Vapor-Liquid Phase Coexistence of Alkane−Carbon Dioxide and Perfluoroalkane−Carbon Dioxide Mixtures

We carried out a molecular simulation study of the vapor−liquid equilibria of alkane−CO 2 and perfluoroalkane−CO 2 binary mixtures using the Gibbs ensemble Monte Carlo method. We used simple interaction site models and the conventional Lorentz−Berthelot combining rules for the cross interaction between the solute and solvent species with no adjustable parameters to predict the vapor-liquid phase equilibrium of the hexane−CO 2 and perfluorohexane−CO 2 mixtures. The predicted CO 2 mole fraction on the liquid branch is higher than the experimental results by about 10−13%. The gas-phase solubility of hexane and perfluorohexane in CO 2 is generally smaller than the experimental results. The model predicts a higher solubility for the perfluoroalkanes in CO 2 in comparison with alkanes in CO 2, consistent with experiment. The simulation results suggest that the dispersion interaction and the geometric packing may have a predominant role in accounting for the solubility difference between alkane and perfluoroalkane in CO 2 .