Phase equilibrium modeling for carbon dioxide Capture and Storage (CCS) fluids in brine using an electrolyte association equation of state

A modified electrolyte cubic plus association equation of state (eCPA EoS) is proposed here as a suitable model for CO2 Capture and Storage (CCS) fluids to model CO2, CH4, H2S, N2, O2, Ar, and air solubility in multi-component brines containing NaCl, KCl, CaCl2, MgCl2, and Na2SO4. A new correlation of the g-factor of water as a function of temperature is presented to accurately calculate the dielectric properties of pure water with CPA EoS and a new formula related to ions associated with polar molecules is presented to describe the mixed solvents containing salts by neglecting ion–solvent association, which avoid the computational complexity of hydrogen bond formation. The performance of the modified eCPA model is improved for modeling the gas–water system by considering the cross association between H2S/CO2 and water. The modified eCPA model can accurately calculate the gas solubility in brine and water content in gas phase for water-salt-gas systems.