MULTIPHASE BEHAVIOR IN TERNARY FLUID MIXTURES (BEHAVIOR, EQUATION OF STATE, PHASE STABILITY, EQUILIBRIUM, SUPERCRITICAL EXTRACTION)

Phase equilibria involving three and four fluid phases were studied for isopropanol-water-carbon dioxide mixtures at temperatures and pressures near the critical point of carbon dioxide. The complex multiphase behavior exhibited by this system has important process implications for supercritical-fluid solvent extractions. The multiphase equilibria can pose difficulties when operating continuous extraction processes; alternatively the phenomenon can be used to achieve desired separations using different processing techniques.;Three-phase liquid-liquid-gas and liquid-liquid-liquid equilibria and four-phase liquid-liquid-liquid-gas equilibrium compositions were measured at 40(DEGREES)C, 50(DEGREES)C, and 60(DEGREES)C over pressures ranging from 1000 psig to 2000 psig. A new experimental technique was developed for obtaining accurate measurements of both phase compositions and molar volumes. The experimental technique allows the phase compositions to be determined from visual measurements only; no sampling is required. Gas-liquid and liquid-liquid critical endpoints bounding the multiphase behavior were also observed.;The Peng-Robinson cubic equation of state was used to describe both three-phase and four-phase behavior observed experimentally, and to predict global multiphase behavior for the isopropanol-water-carbon dioxide system. Binary mixture three-phase equilibria and limiting critical phenomena, such as tricritical points and multiphase critical endpoints were identified. Multiphase equilibria for the ethanol-water-carbon dioxide system were also examined using the equation of state. Significant differences in phase behavior were discovered for these two ternary systems. These differences were shown to be related to limiting constituent binary liquid-liquid-gas equilibrium.