An experimental study of three- and four-phase equilibria for isopropanol-water-carbon dioxide mixtures at elevated pressures

Compositions and molar volumes of the three phases in liquid-liquid-gas equilibrium are reported for ternary mixtures of isopropanol, water and CO₂ at elevated pressures and at temperatures of 50 and 60°C. Phase compositions and molar volumes were also obtained for three-phase, liquid-liquid-liquid equilibrium and four-phase, liquid-liquid-liquid-gas equilibrium at 40°C. Gas-liquid and liquid-liquid critical endpoints, which represent pressure bounds on the liquid-liquid-gas region at 60°C, were determined from observations of critical opalescence. The phase behavior exhibited by the isopropanol-water-CO₂ system is quite complex, particularly at conditions near the critical point of CO₂. These conditions are well within the range of operating conditions proposed for supercritical-fluid extraction of organic compounds from water using CO₂. Therefore, the existence of multiple coexisting phases can be an important factor in designing and operating such extraction processes.