ZEOLITE SYNTHESIS IN UNSTIRRED BATCH REACTORS .3. EFFECT OF NONUNIFORM PRE-MIXING ON THE CRYSTALLIZATION OF ZEOLITE-A AND ZEOLITE-X

The effects of deliberate non-uniform pre-mixing of the aluminate and silicate solutions in the unstirred batch syntheses of zeolites A and X were studied. Poorly mixed hydrogels gave rise to impurity phases, w ith the amount of impurity decreasing with improved pre-mixing. Experi ments were carried out in reactors specially designed for the growth o f large zeolite crystals under microgravity conditions, and in a paral lel study using high-density polyethylene bottles. Both studies eviden ced the appearance of impurities if the hydrogel was not well mixed pr ior to heating. No consistent effect was observed on the particle size distributions of the zeolite products. These results underlined the i mportance of proper reactor design for unstirred syntheses, and the us efulness of a non-invasive diagnostic technique for mixing effectivene ss, such as nuclear magnetic resonance (NMR) imaging. The applicabilit y of NMR imaging to the systems studied here was demonstrated in Part I of this series.