Thermodynamic and Raman Spectroscopic Studies on Difluoromethane (HFC-32) + Water Binary System

The three-phase equilibrium (pressure temperature) relation of the difluoromethane + water binary system containing gas hydrates was measured in the pressure range from (0.20 to about 11.0) MPa and temperature range from (275.15 to 300.15) K. On the basis of each three-phase equilibrium curve, the quadruple point which consists of gaseous and liquid difluoromethane, water, and hydrate was determined as 1.45 MPa and 293.16 K. The in situ Raman spectroscopy under the three-phase (gas, water, and hydrate) equilibrium conditions showed that the crystal structure of difluoromethane gas hydrate was structure-I, where both small and large cages were occupied by the difluoromethane molecule. The overall hydration enthalpy of simple structure-I difluoromethane gas hydrate under the three-phase equilibrium conditions was evaluated by means of the Clapeyron equation.