Hydrogen separation of methyltriethoxysilane templating silica membrane

Hydrogen separation on microporous methyltriethoxysilane-templating silica composite/α-alumina membranes (below MTES membrane) was studied using three binary gas mixtures: H₂/N₂, H₂/CO ₂, and H₂/CH₄. The characteristics of unsteady and steady-state permeation/separation on the MTES membrane were compared to each other. Although permeation flux in the H₂/N₂ mixture was comparatively low, H₂ selectivity was high (H₂/N ₂ SF ≈ 30-60). On the contrary, the H₂/CO₂ mixture showed high permeation flux but low H₂ selectivity (H ₂/CO₂ SF ≈ 1.5-6.5). The H₂/CH₄ mixture showed a large difference between permselectivity (28-48) and separation factor (10-22). Results from this study revealed that it was difficult to predict the separation factor using the one-component permeation ratio (permselectivity) over the experimental range tested. These separation characteristics could be primarily ascribed to the molecular size and structure of each gas, which likely contributed to steric hindrance or molecular sieving within the membrane pore. In addition, the adsorption affinity of each molecule on the membrane surface acted as a key factor in separation performance because it significantly influenced surface diffusion. The generalized Maxwell-Stefan model incorporating the dust gas model, and the Langmuir model could successfully predict the transient and steady-state permeation/separation.