Synthesis of Thin, Oriented Zeolite A Membranes on a Macroporous Support

Continuous, thin, oriented zeolite A membranes are produced by a two-step synthesis on macroporous α-Al 2 O 3 supports. In the first step, zeolite A nano-cubes with ∼350-nm edges are prepared as a native impurity phase in zeolite Y synthesis dispersions, the support surface is pre-modified with a cationic polymer having a selective affinity for zeolite A. The thus-treated support is contacted with a colloidally stable dispersion of zeolite A and Y mixture in water, which results in selective, dense-packed deposition of the zeolite A cubes with one face aligned to the average support surface. In a second step of hydrothermal epitaxial growth, the seed layer grows epitaxially into a continuous, meso-defect free, ∼1 μm thick zeolite A layer, already after 1 h of treatment. This microstructure of the membrane compares very favorably to what is commonly obtained. The pH value of the zeolite mixture suspension is found to have a major influence on seed layer morphology, and thereby, on the quality and orientation of zeolite A membrane after short synthesis times. The final zeolite A membrane thickness and morphology is controlled by varying secondary growth synthesis time. The approach presented is thought to be of generic use for the preparation of oriented zeolite membranes.