gSAFT application areas

Electrolytes

Electrolytes can be treated in a relatively straightforward manner in SAFT-VR by including the additional contributions due to the ionic interactions:

Water and other mixed solvents are modelled explicitly
Electrolyte thermodynamics are treated with the Debye-Hückel (DH) or Mean-Spherical Approximations (MSA)
Mixed salts can be handled easily
Parameters for non-ionic species are fully transferable, meaning that parameters determined for one molecule can be applied to other molecules within the same class.

Recent extensions mean that differences in dielectric properties of the coexisting phase can be taken into account, and that direct solvation of ions and ion pairing can also be treated.

The SAFT representation makes it possible to determine the effect of added salt on the properties of the solvent. 'Salting out' effects (e.g. of hydrocarbons from aqueous solutions by adding electrolyte) and the influence of salt on the overall fluid phase behaviour are also predicted.

The approach can be used to determine properties of aqueous solutions up to high molality.

General references

A. Galindo, A. Gil-Villegas, G. Jackson, and A. N. Burgess, SAFT-VRE: phase behavior of electrolyte solutions with the statistical associating fluid theory for potentials of variable range, Journal of Physical Chemistry B, 103, 10272-10281 (1999)

A. Galindo, A. Gil-Villegas, and G. Jackson,A statistical associating fluid theory for electrolyte solutions (SAFT-VRE), Molecular Physics, 99, 531-546 (2001).

Electrolytes – mixed salts

SAFT representation of ionic species in water

Example: Mixed salts

The predictive capability of the SAFT-VRE approach is shown below by comparison with experimental data for NaOH and an NaOH and NaCl mixture. Parameters are fully transferable for different electrolytes.

P. Paricaud, A. Galindo, and G. Jackson, Recent advances in the use of the SAFT approach in describing electrolytes, interfaces, liquid crystals, and polymers, Fluid Phase Equilibria, 194, 87-96 (2002).

Electrolytes – salting out

Study undertaken in conjunction with Schlumberger

Example: Salting out of methane from water by NaCl

The prediction of solubilities at very low concentration can be seen in the P–composition diagrams below.

Reference

Patel BH, Paricaud P, Galindo A, Maitland GC, Prediction of the salting-out effect of strong electrolytes on water plus alkane solutions. Ind. Eng. Chem. Res.,42, 3809-3823 (2003).