Experimental investigation of the ideal selectivity of MFI-ZSM-5 zeolite-type membranes for a first evaluation of the separation of hydrogen isotopologues from helium

Abstract In future fusion power plants, the tritium (T) breeding inside the reactor is a key aspect to ensure the so-called tritium self-sufficiency. The continuous availability of the fuel for further fusion reactions requires the continuous separation of small molecules such as hydrogen isotopologues (e.g., HT) from helium. Pressure-driven separation with membranes is a promising method to fulfill these requirements, especially if molecular-sieving membranes are available to separate these gas species. In this work, the single gas permeances of He, H 2 and D 2 were measured with a MFI-ZSM-5 zeolite-type tubular membrane. These experiments were performed in the membrane’s temperature range: 298 – 398 K . At these temperatures, a transition in the transport regime was observed at 360 K , which is attributed to the transition from surface-diffusion dominant to gas-translational diffusion dominant. Using the measured permeances, the permselectivities for H 2 /He and D 2 /He were calculated. In the temperature range tested, the permselectivities exceed the Knudsen selectivity, indicating that the membrane is of rather high-quality. Instead, the H 2 /D 2 permeances ratio was around the Knudsen ratio (i.e., ∼ 1.41 ). Moreover, the permeances of the binary mixture H 2 /D 2 , at the whole concentration range, were also measured at 298 K to study the isotopic effects on the transport through the MFI-ZSM-5 membrane. We found that the mixed gas behaves macroscopically as a hydrogen isotopologue molecule, and its permeance falls with M eff - 0.5 , where M eff is the effective mass of the mixture determined by the concentrations of H 2 and D 2 . Using this result, the Q 2 permeances and the Q 2 /He permselectivities (where Q = H, D, T) for the other hydrogen isotopologues (i.e., HD, HT, DT and T 2 ) were also calculated.