Aspen Physical Property System - Physical Property Models

Ionic components with symmetric reference state
Applying Eq. 10, the symmetric activity coefficients for ionic components from
the long range contribution are given as follows:
where I applies to all molecular components in the solution.
126 2 Thermodynamic Property Models
(54)
(55)
(56)
Ionic components with infinite dilution aqueous solution
Applying Eq. 12, the unsymmetric activity coefficients for ionic components
from the long range contribution in aqueous solutions are given as follows:
Segment based Born correction term to activity coefficient
(57)
(58)
If the infinite dilution aqueous solution is chosen as the reference state, we
need to correct the change of the reference state from the mixed-solvent
composition to aqueous solution for the Debye-Hückel term. The Born term
(Robinson and Stokes, 1970; Rashin and Honig, 1985) is used for this
purpose:
where ri is the Born radius of segment species i and �w is the dielectric
constant of water. �G Born is the Born term correction to the unsymmetric
Pitzer-Debye-Hückel formula G ex,PDH .
The Born correction activity coefficient of component i can be derived as
follows:
(60)
For a molecular segment, the correction to the activity coefficient is zero:
(61)
For the univalent cation or anion segment, the activity coefficient can be
carried out as follows:
(59)