Determination of valley and ridge of isobaric vapor–liquid equilibrium for ternary system

The aim of this paper is to describe a method for the determination of the valley and ridge of isobaric vapor–liquid equilibrium (VLE) for ternary systems which have a ternary azeotropic point at atmospheric and at lower pressure. The extended Redlich–Kister equation was employed as an activity coefficient for calculating the isobaric VLE, because this equation can be applied to the isobaric conditions provided by the Gibbs–Duhem equation, and to complete calculation of the ternary and binary azeotropes. It is possible by this method to determine the rigorous valley and ridge curves thermodynamically. In order to test the reliability of the proposed method, it has been applied to determine the valley and ridge for the system of acetone + chloroform + methanol, with a saddle point azeotrope at 101.3 kPa, and the details of the obtained curves are reported.