Aspen Physical Property System - Physical Property Models

Therefore, the simplified Pitzer equation has two types of binary interaction
parameters, � 's and �''s. There are no ternary interaction parameters with
the simplified Pitzer equation.
Note that the Pitzer model parameter databank described in Physical Property
Data, Chapter 1, is not applicable to the simplified Pitzer equation.
A built-in empirical correlation estimates the � (0) and � (1) parameters for
cation-anion pairs from the Bromley ionic parameters, �ion and �ion (Bromley,
1973). The estimated values of � (0) 's and � (1) 's are overridden by the user's
input. For parameter naming and requirements, see Bromley-Pitzer Activity
Coefficient Model.
References
L.A. Bromley, "Thermodynamic Properties of Strong Electrolytes in Aqueous
Solution, " AIChE J., Vol. 19, No. 2, (1973), pp. 313 – 320.
W. Fürst and H. Renon, "Effects of the Various Parameters in the Application
of Pitzer's Model to Solid-Liquid Equilibrium. Preliminary Study for Strong 1-1
Electrolytes," Ind. Eng. Chem. Process Des. Dev., Vol. 21, No. 3, (1982),
pp. 396-400.
Parameter Conversion
For n-m electrolytes, n and m>1 (2-2, 2-3, 3-4, and so on), the parameter
� (3) corresponds to Pitzer's � (1) ; � (2) is the same in both Aspen Physical
Property System and original Pitzer models. Pitzer refers to the n-m
electrolyte parameters as � (1) , � (2) , � (0) . � (0) and � (2) retain their meanings in
both models, but Pitzer's � (1) is Aspen Physical Property System � (3). Be
careful to make this distinction when entering n-m electrolyte parameters.
Chien-Null
The Chien-Null model calculates liquid activity coefficients and it can be used
for highly non-ideal systems. The generalized expression used in its derivation
can be adapted to represent other well known formalisms for the activity
coefficient by properly defining its binary terms. This characteristic allows the
model the use of already available binary parameters regressed for those
other liquid activity models with thermodynamic consistency.
The equation for the Chien-Null liquid activity coeficient is:
Where:
Rji = Aji / Aij
Aii = 0
2 Thermodynamic Property Models 89