Chemical composition, various zeolites

The EPMA technique is developed for individual particles of fine-dispersed zeolite powder of various trademarks ZSM-5, ZSM-12, MOR, BEA. The phase and chemical composition of zeolite powder, the surface, shape of particles, stmcture and their distribution in terms of the size were studied using Superprobe-733 device. 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

Hydrolysis oftricaprylin in trimethylpentane by Fusarium solani pisi recombinant cutinase immobilized on various zeolites (NaA, NaX, NaY, LZY-82, dealuminated Y) was investigated in order to assess the effect of chemical composition (Si/Al ratio), hydrophilic character and acidity on the catalytic activity [221]. The adsorption of... 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

Various zeolites have been studied as the dispersed phase in the mixed-matrix membranes. Zeolite performance in the zeolite/polymer mixed-matrix membrane is determined by several key characteristics including pore size, pore dimension, framework structure, chemical composition (e.g., Si/Al ratio and cations), crystal morphology and crystal (or particle) size. These characteristics of zeolites are summarized in Chapter 6. 

Table 11. Nature crystallinity and chemical composition of various zeolites synthesized in presence of Na+ and HM++ ions...

Calculations that attempt to reproduce the observed vertical successions of zeolite minerals seen in various sedimentary piles (e.g., Miyashiro and Shido, 1970) typically assume that hydrostatic and lithostatic pressures are equal and that the pore fluid is pure water. The broad features of the successions can be predicted, but there is a bewildering overlap of zeolite subfacies (Coombs, 1971). In addition to the complexities already noted, it should be recalled that zeolites occur in an unusually rich variety of crystal structures, with several different major cations, extensive cation solid solution, significant Si/Al ratio differences in different structures, and frequent growth and persistence of metastable phases. The bulk chemical composition of the parent-rock is important in determining which zeolite mineral forms, and the Pco of the diagenetic environment may determine whether a non-zeolitic clay—carbonate assemblage persists (Zen, 1961). 

Table 3 gives the chemical composition of the various of ZSM-48 samples. The amount of incorporated water per unit cell is similar in all samples, its low value confirming the hydrophobicity of the high-silica zeolite. 

The size and shape of zeolite pores and channels are not the only factors that influence their use in catalysis - the chemical composition of the framework plays a major role in determining the catalytic properties. The chemical nature of the zeolite can be altered after the initial synthesis to enhance the catalytic properties for desired processes. The composition of zeolites is often referred to by the ratio of different T-atoms that are present. This is because the assembly process is essentially random and a regular distribution is not obtained. The positions of certain atoms cannot therefore be distinguished by diffraction techniques where the disorder of atom types makes accurate assignment impossible, solid state NMR spectroscopy has been of some use with this problem as Si chemical shifts are sensitive to the neighbouring Si/Al distribution which can lead to knowledge of the ratio of various Si environments. 

With the above studies, the influence of various parameters on the three most important properties (phase purity, particulate properties and chemical composition) of ZSM-5 zeoUtes can be clearly concluded in Table 2. From this smnmary, the most pronounced influence is attributed to the batch alkalinity, which changes all the relevant properties of the crystaUine-end product. In the large-scale synthesis of ZSM-5 zeolites for apphcation, the batch alkalinity should be strictly controlled to obtain the qualified product. Qn the other hand, among the mentioned three properties of ZSM-5 zeolites, the particulate properties are most sensitive to the change of the environment of crystallization. Thus, the synthesis of ZSM-5 zeolites with controllable imiform crystal sizes is always a hot, attractive and enduring topic in the field of zeolites. 

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