The equivalent conductance at infinite dilution, Λ°, is a fundamental property of an aqueous electrolyte that is directly proportional to diffusion coefficients. Previous work on determination of Λ° over a wide range of temperature and pressure, from room temperature and 0.101 MPa to 800°C and about 500 MPa, has shown that Λ° is well described by a simple function of viscosity and density. Using a new extrapolation of transference number data of NaCl and KCl, fits for the equivalent conductance of ions were found, using the additive property of Λ° for salts, where Λ°= λ++λ-. The resulting ionic λ° were then regressed to the equation: λ°= b η(a+c/ρ) where η is the solvent viscosity, ρ is the solvent density, and a, b, and c are fitting parameters for each ion for which there was available data. An attempt was then made to correlate the parameters to room temperature physical properties of the ions, such as partial molar entropy, partial molar volume, and λ° itself. It was found that the best correlating quantity was λ°. Using linear fits of the parameters along with known λ° at 25°C and 0.1 MPa for ions for which there is no high temperature data, the three parameters required to predict λ° at high temperatures and pressures were calculated. It is believed that these parameter estimates will yield λ° accurate to 20 percent to temperatures up to 873 K and solvent densities between than 0.5 and 1.0 g/cm3.

Determination and prediction of infinite dilution equivalent conductivities for ions in water at high temperatures and pressures

249th National Meeting (2015)

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