A novel seeding procedure for preparing tubular NaY zeolite membranes

A good seeding is a mandatory step to have defect-free zeolitic membranes prepared by means of a secondary growth method. The transport properties of the zeolitic membranes depend strongly on the seeding procedure of zeolite crystals during which the whole support surface has to be covered uniformly and sufficiently. A new seeding procedure, involving cross-flow filtration of a water suspension combined with rotation and tilting of the membrane support, was developed and utilized for the first time. Porous a-alumina tubes were seeded using a water suspension of 0.2 wt.% in zeolite crystals, at a pH of ca. 9.2 and room temperature. Cumulative stage-cut of the seeding phase was used as design parameter in order to tailor the permeation properties (e.g., permeance) of the resulting NaY zeolite membranes. The secondary growth was accomplished by a hydrothermal treatment. SEM, EDX and XRD analyses show dense intergrown FAU layers with Si/Al ratios of 1.8-2.0 typical of the NaY zeolite. The measured permeance was 5-10% of that showed by the bare support. Another evidence of the membrane quality can be found considering their application in CO selective oxidation reaction [P. Bernardo, C. Algieri, G. Barbieri, E. Drioli, Catal. Today 118(1-2) (2006) 90]: a complete conversion of carbon monoxide which falls down 1000 times from 10,000 to ca. 10 ppm indicates very few defects in the zeolite layer.