Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

• Measurements are reported of the phase behavior of mixtures of CO2 and NaCl and KCl brines.
• Temperatures are from 323.15 K to 423.15 K and pressures are from 1.5 MPa to 18.0 MPa.
• Coexisting liquid-phase and vapor-phase compositions are reported.
• The data have been correlated by means of an asymmetric approach.
• The electrolyte-NRTL model was used for the liquid and the Peng–Robinson EoS was used for the vapor.

We report experimental measurements of the phase behavior of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg−1. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO2 in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO2 + H2O) the values of the Henry's law constant and the partial molar volume of CO2 at infinite dilution Hou et al. [22]. The activity coefficients of CO2 in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO2 in brines is tested against our liquid-phase data.

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