Phase equilibria, surface tensions and heat capacities of hydrofluorocarbons and their mixtures including the critical region

Hydrofluorocarbons (HFCs) have been used in the last years as common refrigerants, substituting the classical chlorinated compounds (CFCs and HCFCs), once it was shown that the latter ones are a major source of inorganic chlorine in the stratosphere and destroyers of the ozone layer. In this contribution, we present a thermodynamic characterization of fifteen HFCs using the extended soft-SAFT equation of state, including phase equilibria, interfacial tensions and heat capacities. A robust and transferable molecular model was developed for the description of the vapor-liquid equilibria of HFCs including the critical region and interfacial tensions. Interfacial properties were obtained by coupling the crossover soft-SAFT equation with the Density Gradient Theory of van der Waals, while near critical properties could be accurately obtained thanks to the use of a crossover term to take into account the fluctuations in the critical region. Correlations of the molecular parameters with the molecular weight of the compounds allowed predictions for new HFCs without the need of experimental data. Then, the behavior of binary mixtures of blends of refrigerants, commonly used for particular applications, was predicted with high accuracy by the theory when compared to available experimental data, without using binary data. Mixtures of refrigerants with alkanes and carbon dioxide were also investigated, showing the capabilities of the equation to capture the intermolecular interactions in these mixtures in a precise manner. The results obtained give confidence about the transferability of the model to other chemical families using the soft-SAFT equation, and provide a step towards modeling a new generation of refrigerants, such as hydrofluoroethers (HFEs). (C) 2010 Elsevier B.V. All rights reserved.