THE INFLUENCE OF SURFACTANTS AND WATER-SOLUBLE POLYMERS ON THE CRYSTALLIZATION OF ZEOLITE NAA

The crystallization of zeolite NaA in the presence of various surfactants (sodium dodecyl sulfate, Aerosol OT, cetyltrimethylammonium bromide, Nonidet P40) and of poly(ethylene glycol) was studied and compared to a control crystallization with no additive present. Crystalline-growth curves were determined by quantitative X-ray diffraction studies of samples removed periodically from the hydrothermal system. Crystal-size distributions and linear crystal-growth rates were determined by scanning electron microscopy, and from these data, nucleation profiles were constructed. Changes in the concentrations of soluble aluminum and silicon in the aqueous phase of the hydrothermal system during crystallization were monitored by inductively coupled plasma atomic emission spectroscopy. The additives were shown to lengthen the prenucleation period, shorten the nucleation period, and increase the linear rate of crystal growth. All but Aerosol OT increased the total number of nuclei produced and gave crystals with a reduced mean size and narrower size distribution. These effects may be attributed to an effective reduction in the water content of the hydrothermal system. Aerosol OT reduced the number of nuclei produced and gave larger crystals, an effect that may be attributed to a specific interaction with aluminum species. In general, the aluminum concentration in the aqueous phase was found to decrease dramatically during the period of crystal growth.