Modeling Phase Equilibria of Asymmetric Mixtures Using a Group-Contribution SAFT (GC-SAFT) with a <i>k</i>_<i>ij</i> Correlation Method Based on London’s Theory. 1. Application to CO₂ + <i>n</i>-Alkane, Methane + <i>n</i>-Alkane, and Ethane + <i>n</i>-Alkane Systems

Abstract

Here, a group contribution statistical associating fluid theory equation of state (SAFT EOS) (GC-SAFT) proposed earlier by our group (Tamouza et al., Fluid Phase Equilib. 2004, 222−223, 67−76) is extended to some asymmetric systems, using a method for correlating the kij binary parameters, using only pure compound parameters. The method is inspired by London’s theory of dispersive interactions and correlates the kij values to the “pseudo-ionization energies” of compounds i and j (denoted as Ji and Jj, respectively). A group contribution for the latter parameters is also proposed, in view of obtaining a more-predictive model. Correlation tests of phase equilibria are conducted on some CO2 + n-alkane systems. Using the parameters thus obtained, the phase envelopes of other CO2 + n-alkane systems, as well as methane + n-alkane and ethane + n-alkane systems, were fully predicted. Correlation and predictions are qualitatively and quantitatively satisfactory. The deviations are within 4%−5% (i.e., comparable to those obtained on previously investigated systems).