Volumetric properties of hexafluoropropylene and hexafluoropropylene oxide. Determination of phase diagram and critical properties

Hydrofluoroalkenes, like hexafluoropropylene (R1216) and hexafluoropropylene oxide (HFPO), are being investigated as potential new fluids for refrigeration systems or as fluids for extraction. Considering the different possibilities of utilisation, one of the most interesting properties is the density at and outside saturation. A vibrating tube densitometer technique is used to determine densities for several temperatures between 263 and 383 K and pressures between 0 and 15 MPa. The Forced Path Mechanical Model (Bouchot and Richon, 2001) is used to correlate, at temperature and pressure, the density to the U-tube vibrating period. A sapphire tube cell is also used to determine the pure component vapour pressures. Using the experimental density values and critical divergence theory concerning density difference between the liquid and vapour phases on the coexistence curve, the critical properties and the phase diagram can be determined.