Zeolite hydrogen

Aikaiinity Bicarbonate (HCOs" ), carbonate (COs , and hydroxyl (OH ), expressed as CaCOs Foaming and carryover of solids with steam embrittlement of boiler steel bicarbonate and carbonate produce CO2 in steam, a source of corrosion Lime and lime-soda softening, acid treatment, hydrogen zeolite softening, demineralization, dealkalization by anion exchange, distillation, degasifying... 

Ammonia NH3 Corrosion of copper and zinc alloys by formation of complex soluble ion Cation exchange with hydrogen zeolite, chlorination, deaeration, mixed-bed demineralization... 

Dissolved Solids None Dissolved solids is measure of total amount of dissolved matter, determined by evaporation high concentrations of dissolved solids are objectionable because of process interference and as a cause of foaming in boilers Various softening processes, such as lime softening and cation exchange by hydrogen zeolite, will reduce dissolved, solids demineralization distillation reverse osmosis electrodialysis... 

Jacobs, P.A. and Mortier, W.J. (1982) An attempt to rationalize stretching frequencies of lattice hydroxyl groups in hydrogen-zeolites, Zeolites, 2, 226. 

Kerr, G.T. (1973). Hydrogen zeolite Y, ultrastable zeolite Y, and aluminum-deficient zeolites. Adv. Chem. Ser. 121, 219-229... 

Fig. 1. Generation and collapse of C0H g ion formed by chemical ionization (CHg ) or by hydrogen zeolite (HZ).

Hydrogen Zeolite Y, Ultrastable Zeolite Y, and Aluminum-Deficient Zeolites... 

Recent Developments in Hydrogen Zeolites with Emphasis on Zeolite Y... 

Barrer showed these hydrogen zeolites, mordenite and chabazite, to be crystalline using x-ray diffraction, and stated, Hydrogen zeolites are effectively crystalline aluminosilicic acids, the salts of which are their diverse cation exchange products." Szymanski, Stamires, and Lynch (13) used simple thermal decomposition of an ammonium zeolite X in an attempt to prepare the hydrogen zeolite... 

These workers conducted an infrared study on the presumed hydrogen zeolite and concluded, quite rightly, that constitutive or chemical water is lost from the hydrogen ion containing solid at temperatures above 400° C. In view of recent studies, however, it is unlikely that the zeolite... 

Later, Cattanach, Wu, and Venuto did an elaborate thermogravi-metric study on the calcination of ammonium zeolite Y and the resulting products (19). They found that the hydrogen zeolite reacted with anhydrous ammonia to yield an ammonium zeolite identical in ammonia content with the initial ammonium zeolite. Further, these workers reported that after loss of chemical water ( dehydroxylation according to Uytter-hoeven, Christner, and Hall or decationization according to Rabo, Pickert, Stamires, and Boyle) the sample became amorphous when exposed to moisture. This observation conflicted with the statement of Rabo et al. (16) in which they emphasized the extreme stability of their decationized Y. The data of Cattanach, Wu, and Yenuto prove, beyond any doubt, that they obtained the expected normal hydrogen zeolite Y prior to the loss of chemical water above 450°. Rabo et al., however, did not prove that the material from which they removed chemical water, was in fact, the hydrogen zeolite. They probably prepared, unknown to them at the time, the ultrastable zeolite described below. 

From 1967 to 1969, Kerr published a series of papers on the question of thermal and hydrothermal stabilities of sodium and hydrogen zeolite Y (22-26). These studies indicated that upon removal of about one-third of the aluminum from zeolite Y, using ethylenediaminetetraacetic acid (H4EDTA), the thermal and hydrothermal stabilities were much enhanced. This was observed for both sodium (23) and hydrogen (25) forms of the zeolite. The latter was prepared by careful calcination of an ammonium zeolite from which about 30% of the ammonium and aluminum had been removed. Kerr also showed that the true or normal hydrogen zeolite with... 

The expected true or normal hydrogen zeolite as indicated by Reaction 4 ... 

Ambs and Flank correctly observed that variables can be introduced into the calcination of ammonium Y so that a variable series of products can be obtained 33). However, there is no doubt that the normal hydrogen zeolite can be obtained from the ammonium form by carefully controlled calcination. In addition, carefully controlled calcination of the acid yields the dehydroxylated form. The ultrastable form, which can be prepared by a number of procedures described below, differs drastically in stability and composition from the other two forms. That it may contain some sites similar to, or perhaps identical with, sites in the hydrogen and dehydroxylated forms cannot be refuted. Unquestionably, however, the ultrastable form differs significantly from the other two forms. 

Direct Conversion of Hydrogen Zeolite Y. Kerr has reported that the normal hydrogen Y can be converted directly to the ultrastable form by heating in an inert static atmosphere at 700-800°C 22) or heating in a static ammonia atmosphere at 500°C 24). At 700-800°C, chemical water is thermally labilized and is envisioned by Kerr to effect hydrolysis of the acid zeolite. At 500° C ammonia labilizes chemical water whereby hydrolysis can occur. 

Y. Kerr showed that about one-third of the ammonium and aluminum could be removed from ammonium Y using H4EDTA 25). Carefully controlled calcination of this material (under conditions which yield the relatively unstable, normal hydrogen form from the normal ammonium form) yielded a hydrogen zeolite of very high stability. Kerr proposed the following reaction steps to explain the stability 23,25). 

The relationship between acid site density and effective acidity may account for the interesting observation of Hopkins that maximum cracking activity of n-hexane was obtained over a partially dehydroxylated hydrogen zeolite Y (45). While the normal hydrogen form would contain a greater overall concentration of acid sites, the partially dehydroxylated form may have a greater overall acid activity because of the increased effective acidity of the remaining sites. 

If the cations are hydrogen ions (see Section 3.2.4.), guest molecules may add to them to give, for example, hydronium, ammonium, oxonium, or carbenium cations. The latter two may rearrange, and then decompose or dissociate to give product(s) which can leave the zeolite. Oxonium ions in particular are central to the most economically important processes of petrochemical industry. In simpler words, hydrogen zeolites are very important catalysts. 

The thermal stabilities of hydrogen faujasites and mordenites with different Si/Al ratios are reported. The temperature fields are outlined which characterize the thermal resistance of the lattice, framework Al, hydroxyl coverage, and the active sites. By choosing the proper conditions for activation of hydrogen zeolites, it is possible to induce the release of Al from the framework and in this way to promote the formation of strong add sites and enhance the catalytic activity. 

Reports on the thermal stabilities of faujasites and mordenites are largely confined to their resistance to collapse at elevated temperatures. There is, however, a need to extend these works to the investigations of reactions which occur during the thermal treatment of hydrogen zeolites. These include aluminum migration, dehydroxylation and formation of new active sites. The present study is concerned with the effect of calcination temperature on the crystallinity, the extent of thermal dealumination, concentration of hydroxyl groups and catalytic activity of hydrogen faujasites and mordenites with different Si/Al framework ratios. 

G.T. Kerr and G.F. Shipman, The Reaction of Hydrogen Zeolite Y with Ammonia at Elevated Temperatures. J. Phys. Chem., 1968, 72, 3071-3072 G.T. Kerr, Chemistry of Crystalline Aluminosilicates. V. Preparation of Aluminum-Deficient Faujasites. J. Phys. Chem., 1968, 72, 2594-2596. 

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