The application of the principle of congruence to mixtures of n-alkanes, 1-alcohols, methyl esters or n-carboxylic acids in carbon dioxide

The application of the principle of congruence to mixtures of n-alkanes, 1-alcohols, carboxylic acid and methyl ester in carbon dioxide was investigated. Four ternary CO 2 + (50 mole% solute + 50 mole% solute) mixtures were measured, where the solutes are from the same homologous series. Data were measured between 308.15 K and 358.15 K and for total solute fractions between 0.019 and 0.610 g·g −1 thus ensuring the dew-point, mixture critical and bubble-point regions have been characterised. The mixture data were compared to the corresponding mole-fraction-averaged binary systems, and good agreement between the ternary and binary data were evident. Slight deviations were evident for the 1-alcohol and carboxylic acid mixtures, indicating deviation from the principle of congruence, presumably due to hydrogen bonding effects that are present in these systems. The RK-Aspen model provided adequate description of all the mixtures, without the inclusion of solute + solute binary interaction parameters. Slight deviations are again evident for the 1-alcohol and carboxylic acid mixtures, further reinforcing the idea that solute + solute interactions are prevalent, leading to the deviation from the principle of congruence that was observed experimentally. Despite these deviations, the RK-Aspen model is still able to provide good quantitative description of each of the mixtures.