Interactions of carbon dioxide with liquid fluorocarbons

The interactions of carbon dioxide with liquid fluorinated and hydrogenated hydrocarbons, perfluoro-n-hexane and n-hexane, are investigated by computer simulation. Conformational and structural properties of the liquid phases were obtained applying the molecular dynamics method using flexible, all-atom force fields containing electrostatic charges. It was verified that spontaneous cavities are larger and more easily formed in the fluorocarbon, corresponding to smaller free energies of cavity formation, than in the equivalent hydrocarbon. These facts do not explain the high solubility of carbon dioxide compared to that of other gases, a behavior resulting from differences in solute-solvent interactions. The chemical potential at infinite dilution and the solubility of carbon dioxide and oxygen in the solvents were determined from the simulation runs by the method of test-particle insertion. It is demonstrated that electrostatics play a minor role in the forces between carbon dioxide and both alkanes and perfluoroalkanes, which are mainly governed by dispersion terms. No evidence of a particular affinity of carbon dioxide for perfluorinated liquids was found either from the results of the present or from analysis of literature data on gas solubility.