SAFT1-RPM Approximation Extended to Phase Equilibria and Densities of CO₂−H₂O and CO₂−H₂O−NaCl Systems

Abstract

In SAFT1-RPM approximations of CO2−H2O and CO2−H2O−NaCl systems, relevant to oil recovery and CO2 sequestration, CO2 is modeled as a molecule with three association sites, two sites of type O and one site of type C. H2O is modeled as a molecule with four association sites, two sites of type O and two sites of type H. The salt is modeled as a molecule composed of two charged, but nonassociating, spherical segments, of which one represents the cation and one represents the anion. For the CO2−H2O system, only one type of cross-association is assigned, i.e., between the site of type O in CO2 and the site of type H in H2O. Using temperature-dependent parameters, SAFT1-RPM is found to represent the density and equilibrium data for the CO2−H2O system, including the minimum H2O concentration in the CO2-rich phase in the y-P diagram. For the CO2−H2O−NaCl system, an additional binary interaction constant is used, the same for both CO2−Na+ and CO2−Cl- pairs, which is needed to correct the short-range interactions. SAFT1-RPM is also found to represent the equilibrium and density data for the CO2−H2O−NaCl system.