Zeolite production

Figure 4.7 Zeolite production in United States, Western Europe and Japan in Year 2000 (total 1.3 Mio t/years).

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... 

Zeolite Typical composition, mol/ mol AI Oi Zeolite product composition, mo)/ mol AtiOj ... 

Figure 10 Zeolite products from thermal treatment of gelled solutions. Zeolites are identified by the structures codes given in ref 21. Am is amorphous, Soln indicates no solid product was obtained and zeolites W and Rb-M are described in refs 22 and 23.

Effect of the TMA/Na Ratio on the Product. Changing the TMA/Na ratio in reaction series 1 and 2 had a pronounced effect on the nature of the zeolite product as shown in Table II. 

Table II. Effect of Tetramethylammonium on the Nature of the Zeolite Product...

As the TMA/Na ratio increased in another reaction series the zeolite product changed first from gmelinite to omega and finally to HS. 

The zeolite products with the highest XRD intensities and with the lowest amorphous material impurities were used as the quantitative standards for both Na-ZSM-5 and mordenite. The degree of crystallization was estimated by comparing the sum of the respective XRD peak areas (around 20 = 20-30°) with those of the standard. 

Chemical analyses and physical property measurements made on the starting materials and the products of the ammonium fluotitanate reactions are shown in Table 2. The analytical data for the products of the iron ammonium fluoride reaction are shown in Table 3. Following treatment, the various zeolite products contained up to 16.1 wt.% Ti02 in the zeolites treated with ammonium fluotitanate, and up to 16.9 wt.% Fe203 in the zeolites treated with ammonium Iron fluoride. X-ray powder diffraction intensity is decreased in the substituted products, but retention of oxygen and water adsorption capacity indicates that pore volume has been retained. No extraneous peaks due to other crystalline phases were observed in the X-ray powder diffraction patterns of well washed products. 

Dealuminated Y zeolites which have been prepared by hydrothermal and chemical treatments show differences in catalytic performance when tested fresh however, these differences disappear after the zeolites have been steamed. The catalytic behavior of fresh and steamed zeolites is directly related to zeolite structural and chemical characteristics. Such characteristics determine the strength and density of acid sites for catalytic cracking. Dealuminated zeolites were characterized using X-ray diffraction, porosimetry, solid-state NMR and elemental analysis. Hexadecane cracking was used as a probe reaction to determine catalytic properties. Cracking activity was found to be proportional to total aluminum content in the zeolite. Product selectivity was dependent on unit cell size, presence of extraframework alumina and spatial distribution of active sites. The results from this study elucidate the role that zeolite structure plays in determining catalytic performance. 

Table VI. Hexadecane Cracking Results for Calcined Zeolites. Product Slate at 50% Conversion...

Mechanical activation of the reaction mixtures by ball-milling before crystallization has been applied to the preparation of high-silica MWW crystals. Adsorption of water and toluene was used to characterize of zeolite products. 

Resins may also act as a substrate for metallic hydrogenation catalysts such as platinum, palladium, nickel, etc., but for high temperature petrochemical cracking and reforming reactions the thermally more stable zeolite products dominate this particular use. 

Powder x-ray diffraction (Siemens D-500 diffractometer) and scanning electron microscopy (JEOL, JSM-840) methods were used for characterization of zeolite products. Infrared spectra (Perkin Elmer 783 infrared spectrophotometer) were used for investigation of nucleation gel. The amount of Si, Al, Na in zeolite products was analysed by conventional analytical method, i.e. gravimetric for Si, gravimetric and volumetric methods (titration by EDTA) for Al and flame photometric method for Na. The WL value in Table 1 was used to estimate the amount of water and organic species in an as-synthesized zeolite product. 

Cesium will be separated from the supemate and loaded onto zeolite. The cesium-zeolite product could then be mixed with a solid matrix, such as cement or glass, to further reduce the cesium leach rate. A possible alternative is to mineralize the cesium by methods developed by Robert Barrer in England (2) and by Atlantic Richfield Co. at Hanford... 

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