Using solid-solution aqueous-solution theories to model the crystallization of ZSM-5 zeolites

Zeolites are extensively used throughout industry and are applied to a variety of areas, such as petrochemicals, commercial drug manufacturing, separations, and ion-exchange processes. Zeolites are crystalline aluminosilicate materials in an open microporous framework structure, which is comprised of SiO4 and AlO4 tetrahedron rings. Each zeolite has a unique framework and pore size (diameters ranging from 3--13 A), which determines its application as a molecular sieve for gas or liquid adsorption, catalysis, etc. To date, zeolite growth mechanisms are poorly understood, and few empirically verifiable models have been derived to describe the growth. Understanding zeolite growth is crucial for further advancement in zeolite science.; ZSM-5 is one of the more important and commonly used zeolites. It is the second most used zeolite in catalysis due to its unique framework and three-dimensional pore structure. The work in this thesis focuses on the formation of ZSM-5 through non-organic synthesis. To understand the formation of this zeolite, solid-solution aqueous-solution (SSAS) theories and thermodynamics are applied to quantify the relationship among the compositions of the resulting crystalline zeolite, the synthesis gel, and the aqueous phase during the synthesis.; A complete range of SiO2/Al2O3 ratios (18--60) for non-organic ZSM-5 formation is studied to explore the differences in crystal growth, crystal properties, and aqueous phase compositions as a function of the synthesis ratio. The techniques of x-ray diffraction (XRD), atomic absorption (AA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and inductively coupled plasma atomic emission spectroscopy (ICP-AE) are used in this research. Through AA and EDX measurements, our research shows a direct correlation between the amount of aluminum in the synthesis gel and that in the resulting ZSM-5. We also show that after synthesis the supernatant liquid contains exceedingly small amounts of aluminum, which implies that the aluminum is rapidly consumed during synthesis. Unit cell measurements show that as the amount of aluminum increases in the zeolite, the unit cell volume increases. SEM images of the ZSM-5 crystals show distinctly different morphologies as the SiO2/Al2O3 ratio is varied. At low SiO2/Al2O3 ratios, the ZSM-5 crystals transform, from the uniform ZSM-5 crystal commonly reported, to an irregular spike-like morphology.; Solid-solution aqueous-solution (SSAS) theories are investigated to describe the crystallization process of ZSM-5. These theories are commonly used for simple two-phase salt-water solutions. The description of ZSM-5 crystallization is more complex since an amorphous phase must be accommodated for in the system. The approach used by Doerner-Hoskins is employed in our studies to describe the layer-by-layer growth of the crystal. We analyzed results from a program using MATLAB. The model results are compared to experimental data, and adjustments are made to improve the model. A non-ideal version of the model is also discussed. The model is consistent with the experimental data for the aqueous phase, however, model outputs for the crystal composition differ from those seen experimentally. We conclude that because of the crystal morphologies, the Doerner-Hoskins crystal growth assumptions are acceptable only at high SiO 2/Al2O3 ratios, but are inconsistent with experimental observations at low SiO2/Al2O3 ratios.