Aspen Physical Property System - Physical Property Models

2 Thermodynamic Property Models 163
(70)
(71)
where s is a solvent component in the mixture and Msis the solvent molecular
weight. Each sum is over all solvent components in the solution.
Born term correction
If the infinite dilution aqueous solution is chosen as the reference state, we
need to correct the the Debye-Hückel term for the change of the reference
state from the mixed-solvent composition to aqueous solution. The Born term
(Robinson and Stokes, 1970; Rashin and Honig, 1985) is used for this
purpose:
(72)
where NA is the Avogadro constant and R is the gas constant. is the
Born term correction to the unsymmetric Pitzer-Debye-Hückel formula,
, and �w is the dielectric constant of water, and ri is the Born radius
of species i.
The Born contribution to the activity coefficient of component i can be derived
as follows:
For a cation or anion component, this is:
(73)
The correction to the activity coefficient for a solvent component is zero:
(75)
Henry Components in the Symmetric and
Unsymmetric Electrolyte NRTL Models
(74)
Light gases (Henry components) are usually supercritical at the temperature
and pressure of the system. In that case, pure component vapor pressure is