Prediction of vapor–liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part II: Application to H2O–NaCl and CO2–H2O–NaCl System

Abstract

The SAFT-LJ equation of state improved by Sun and Dubessy (2010) can represent the vapor–liquid equilibrium and PVTx properties of the CO2–H2O system over a wide P–T range because it accounts for the energetic contribution of the main types of molecular interactions in terms of reliable molecular based models. Assuming that NaCl fully dissociates into individual ions (spherical Na+ and Cl−) in water and adopting the restricted primitive model of mean spherical approximation to account for the energetic contribution due to long-range electrostatic forces between ions, this study extends the improved SAFT-LJ EOS to the H2O–NaCl and the CO2–H2O–NaCl systems at temperatures below 573K. The EOS parameters for the interactions between ion and ion and between ion and water were determined from the mean ionic activity coefficient data and the density data of the H2O–NaCl system. The parameters for the interactions between ion and CO2 were evaluated from CO2 solubility data of the CO2–H2O–NaCl system. Comparison with the experimental data shows that this model can predict the mean ionic activity coefficient, osmotic coefficient, saturation pressure, and density of aqueous NaCl solution and can predict the vapor–liquid equilibrium and PVTx properties of the CO2–H2O–NaCl system over the range from 273 to 573K, from 0 to 1000bar, and from 0 to 6mol/kg NaCl with high accuracy.