Abstract
The topolayers of mesoporous ceramic γ-alumina membranes (rpore = 2.3 nm, 50% porosity) are modified with silica-based, microporous (rpore < 1 nm) systems using a sol-gel technique. These systems remain microporous up to 600°C with a porosity ≈ 30%. At 700°C the porosity is decreased to 10%, but the material is still microporous. Gas transport through these modified membranes is activated, with an activation energy of ≈ 11 kj/mol for hydrogen. A typical hydrogen permeability is 15*10-7 mol/m2 s.Pa at 100°C. Separation factors for H2/CH4 at 150°C of 200 are measured. The separation principle is probably 'molecular sieve'-like. Aging of silica modified membranes occurs in a water-containing atmosphere. In a period less than 1 month the activation energy for hydrogen permeation decreased, but no drastic changes in separation properties are observed. After two months, however, the permeability increased to a level of the nonmodified γ-alumina membranes.
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