PROBING VAPOR LIQUID EQUILIBRIA OF NEAR-CRITICAL BINARY GAS-MIXTURES BY ACOUSTIC MEASUREMENTS/

Phase behavior is a fundamental aspect of supercritical fluids. A simp le acoustic method is described for investigating vapor/liquid equilib ria. The method is used lu investigate three different pure components (CO2, C2H6, and CF3CH2F, refrigerant R134a) and binary mixtures of CF 3CH2F with CO2 or C2H6. For the pure components, the reciprocal of the speed of sound was measured at selected temperatures around the criti cal point. The data obtained are in good agreement with literature val ues. The binary mixtures were investigated over the whole composition range (i.e., mole fraction of CF3CH2F from 0 to 1.0), and their critic al curves were determined. The critical lines show the expected type I fluid phase behavior, but the critical Line in C2H6 + CF3CH2F shows a n unusual pressure minimum and maximum. The resulting critical Lines a re discussed with respect to thermodynamics, the use of these mixtures for supercritical fluid chromatography and extractions, and the possi bility of using CF3CH2F as a modifier.