(441a) Modeling of CO2 Solubility in Electrolyte Solutions and Brines Using Statistical Associating Fluid Theory

Understanding the behavior of CO₂, especially its solubility, in electrolyte solutions and brines is of great importance to the design of a CO₂ geologic sequestration project. Since the properties of CO₂ bearing electrolyte solutions are strongly affected by the long-rang Coulomb interactions of ions, an accurate description of ion-ion interactions is important to the modeling of CO₂-H₂O-electrolyte system. In this work, CO₂ solubilities in single and mixed electrolyte solutions as well as synthetic geologic formation brines were correlated or predicted with statistical associating fluid theory (SAFT). [1, 2] In the proposed SAFT equation of state, the ion-ion interactions were represented by an improved mean spherical approximation in the primitive model using a parameter K to correct the excess energies (â??KMSAâ? for short). [3] The universal correction factor K was obtained by adjusting the internal and excess energies of mean spherical approximation to Monte Carlo simulation data. With the SAFT-KMSA model, we studied a range of aqueous electrolyte solutions including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, Br^- and SO₄^2- from 298.15 K to 473.15 K. The cross interactions for CO₂-H₂O and CO₂-ion dispersion interactions were adjusted with binary interaction parameters k_ij, which were fitted to CO₂ solubility data in water and single electrolyte solutions. Without additional parameters to fit, the proposed model was conveniently extended to predict CO₂ solubilities in mixed electrolyte solutions, including NaCl+KCl, KCl+CaCl₂, NaCl+KCl+CaCl₂, and in synthetic geologic formation brines. The proposed model shows good predictive power for CO₂ solubility in mixed electrolyte solutions and brines.

[1] Jiang, H.; Panagiotopoulos, A. Z.; Economou, I. G. Geochim. Cosmochim. Acta. 2016, 176, 185.

[2] Tan, S. P.; Ji, X.; Adidharma, H.; Radosz, M. J. Phys. Chem. B. 2006, 110, 16694.

[3] Jiang, H.; Adidharma, H. Mol. Simul. 2015, 41, 727.