Synthetic zeolites preparation

Table 3. Some Synthetic Zeolites Prepared from Sodium Aluminosilicate Gels...

Sodium aluminate, 2 345t, 358-359 analysis, 2 275-276 economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 neutralization, 2 424 physical and chemical properties of, 2 273-274 uses of, 2 276-277 in water treatment, 26 111 Sodium aluminosilicate gels, synthetic zeolites prepared from, 16 831t Sodium aluminosilicates, 12 578 Sodium aluminum hydride, 13 621, 623-624... 

TABLE 2. SOME SYNTHETIC ZEOLITES PREPARED FROM SODIUM ALUMINOSILICATE OELS... 

Hydrogel drug carriers, 18 710 Hydrogel formation, PVA and, 25 603 Hydrogel processes, for preparing synthetic zeolites, 16 831-833... 

Kerr, G.T. (1964) Synthetic zeolite and method for preparing the same. US Patent 3,247,195. 

Japanese workers prepared examples of 2-alkenyl-4,5-oxazolediones 40a and 40b, which are key intermediates in the synthesis of alkenoyl isocyanates 41a and 41b (Scheme 6.13). These reactive monomers are precursors to a variety of functionalized polymers including instantaneously curable compositions. Thus, reaction of oxalyl chloride with acrylamide 39a or methacrylamide 39b affords 40a and 40b isolated as hydrochloride salts in high yields. Subsequent decomposition of the 2-alkenyl-4,5-oxazolediones in the presence of a metal halide or synthetic zeolite affords 41a and 41b contaminated with varying amounts of 42a and 42b. The synthesis and reactions of other 2-substituted 4,5-oxazolediones have been described independently by Speziale and co-workers ° and Sasaki and co-workers. ... 

More efficient use of the titanate material was achieved by passing the column effluent through a synthetic zeolite bed (Zeolon 900 Na from the Norton Co., Akron, Ohio) to sorb Cs which "leaked" from the column. A zeolite bed equal to 20% by weight of the titanate was sufficient to produce a Cs DF>10° in the effluent from a titanate column loaded to slightly more than 100% of the calculated capacity. The use of the zeolite does not effect the overall process conditions since it can be incorporated directly into the sodium titanate during preparation. A Dowex 1-X8 resin bed was used to remove the from the effluent and also served... 

Tn the course of experimentation with formulations of silica, alumina, and A various alkali metal oxides in attempts to prepare new synthetic zeolites, a formulation containing cesium replacing some of the sodium in a typical faujasite preparation yielded a new crystalline zeolitic product which showed a typically cubic powder diagram having a body-centered pattern of... 

Zeolites. We used the most open of the available synthetic zeolites, and Zn-exchanged forms of 1.87 Y and 2.62 Y were prepared as described previously (14). (The numerical prefixes refer to the Si-Al content of the zeolites). 

The computed values of WQ lie near those calculated from crystallographic data for synthetic zeolites. The value Wo = 0.195 cm3/gram estimated here for zeolite 5A also compares favorably with the mean value Wo = 0.20 cm3/gram previously obtained 21) for the adsorption of various adsorbates on the same adsorbent, without reference to any isotherm equation. For the synthetic zeolite, the preparation method may lead to variations in adsorption properties, and this may explain the difference between values of W0 shown in the Table I. Finally, for Cecalite, where no theoretical value is known, the values obtained here for W0 with two different adsorbates are consistent with each other. Thus, the proposed method gives realistic values for W0. 

A study is presented of the synthesis and properties of the novel synthetic zeolite omega. The synthesis variables and kinetics of formation are discussed, as well as the ion exchange, sorption, and thermal properties. By decomposition of imbibed tetra-methylammonium ions and exhaustive treatments of the zeolite with ammonium ions, a pure hydrogen form can be obtained which is a suitable substrate for the preparation of hydrocarbon conversion catalysts. Several catalysts were prepared and utilized to isomerize n-hexane, and to hydrocrack a heavy gas oil. 

In order to utilize the absorption properties or the synthetic zeolite crystals in processes, the commercial materials arc prepared as pelleted aggregates combining a high percentage of the crystalline zeolite with an inert binder. The formation of these aggregates introduces macro pores in the pellet which may result in some capillary condensation at high adsorhate concentrations. In commercial materials, the inacropores contribute diffusion paths. However, the main pan of the adsorption capacity is contained in the voids within the crystals. 

