Aspen Physical Property System - Physical Property Models

Where:
xca = Apparent mole fraction of electrolyte ca
Vca = Liquid molar volume for electrolyte ca
The mole fractions xca are reconstituted arbitrarily from the true ionic
concentrations, even if you use the apparent component approach. This
technique is explained in Electrolyte Calculation in Physical Property Methods.
The result is that electrolytes are generated from all possible combinations of
ions in solution. The following equation is consistently applied to determine
the amounts of each possible apparent electrolyte nca:
Where:
198 2 Thermodynamic Property Models
(3)
(4)
(5)
(6)
(7)
nca = Number of moles of apparent electrolyte ca
zc = Charge of c
zfactor = zc if c and a have the same number of
charges; otherwise 1.
nc = Number of moles of cation c
na = Number of moles of anion a
For example: given an aqueous solution of Ca 2+ , Na + , SO4 2- , Cl - four
electrolytes are found: CaCl2, Na2SO4, CaSO4, and NaCl. The Clarke
parameters of all four electrolytes are used. You can rely on the default,
which calculates the Clarke parameters from ionic parameters. Otherwise, you
must enter parameters for any electrolytes that may not exist in the
components list. If you do not want to use the default, the first step in using
the Clarke model is to add any needed components for electrolytes not in the
components list.
True Component Approach
The true molar volume is obtained from the apparent molar volume: