PHASE-EQUILIBRIA OF CH4 + CF4 AND OF CH4 + CHF3 IN THE TEMPERATURE-RANGE 90-K TO 140-K AND AT PRESSURES UP TO 190-MPA

The liquid + liquid phase equilibria in the binary systems CH4 + CF4 and CH4 + CHF3 were measured in the temperature range 90 to 140 K and at pressures up to 190 MPa. Additionally the liquid + solid phase equilibria were determined for CH4 + CF4 at low and at high mole fractions of CF4, and the melting pressure curve of pure tetrafluoromethane was measured up to 160 MPa. The measurements were made in an optical lowtemperature high-pressure cell made from copper beryllium; it is fitted with sapphire windows and indium seals and employs magnetic stirring. Both binary systems show upper critical solution temperatures that rise with increasing pressure by about 0.12 K MPa-1 for CH4 + CF4 and 0.085 K MPa-1 for CH4 + CHF3. The experimental results are discussed from a thermodynamic and a phase-theoretical point of view and are compared with different theories. © 1979.