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

The prediction of the properties of mixtures containing n-alkanes is of great interest in the petroleum industry and consequently the critical properties of n-alkane+n-alkane mixtures have been investigated by many workers.Previously we used the segment concept to correlate the critical temperatures of n-alkanefnalkane mixtures using only the pure n-alkane critical temperatures.1We have also compared the critical temperatures of a range of quasi-spherical molecule mixtures with those predicted from the van der Waals theory.2-4There are several reasons for expecting that the agreement between the van der Waals treatment and experiment will be poor4 for mixtures containing n-alkanes.The component molecules are not, in general, even approximately spherical and the molecules do not obey the same principal of corresponding states.5However, in this paper it is shown that agreement is surprisingly good.Theory Elsewherez-4>6 it has been shown that for the van der Waals one-fluid model the critical temperature of a mixture T& is given by whereand r is the size ratio.Tij and Vij are the pseudo-critical parameters characterizing the interaction between i and j molecules.The approximations in the derivation of these equations have been discussed elsewhere.2-4~6