Synthesis and perfection evaluation of NaA zeolite membrane

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support from clear solution and the evaluation of the perfection of the as-synthesized membrane by gas permeation were investigated. When an unseeded support was used, the NaA zeolite began to transform into other types of zeolites befor e a continuous NaA zeolite membrane formed. When the support was coated wit h nucleation seeds, not only the formation of NaA zeolite on the support su rface was accelerated, but also the transformation of NaA zeolite into othe r types of zeolites was inhibited. A continuous NaA zeolite membrane can be formed. Perfection evaluation indicated that the NaA zeolite membrane with the synthesis time of 3 h showed the best perfection after a one-stage syn thesis. The perfection of NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesi s time of 2 h after a two-stage synthesis showed the best gas permeation pe rformance, The permselectivity of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8 , respectively, higher than those of the corresponding Knudsen diffusion se lectivity of 5.39 and 0.94, which showed the molecular sieving effect of Na A zeolite. However, the permeation of n-C4H10 also indicated that the NaA z eolite membrane had certain defects, the diameter of which were larger than the NaA zeolite channels. (C) 2001 Elsevier Science B.V. All rights reserv ed.