Interfacial tensions of systems comprising water, carbon dioxide and diluent gases at high pressures: Experimental measurements and modelling with SAFT-VR Mie and square-gradient theory

The parameters in the SAFT-VR Mie equation of state are estimated entirely from phase-equilibrium data for the pure components and binary mixtures. For pure water, the SGT influence parameter is determined from vapour-liquid surface-tension data, as is common practice. Since the other components are supercritical over most or the entire temperature range under consideration, their pure-component influence parameters are regressed by comparison with the binary interfacial-tension data. A geometric-mean combining rule is used for the unlike influence parameter in mixtures without incorporation of adjustable binary parameters. The SAFT-VR Mie + SGT approach is found to provide an excellent correlation of the surface tension of water and of the interfacial tensions of the binary systems comprising H2O with CO2 or Ar or N2. When applied to predict the interfacial tensions of the two ternary systems, generally good results are found for (H2O + CO2 + N2) while, for (H2O + CO2 + Ar), the theory performs well at high temperatures but significant deviations are found at low temperatures. Overall, the SAFT-VR Mie + SGT approach can be recommended as a means of modelling the interfacial properties of systems comprising water, carbon dioxide and diluent gases.