Gas-Phase Fugacity Coefficients for Propylene

SRK

PR

vary P

comparison with Aspen Plus

pressure P

10

In the gas phase, deviation from ideal behavior is taken into account by introducing the fugacity coefficient

ϕ

. In this Demonstration,

ϕ

is defined for a pure species by

ln(ϕ)=

R

G

RT

,

where

R

G

is the residual Gibbs free energy,

T

is the temperature, and

R

is the universal gas-constant. As pressure approaches zero, the gas behaves like an ideal gas (i.e.

R

G

=G-

ig

G

=0

) and the fugacity coefficient approaches unity.

This Demonstration plots the gas-phase fugacity coefficient

ϕ

for the gas propylene versus temperature (in K) 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). At

P=10bar

we get excellent agreement between the results of our calculations (red curve for the SRK EoS, blue for the PR EoS) and the corresponding values obtained with the Aspen Plus process simulator [3] (green squares).