Measurement and correlation of solubilities for trifluoromethylbenzoic acid isomers in supercritical carbon dioxide

The solubilities of 2-, 3- and 4-trifluoromethylbenzoic acids in supercritical carbon dioxide were measured at 308.2, 313.2 and 323.2 K by a flow-type apparatus. The pressure range of the measurement was from 9 to 23 MPa. The enhancements of solubility by fluorination were markedly observed for 2- and 3-trifluoromethylbenzoic acids. The solubilities of 4-trifluoromethylbenzoic acids are almost the same as those of 4-methylbenzoic acid. The experimental data were correlated by the Peng-Robinson equation of state. The correlated results show good agreement with the experimental data by adjusting binary interaction parameters. The results can represent the tendency of solubility enhancement. The interaction parameter between carbon dioxide and 3-trifluoromethylbenzoic acid is smaller than that between carbon dioxide and 2-trifluoromethylbenzoic acid or methylbenzoic acid isomers. While the estimated sublimation pressure for 4-trifluoromethylbenzoic acid is smaller than those for the other compounds, the solubilities of 4-trifluoromethylbenzoic acids are almost the same as those of 4-methylbenzoic acid. The interaction parameter between carbon dioxide and 4-trifluoromethylbenzoic acid show the negative values. This fact indicates that the interaction between carbon dioxide and 4-trifluoromethylbenzoic acid is stronger than those between carbon dioxide and the other compounds.