Breaking the Azeotrope between Cyclohexane and Benzene Using Aniline
Consider a binary mixture of cyclohexane (BP ) and benzene (BP ) at . This mixture presents a minimum-boiling azeotrope. It is possible to break this azeotrope using aniline. The vapor-liquid equilibrium (VLE) behavior of the ternary mixture is described by a modified form of Raoult's law with activity coefficients predicted by the Wilson model . This Demonstration plots the pseudo-binary phase diagram for user-set values of the aniline mole fraction. We plot the benzene liquid mole fraction versus the benzene vapor mole fraction with both mole fractions calculated on an aniline-free basis. It is clear from the first snapshot that, when no aniline is present, the binary mixture exhibits a positive azeotrope. On the other hand, when enough aniline is used (see snapshots 3 and 4), the azeotrope disappears and there is an inversion of volatility, so that the heavy-boiling cyclohexane distills overhead in an extractive distillation process [2, 3]. In this case, the VLE data is below the diagonal black line.
 G. M. Wilson, "Vapor-Liquid Equilibrium XI: A New Expression for the Excess Free Energy of Mixing," Journal of the American Chemical Society, 86(2), 1964 pp. 127–130.
 M. F. Doherty and J. P. Knapp, "Distillation, Azeotropic and Extractive," in Kirk-Othmer Encyclopedia of Chemical Technology, New York: John Wiley & Sons, 2004.
 B. Kolbe, J. Gmehling, and U. Onken, "Selection of Solvents for Extractive Distillation Using Predicted and Correlated VLE Data," Inst. Chem. E. Symp. Ser., 56(1), 1979 pp. 1.3/23–40.
"Breaking the Azeotrope between Cyclohexane and Benzene Using Aniline"
Wolfram Demonstrations Project
Published: September 21 2011