SYNTHESIS OF STABLE SUSPENSIONS OF DISCRETE COLLOIDAL ZEOLITE (NA,TPA)ZSM-5 CRYSTALS

Synthesis of zeolite ZSM-5 in the form of stable suspensions of colloi dal crystals from clear homogeneous solutions has been achieved from s ynthesis mixtures with low sodium and high TPAOH concentrations, The u ltimate size of the discrete crystals is in the range 130-230 nm with a narrow particle size distribution. The crystal growth was monitored by the direct method of dynamic light scattering. An increasing alumin a concentration was found to decrease the crystal growth rate, the num ber of crystals produced, and the ZSM-5 yield. The final crystal size was found to increase with increasing alumina concentration in the syn thesis solution. The number of crystals produced decreased with an inc reased alkalinity in contradiction to what has been found for colloida l TPA-silicalite-1. This together with the presence of the two competi ng processes, crystal growth and crystal dissolution, which are both c atalyzed by hydroxide ions, suggests the presence of an optimum alkali nity (depending on the alumina concentration).