Zeolite synthesis mineralizers

This is the first monograph that was devoted to structure, chemistry and use of zeolites. It reviews zeolite synthesis to 1973, gives a detailed structural description of synthetic and mineral zeolites, illustrates their physical properties and describes applications. 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

There are about a hundred zeolite framework types. Some of these are found in nature, and are classified as minerals. However, most zeolite framework types are not found in nature but are synthetic, with the first having been reported in 1956. More are reported every year due to active research efforts in zeolite synthesis. 

In 1955 Union Carbide announced the commercial availability of a number of cationic forms of two synthetic zeolites designated A and X, the latter a synthetic form of the rare mineral faujasite. At this announcement, Mobil Research and Development Corporation, as well as the research and development laboratories of other major petroleum companies, hastened to obtain samples from the Linde Division. In 1955 and 1956 Mobil began to explore the potential use of these materials as adsorbents and catalysts and also began its own program on zeolite synthesis. 

It has been reported that methylene blue (MB) reacts readily with clay minerals by ion exchange and electrostatic bonding [3]. This mechanism should also hold for the found adsorption of MB at the external surface of zeolite crystals [4]. The incorporation of MB into zeolite voids has not yet been reported. In the following the accomodation of MB in NaY by either ion exchange or during zeolite synthesis is described. First evidence of persistent spectral hole burning in the described system is given. 

Until relatively recently, the only zeolites which were known were those which occur naturally as minerals, however, considerable advances have been made in the area of zeolite synthesis, and this has led to an enormous effort being channelled into the development of new and novel zeolite structures. There has also been a great deal of interest shown in incorporation of elements other than silicon and aluminium to tailor the electronic properties for specific applications. The major advantage of synthetic zeolites over naturally occurring ones is that, by a judicious choice of reactants, conditions, etc., it is possible to create structures of the required composition and dimensions. 

Although topology and chemical composition determined by zeolite synthesis are at the basis of the shape, size, dimensionality, intersections of pores, and cages formed in the zeolite crystals and therefore are directly responsible for shape selectivity and diffusivity, the catalyst in the final process always requires further fine tuning by a number of secondary treatments. A notorious example consists in the ultrastabilization of zeolite Y, via subsequent exchanges with ammonium ions, steaming, and mineral add treatment [19]. 

Murayama, N., Yamamoto, H., Shibata, J. Mechanism of zeolite synthesis from coal fly ash by alkali hydrothermal reaction. Inter. J. Miner. Process. 64, 1-17 (2002)... 

Y zeolites synthesized from pure chemicals have now been used as the main composition of FCC catalysts [1-4]. However, the application of Y zeolites synthesized from kaolin in the catalytic processes is still limited. The refinery and petrochemical industry is being built in Vietnam, so the synthesis of Y zeolites from domestic materials and minerals is necessary [4]. In this paper, the initial results in the synfliesis of Y zeolites with Si02/Al203 ratio of 4.5 fiom kaolin taken in Yen Bai-Vietnam and their catalytic activity for the cracking of n-heptane are reported. 

Many standard reactions that are widely applied in the production of fine chemicals employ. strong mineral or Lewis acids, such as sulphuric acid and aluminium chloride, often in stoichiometric quantities. This generates waste streams containing large amounts of spent acid, which cannot easily be recovered and recycled. Replacement of these soluble mineral and Lewis acids by recyclable. solid acids, such as zeolites, acid clays, and related materials, would represent a major breakthrough, especially if they functioned in truly catalytic quantities. Consequently, the application of solid acids in fine chemicals synthesis is currently the focus of much attention (Downing et al., 1997). 

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