A calculational method is presented for determining the solubility of condensed, nonvolatile components in supercritical solvents by treating the supercritical fluid-phase mixture as an expanded liquid. The procedure is directly applicable to phase equilibrium calculations associated with extraction processes utilizing supercritical solvents. Two mixture parameters are required in the formulation for a binary system—an activity coefficient at infinite dilution for the heavy solute and a binary interaction parameter (i.e., k12 in the Redlich-Kwong equation of state). The advantage of this approach is that both mixture parameters exhibit consistent, predictable behavior for highly asymmetric mixtures in the vicinity of the critical region. The utility of this method is illustrated using experimental data for the solubility of solid naphthalene in supercritical carbon dioxide and in supercritical ethylene.
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