Gas-Phase Fugacity Coefficients for Propylene

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In the gas phase, deviation from ideal behavior is taken into account by introducing the fugacity coefficient . In this Demonstration, is defined for a pure species by



where is the residual Gibbs free energy, is the temperature, and is the universal gas-constant. As pressure approaches zero, the gas behaves like an ideal gas (i.e. ) and the fugacity coefficient approaches unity.

This Demonstration plots the gas-phase fugacity coefficient 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 (in bar). At 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).


Contributed by: Housam Binous and Ahmed Bellagi (December 2016)
Open content licensed under CC BY-NC-SA




[1] J. M. Smith, H. C. Van Ness, and M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th ed., Boston: McGraw-Hill, 2005.

[2] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, 2nd ed., Englewood Cliffs, NJ: Prentice Hall International Editions, 2012.

[3] Aspentech. "Aspen Plus." (Dec 16, 2016)

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