Thermodynamics of liquid mixtures of xenon with alkanes: (xenon plus ethane) and (xenon plus propane)

Total vapor pressures for liquid mixtures of xenon + ethane at 161.40 and 1 82.34 K. and of xenon + propane at 161.40, 182.34, and 195.49 K have been m easured. Both systems show negative deviations from Raoult's law at all tem peratures. The corresponding excess molar Gibbs energies (G(m)(E)) have bee n calculated from the vapor pressure results. Liquid molar volumes have als o been measured for both mixtures at 161.40 K, leading to calculated excess molar volumes (V-m(E)) which are negative in all cases. Additionally, the excess molar enthalpies (H-m(E)) for th, xenon + ethane system have been de termined directly using a batch calorimeter and found to be negative. Xenon + ethane is thus the simplest system which exhibits negative values for al l three major excess molar functions. The results were interpreted using th e statistical associating fluid theory for potentials of variable attractiv e range (SAFT-VR). The theory is able to predict the phase behavior of both systems in close agreement with the experimental results. It was found tha t the xenon + n-alkane mixtures obey Lorentz-Berthelot combining rules, so that no unlike interaction parameters are fitted to experimental mixture da ta. The theory is therefore totally predictive. It was also found that the parameters calculated for xenon using this model lie within the average val ues of the parameters obtained for the n-alkanes. This implies that, in con trast with the anomalous behavior of methane, xenon can be treated as the f irst member of the n-alkane family. Furthermore, the xenon + n-alkane mixtu res can be thought as a particular case of mixtures of n-alkanes.