Control of Loading Behavior of Y-Type Zeolite Seeds On Tubular Alumina Support

Zeolite membranes have often been prepared by the secondary growth method including dip-coating of zeolite seeds on the surface of porous support. Whereas the amount of seed crystals caught on the support surface would have critical influence of membrane formation, the dip-coating step itself and the effect of dip-coating on the quality of membrane have rarely been studied.  In this study, we measured both zeta-potential of alumina support and Y-type zeolite seed slurry, and studied the effect of zeta-potential of them on the adhesion behavior of zeolite seeds on porous alumina support.

Y-type zeolite seed-water slurry was prepared using ca. 200 nm of ultra stable Y crystals. The value of pH was controlled by adding NaOH or HCl solution. The concentration of zeolite slurry was controlled in the range of 1-5 g-zeolite/L. At lower pH, alumina support has positive charge, while zeolite seeds stayed at the isoelectric point.  Under these conditions, zeolite seeds formed aggregated particles in size of ca. 6000 nm.  Zeolite-water slurry was dip-coated on the surface of tubular porous alumina support with the average pore size of 0.15 μm.  Thus, at lower pH, in the course of dip-coating procedure, zeolite seeds were exclusively trapped on the surface of porous tube.

Hydrothermal treatment of seeded support was carried out to form a Y-type zeolite thin layer on the surface of tubular alumina support. The support seeded at lower pH value successfully gave a thin and compact layer of Y-type zeolite.  The membrane prepared under such conditions showed a high perm selectivity to water in vapor permeation of isopropyl alcohol and water mixture.