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.
A simple acoustic method has been used to investigate
the two ternary systems CO2 +
CH2F2 +
CF3CH2F
and CO + C2H4 +
CH3CHCH2. Vapor−liquid equilibria
data were measured for four of the six binary
subsystems as well as the two ternary systems. The binary systems
containing either CO2 or a refrigerant
(CH2F2, CF3CH2F)
have been investigated over the whole mole fraction range. For the
subsystems containing
CO, only the range from 0 to 40 mol % CO could be investigated.
The ternary systems were measured by
the quasibinary method (i.e. the ratio between two components being
held constant). For the system CO2 +
CH2F2 + CF3CH2F,
three different quasibinary mixtures, with three different compositions
each, were measured.
For the ternary system CO + C2H4 +
CH3CHCH2, one quasibinary mixture with
three different compositions
was investigated. Additionally, two specific mixtures were
investigated in the ternary system CO + C2H4
+
CH3CHCH2, because of the importance of
this system in the synthesis of aliphatic polyketone polymers.
For
each mixture the critical point was determined. Different ways of
presenting binary and ternary critical data
and the topology of the resulting ternary critical surfaces are
discussed with respect to thermodynamics.
Some limitations of the acoustic method for probing phase behavior
are explained The critical data have
been modeled using the Peng−Robinson equation of state.
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