Synthesis Of Magadiite And Recrystallization Of It Into Zeolites

Nowadays, research and development (R&D) of magadiite related materials are still in bugeoning in the field of material chemistry. Due to its excellent performance in ion exchange, adsorption and intercalation, magadiite is widely applied in catalysis, adsorption and noval advanced materials and so on. Recently, the applications of magadiite are not confined in the traditional adsorpotion and intercalation but in finding an alternative synthesis strategy of zeolites. In this dissertation, hydrothermal synthesis of magadiite using diatomite as raw material has been studied in details. The effects of synthesis conditions to the crystallization of magadiite have been analyzed by using X-ray powder diffraction (XRD). Futhermore, several zeolites such as offretite, mordenite, ferrierite and ZSM-5 have been prepared through recrystallization of magadiite. A series of methods, including XRD, scanning electron microscopy (SEM), X-Ray Fluorescence (XRF), infrared spectra (IR), thermogravimetry and differential thermal analysis (TG/DTA) and N2 analysis, have been introduced to characterize the zeolites from the crystal phase, images, chemistry contents, thermal stability and BET surface area. In addition, the influence of key reaction parameters on the formation of zeolite and the role of short-chain tetraalkylammonium (TAA+) cations on recrystallization have been examined. The main results are as follows:1. Magadiite has been synthesized hydrothermally from diatomite, a natural clay mineral. A series of methods have been introduced to characterize the magadiite. The basal space of the synthesized magadiite is 15.5 A and the image of magadiite reveals a rosette-like shape. The layered structure could be retained when the temperature is below 250℃. Some key factors in the formation of magadiite were investigated. Generally, the synthesis of magadiite from low-cost mineral may greatly reduce the cost of synthesis and pave the way for the following works.2. Using the as-sythesized magadiite, offretite has been prepared successfully in the presence of tetramethylammonium (TMA+) cations through recrystallization. A series of methods have been introduced to characterize the offretite. The image of as-synthesized offretite reveals that it is composed of small crystal agglomerates and the organic template was removed when the sample was calcined at 550℃for 10 h. The SiO2/Al2O3 of offretite is similar with the composition of reactants and the potassium content of offretite is more than the sodium. The structure of offretite is retained when the temperature is below 1000℃. The as-made offretite is pure and not intergrow with the erionite through the N2 analysis and the determination of sorption prosperity in water vapor. The influence of key reaction parameters on the formation of offretite was examined. The resultes indicate the feasibility of a synthetic route to offretite through recrystallization of magadiite in the presence of TMA+ cations and provide a new route to offretite.3. Using different types of short-chain tetraalkylammonium (TAA+) cations under various reactant conditions, offretite, mordenite and ZSM-5 zeolites are obtained respectively. The short-chain tetraalkylammonium cations includes tetramethylammonium (TMA+) cations, tetraethylammonium (TEA+) cations, tetrapropylammonium (TPA+) cations and tetrabutylammonium (TBA+) cations. The rule of recrystallization was investigated under various SiO2/Al2O3, Na2O/SiO2 and H2O/Na2O in the presence of four kinds of TAA+ cations. A series of methods have been introduced to characterize mordenite and ZSM-5 zeolite. The results indicate that TEA+ cations participate in the recystallization process and exist in the micropore of mordenite. The surface area of ZSM-5 zeolite by using TPA+ cations is larger than those by using TBA+ cations, most likely because the longer chain of TBA+ cations occupies more space in the intersection of ZSM-5 zeolites. The recrystallization of magadiite into ZSM-5 zeolite as a function of treatment time was investigated. The TPA+ cations are not intercalated into the layered space of magadiite. The influence of TPA+ cations and TBA+ cations is structure-directing on the magadiite recrystallization. It is possible that offretite and mordenite could be prepared easily when a small quantity of TMA+ cations and TEA+ cations are used and the synthetic process are promoted.4. Ferrierite was synthesized through recrystallization of magadiite in Al2O3-Na2O-ethylenediamine (EDA)-H20 system. A series of methods have been introduced to characterize ferrierite. The as-synthesized ferrierite is pure and is constituted by agglomerates of crystals that exhibit the platelet morphology. The thermal stability of as-made ferrierite is bad but the acid stability is excellent. The influence of various parameters such as reaction temperature, time, alkalinity and EDA/SiO2 ratio were examined. The resultes indicate the feasibility of a synthetic route to ferrierite through recrystallization of magadiite in the presence of EDA and provide a new route to ferrierite.