Hydrogen Isotope Separation in “Trapdoor” Chabazite as Measured by a Novel Breakthrough Sonic Gas Sensor
Clean energy from nuclear fusion requires the development of an efficient technology for hydrogen isotope separation capable of high separation efficiency with lower energy costs and lower tritium inventory. Isotope separation using adsorbents such as zeolites and MOFs shows great promise due to their high isotope selectivity, but are limited to very low temperatures (<100 K), making them less practical for fusion applications. In this paper, the hydrogen isotope selectivity of ‘trapdoor’ chabazite is measured for the first time, and shown to be able to operate at relatively mild temperatures, with high selectivity. Using H2 and D2 isotherm measurements, it was observed that at temperatures between 143-195 K, the trapdoor mechanism was able to block H2 and permit D2 adsorption in potassium chabazite (K-CHA) and sodium/potassium chabazite (NaK-CHA) leading to high ideal isotope selectivity (D2/H2 = 1.83 at 143 K, 100 kPa). Zeolite 5A, zeolite 3A, HKUST-1 and MOF-74(Ni) adsorbents were also tested using H2 and D2 isotherms. Evidence is presented for the first time of hysteresis in the trapdoor chabazites and this is also observed for the first time in zeolite 3A, in which it is postulated that a trapdoor effect is also in evidence. An innovative adsorption breakthrough setup was developed to measure D2/H2 separation factor of sodium/potassium chabazite (NaK-CHA) and zeolite 5A under industrially relevant conditions. To provide online measurements of deuterium in hydrogen, a bespoke whistle gas density sensor was successfully tested and used in the setup. The D2/H2 separation factor of Na-K chabazite from frontal breakthrough was measured to be 2.71 ± 0.70 at 159 K, much higher than for zeolite 5A at 1.25 ± 0.24 at 159 K and 1.7 ± 0.2 at 77 K. These results show for the first time that efficient hydrogen isotope separation can be achieved in chabazite adsorbents at relatively mild temperatures.