Adsorbent/membrane hybrid (AMH) system for hydrogen separation: Synergy effect between zeolite 5A and silica membrane

A hitherto unknown adsorbent/membrane hybrid (AMH) system was developed to enhance the hydrogen separation performance, especially selectivity. The basic idea of this system is to embed zeolite 5A (adsorbent) into a tubular-type methyltriethoxysilane templating silica membrane (MTES membrane) structurally analogous to well-known catalytic-packed membrane reactors. As case studies, transient and pseudo-steady-state permeation/separation performances of AMH system were investigated by using three H₂ binary mixtures, H₂/CH₄, H₂/N₂ and H₂/CO (50:50vol.%). The separation characteristics were ascribed to the molecular size/structure as well as to the adsorption affinity of each molecule due to the mechanisms of steric hindrance, surface diffusion and adsorption equilibrium in the AMH system. In the mixtures which are mainly affected by kinetic separation in the MTES membrane (outside), such as H₂/CH₄ and H₂/N₂, the AMH system enhances the H₂ selectivity (H₂/CH₄: 109.8-199.0, H₂/N₂: 28.2-55.0) owing to synergy effect with the equilibrium separation in an adsorbent bed (inside). Alternatively, in the mixture which is dominated by equilibrium separation in the MTES membrane, such as H₂/CO, H₂ selectivity of the AMH system (H₂/CO: 14.0-32.0) became worse. A rigorous mathematical model, which combined the tubular-type membrane model with the packed adsorption bed model, could successfully predict the transient and pseudo-steady-state permeation/separation in the AMH system.