Control of crystal size and distribution of zeolite A

In the present work, we have explored-numerous ways of reducing the mean particle size of zeolite A, keeping the economic imperatives in mind. Efforts were directed toward reducing the crystallization time and having a narrower particle size distribution. In addition to the study of more conventional parameters, such as temperature, alkalinity, and water content, the effect of using microwaves, centrifuging, and ultrasonication was also explored. Highly localized temperatures of thousands of Kelvin and pressures of hundreds of atmospheres produced by ultrasonication were expected to disrupt the nucleation process in a manner that led to smaller crystals. Surprisingly, it was found that the application of ultrasonication did not lead to any decrease in particle size. The crystal morphologies obtained in the case of ultrasonication and stirring were completely different, which was rather unexpected. Subjecting the zeolite batch to short periods of microwave radiation led to a narrow particle size distribution with small crystal size. A direct correlation between the nominal SiO2/Al2O3 ratio and the particle size was observed. Decreasing SiO2/Al2O3 ratios led to a narrower particle size distribution. The yield dropped dramatically when the SiO2/Al2O3 ratio dropped below 1. The use of some of these parameters has a synergistic effect and can be coupled to finally obtain a mean crystal size of about 0.5 mum within a very reasonable time frame of 5-6 h, which we believe can be easily tailored for the commercial synthesis of zeolite A. X-ray diffraction (XRD), laser scattering particle size analysis, scanning electron microscopy (SEM), EDAX, and energy-dispersive XRF have been used to characterize the zeolites synthesized.