Phase behavior is a fundamental aspect of supercritical
fluids. A simple acoustic method is described for
investigating vapor/liquid equilibria. The method is used to
investigate three different pure components
(CO2,
C2H6, and CF3CH2F,
refrigerant R134a) and binary mixtures of
CF3CH2F with CO2 or
C2H6. For the pure
components, the reciprocal of the speed of sound was measured at
selected temperatures around the critical
point. The data obtained are in good agreement with literature
values. The binary mixtures were investigated
over the whole composition range (i.e., mole fraction of
CF3CH2F from 0 to 1.0), and their critical
curves
were determined. The critical lines show the expected type I fluid
phase behavior, but the critical line in
C2H6 + CF3CH2F
shows an unusual pressure minimum and maximum. The resulting
critical lines are discussed
with respect to thermodynamics, the use of these mixtures for
supercritical fluid chromatography and extractions,
and the possibility of using CF3CH2F as a
modifier.