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

Total vapor pressures for liquid mixtures of xenon + ethane at 161.40 and 182.34 K and of xenon + propane at 161.40, 182.34, and 195.49 K have been measured. Both systems show negative deviations from Raoult's law at all temperatures. The corresponding excess molar Gibbs energies (G_m^E) have been calculated from the vapor pressure results. Liquid molar volumes have also 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 the xenon + ethane system have been determined directly using a batch calorimeter and found to be negative. Xenon + ethane is thus the simplest system which exhibits negative values for all three major excess molar functions. The results were interpreted using the statistical associating fluid theory for potentials of variable attractive 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 that the xenon + n-alkane mixtures obey Lorentz-Berthelot combining rules, so that no unlike interaction parameters are fitted to experimental mixture data. The theory is therefore totally predictive. It was also found that the parameters calculated for xenon using this model lie within the average values of the parameters obtained for the n-alkanes. This implies that, in contrast with the anomalous behavior of methane, xenon can be treated as the first member of the n-alkane family. Furthermore, the xenon + n-alkane mixtures can be thought as a particular case of mixtures of n-alkanes.