Aspen Physical Property System - Physical Property Models

This section provides theoretical background for the model. All model
equations and parameter requirements are included.
The Pitzer model is commonly used in the calculation of activity coefficients
for aqueous electrolytes up to 6 molal ionic strength. Do not use this model if
a non-aqueous solvent exists. Henry's law parameters are required for all
other components in the aqueous solution. The model development and
working equations are provided in the following sections. Parameter
conversion between the Pitzer notation and our notation is also provided.
The Pitzer model in the Aspen Physical Property System involves usersupplied
parameters that are used in the calculation of binary and ternary
parameters for the electrolyte system.
Five elements (P1 through P5) account for the temperature dependencies of
parameters � (0) , � (1) , � (2) , � (3) , C � , �, and �. These parameters follow the
temperature dependency relation:
Where:
T ref
The user must:
= 298.15 K
� Supply these elements for the binary parameters using a Properties |
Parameters | Binary | T-Dependent form.
� Supply these elements for � on the Properties | Parameters |
Electrolyte Ternary form.
� Specify Comp ID i and Comp ID j (and Comp ID k for �) on these forms,
using the same order that appears on the Components Specifications
Selection sheet.
The parameters are summarized in the following table. There is a Pitzer
parameter databank in the Aspen Physical Property System (see Physical
Property Data).
Parameter
Name
Provides
P1 - P5 for
Cation-Anion Parameters
136 2 Thermodynamic Property Models
No. of
Elements
Default MDS Units
GMPTB0 � (0) 5 0 x —
GMPTB1 � (1) 5 0 x —
GMPTB2 � (2) 5 0 x —
GMPTB3 � (3) 5 0 x —
GMPTC C � 5 0 x —
Cation-Cation Parameters
GMPTTH � cc'
Anion-Anion Parameters
GMPTTH � aa'
Ternary Parameters
5 0 x —
5 0 x —