotropicsystem.