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WOLFRAM|DEMONSTRATIONS PROJECT

Residual Functions for the SRK and PR Equations of State

​
SRK
PR
residual property
enthalpy
entropy
Gibbs free energy
vary P
comparison with Aspen Plus
pressure P
10
300
350
400
450
500
-1500
-1000
-500
0
temperature (K)
residual enthalpy (J/mol)

In the gas phase, deviation from ideal behavior is taken into account by introducing residual functions, of the form
M
R
=M-M
ig
. As pressure approaches zero, the gas behaves like an ideal gas, so that
M
R
=M-M
ig
→0
.

This Demonstration plots the gas-phase residual properties for the gas propylene versus temperature (in Kelvin) using either the Soave–Redlich–Kwong (SRK) or the Peng–Robinson (PR) equation of state (EoS) [1, 2]. Use the slider to set the value of the pressure
P
(in bar) and choose among three thermodynamic properties:
H
(enthalpy in J/mol),
S
(entropy in J/mol.K) or
G
(Gibbs free energy in J/mol). At
P=10bar
, we get an excellent agreement between the results of our calculations (red curve for the SRK EoS, blue for PR EoS) and their counterparts obtained with the Aspen Plus process simulator [3] (green squares).