High-pressure vapor-liquid equilibrium of binary systems with R236fa

Within the European Union Joule project aimed at the substitution of R114 in high temperature heat pumps with chlorine-free, environmentally benign fluids, R236fa has been chosen as one of the components of mixtures to consider as alternative fluids for R114 (1,2-dichlorotetrafluoroethane). The results of VLE measurements performed at our laboratory on mixtures including R236fa are summarized and discussed for the systems R600a (isobutane) + R236fa (1, 1,1,3,3,3-hexafluoropropane) at 303 K, RE170 (dimethyl ether) + R236fa at 303 and 323 K, R134a (1,1,1,2-tetrafluorethane) + R236fa at 283 and 303 K, R32 (difluoromethane) + R236fa and R125 (pentafluoroethane) + R236fa, both at 303 and 323 K. All data were correlated by means of the CSD EOS. Generally small deviations between experimental and calculated vapor compositions confirm the thermodynamic consistency of the experimental results and the model used for data reduction. An extensive discussion of the deviations from Raoult's law is performed through analysis of the excess Gibbs energy. All systems formed by HFCs show a very small g(E), with small deviation from Raoult's law. A much higher gE is shown by the systems R600a + R236fa, with a positive deviation from Raoult's law, and RE170 + R236fa, with a negative deviation clearly coming from the hydrogen bonding.