Gas-liquid critical temperatures of n-alkane + n-alkane mixtures

Abstract

The critical temperatures of n-pentane with a series of n-alkanes (C₈ to C₁₃) mixtures have been measured using the sealed capillary tube method. The results together with published data have been analyzed in terms of the segment concept previously used in the discussion of activity coefficients for n-alkane mixtures. The critical temperatures of the pure n-alkanes have been analyzed in terms of hypothetical critical temperatures corresponding to pure “end” and “middle” groups. The critical temperature of a mixture is thermodynamically different from that of a pure component and this has been allowed for by use of a treatment similar to that of Brown. The critical temperatures of the mixtures, corrected for this difference, have been predicted by assuming that the critical temperature of an equivalent (one-component) substance is the same as that of the hypothetical n-alkane with the same fraction of end groups.

Theoretical and experimental values have been compared for the present six systems and for twenty-one systems from the literature. The agreement between predicted and experimental data is good except for systems of n-alkanes of widely differing chain lengths. Hence the segment concept enables the critical temperatures of n-alkane mixtures to be predicted solely from a knowledge of the critical properties of the pure-n-alkanes.