The Ñuid phase behaviour of binary mixtures of xenon and the lighter perÑuoro-n-alkanes, and and CF 4 C 2 F 6 , of propane and sulfur hexaÑuoride has been examined using the statistical associating Ñuid theory for (SF 6) potentials of variable attractive range (SAFT-VR). We found that the binary interaction parameters calculated in previous work for (n-alkane ] perÑuoro-n-alkane) systems and for can be used to predict the (Xe ] SF 6), existing phase diagrams of (Xe ] perÑuoro-n-alkane) and mixtures, respectively. These results (propane ] SF 6 ) are consistent with the view that mixtures of (xenon ] perÑuorinated-compound) can be regarded as a special case of mixtures of (n-alkane ] perÑuorinated-compound) and provide another example of the "" alkane-like ÏÏ behaviour of xenon previously reported.

A new apparatus for the study of vapor-liquid or vapor-liquid-liquid equilibrium has been assembled. The apparatus, based on a static and analytical method, can perform measurements at temperatures from 185 to 320 K and pressures up to 8 MPa. The equilibrium vapor pressures of (xenon + methane) binary mixtures have been measured at seven temperatures, from 189.78 to 273.18 K, and at pressures up to 6.8 MPa. The mixture critical line has been estimated and found to be continuous between the critical points of the pure components. The system is found to display type I behavior in the classification scheme of Scott and van Konynenburg. The results have been correlated by the Peng-Robinson equation of state and a more rigorous theoretical study performed with the statistical associating fluid theory for potentials of variable range (SAFT-VR).

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Using the statistical association fluid theory−hard spheres (SAFT-HS) equation of state for chain molecules and its recent extension to ring molecules, phase diagrams for model mixtures of types (m 1-sphere chain + m 2-sphere chain) and (m 1-sphere chain + m 2-sphere ring) have been calculated. The influence of chain length, relative sphere size, relative mean-field attraction, and reduced temperature has been investigated. In a first ever application of the SAFT-HS model to cyclic molecules, the theoretical predictions have been compared with experimental data for a variety of systems involving both chain and cyclic molecules. The experimental results confirm the predictions of the theory for the effect of a cyclic molecular structure on the phase behavior of binary mixtures.