Study On Synthesis Of Si-Al Zeolite In Ionic Liquid And Its Structure

Recently, as a new type of green environment-friendly solvent, ionic liquid(ILs) have attracted much interest of the researchers. ILs are salts composed of big organic cations and small inorganic anions. Different from other ionic compounds, melting points of ILs are close to the room temperature. They have unique properties: (1) nonvolatile, nonflammable; (2) good solvents for a wide range of organic, inorganic materials and polymer; (3) high thermal stability and chemical stability, wide range of liquidus temperatures (-90～300℃), (4) good ionic conductivity and large electrochemical window. Up to now, They are widely used in different chemical processes such as heterogeneous catalysis, organic synthesis, electrochemistry and analytical chemistry. However, In contrast to their successful applications above, the use of ILs in zeolite synthesis is still lack of reporting. The research according to the using of ILs in zeolite synthesis was first reported in 2004. Cooper et al. used [C₂mim]Br as both solvents and templates in the synthesis of AlPO₄-11 and molecular sieves with other frameworks under ambient pressure, but there is no report about the synthesis of Si-Al zeolite by this method.In the thesis, we investigated the synthesis ionic liquid of [C₂mim]Br and the Si-Al zeolite in the synthesized ionic liquids, namely ionothermal process, which is a novel method for zeolite synthesis. ILs can be used as the synthesis solvent, and reactions is conducted under ambient pressure due to their wide range of liquidus temperatures and high thermal stability in a wide range of temperatures. ILs have feature of self-organization since they have extended hydrogenbond systems in the liquid state and "supramolecular" structure is formed. Therefore, the organic cations of ILs can play a role of templates in the synthesis of zeolite, and synthesized process is template free. Sodalite (SOD) zeolite with micropores are successfully synthesized in our experiments, which has spherical morphology with 200～500 nm diameters. The synthesis started from aqueous basic aluminosilicate precursor gels and the zeolite crystallization completes in an imidazolium-based ionic liquid of 1-ethyl-3-methylimidazolium bromide. The effects of weight ratios of aqueous gels to ionic liquids, Si/Al molar ratios in gels and crystallization variables, such as temperature and time, on the crystallization of SOD zeoliet are investigated, and we dicuss the possible mechanism in the ionothermal synthesis. The results showed that a mixture of sodalite and zeolite X is initially formed in ionic liquid at a ratio 1:3 of aqueous gel to ionic liquid, and finally transformed to pure sodalite as the crystallisation time is prolonged. The best temperature of sodalite synthesis was between 60 and 90℃under ambient pressure. The crystallinity of sodalite increased with the increasing of Si/Al from 1.1 to 10. Increasing the ratio of aqueous gel to ionic liquid, zeolite X was favorable to crystallize, and it is the only product in the hydrothermal condition.