Isothermal vapour + liquid equilibrium measurements and correlation for the dimethyl ether + 1,1,1,2,3,3,3-heptafluoropropane and the propane + 1,1,1,2,3,3,3-heptafluoropropane systems

Isothermal vapour + liquid equilibria (VLE) data were measured for the dimethylether (RE170) + 1,1,1,2,3,3,3-heptafluoropropane (R227ea) and propane (R290) + R227ea systems at 278.15, 293.15 and 308.15 K, using a static analytical method. The phase compositions at equilibrium were measured by gas chromatography. The experimental estimated accuracies are ±0.02 K for temperature, ±1 kPa for pressure, and ±0.003 in mole fraction for both liquid and vapour phase composition. The R290 + R227ea system shows strong positive deviations from Raoult’s law, while the RE170 + R227ea system shows strong negative deviations. The deviations from Raoult’s law observed for the RE170 + R227ea system are attributed to hydrogen bonding. On the basis of the homomorphic concept, the excess Gibbs free energy (gE) of the H-bonding is estimated as the difference between the gE of corresponding homomorphic pairs of systems. The experimental data are firstly regressed with the Carnahan-Starling-De Santis (CSD) equation of state (EoS) together with the classical mixing rule, and then by means of the Redlich-Kwong-Soave (RKS) EoS, with the Huron-Vidal mixing rule (HV), using the NRTL equation for the gE at infinite pressure. Better results are achieved with the latter, and the gE of these two systems is calculated using the resulting coefficients. On the basis of the RKS-HV-NRTL model, a comparison with the available literature data is performed.