Studies on the Mechanism of Zeolite X Crystallization. I. Effects of Silica Sources of Starting Materials on the Crystallization of Zeolite X

Abstract

Abstract The crystallization mechanism for zeolite was investigated. Tetraethyl orthosilicate and silica sol were used as silica sources. Many kinds of solid phases were obtained at various reaction times. These solid phases were characterized by analyses for chemical compositions, X-ray diffraction, adsorption of nitrogen gas and water vapor, and IR spectroscopy. The results obtained suggest that the solid phase derived from tetraethyl orthosilicate at an early stage of reaction is composed of slightly ordered skeletons. In addition, during aging of gel at room temperature, the structure of the solid phase of gel undergoes a rearrangement to form a crystalline structure. On the other hand, the gel phase obtained from silica sol is predominantly made up by the coagulation of disordered aluminosilicate polymers or silicic polymers. These gel phases act as a precursor, and a part of the gel dissolved into the liquid phase and the dissolved species are converted into crystals in the liquid phase. Thus, the silica sources influence the structure of gel and crystals. In general, the crystallization mechanism is strongly influenced by the starting materials, especially by the silica sources.