Correlation for the Carbon Dioxide and Water Mixture Based on The Lemmon–Jacobsen Mixture Model and the Peng–Robinson Equation of State

Models representing the thermodynamic behavior of the CO2-H2O mixture have been developed. The single-phase model is based upon the thermodynamic property mixture model proposed by Lemmon and Jacobsen. The model represents the single-phase vapor states over the temperature range of 323-1074 K, up to a pressure of 100 MPa over the entire composition range. The experimental data used to develop these formulations include pressure-density-temperature-composition, second virial coefficients, and excess enthalpy. A nonlinear regression algorithm was used to determine the various adjustable parameters of the model. The model can be used to compute density values of the mixture to within +/-0.1%. Due to a lack of single-phase liquid data for the mixture, the Peng-Robinson equation of state (PREOS) was used to predict the vapor-liquid equilibrium (VLE) properties of the mixture. Comparisons of values computed from the Peng-Robinson VLE predictions using standard binary interaction parameters to experimental data are presented to verify the accuracy of this calculation. The VLE calculation is shown to be accurate to within +/-3 K in temperature over a temperature range of 323-624 K up to 20 MPa. The accuracy from 20 to 100 MPa is +/-3 K up to +/-30 K in temperature, being worse for higher pressures. Bubble-point mole fractions can be determined within +/-0.05 for CO2.