Influence of Si/Al ratio, pre-treatment and measurement conditions on permeation properties of MFI membranes on metallic and ceramic supports

MFI membranes with Si/Al ratios between 57 and ∞ were prepared on metallic and ceramic supports as part of ongoing work to develop membranes for membrane reactor applications. The membranes were characterized by H2 and SF6 single gas permeation measurements under various conditions, by mixture permeation studies of H2:SF6 = 1:1, and of n-pentane:i-pentane = 1:1 as well as by permporosimetry in order to estimate the relative contributions of inter- and intracrystalline membrane transport. The permeation properties are mainly influenced by the Al content in the MFI layers but not by the type of the support. From permporosimetry and the n/i-pentane and H2/SF6 mixture permeation it follows that the intercrystalline permeance increases with increasing Al content and therefore the mixture selectivities are low for Al-rich MFI membranes. The ZSM-5 membrane with the highest Al content (Si/Al = 57) behaves exceptionally since it separates H2/SF6 mixtures but not n/i-pentane mixtures. The permeation results depend strongly on the measurement conditions such as the pressure difference across the membrane and are influenced by the calcination parameters of the membrane.