Gas permeability of silicalite membranes formed on alpha-alumina support tube

Silicalite membranes were synthesized by hydrothermal reaction on the surface of a porous alpha-alumina support tube. The silicon source was a fine silica powder and the template was a mixture of tetrapropylammonium-hydroxide and bromide. Three zones were observed on the fractured surface of the film. The top zone was a polycrystalline silicalite layer and the inner zone was a layer of alpha-alumina macropores partially filled with deposits. The intermediate zone was a mixture of alumina particles and deposits. The permeance of the silicalite membranes increased with decreasing thickness of silicalite layer, but permselectivity was not directly connected with membrane morphology. The permselectivity of n-butane to i-butane was 10-50 in the range of 30-100 degrees C, which evidently showed the molecular sieving ability of the formed membranes.