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-CO2 and perfluoro-alkane-CO2 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-CO2 and perfluorohexane-CO2 mixtures. The predicted CO2 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 CO2 is generally smaller than the experimental results. The model predicts a higher solubility for the perfluoroalkanes in CO2 in comparison with alkanes in CO2, 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 CO2.