Electrolyte thermodynamics
Aqueous (AQ) Model

OLI's basic electrolyte thermodynamic model - the AQ model - is based on a true speciation model, a predictive equation of state (Helgeson EOS), an activity coefficient model, and convergence heuristics. Combined with 38 years of R & D and a full-time staff of four thermophysical modelers, the OLI AQ model covers 80+ elements of the periodic table.

The model is based upon published experimental data. The model uses data regression wherever possible and estimation and extrapolation where required. This model provides general simulation capability giving accurate prediction for almost any water chemistry mixture over the range

Temperature: -50 to 300 C
Pressure: 0 to 1500 bar
Ionic strength: 0 to 30 molal

OLI's Thermodynamic Models

Mixed Solvent Electrolyte (MSE) Model

With the MSE model, OLI has removed the concentration limit. Where the AQ model is valid to a concentration limit of 30 molal ionic strength, The MSE model predicts electrolyte behavior from infinite dilution to molten salts.

The MSE model utilized all prior work on the Helgeson EOS and supporting databank through a conversion of the standard-state chemical potentials provided for aqueous systems. This means that the equilibrium constants and other standard state partial molal thermodynamic properties are readily predicted for mixed solvent environments.

The activity coefficient model is new and is based upon an extended Debye-Huckel term, a Uniquac term, and a middle-range electrolyte term.

Temperature: -50 to 90% of Tcrit of mixture
Pressure: 0 to 1500 bar
Ionic strength: no limit

Which model to use?

The AQ model is a good working model within its limits. It has 38 years of development and an extensive database to support it. OLI recommends the AQ model as your first choice.

However, if you are working with electrolytes that are highly miscible in water and that will form a second solvent, OLI recommends the MSE model. If your chemistry is not completely addressed in this model, OLI thermophysical modeling service can help.

More information

MSE 2010 Consortium info
Understanding Electrolytes pdf
Selected technical papers

OLI predictions: how accurate?

OLI's goal is to provide accurate and reliable electrolyte simulations. We do this through quality data regressions and fits over the range of interest for our clients' applications.

Actual data exists for many chemical systems of common industrial interest and, in most cases, we have utilized this data in building our databanks. Where data is limited or nonexistent, we rely on estimation techniques.

For high concentration multicomponent systems, particularly at high temperatures where estimation has been used, the predictions can reflect significant error.

If you have questions about the accuracy of simulations for your system, please send us your chemistry model and conditions of interest. We will evaluate the level of uncertainty that you can expect for your system.