Unusual critical temperature phenomena in fluid mixtures containing perfluorotributylamine

Abstract

Abstract Sadus, R.J., 1992. Unusual critical temperature phenomena in fluid mixtures containing perfluorotributylamine. Fluid Phase Equilibria , 77: 269-283. The critical temperatures of binary mixtures containing perfluorotributylamine and a hydrocarbon are calculated and compared with experimental data. Systems containing low molecular weight hydrocarbons exhibit a positive deviation from linearity whereas a temperature minimum is reported for mixtures containing a higher molecular weight alkane. Between these extremes some mixtures display both a temperature minimum and a positive deviation. Theory can qualitatively reproduce this phenomenon. The calculations using an optimized value of the combining rule adjustable parameter (ξ) yield good results whereas calculations with the van der Waals prescription (ξ = 1) do not predict the behaviour. Better results are obtained using a theoretical alternative to mixture prescriptions for the attractive equation of state parameter. The critical temperatures of some ternary perfluorotributyl-amine + hydrocarbon mixtures are also reported. The anomalous behaviour is also observed in the ternary systems. The critical conditions for a ternary mixture are solved. The comparison between theory and experiment indicates that the temperature minimum of these ternary mixtures can be predicted but a positive deviation is not observed.