Phase behavior of carbon dioxide mixtures with n-alkanes and n-perfluoroalkanes

The phase behavior of mixtures containing carbon dioxide, n-alkanes and n-perfluoroalkanes is studied using the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR). The molecules are modeled as fully flexible chains of tangentially bonded attractive spherical segments of hard-core diameter sigma. The attractive interactions are treated via square-well potentials of depth epsilon and range lambda. The pure component intermolecular parameters for carbon dioxide and the n-alkane molecules were determined in previous works by fitting to vapor pressures and saturated liquid densities; the same procedure is followed in this work to determine the parameters for the n-perfluoroalkane molecules. The optimized conformal parameters (sigma and epsilon) are resealed with the experimental critical point of each of the pure components. A set of transferable mixture parameters is presented, which provide a good description of the mixtures phase behavior, and additionally offer an insight into the higher solubility of n-perfluoroalkanes in carbon dioxide as compared to the solubility of n-alkanes.