The perturbed-chain statistical associating fluid theory (PC−SAFT) and density-gradient theory (DGT) are
used to construct an equation of state (EOS) applicable for nonuniform fluids. In the bulk phases, the nonuniform
EOS reduces to PC−SAFT and the phase equilibria inside the critical region are calculated by combining the
renormalization-group theory (RGT). In the vapor−liquid surface, the density profile, surface thickness, and
surface tension are calculated by using the nonuniform EOS with the equilibrium bulk properties as input.
Investigation shows that PC−SAFT is able to provide accurate critical properties by combining the RGT and
correlating the surface tensions for both the light and heavy n-alkanes satisfactorily by combining the DGT.
The perturbed-chain statistical associating fluid theory (PC-SAFT) is used to investigate the vapor-liquid equilibria for binary supercritical carbon dioxide (CO 2 ) and hydrocarbon mixtures. The molecular parameters m, σ, and /k for pure CO 2 and hydrocarbons with carbon number n e 20 are taken from the work of Gross and Sadowski. m, σ, and /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 vaporliquid-phase equilibria for both CO 2 -light hydrocarbon and CO 2 -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 CO 2 -eicosane, CO 2 -octacosane, CO 2hexatriacontane, and CO 2 -tetratetracontane binary mixtures.
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