Density-Based Correlation for Solid Solubility in Supercritical Solvents

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Abstract
The use of solvents at conditions above their critical points is increasing because of their increased dissolving power and enhanced transport properties, as in caffeine extraction, etc. This research sought an improved method for correlating the solubility of materials in light solvents from conditions below the critical point of the solvents to those above it, especially to facilitate prediction, interpolation, and extrapolation of solubility data better than existing equations. Solvent density was recognized early as a factor in solvent dissolving power but not used as a correlating parameter. A density approach based on mass-action equilibrium law employing the solvation concept was used to correlate the data on selected binary mixtures with excellent results. For high pressures the relationship yields a plot of log solute solubility (g/L solution) versus log solvent density (g/L solution) which is sectionwise linear. A simplification of the relationship applies well at lower pressures. For both regions, experimental data are represented more easily and better than by conventional equations of state.