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<p>Clathrate-hydrate-based tritium separation from isotope water is a promising process for removing tritium that is not effectively separated by conventional methods. Clathrate hydrates (hereafter hydrates) are crystalline compounds composed of water and guest molecules. Hydrate-based tritium separation utilizes the property that heavy water (D<sub>2</sub>O) forms hydrates under milder temperatures than light water (H<sub>2</sub>O). Efficient industrial operation requires a guest compound that forms hydrates at high temperatures and low pressures and has a large difference in phase equilibrium temperature between H<sub>2</sub>O and D<sub>2</sub>O hydrates (Δ<i>T</i><sub>DH</sub>). In this study, we measured the phase equilibrium conditions of D<sub>2</sub>O hydrates formed with HFC-134a, HFC-32, and HFC-23. The formation of D<sub>2</sub>O hydrates with these guests can be a route to tritium separation through co-precipitation of T<sub>2</sub>O. HFC-134a formed hydrates under the mildest conditions, with Δ<i>T</i><sub>DH</sub> values of 2.8 K, 1.8 K, and 2.4 K for HFC-134a, HFC-32, and HFC-23. In addition to the three investigated guests, the potentials of propane, cyclopentane, and cyclopentane + CO₂ hydrate systems for hydrogen isotope separations were also compared, suggesting that HFC-134a and cyclopentane may be suitable guests for tritium separation. Present and previous studies have also shown a strong positive correlation between the hydration number and Δ<i>T</i><sub>DH</sub> (correlation coefficient = 0.76). This trend may be ascribed to the fact that a higher proportion of water molecules in the hydrate amplifies the effect of replacing H<sub>2</sub>O with D<sub>2</sub>O. These results indicate that the equilibrium conditions of D₂O hydrates may be approximately predicted to identify suitable guests for tritium separation.</p>

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Phase Equilibria of D2O Hydrates for Hydrate-Based Tritium Separation

  • 期刊论文

  • 发表日期：

    2025年10月18日

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  • Ryonosuke Kasai,
  • Haruki Ito,
  • Hitoshi Kiyokawa,
  • Leo Kamiya,
  • Saman Alavi,
  • Ryo Ohmura

摘要

Clathrate-hydrate-based tritium separation from isotope water is a promising process for removing tritium that is not effectively separated by conventional methods. Clathrate hydrates (hereafter hydrates) are crystalline compounds composed of water and guest molecules. Hydrate-based tritium separation utilizes the property that heavy water (D2O) forms hydrates under milder temperatures than light water (H2O). Efficient industrial operation requires a guest compound that forms hydrates at high temperatures and low pressures and has a large difference in phase equilibrium temperature between H2O and D2O hydrates (ΔTDH). In this study, we measured the phase equilibrium conditions of D2O hydrates formed with HFC-134a, HFC-32, and HFC-23. The formation of D2O hydrates with these guests can be a route to tritium separation through co-precipitation of T2O. HFC-134a formed hydrates under the mildest conditions, with ΔTDH values of 2.8 K, 1.8 K, and 2.4 K for HFC-134a, HFC-32, and HFC-23. In addition to the three investigated guests, the potentials of propane, cyclopentane, and cyclopentane + CO₂ hydrate systems for hydrogen isotope separations were also compared, suggesting that HFC-134a and cyclopentane may be suitable guests for tritium separation. Present and previous studies have also shown a strong positive correlation between the hydration number and ΔTDH (correlation coefficient = 0.76). This trend may be ascribed to the fact that a higher proportion of water molecules in the hydrate amplifies the effect of replacing H2O with D2O. These results indicate that the equilibrium conditions of D₂O hydrates may be approximately predicted to identify suitable guests for tritium separation.