A vapor–liquid phase equilibrium model for binary CO2–H2O and CH4–H2O systems above 523 K for application to fluid inclusions

Accurate prediction of both volumetric and vapor–liquid phase equilibria of binary CO2–H2O and CH4–H2O mixtures with a single equation of state proves to be difficult. In this study we use an activity–fugacity model to predict the vapor–liquid phase equilibria above 523 K and adapt a Helmoholtz model to calculate volumetric properties of these two binary systems. The average deviations of water content in the vapor phase from experimental data are 3.25% and 3.19% for the CO2–H2O and CH4–H2O mixtures, respectively, and the average deviations of gas solubility in liquid phase from experimental data are 4.29% and 3.50%, respectively. The model can find wide applications, and an example is given for the analysis of fluid inclusions in geochemistry.