Thermodynamics of mixtures from gas chromatography. The activity coefficients of hydrocarbon solutions and the second virial coefficients of hydrocarbon vapour and permanent gas mixtures

Abstract

This paper reports work designed to establish the reliability of the gas chromatographic method for the determination of the mixed second virial coefficients B₁₂ of mixtures of hydrocarbon vapours and permanent gases, and of activity coefficients γ^∞₁ at infinite dilution in hydrocarbon liquid mixtures. This work confirms for eight carrier gases that, except for CO and methane, the activity coefficients are independent of carrier gas employed to within about ±0.003 in log₁₀γ. The values of B₁₂, determined with three stationary phases, agree to within about ± 10 cm³ mole^–1; in five cases comparison was possible with values of B₁₂ obtained by independent experimental methods and agreement within the above limits was found.

The B₁₂ values determined in this and earlier work are correlated using the principle of corresponding states. The Hudson and McCoubrey rule for the estimation of the mixed critical temperature gives values of B₁₂ in closer agreement with experiment than the geometric mean rule. The former procedure gives excellent agreement over a wide range of temperature for the system benzene + N₂, but predicts values which are somewhat too high for longer chain n-alkanes. The activity coefficients at infinite dilution have been used to evaluate the interaction parameter χ of the Flory-Huggins theory : values of χ for aliphatic + aliphatic, aromatic + aromatic and aliphatic + aromatic systems are compared.