Although zeolites have been known for their adsorption properties for over a century, it was not until 1952, when the first synthetic zeolite was prepared, that their utility in chemical transformations was explored. Since that time, zeolites have been used for a multitude of purposes, and to this day, they are essential catalysts in the petroleum industry, converting large and small hydrocarbons into high-octane compounds. As an outgrowth of this work, zeolites have found utility in industrial fine chemical synthesis for the construction of aromatics, heterocycles, aliphatic amines, and ethers, and the photochemistry within zeolites has already grown out of its infancy. 

Since their discovery more than a century ago, many studies on zeolite minerals have been carried out. Moreover, in the late 1940 s the preparation of synthetic zeolites was the start of a large range of zeolitic materials reflecting the complete range of framework substituted tectosilicate including phosphates. 

Synthetic zeolites are the most important materials used currently in industry for catalyst preparation. However, natural zeolites are not contemplated in catalyst manufacturing because of the impurities present in the natural raw materials nevertheless, in some reactions, such as the isomerization of hydrocarbons, this contamination does not affect the catalytic transformation therefore, acid natural zeolites can be used for this purpose [19]. Furthermore, acid clinoptilolites were tested for catalytic cracking with success [19,21,137-143], We have shown [19,21,138-143] that the acid clinoptilolite, used as catalyst in the reaction of ethanol dehydration, exhibits high selectivity for ethylene production due to steric restrictions imposed on the formation of diethyl ether. The scheme of the ethanol dehydration reaction is shown in Figure 9.18 [145],... 

Series of zeolite-supported iron-containing catalysts with weight percent iron (% Fe) varying from 1 to 17% Fe have been prepared from Fe3(CO) 2 and the synthetic zeolites ZSM-5, mordenite and 13X by an extraction technique. The zeolites ZSM-5 and mordenite were used in the acid form, 13X in the sodium form. 

Before going on to list these families, one further point needs to be made. This arises because there are several instances where a unique zeolite framework has been first characterized from a laboratory preparation and later identified as a natural species. The first of these was mazzite, prepared first as synthetic zeolite ZSM-4 (or omega) but known in naMe prior to the allocation of the lUPAC code hence its inclusion in Table 7. The other species have been discovered in naMe after an lUPAC code had been allocated to their synthetic analogs. The details for these materials are given in Table 8. 

Particularly attractive method for preparation of synthetic zeolite is recrystallization of natural aluminosilicates, such as kaolinite (halloysite), previously formed for elimination of plastic flow of highly thixotropic, pulverized zeolite. Some additional components of initial mixtures, such as texture modifiers (hard coal, lignite, cellulose, silica, aluminum oxide) are also introduced. They enrich the structure of zeolite adsorbent in transport pores and prevent an excessive compression of the clay material during the formation process. This results in an increase in product efficiency during the crystallization of zeolite phase. 

Another major reason for studying mixed metal oxide membranes from double metal alkoxides is the potential for preparing zeolite>like membranes which can exhibit not only separation but also catalytic properties. It has been suggested that combinations of silica and alumina in a membrane could impart properties similar to those of natural and synthetic zeolites [Anderson and Chu, 1993]. Membranes with a pore diameter of 10 to 20 nm and consisting of combinations of titania, alumina and silica have been demonstrated by using a mixture of a meta>titanic acid sol, an alumina sol and silicic acid fine particles followed by calcining at a temperature of 500 to 900 C [Mitsubishi Heavy Ind., 1984d]. 

Many natural zeolites have a variable composition. It may be that the degree of Si—A1 order-disorder in synthetic zeolites may vary with preparation procedures. However, it would be of interest to determine what effect the order—disorder has on adsorptive and/or catalytic properties. 

Organometallics as a novel class of SDAs also offer the chance to generate new framework topologies, and this has in fact been accomplished in one case (see below) In particular, it might also be possible to discover the "Holy Grail" of synthetic zeolite chemistry, namely, the preparation of a chiral zeotype structure by using metal complexes as SDAs with a chiral shape. 

Johansson, G., Risinger, L., and Faelth, L. 1977. A cesium-selective electrode prepared from a crystalline synthetic zeolite of the mordenite type. Analytica Chimica Acta 119, 25-32. 

The synthetic zeolites NaX and NaY were obtained from Strem Chemicals Inc. CsY, LaY and HY were prepared by repeated ion-exchange of NaY as described elsewhere (ref. 11). The unit cell composition of the zeolites was determined by flame spectroscopy and EDX. The preparation of the molybdenum-zeolites and the CO hydrogenation experimental procedures have been reported earlier (refs. 

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