Aspen Physical Property System - Physical Property Models

other related to the local interactions that exist at the immediate
neighborhood of any central species.
The unsymmetric Pitzer-Debye-Hückel model and the Born equation are used
to represent the contribution of the long-range ion-ion interactions, and the
Non-Random Two Liquid (NRTL) theory is used to represent the local
interactions. The local interaction contribution model is developed as a
symmetric model, based on reference states of pure solvent and pure
completely dissociated liquid electrolyte. The model is then normalized by
infinite dilution activity coefficients in order to obtain an unsymmetric model.
This NRTL expression for the local interactions, the Pitzer-Debye-Hückel
expression, and the Born equation are added to give equation 1 for the
excess Gibbs energy (see the following note).
This leads to
Note: The notation using * to denote an unsymmetric reference state is wellaccepted
in electrolyte thermodynamics and will be maintained here. The
reader should be warned not to confuse it with the meaning of * in classical
thermodynamics according to IUPAC/ISO, referring to a pure component
property. In fact in the context of G or �, the asterisk as superscript is never
used to denote pure component property, so the risk of confusion is minimal.
For details on notation, see Chapter 1 of Physical Property Methods.
References
C.-C. Chen, H.I. Britt, J.F. Boston, and L.B. Evans, "Local Compositions Model
for Excess Gibbs Energy of Electrolyte Systems: Part I: Single Solvent, Single
Completely Dissociated Electrolyte Systems:, AIChE J., Vol. 28, No. 4, (1982),
p. 588-596.
C.-C. Chen, and L.B. Evans, "A Local Composition Model for the Excess Gibbs
Energy of Aqueous Electrolyte Systems," AIChE J., Vol. 32, No. 3, (1986), p.
444-459.
B. Mock, L.B. Evans, and C.-C. Chen, "Phase Equilibria in Multiple-Solvent
Electrolyte Systems: A New Thermodynamic Model," Proceedings of the 1984
Summer Computer Simulation Conference, p. 558.
B. Mock, L.B. Evans, and C.-C. Chen, "Thermodynamic Representation of
Phase Equilibria of Mixed-Solvent Electrolyte Systems," AIChE J., Vol. 32, No.
10, (1986), p. 1655-1664.
Long-Range Interaction Contribution
The Pitzer-Debye-Hückel formula, normalized to mole fractions of unity for
solvent and zero for electrolytes, is used to represent the long-range
interaction contribution.
98 2 Thermodynamic Property Models
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