The Second Virial Coefficients of n-Alkanes and Their Mixtures from the Kihara Convex Core Intermolecular Pair Potential

Abstract

The second virial coefficients for a series of C2 to C8 n-alkanes and the second virial cross coefficients for their binary mixtures were calculated as a function of temperature from the exact expressions derived for the Kihara rod-like molecules. The three parameters of Kihara pair potential, ε/k, σ and l for the individual compounds were either used as determined from vapour-liquid equilibrium and saturated liquid density data in a previous study or with ε/k adjusted to the second virial coefficient data. The results are accurate almost within experimental uncertainty estimates of the data. In the case of mixtures the second virial cross coefficients were calculated from a similar expression in which only the ε12/k parameter was adjusted whereas σ12 = (σ1 + σ2)/2 and l1 and l2 of pure compounds were employed. It appears that the correction factor to the geometric mean combining rule for ε12/k is always less than and close to unity. Comparison with the values obtained from the Tsonopoulos generalized correlation reveals fair agreement between the characteristic binary k12 parameters from the two methods.