DETERMINATION OF PARTIAL MOLAR VOLUMES AT CRITICAL END-POINTS

There has been considerable interest in the volumetric behavior of sup ercritical binary (and higher) fluid mixtures near the solvent critica l point. It is in the vicinity of this critical point that supercritic al extraction processes are generally considered to be most effective, In the case of a solvent + solute system that exhibits liquid-liquid- vapor (llg) partial miscibility, properties of the dense gas phase nea r an ll = g upper critical end point are most interesting. The partial molar volumes of the solvent and solute at these conditions are diffi cult to measure directly, In this note, we show that the solvent and s olute partial molar volumes of the critical phase of a binary critical end point are readily determined from the associated three-phase liqu id-liquid-vapor (llg) volume-composition data.