(191ae) Equation of State for Brine Systems with CO2

In this work, we develop an equation of state to describe thermodynamic properties and phase behavior of brine systems. The main motivation in our work is the need for practical applications in improved oil recovery and CO2 sequestration in saline aquifers. Brine and electrolytes are also present in most biological systems.

In this work the non-ionic interactions are described accurately by a cubic-plus-association equation of state that was proposed recently (Li and Firoozabadi, AIChE J., 2009). In that work the cross association between water and CO2 molecules showed to be of high importance in advancing the predictive capability of our proposal. In this work the ionic interactions are modeled based on the screened primitive model which can be decomposed into two terms. The charge-charge interactions between ions are described by using the mean-spherical approximation with consideration of the solvation effect of solvent molecules. The charge-dipole interactions between an ion and H2O and charge-quadrupole interactions between an ion and CO2 are described by the thermodynamic perturbation theory. With ion-specific parameters, our proposed equation of state represents solubility data, saturation pressure, liquid density, mean ionic activity coefficients, osmotic coefficients, and phase behavior.