Synthesis Of Zeolites From Cationic Polymer Template

Microporous zeolite type materials are widely used in ion-exchange, adsorption, separation, and catalytic areas. Up to now, 176 identified zeolite structure types have been reported by IZA, but only a few of them find industrial applications. The developments of zeolite materials are mainly focus on two directions: (1) synthesis of zeolite materials with new structures, and (2) extension of the composition of known materials byond known limits. Notably, these developments in zeolite area close related with templates used in the zeolite synthetic procedure. Since R. M. Barrer and P. J. Denny introduced organic quaternary ammonium in the synthesis of zeolites system in 1961 and proposed the concept of template, various inorganic and organic molecules have been used in the synthesis of zeolite materials and many new types of zeolite materials have been synthesized, promoting the development of microporous zeolite materials. Therefore, template has become one of the important topics of zeolite study area.The main aim of this paper is to find new type of templates used for the synthesis of zeolite materials. In this paper, we have successfully synthesized EMT, RHO, and Meso-NaX zeolites using novel organic template in different synthesis systems. The organic template used in our synthesis procedure is cationic polymer polydiallyldimethylammonium chloride (PDADMAC). Additionally, in the synthesis of Meso-NaX zeolite spirulina is also used as template.In this paper, we first have successfully prepared EMT zeolite with 12R channels (hexagonal polymorph of faujasite-type zeolites) used cationic polymer polydiallyldimethylammonium chloride as organic template. Usually, to synthesize EMT zeolite, the template used must contain high-cost and toxic 18-crown-6, which makes the high cost for preparing EMT zeolite and environmental pollution, limiting the practical application of EMT zeolite. In this paper, we have first investigated the systemic conditions for the synthesis of EMT zeolite using polydiallyldimethylammonium chloride as organic template in the absence of 18-crown-6. Additionally, cationic polymer used in the synthesis is low cost and nontoxic, which reduces the cost and environmental pollution producing from the synthsis of EMT zeolite. Otherwise, in the synthesis procedure of EMT zeolite, low-cost water glass was used as silica source taking the place of silica sol used in the traditional method. Additionally, we first used zeolite precursor solution to provide zeolite seeds in synthesis, saving the aging time of starting gels at room temperature. According to the results of experiments, we got the best synthetic condition for the preparation of EMT zeolite, including the amount of template, crystallization time, and crystallization template. In addition, the acid amount of EMT-rich faujasite is slightly higher than that of Y zeolite based on the results of NH3-TPD, and EMT-rich faujasite has higher conversion than Y zeolite in the cumene cracking reaction.The pore size of microporous zeolite materials is relative small, which limits the transmission of bulky molecules to the channels and limits the practical applications of zeolites. The mesoporous zeolites contain not only crystal wall and pore structure of microporous materials maintaining the properties of zeolite such as high hydrothermal stability, but also the mesopores improving the transmission of bulky molecules and increasing the catalytic and ion-exchange property. In this paper, we first use the combination of zeolite precursor and organic templates to prepare mesoporous NaX zeolite. In the synthesis procedure of mesoporous NaX zeolite, FAU zeolite precursor solution provides total silica source and zeolite seeds, cationic polymer polydiallyldimethylammonium chloride and spirulina provide organic templates. Under the synthetic conditions, FAU zeolite precursors assemble with organic templates, grow gradually, and form mesoporous NaX zeolite finally. According to high resolution SEM images of the samples, mesopores with the size mainly in the range of 4-50 nm can be clearly observed, and the sizes of most of mesopores are smaller than 10 nm. Additionally, we also can observe the connection of small particles into large NaX crystal in the SEM images of Meso-NaX zeolite. According to the results of N₂ adsorption-desorption of the Meso-NaX zeolites, the samples exhibit N₂ adsorption behavior of both microporous materials at low relative pressure (P/P0 <0.02) and mesoporous materials at high relative pressure (P/P0=0.4-1.0), conforming the coexistence of micropore and mesopore in Meso-NaX zeolites. Otherwise, the calcium ion exchange rates of Meso-NaX zeolites are higher than that of conventional NaX zeolites, and we think that the existences of mesoporous and small particles in Meso-NaX zeolites accelerate transmission of calcium ion in the channels, increasing the calcium ion exchange rate, which would be helpful for the application of X zeolite as ion-exchanger.RHO zeolite is one of small pore size zeolites with 8R channels. Now, various types of RHO zeolites with different framework components have been successfully synthesized with organic or inorganic cations templates in the synthetic procedures. However, although the RHO zeolite with aluminosilicate framework can be synthesized in the absence of organic template, the inorganic cation must contain high-cost cesium ion, limiting the application of RHO zeolite in industry. Based on the seeking of novel template for preparation of RHO zeolite with aluminosilicate framework, we have first successfully synthesized aluminosilicate RHO zeolite using cationic polymer polydiallyldimethylammonium chloride as template in the absence of cesium ions. Additionally, we have systematically studied the effect of organic template, basicity, crystallization time, and crystallization temperature on the growth of RHO zeolite. We have characterized the RHO zeolite by H2O and N2 adsorption experiments. Owing to the small pore size, RHO zeolite only has adsorption behavior to water molecules. Therefore, aluminosilicate RHO zeolite could be used as dryer for gases such as nitrogen. The new approach to synthesizing aluminosilicate RHO zeolite in the presence of cationic polymer greatly decreases the cost of preparing RHO zeolite and the pollution to environment, which is helpful for practical applications of RHO zeolite.The samples were characterized by X-ray diffraction, scanning electron microscopy, N₂ adsorption-desorption, ²⁹Si NMR, NH₃-TPD, the cracking of cumene, calcium ion exchange, and water adsorption. According to the results of different characterizations, zeolites synthesized in the paper display different potentials in various areas.