Aspen Physical Property System - Physical Property Models

Parameter Symbol No. of
Name
Elements
Dielectric Constant Unary Parameters
2 Thermodynamic Property Models 153
Default MDS Units
GMENCD D ca,m 1 0 x TEMPERATURE †
D m,ca 1 0 x TEMPERATURE †
GMENCE E ca,m 1 0 x —
GMENCN � ca,m = � m,ca
E m,ca 1 0 x —
Electrolyte-Electrolyte Pair Parameters
1 .2 x —
GMENCC C ca,c'a 1 0 x —
C c'a,ca 1 0 x —
C ca,ca' 1 0 x —
C ca',ca 1 0 x —
GMENCD D ca,c'a 1 0 x TEMPERATURE †
D c'a,ca 1 0 x TEMPERATURE †
D ca,ca' 1 0 x TEMPERATURE †
D ca',ca 1 0 x TEMPERATURE †
GMENCE E ca,c'a 1 0 x —
GMENCN � ca,c'a = � c'a,ca
E c'a,ca 1 0 x —
E ca,ca' 1 0 x —
E ca',ca 1 0 x —
� ca,ca' = � ca',ca
1 .2 x —
1 .2 x —
Zwitterions in Symmetric and Unsymmetric
Electrolyte NRTL
The Symmetric and Unsymmetric Electrolyte NRTL models support
zwitterions, compounds with both positive and negative charges but net
charge of zero. Zwitterions are defined as:
� Components of type Conventional, similar to solvents
� Parameter ZWITTER set to 1; all other components in the Aspen Physical
Property System default to zero for ZWITTER
� Parameter PLXANT/1 less than -1.0E10 so that they are non-volatile.
Zwitterions are handled as follows:
� A zwitterion interacts with other molecular species through NRTL
parameters only, excluding any interactions through Henry constants and
pair parameters.
� The activity coefficient is calculated as a solvent.
� The contribution from zwitterions to the solution enthalpy and Gibbs free
energy are calculated as solutes using the infinite dilution heat capacity
model CPAQ0, DGAQFM, and DHAQFM.