Second and third interaction virial coefficients of the (methane plus propane) system determined from the speed of sound

The speed of sound has been measured in the binary gaseous mixture (0.85CH(4) + 0.15C(3)H(8)) along seven isotherms at temperatures between 225 and 375 K and at pressures up to 1.4 MPa. From the measurements, second and third acoustic virial coefficients of the mixture were obtained. These results were analyzed together with values of the second and third acoustic virial coefficients of the two pure components to obtain a set of model intermolecular potential-energy functions for the methane-propane system. Nonpairwise additivity of the intermolecular forces was included in this analysis. Ordinary second and third interaction virial coefficients calculated from the model are reported, as are the second and third virial coefficients of the pure components. Gas densities calculated by means of these virial coefficients for the mixture (0.9298CH(4) + 0.0702C(3)H(8)) were found to agree with experimental values at temperatures between 280 and 330 K to within 0.02% at pressures up to 3 MPa and to within 0.08% at 4MPa.