Modeling of CO₂ solubility in single and mixed electrolyte solutions using statistical associating fluid theory

Statistical associating fluid theory (SAFT) is used to model CO₂ solubilities in single and mixed electrolyte solutions. The proposed SAFT model implements an improved mean spherical approximation in the primitive model to represent the electrostatic interactions between ions, using a parameter K to correct the excess energies ("KMSA" for short). With the KMSA formalism, the proposed model is able to describe accurately mean ionic activity coefficients and liquid densities of electrolyte solutions including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, Br^- and SO₄^2- from 298.15K to 473.15K using mostly temperature independent parameters, with sole exception being the volume of anions. CO₂ is modeled as a non-associating molecule, and temperature-dependent CO₂-H₂O and CO₂-ion cross interactions are used to obtain CO₂ solubilities in H₂O and in single ion electrolyte solutions. Without any additional fitting parameters, CO₂ solubilities in mixed electrolyte solutions and synthetic brines are predicted, in good agreement with experimental measurements.