Dense A-type zeolite membrane synthesized by seeding

Abstract

The synthesis of A-type zeolite membranes on porous alpha -Al2O3 supports via the method of seeding plus secondary hydrothermal crystallization has been studied. The seed layers, which were prepared from colloidal A-type zeolite synthesized from the reaction mixture of n[(TMA)(2)O] : n(SiO2) n (Al2O3) : n(Na2O) : n(H2O) = 13.4 : 11.25 : 1.8 : 0.3 : 700, were treated by steam of ammonia to inhibit the formation of cracks when dried. Compact zeolite membranes constituted with multiple-twined zeolite crystals were accessed by hydrothermal growth of seed layers in the reaction sol of n (Na2O) n(Al2O3) : n(SiO2) = n(H2O) = 3 : 1 : 1 : 800. In highly alkaline hydrothermal solutions, seed layers tended to dissolve and loose zeolite membranes with many defects were obtained. The gas permeanbility on A-type zeolite membrane dried at 393 K, in which water molecular still inhabited the zeolitic channels, was quite low, suggesting that the membrane was close to free of defects. Defects were formed mainly due to different thermal expansion coefficients between alpha -Al2O3 support and zeolite membrane when the calcinations at 823 K was carried out to free the channel of membrane zeolites.