Determination of the interaction second virial coefficients for the carbon dioxide-ethane system from refractive index measurements

The compressibility behavior of the CO₂-C₂H₆ system was investigated experimentally. In this work, the refractive indexes of the pure gases and the mixtures were measured using an optical apparatus. On the basis of these data, density and compressibility factors were computed using the Lorentz-Lorenz law. For the pure components, carbon dioxide and ethane, the data from the optical system were slightly adjusted by a fit to Burnett apparatus data measured separately. The experiments produced very accurate virial coefficients and refraction virial coefficients. This paper reports on the effect of temperature on the second and third virial coefficients. For the first refraction virial coefficient, no influence of temperature was found with the equipment used. The interaction second virial coefficient B₁₂ (as a function of temperature) was computed from experimental data for the CO₂-C₂H₆ binary system. The data, for which an accuracy of ±1.5 cm³ · mol^–1 was estimated, are in agreement with the data published by Holste et al.