Green Synthesis Of Zeolites And Hierarchically Porous Materials

Zeolites have drawn increasing interests in industrial separation and purification and petrochemical fields, as well as widely used in medicine, agriculture and detergent industries. The development of zeolites has been hundreds of years,however, there are many deficiencies in production. In particular, the procedure of synthesis brought some adverse impacts on the environment, such as expensive organic used as templating agent, complex operation and pollution caused by combustion of the organic template. Alternatively, green synthetic route and/or sustainable development of zeolites can optimize synthesis methods, making the synthesis process simple and efficient. This paper combined their respective advantages of microwave method, solvent-free synthesis and steam assisted conversation. Thus, the porposed method makes the zeolite synthesis and environment coordinated development. The main work in this paper includes the following aspects:1. Low silica zeolites(such as A, X, SOD) have relatively high aluminum contents and exchangeable cations, as well as a large number of applications in adsorption and ion exchange. Since 2011, annual global consumption of synthetic zeolite has reached 2.87 million tons, of which 73% are for detergent additives industry. Generally, zeolite A is synthesized under hydrothermal conditions, wherein the solid product is probably accounted for about one-fifth of the total volume, the results are not high yields owing to the participation of plenty of water. Since the Si/Al ratios in frameworks of zeolite A and X are equal to or close to 1, they have the greatest calcium and magnesium ion exchange capacities in theory. Thus, they also can replace the traditional sodium tripolyphosphate and become environmentally friendly detergent additives. In recent years, low-silica zeolites have served as oxygenadsorbent agents(5A, Ca X, Li X) and applied in the fields of pressure swing adsorption(PSA), however, the current market price of the common oxygen adsorbent is expensive, which limits its further promotion. Based on the potential market, we developed a method for green synthesis of low-silica zeolite, not only making the use of resources and energy rational, but also reducing the discharge and thus the product costs. In the second chapter, we used a strategy make the zeolite synthesis in a short time, that is heating the solid mixtures of raw materials by microwave radiation.Compared to traditional X zeolite, sub-micron MS-Na X has higher crystallinity and smaller particles by microwave solventless method. Additionally, the MS-Na X has a higher calcium ion exchange rate. Microwave solventless synthesis can also be used in preparation on other zeolites, such as LTA, LTA /FAU, SOD. The proposed zeolite synthesis method is more competitive in the future market thanks to high efficiency,energy saving, environmental protection.2. Silicalite-1 is a pure silica MFI-type zeolite with 10-ring channels used in gas separation, catalysis and chemical fields. Zeolites play an less important role in macro-molecular catalysis because of limitations of small pore diameter. Many researchers committed into the synthesis of multi-level and nano- zeolite structures in recent years. There are some problems exposed in current techniques such as soft template, hard template, alkali treatment and post-synthesis. In general, the use of expensive mesoporous templating agent increases costs and may lead to decline in crystallinity; alkaline etching will also decrease crystallinity, the biggest problem is low yields which resulted in difficulties in industrial production at a large scale. In order to solve the above problems, in third chapter we invented a novel method that solid materials can be transformed into hierarchical zeolites without mesoporous template, allowing the synthesis process simple, high yields and easy separation.Compared with traditional hydrothermal synthesis of Si-MFI zeolite, the HS-silicalite-1 has a higher adsorption capacity of methylene blue form aqueous solution. This green synthesis method would be expected to apply in the synthesis of other zeolites(such as ZSM-5, Beta, etc.), since they are of importance in the field of industrial catalysis.3. SOD zeolite is a small pore zeolite(2.8 ?) and used as a base catalyst because of their high aluminum contents and thermal stability. Typically, sodalite are synthesized under hydrothermal conditions, the synthesis mixtures charged in a sealed autoclave are heated under autogenous pressure at 60–100 °C. A large amount of water with low contents of silica and alumina necessitate the use of a large reactor,and accordingly, need a large amount of energy to carry out the reaction. Furthermore,the use of water to wash alkaline species off the synthesized zeolite SOD particles produces a large amount of alkaline wastewater. Therefore, we have adopted the solvent-free synthesis of zeolite, making the process eco-friendly and efficient. The solid-phase synthesis method is not only high yields, but a multi-hollow structure obtained in terms of SOD zeolite, which opened up a green pathway of synthesis of alkali catalyst.4. Compared to ordinary silicon-based mesoporous materials,aluminum-containing organic-inorganic hybrid mesoporous materials(Aluminum containing Periodic Mesoporous Orgaosilica) exhibit more excellent performance in the field of catalysis and adsorption because of containing a hydrophobic organic group. In recent years, periodic mesoporous hybrid materials is widely used in drug delivery, and other aspects of the catalyst carrier due to organic fuctional groups. In this paper, mesoporous materials PMO with ultra-high alumina contents were synthesized by self-assembly of surfactants. In the fifth chapter, Mesoporous organo-aluminosilicate spheres with high aluminium contents have been synthesized through a facile procedure under static conditions at room tempreture. The HMAS exhibit mainly tetrahedral coordination of aluminium after template removal with mild alkaline solutions, which can avoid both the destruction of hybrid mesoporous structure and dealumination. Moreover, the particle size of the HMAS can be easily tailored by controlling the concentration of the solution. The HMAS exhibits excellent removal capabilities of methylene(397 mg/g), which are higher than conventional silica-based mesoporous such as MCM-41. Thus, hybrid organosilica microspheres with ultra-high aluminium contents may provide a new chance for the application of periodic mesoporous oganosilicas for adsorption and catalysis. The higher adsorptioncapacity will play a major role in the field of wastewater treatment, it is expected to become the next generation of sorbent products.