Aspen Physical Property System - Physical Property Models

References for Symmetric and Unsymmetric
Electrolyte NRTL
C.-C. Chen and L.B. Evans, "A Local Composition Model for the Excess Gibbs
Energy of Aqueous Electrolyte Systems," AIChE Journal, 1986, 32, 444.
Y. Song and C.-C. Chen, "Symmetric Nonrandom Two-Liquid Activity
Coefficient Model for Electrolytes" (to be published).
K.S. Pitzer, "Electrolytes. From Dilute Solutions to Fused Salts," J. Am. Chem.
Soc., 1980, 102, 2902-2906.
K.S. Pitzer and J.M. Simonson, "Thermodynamics of Multicomponent, Miscible,
Ionic Systems: Theory and Equations," J. Phys. Chem., 1986, 90, 3005-3009.
R.A. Robinson and R.H. Stokes, Electrolyte Solutions, Second Revised Edition.
Butterworths: London, 1970.
A.A. Rashin and B. Honig, "Reevaluation of the Born Model of Ion Hydration,"
J. Phys. Chem., 1985, 89 (26), pp 5588–5593.
UNIFAC Activity Coefficient Model
The UNIFAC model calculates liquid activity coefficients for the following
property methods: UNIFAC, UNIF-HOC, and UNIF-LL. Because the UNIFAC
model is a group-contribution model, it is predictive. All published group
parameters and group binary parameters are stored in the Aspen Physical
Property System.
The equation for the original UNIFAC liquid activity coefficient model is made
up of a combinatorial and residual term:
ln � = ln �i c + ln �i r
ln �i c =
Where the molecular volume and surface fractions are:
and
Where nc is the number of components in the mixture. The coordination
number z is set to 10. The parameters ri and qi are calculated from the group
volume and area parameters:
and
Where �ki is the number of groups of type k in molecule i, and ng is the
number of groups in the mixture.
The residual term is:
172 2 Thermodynamic Property Models