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 Mw. The binary interaction parameters (kij) 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 C44) binary mixtures. When the carbon number n in each hydrocarbon ranges from 1 to 20, the regressed kij increases monotonically with the increase of n. However, when n is greater than 20, there is a unique binary interaction parameter (kij = 0.16) that can well describe the vapor-liquidphase equilibria for CO2-eicosane, CO2-octacosane, CO2-hexatriacontane, and CO2-tetratetracontane binary mixtures.