Suppose the liquid phase consists of an equimolar mixture of compounds 1 and 2 at 350 K. Set up a system of equations that would allow you to calculate the pressure and composition of the vapor phase in equilibrium with this liquid at 350 K. You don’t need to solve the equations, but the number of equations and unknowns should be balanced such that they could be solved. You may assume the Margules parameters A12 and A21 are known even if you have no final answer to part A.

Question

A pair of compounds identified as 1 and 2 have the following properties:

This pair of compounds forms an azeotrope at 350 K and P = 8.5 bar, with x1 = y1 = 0.31.

Answer 1

We are looking to solve 2 equations and 2 unknowns (P, and y_2):





Where:

y_1=1-y_2

Everything in these equations is known except for the unknowns (P and y) that we are trying to find, the activity coefficients and the fugacity coefficients, as:



So we need to express the fugacity coefficients and the activity coefficients in terms of known information and/or the unknowns P and y.

Applying Equation 8.62 to the Virial EOS for pure 1 and 2 gives:



Applying equations 12.31 and 12.32:





With:



And applying equations 11.91 and 11.92: