Synthesis of zeolite Y membranes from submicrometer (>100 nm) and nano seed (<100 nm) crystals on alumina supports was examined and the separation characteristics of these membranes for CO(2) and N(2) were studied. Two secondary growth solutions were examined, one for a rapid growth (hours) and one for a slower growth process (days). Membranes formed from the rapid growth solution resulted in 2-2.5 microm thickness, while for the slower growth solution, a dense membrane of 350-600 nm thickness was formed, covered by a 25 microm porous zeolite layer. With the nano seeds as the seeding layer, no membrane was formed. A mechanism involving seed dissolution to initiate membrane formation is concluded. The separation characteristics of membranes for CO(2)/N(2) separation were similar, with very high selectivities for separation (alpha(CO(2),N(2)) > 500). The thicker membrane had lower permeance. By investigating both single gas and mixed gas permeances, strong evidence for a percolative type separation process is obtained.

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Strong and permeable macro-porous a-Al 2 O 3 membrane supports are made by colloidal filtration of 20 vol% dispersions of a-Al 2 O 3 with an average particle size of 600 nm. Intact compacts with very good surface quality were obtained at an optimum pH of 9.5 and dosage of 0.2 wt% ammonium aurintricarboxylate (Aluminon), based on dry alumina. The colloidal stability of the aluminon-stabilized slurries is confirmed by n potential measurements. Slight sintering of dense-packed a-Al 2 O 3 compacts was found to result in 467% packing density and a bimodal pore-size distribution as derived from shrinkage behavior and gas adsorption studies. Non-stationary single gas permeation measurements showed improved gas permeability, compared with a-Al 2 O 3 compacts prepared using powder with a smaller particle size (300 nm). The strength of the disk-shaped alumina compacts within the porosity range of 30%-20% increased from 100 to 300 MPa with a standard deviation of 20 and 50 MPa, respectively. J ournal

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