Investigation of vapor-liquid equilibria for supercritical carbon dioxide and hydrocarbon mixtures by perturbed-chain statistical associating fluid theory

The perturbed-chain statistical associating fluid theory (PC-SAFT) is used to investigate the vapor-liquid equilibria for binary supercritical carbon dioxide (CO2) and hydrocarbon mixtures. The molecular parameters m, sigma, and epsilon/k for pure CO2 and hydrocarbons with carbon number n <= 20 are taken from the work of Gross and Sadowski. m, sigma, and epsilon/k for n-alkanes with n > 20 are obtained by extrapolation from the linear relationships between molecular parameters and molecular weight M-w. The binary interaction parameters (k(ij)) are regressed by using the experimental data. Investigation shows PC-SAFT is able to accurately describe the vapor-liquid-phase equilibria for both CO2-light hydrocarbon and CO2-heavy n-alkane (up to C-44) binary mixtures. When the carbon number n in each hydrocarbon ranges from 1 to 20, the regressed k(ij) increases monotonically with the increase of n. However, when n is greater than 20, there is a unique binary interaction parameter (k(ij) = 0.16) that can well describe the vapor-liquid-phase equilibria for CO2-eicosane, CO2-octacosane, CO2-hexatriacontane, and CO2-tetratetracontane binary mixtures.