Aspen Physical Property System - Physical Property Models

The electrolyte NRTL model uses the infinite dilution aqueous solution as the
reference state for ions. It adopts the Born equation to account for the
transformation of the reference state of ions from the infinite dilution mixed
solvent solution to the infinite dilution aqueous solution.
Water must be present in the electrolyte system in order to compute the
transformation of the reference state of ions. Thus, it is necessary to
introduce a trace amount of water to use the model for nonaqueous
electrolyte systems.
The Aspen Physical Property System uses the electrolyte NRTL model to
calculate activity coefficients, enthalpies, and Gibbs energies for electrolyte
systems. Model development and working equations are provided in
Theoretical Basis and Working Equations.
The adjustable parameters for the electrolyte NRTL model include the:
� Pure component dielectric constant coefficient of nonaqueous solvents
� Born radius of ionic species
� NRTL parameters for molecule-molecule, molecule-electrolyte, and
electrolyte-electrolyte pairs
The pure component dielectric constant coefficients of nonaqueous solvents
and Born radius of ionic species are required only for mixed-solvent
electrolyte systems. The temperature dependency of the dielectric constant of
solvent B is:
Each type of electrolyte NRTL parameter consists of both the nonrandomness
factor, �, and energy parameters, �. The temperature dependency relations
of the electrolyte NRTL parameters are:
� Molecule-Molecule Binary Parameters:
� Electrolyte-Molecule Pair Parameters:
� Electrolyte-Electrolyte Pair Parameters:
For the electrolyte-electrolyte pair parameters, the two electrolytes must
share either one common cation or one common anion:
2 Thermodynamic Property Models 95