Three-Phase Equilibrium Relations and Hydrate Dissociation Enthalpies for Hydrofluorocarbon Hydrate Systems: HFC-134a, -125, and -143a Hydrates

The three-phase equilibrium (pressure−temperature) relations were measured for the hydrofluorocarbon (HFC) (1,1,1,2-tetrafluoroethane (-134a), pentafluoroethane (-125), or 1,1,1-trifluoroethane (-143a)) + water binary systems containing gas hydrate. The measurements were performed in the pressure range up to 10.0 MPa and the temperature range of (273.15 to 295.15) K. The invariant quadruple points (gaseous HFC, liquid HFC, aqueous, and hydrate phases) were located at 283.19 K and 0.416 MPa (HFC-134a), 283.95 K and 0.930 MPa (HFC-125), and 283.33 K and 0.838 MPa (HFC-143a), respectively. The enthalpies of hydrate dissociation to gaseous HFC and water were calculated with the Clapeyron equation, and the value was about 140 kJ·mol −1 for all HFC hydrate systems.