Low-pressure adsorption of hydrogen isotopologues on LTA4A zeolites - A grand canonical Monte Carlo simulation study

Abstract

Effective removal of the trace quantities of hydrogen and its isotopologues is crucial for the proper functioning of the tritium extraction system (TES) in the fuel cycle system of the fusion reactor. Zeolite molecular sieves of Linde Type A (LTA) framework are considered potential adsorbent materials for the cryogenic molecular sieve bed (CMSB) of the TES. However, the adsorption isotherm data of H2, HD, D2, HT, DT, and T2 on LTA 4A zeolites at low pressures (1–1000 Pa) and 77.4 K temperature is scarce in the literature. Grand canonical Monte Carlo (GCMC) simulations were performed to study the hydrogen isotopologues adsorption in the pressure and temperature ranges of operation of the CMSB of TES. The adsorption isotherms show that the equilibrium loading capacity is larger for T2, followed by D2 and H2 at 77.4 K. In the case of heteronuclear isotopologues, the loading capacity is larger for DT, followed by HT and HD under the same conditions of interest. The increase in the equilibrium adsorption capacity with isotopic mass could be attributed to the difference in the zero-point energies of the isotopologues. The effect of Si/Al ratio in the LTA zeolites on the cryosorption of hydrogen isotopes is investigated. The results show that, as the Si/Al ratio decreased, the equilibrium loading of the hydrogen molecules increased. The results obtained from this work are in good agreement with our experimental results and published data in the literature.