Example 05.03 Activity Coefficients from Experimental xyPT-Data

problem:

Calculate the activity coefficients for the system ethanol (1) - water (2) at theta = 70 °C from experimental VLE data at a given composition.

general

constants

and

definitions:

input data

Liquid and vapor mole fractions, temperature, pressure

Vapor pressure of the pure components

Liquid molar volume

Virial coefficients at theta = 70°C

Solution a) neglecting the real vapor phase behavior and the Poynting correction

Solution b) taking into account the real vapor phase behavior using the Virial

equation and using the Poynting correction

The second virial coefficient of the mixture is calculated by:

Calculation of the fugacity coefficients of the components in the mixture:

Calculation of the fugacity coefficients of the pure components in the saturated state:

Calculation of the Poynting factor:

Calculation of the activity coefficients

In this low pressure case, the real vapor phase behavior and the Poynting correction are not very important. Things become different if higher pressures are involved.