We report new interfacial tension (IFT) measurements of the (H2O + CO2 + H2) and (H2O + H2) systems at pressures of (0.5 to 45) MPa, and temperatures of (298.15 to 448.15) K, measured by the pendant-drop method. The expanded uncertainties at 95 % confidence are 0.05 K for temperature, 70 kPa for pressure, 0.017•γ for IFT in the both the binary (H2O + H2) system and the ternary (CO2 + H2 + H2O) system. Generally, the IFT was found to decrease with both increasing pressure and increasing temperature. However, for (H2O + H2) at the lowest two temperatures investigated, the isothermal IFT data were found to exhibit a maximum as a function of pressure at low pressures before declining with increasing pressure. An empirical correlation has been developed for the IFT of the (H2O + H2) system in the full range of conditions investigated, with an average absolute deviation of 0.16 mN•m -1 , and this is used to facilitate a comparison with literature values. Estimates of the IFT of the (H2O + CO2 + H2) ternary system, by an empirical combining rule based on the coexisting phase compositions and the interfacial tensions of the binary systems, were found to be unsuitable at low temperatures, with an average absolute deviation of 3.6 mN•m -1 over all the conditions investigated.

Interfacial tension measurements of the (CO2 + N2 + H2O) and (N2 + H2O) systems are reported at pressures of (2 to 40) MPa, and temperatures of (298.15 to 448.15) K. The pendant drop method was used in which it is necessary to know the density difference between the two phases. To permit calculation of this difference, the compositions of the coexisiting phases were first computed from a combination of the Peng-Robinson equation of state (applied to the non-aqueous phase) and the NRTL model (applied to the aqueous phase). Densities of the non-aqueous phase were computed from the GERG-2008 equation of state, while those of the aqueous phase were calculated knowing the partial molar volumes of the solutes. The expanded uncertainties at 95% confidence are 0.05 K for temperature, 0.07 MPa for pressure, 0.019·γ for interfacial tension in the binary (N2 + H2O) system; and 0.032γ for interfacial tension in the ternary (CO2 + N2 + H2O) system. The interfacial tensions in both systems were found to decrease with both increasing pressure and increasing temperature. An empirical correlation has been developed for the interfacial tension of the (N2 + H2O) system in the full range of conditions investigated, with an average absolute deviation of 0.20 mN·m -1 , and this is used to facilitate a comparison with literature values. Estimates of the interfacial tension for the (CO2 + N2 + H2O) ternary system, by means of empirical combining rules based on the coexisting phase compositions and the interfacial tensions of the binary sub-systems, (N2 + H2O) and (CO2 + H2O), were found to be somewhat inadequate at low temperatures, with an average absolute deviation of 1.9 mN·m -1 for all the conditions investigated. To enable this analysis, selected literature data for the interfacial tensions of the (CO2 + H2O) binary system have been re-analysed, allowing for improved estimates of the density difference between the two phases. The revised result on eleven isotherms were fitted with empirical models that generally represent the data to within 1 mN·m -1 .

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Column headings in Table 4 were misplaced and the values of coefficients a1 and a3 in Table 5 were incorrect. The corrected tables are given below.

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