Chapter 13, Problem 13.41P

Interpretation Introduction

Interpretation:

The conditions for the double azeotropy to exist.

Concept Introduction:

Margules equation for excess Gibbs energy in terms of the composition of the binary system in VLE is:

  $\frac{G^E}{RT}=\left(A_{12}{x}_1+A_{21}{x}_2\right)x_1{x}_2$   ...... (1)

Here, $A_{12}\text{ and }{A}_{21}$are the temperature dependent parameters, specific for a system.

Equation $13.57$to be used is:

  $P=x_1{\gamma }_1{P}_1^{\text{sat}}+x_2{\gamma }_2{P}_2^{\text{sat}}$   ...... (2)

Double azeotropy is an unusual low-pressure VLE behavior, in which the dew curve and the bubble curve are both S-shaped. This results in the minimum-pressure and maximum-pressure azeotrope at different compositions.