Aspen Physical Property System - Physical Property Models

R. W. Long, J. H. Hildebrand, and W. E. Morrell, "The Polymerization of
Gaseous Hydrogen and Deuterium Fluorides," J. Am. Chem. Soc., Vol. 65,
(1943), pp. 182–187.
C. E. Vanderzee and W. Wm. Rodenburg, "Gas Imperfections and
Thermodynamic Excess Properties of Gaseous Hydrogen Fluoride," J. Chem.
Thermodynamics, Vol. 2, (1970), pp. 461–478.
Peng-Robinson Alpha Functions
The pure component parameters for the Peng-Robinson equation-of-state are
calculated as follows:
These expressions are derived by applying the critical constraints to the
equation-of-state under these conditions:
The parameter � is a temperature function. It was originally introduced by
Soave in the Redlich-Kwong equation-of-state. This parameter improves the
correlation of the pure component vapor pressure.
Note: You can choose any of the alpha functions described here, but you
cannot define multiple property methods based on this model using different
alpha functions within the same run.
This approach was also adopted by Peng and Robinson:
Equation 3 is still represented. The parameter mi can be correlated with the
acentric factor:
Equations 1 through 5 are the standard Peng-Robinson formulation. The
Peng-Robinson alpha function is adequate for hydrocarbons and other
nonpolar compounds, but is not sufficiently accurate for polar compounds.
Note: Reduced temperature Tr is always calculated using absolute
temperature units.
Parameter Symbol Default MDS Lower Upper Units
Name/Element
Limit Limit
TCPR T ci TC X 5.0 2000.0 TEMPERATURE
PCPR p ci PC X 10 5
OMGPR � i
2 Thermodynamic Property Models 69
10 8
(1)
(2)
(3)
(4)
(5)
OMEGA X -0.5 2.0 —
PRESSURE