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, H2 and D2 were measured with a MFI-ZSM-5 zeolite-type tubular membrane. These experiments were performed in the membrane’s temperature range: 298–398K. At these temperatures, a transition in the transport regime was observed at 360K, which is attributed to the transition from surface-diffusion dominant to gas-translational diffusion dominant. Using the measured permeances, the permselectivities for H2/He and D2/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 H2/D2 permeances ratio was around the Knudsen ratio (i.e., ∼1.41). Moreover, the permeances of the binary mixture H2/D2, at the whole concentration range, were also measured at 298K 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 Meff-0.5, where Meff is the effective mass of the mixture determined by the concentrations of H2 and D2. Using this result, the Q2 permeances and the Q2/He permselectivities (where Q = H, D, T) for the other hydrogen isotopologues (i.e., HD, HT, DT and T2) were also calculated.