Thermodynamic stability and characterization of double clathrate hydrate with carbon dioxide plus cyclopentane plus deuterium oxide

This paper reports characterization of clathrate hydrate formed in CO2 + cyclopentane + deuterium oxide (D2O) system with the phase equilibrium determination and the powder X-ray diffraction (PXRD) measurements towards the development of hydrate-based tritium separation technology. Four-phase (CO2 gas + liquid cyclopentane + liquid D2O + hydrate) equilibrium conditions were measured using the isochoric procedure in the pressure range from 0.279 MPa to 2.735 MPa and the temperature range from 285.35 K to 293.65 K. The equilibrium temperature of CO2 + cyclopentane + D2O system is always higher by 2.0 K to 2.4 K compared to that of CO2 + cyclopentane + H2O system. The detailed crystallographic properties of both CO2 + cyclopentane + D2O hydrate and CO2 + cyclopentane + H2O hydrate including the lattice constants, the radii and volumes of each cage and the cage occupancy were estimated by the PXRD analysis. Based on the obtained results, implications for the development and operation of D2O-hydrate-based process are discussed.