Erionite, synthesis

Figure 1. Erionite synthesis from silica sol, 0.25 K20/(K20 + Nc20),...

One of the earliest direct bonuses of imaging zeolitic catalysts by HRTEM was the discovery (10) that the nominally phase-pure ZSM-5 (structure code MFI) contained sub-unit-cell coherent intergrowths of ZSM-11 (MEL). It soon became apparent (46) that, depending on the mode of synthesis of these and other pentasil (zeolitic) catalysts, some specimens of ZSM-5 contained recurrent (regular) intergrowths of ZSM-11. It also emerged that intergrowths of offretite and erionite are features of both nominally phase-pure erionite and of pure offretite and of many members of the so-called ABC-6 family of zeolites (47). 

Another key step was the demonstration by P.B. Weisz and coworkers (3-5) of the shape selectivity of zeolite catalysts related to molecular sieving (1960). This initiated further research in the synthesis of new zeolites as well as industrial applications based on this property. The first commercial shape-selective process, Selectoforming, was developed by Mobil (1968) and allowed the selective cracking of the low octane (n-alkane) components of light gasoline over a natural zeolite (erionite) (6). 

The synthesis of erionite was reported by Zhdanov (11) in 1965. The medium was described as a mixed sodium-potassium aluminosilicate hydrogel at 90°-100°C but further details are not given. Breck and... 

Acara (1) had reported earlier the synthesis of zeolite T, which appears to be erionite as far as can be seen from the principal x-ray lines. 

Powerful evidence for the liquid-phase mechanism comes from the direct crystallization of zeolite from clear solution. In the early 1980s, Koizumi and coworkers carried out an extensive study on this topic. They directly synthesized analcime, hydroxysodalite, zeolite B, mordenite, zeolite P, faujasite,[30] erionite, and potassium chabazite from clear solution. Pang et al. directly crystallized zeolite A[31] and FAPO-5[32] from clear solution as well. The study on the direct synthesis of faujasite [30, 33] from clear solution will be elaborated below. 

The reaction of mono- and poly-alcohols catalyzed by solid acids has been widely investigated. An important application is the synthesis of five membered cyclic ethers starting from di- or triols. Several authors described such cyclisation reactions, starting from 1,2,4-butanetriol (clay) [1], 1,2,5-pentatriol (pentasile, mordenite, erionite) [2]. Linear ethers like dimethyl ether are formed from methanol (modified aluminosilicate, zeolites) [3,4] or MTBE from methanol and i-butene (zeolite, resin) [5,6] The yields of the desired products are often quite high, e g over 90 % in the case of 1,2,4-butanetriol to 3-hydroxy-tetrahydrofiiran and about 60 % in the case of dimethyl ether. The reactions are either carried out in the presence of water as slurry process [1,2] at 150 - 200 °C or at temperatures > 300 °C in the gas phase with a fixed bed catalyst [2-4]... 

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. 

HUMAN HEALTH RISKS Acute Risks (Fiberglass) cough sore throat asthma ear, eye and skin infections headaches nausea sinusitis insomnia Chronic Risks (Fiberglass) asthma chemical sensitivities respiratory disease Chronic Risks (Erionite) unscheduled DNA synthesis Chronic Risks (Glasswool) respiratory, lung cancer Chronic Risks (Rockwool and Slagwool) lung Cancer. 

ZSM-22 (TON) can be produced from potassium based 1,6 hexamethylenediamine synthesis mixture, while, ZSM-34 (an OFF/ERI intergrowth) is synthesized from the same synthesis mixture with the addition of sodium. NMR analyses of the as-synthesized zeolite samples indicated the presence of a carbonyl species in all of the ZSM-34 samples, but not in any of the preparations that produced ZSM-22. The carbonyl species was present only after the synthesis mixture was heated above ambient temperature. Molecular modeling studies calculated a favorable fit of the carbamic species within the pore system of the Erionite suggesting a reason for the formation of the OFF/ERI intergrowth. 

The declining oil reserves have stimulated considerable efforts towards the exploration of alternative sources of energy and organic chemicals. One solution is to use the abundant supply of coal as a source of synthesis gas (CO + H2) which is readily converted to methanol (MeOH). MeOH can then be transformed into higher molecular weight hydrocarbons (olefins, aliphatics and aromatics) over shape-selective zeolite catalysts, the most successful of which in this respect is H-ZSM-5, capable of converting MeOH to hydrocarbons up to Cio- The selective synthesis of ethylene and propylene, the key intermediates for the production of detergents, plasticizers, lubricants and a variety of chemicals, proceeds over smaller pore zeolites such as chabazite and erionite. 

Small to medium pore size zeolites, such as H-clinoptilolite, H-of6etite or H-eri-onite, are efficient for the hydroamination of ethylene [51-54]. Ethylene and NH3 react at 360°C and 50 bar over H-clinoptilolite to give EtNHi only (11.4% conversion). There is a clear shape selectivity since propene and 1-butene as well as higher amines give rise to extremely low conversions [52]. In contrast to H-cIinoptilolite or H-erionite, H-offretite is effective for proprene hydroamination with NH, (7.2% conversion, 90% i-PrNH -i- 8% i-Pr2NH) [55]. Small pore size H-erionite is the best catalyst in terms of lifetime, conversion and selectivity for the synthesis of ethyl-amine [56]. The efficiency of H-clinoptilolite can be improved by acid or base plus acid treatment of natural clinoptilolite (18% conversion, EtNH2/Et2NH>20) [57]. 

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