A new experimental system was designed to measure the solubility of CO 2 at pressures and temperatures (150 bar, 323.15-423.15 K) relevant to geologic CO 2 sequestration. At 150 bar, new CO 2 solubility data in the aqueous phase were obtained at 323.15, 373.15, and 423.15 K from 0 to 6 mol kg-1 NaCl(aq) for the CO 2-NaCl-H 2 O system. A ߛ െ ߮ (activity coefficientfugacity coefficient) type thermodynamic model is presented for the calculation of both the solubility of CO 2 in the aqueous phase and the solubility of H 2 O in the CO 2-rich phase for the CO 2-NaCl-H 2 O system. Validation of the model calculations against literature data and other models (MZLL2013, AD2010, SP2010, DS2006, and OLI) show that the proposed model is capable of predicting the solubility of CO 2 in the aqueous phase for the CO 2-H 2 O and CO 2-NaCl-H 2 O systems with a high degree of accuracy (AAD < 3.9%) at temperatures from 273.15 to 573.15 K and pressures up to 2000 bar. A comparison of modeling results with experimental values revealed a pressure-bounded "transition zone" in which the CO 2 solubility decreases to a minimum then increases as the temperature increases. CO 2 solubility is not a monotonic function of temperature in the transition zone but outside of that transition zone, the CO 2 solubility is decrease or increase monotonically in response to increased temperature. A link of web-based CO 2 solubility computational tool can be provided by sending a message to Haining Zhao at

CO2 solubility data in the natural formation brine, synthetic formation brine, and synthetic NaCl+CaCl2 brine were collected at the pressures from 100 to 200 bar, temperatures from 323 to 423 K. Experimental results demonstrate that the CO2 solubility in the synthetic formation brines can be reliably represented by that in the synthetic NaCl+CaCl2 brines. We extended our previously developed model (PSUCO2) to calculate CO2 solubility in aqueous mixed-salt solution by using the additivity rule of the Setschenow coefficients of the individual ions (Na(+), Ca(2+), Mg(2+), K(+), Cl(-), and SO4(2-)). Comparisons with previously published models against the experimental data reveal a clear improvement of the proposed PSUCO2 model. Additionally, the path of the maximum gradient of the CO2 solubility contours divides the P-T diagram into two distinct regions: in Region I, the CO2 solubility in the aqueous phase decreases monotonically in response to increased temperature; in region II, the behavior of the CO2 solubility is the opposite of that in Region I as the temperature increases.

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The phase equilibria of CO2 and aqueous electrolyte solutions are important to various chemical‐, petroleum‐, and environmental‐related technical applications. CO2 solubility in aqueous CaCl2, MgCl2, Na2SO4, and KCl solutions at a pressure of 15 MPa, the temperatures from 323 to 423 K, and the ionic strength from 1 to 6 mol kg−1 were measured. Based on the measured experimental CO2 solubility, the previous developed fugacity‐activity thermodynamic model for the CO2‐NaCl‐H2O system was extended to account for the effects of different salt species on CO2 solubility in aqueous solutions at temperatures up to 523 K, pressures up to 150 MPa, and salt concentrations up to saturation. Comparisons of different models against literature data reveal a clear improvement of the proposed PSUCO2 model in predicting CO2 solubility in aqueous salt solutions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2286–2297, 2015

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