Calculating Mixture Critical Temperature and Pressure using Equation of State?

Aug 2018
1
0
Hello Everyone,
I am trying to calculate critical Temperature and Pressure of binary and ternary mixtures using equation of state. In particular, I am using Peng-Robinson Equation of State. I combined this with Van-der Waals critical criterion to get my result, but am way off experimental data.

Vander Waals criteria states: dP/dv = 0 and d2P/dv2=0

My steps:
1. I solve the two partial derivative equations mentioned above to end up with a cubic equation in 'v' (molar volume). Solving this I get the critical molar volume
2. I put this back in either of the partial derivative conditions and calculate Temperature using iteration.
3. Now I know Tc and Vc. I put these values back in the equation of state to get my pressure.

Problem:
My Tc values are still within range or close to experimental data but the Pc values are way off.

Attached Plot:
Attached plot is of a binary mixture of methane(C1) and propane(C3). Tc and Pc plots are attached vs mole fraction of C1
 

Attachments

Sep 2014
32
5
Brasília, DF - Brazil
Can you describe in more details what you did?