Thermodynamic modeling of the vapor–liquid equilibrium of the CO2/H2O mixture

In order to evaluate the feasibility of CO2 sequestration in geological formations detailed knowledge of the mutual solubilities of the CO2/H2O system is required. In this work we employ three models, which all involve the well-known Peng–Robinson equation of state, to study the CO2/H2O phase equilibrium, with emphasis on the solubility of CO2 in the aqueous phase and the solubility of H2O in the CO2-rich phase. The considered models include the Peng–Robinson equation of state coupled with the conventional van der Waals one fluid mixing rules or the universal mixing rules, and the cubic-plus-association equation of state that uses the Peng–Robinson equation of state in order to account for the usual attractive and repulsive forces and an extra association term to account for the strong hydrogen bonding interactions. The required model parameters are calibrated using experimental data up to 1500 bar for pressure, and up to 673 K for temperature. To improve the accuracy of the proposed models we consider two temperature ranges. Temperatures lower than 373 K are of interest to the geological CO2 sequestration, while higher temperatures are of interest to fluid-inclusion studies. Good agreement is obtained between the experimental and the correlated solubilities.