Equilibrium properties and crystal growth of D₂O + cyclopentane hydrate for sustainable tritium separation

This study reports thermodynamic properties and crystal growth observations of D₂O + cyclopentane hydrate toward the development of a hydrate-based tritium separation process. We employed D₂O as a host of hydrate with respect to the investigation into the formation of D₂O hydrate substrate, which is a core component of the tritium separation process. The hydrate phase equilibrium temperature in the liquid D₂O + liquid cyclopentane system was 3.2°C higher than the corresponding H₂O hydrate. Experiments on crystal growth were conducted at temperatures ranging from 5.1 to 8.5°C under atmospheric pressure. Under each thermodynamic condition, polygonal hydrate crystals appeared, growing along the D₂O/cyclopentane interface. The geometric shape and size of the crystals varied depending on the temperature. The variation in crystal morphology was comparable to that of the H₂O + cyclopentane hydrate. Implications based on the obtained results for the hydrate-based isotopic water separation process design are discussed.