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

Abstract

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 ( g E) of the H-bonding is estimated as the difference between the g E 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 g E at infinite pressure. Better results are achieved with the latter, and the g E 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.