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 RE 170 + 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 g(E) of the H-bonding was estimated as the difference between the g(E) 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. (C) 2000 Elsevier Science B.V. All rights reserved.