Natural erionite

Natural erionite-clinoptilolite Selective-forming catalyst... 

In general, bifunctional catalysts are applied in hydrocarbon hydrogenation. In this regard, clinoptilolite [20,21] exchanged with Ni2+, and then thermally reduced, was used for the hydrogenation of ethylbenzene [21] and 1-hexene [24,25], A natural erionite ore exchanged with NH4 and Ni2+ and then calcined was tested for the hydrocracking of n-paraffin the catalyst was tested in a pilot plant and it was demonstrated that a catalytic life of more than 1 year is possible [22,23],... 

Besides, radioactive cobalt is a common radionuclide in liquid wastes from nuclear facilities, and natural erionite is a good exchanger for 60Co2+. Studies carried out with this material reveal its possibilities in the elimination of radioactive cobalt from solutions [73], The exchange of 232Th4+ in natural clinoptilolite and mordenite from liquid solutions has also been studied [74], All these peculiarities of natural zeolites make it suitable to be exploited as natural barriers for the migration of radionuclides and, consequently, natural zeolite deposits can be potential sites for a radioactive waste repository [19]. These materials have also been employed for the removal of radionuclides from polluted areas in places where nuclear power station accidents have occurred or where... 

First commercial process selectoforming (natural erionite, Weisz, Chen)... 

Erionite has been synthesized at i00°-I50°C from a (Na,K) aluminosilicate gel with Si02/AUOs = 10. X-ray and electron diffraction results on the product show intergrowths of the related offretite structure, which is a large-pore zeolite. Adsorption capacity for n-hexane is consistent with the density but adsorption rates are far slower than for zeolite A. Adsorption rates for n-octane are even slower but still better than for natural erionite. Hydrocracking tests on a C /Cq naphtha show strong selectivity for converting normal paraffins to Cf gas, particularly propane. As temperature is increased, other components of the naphtha feed are cracked and selectivity decreases. 

A second and more subtle area of difference is in the crystallography of the erionite phase itself (10). Table I compares x-ray diffraction intensities of low angle lines for a natural erionite (Jersey Valley, Nev.) and a synthetic erionite prepared at Esso Research Laboratories. The agreement is quite good except for those lines which have been marked by an astrisk indicating an intensity of less than half of that for natural erionite. Without exception, the designated lines (101, 201, 103, 211, 213, 311, and 401) have odd values for the 1 index. Further, their intensities are substantially less than the reference. 

Since offretite is a large-pore structure, intergrowth of offretite in the erionite phase would be expected to affect the adsorption properties. Table II compares adsorption capacities for natural and synthetic erionite with Zeolite A (Ca) and synthetic faujasite (Na) (4.8 Si02/Al203). As expected, the more dense erionite structure shows lower capacity (5). There is substantial agreement between natural and synthetic erionite capacity the difference shows in adsorption rates (D/r ). The low apparent diffusivity of n-parafBns in erionite is somewhat a mystery since there does not appear to be that much difference in pore dimensions between erionite and zeolite A as predicted from their structures (6). The difference cannot be attributed to crystallite size since the natural erionite sample (laths, 0.5 /x diameter or less) has finer crystallite size than any of the synthetic materials (1-5 /x). 

The difference is more notable in n-octane adsorption which is shown in the last 2 columns of Table II. Zeolite A shows substantially the same capacity and adsorption rate for n-octane as for n-hexane. But for erionite, both natural and synthetic, n-octane capacities, and particularly the adsorption rates are substantially reduced. Here the difference between synthetic and natural erionite adsorption rate is quite large. It is possible that this is an effect of residual cations. However, simple exchange of Na" and for H" showed little change. We believe the more probable explanation is the intergrowth of offretite in the erionite crystal. The large offretite channels could give more rapid distribution of the sorbate molecule within the synthetic erionite crystal. 

Catalyst Base Faujasite Zeolite A Natural Erionite Synthetic Erionite... 

D. L. Peterson (California State College, Hayward, Calif. 94542) Did you examine the temperature dependence of selectivity and conversion of the Zn or H forms of either the synthetic or the natural erionites ... 

Erionite is not known to be currently mined or marketed for commercial purposes. Natural erionite has been replaced by synthetic nonfibrous zeolites. However, erionite was used as a noble metal impregnated catalyst in a hydrocarbon-cracking process, and erionite-rich blocks was also used for house building materials. Its use to increase soil fertility and to control odors in livestock production has been studied. 

Natural erionite, synthetic nonfibrous zeolite with the composition of erionite, and crocidolite type asbestos were tested at a concentration of 10mg m inhalation in rats. Pleural mesotheliomas were found in 27 of 28 rats exposed to erionite one pulmonary and one pleural tumor were found in 28 rats exposed to synthetic zeolite, and one lung carcinoma was reported in rats exposed to crocidolite. 

A band near 3700 cm appears only in the spectra of synthetic (ref. 12) but not in that of natural erionites (refs. 8,13). This seems to indicate that the 3700 cm band represents OH groups of other phases formed during the (hydrothermal) synthesis. During thermal treatment these groups are irreversibly removed via dehydroxylalion. 

Shape-selective zeolite catalysts were first used in the Selectoforming process by Mobil in 1968. Hydrogen-exchanged natural erionite, containing some nickel,... 

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