Isothermal vapor–liquid equilibrium for the three binary systems 1,1,1,2,3,3-hexafluoropropane with dimethyl ether or propane, and 1,1,1,3,3,3-hexafluoropropane with dimethyl ether

Isothermal vapor–liquid equilibria (VLE) were measured for mixtures of dimethyl ether (RE170) or propane (R290) with 1,1,1,2,3,3-hexafluoropropane (R236ea) or 1,1,1,3,3,3-hexafluoropropane (R236fa), using a recirculation apparatus in which the vapor is forced through the liquid. The phase composition at equilibrium was measured by gas chromatography. The experimental data were regressed with the Carnahan–Starling–De Santis (CSD) equation of state (EOS). A good data fit was achieved and the excess Gibbs energy was calculated using the resulting coefficients. The R290+HFC systems (where HFC, in this case, is one of the isomers of hexafluoropropane) show strong positive deviations from Raoult’s law, whereas the RE170+HFC system shows strong negative deviations. The deviations from Raoult’s law observed for the RE170+HFC systems are attributed to hydrogen bonding and, on the basis of the homomorph concept, the gE of the H-bonding was estimated as the difference between the gE of respective pairs of systems. The behavior of the two HFC isomers is compared in mixtures with the non-polar R290 and the proton acceptor RE170.