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HYDROGEN ION EXCHANGE OF ZEOLITES ( hydrogen-ion-exchange-zeolites )

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UnitedStatesPatentO?lice 1 3,059,993 HYDROGEN-ll0N-EXCHANGE 0F ZEOLITES Richard M. Barrel‘, Brantley, and David C. Sammon, Harwell, England, assignors to Union Carbide Corpo ration,acorporationofNew York NoDrawing. FiledSept.12,1960,Ser.No.55,115 15Claims. (Cl.23-112) , insane Fat'enteoi Got. 23, 1962 2 for the zeolitic exchange sites on the basis of cation size and energy. A small cation wtih a high energy level is more likely to gain an exchange site than a cation of such size that it will just ?t into the framework, having onlytheminimumenergyforexchange. Obviously,ca tion concentration is also a factor that affects the proba bility of ion exchange. Thus, an aqueous solution of potassium chloride provides almost exclusive exchange of potassium ion for sodium ion when in contact with a This invention relates to a method for hydrogen ion exchanging three dimensional crystalline zeolites, and moreparticularlytohydrogenion‘exchangingsilverzeo 10 sodiumzeolite;thesmallamountofhydrogenionpresent lites. Hydrogen ion-exchanged zeolites may be employed as acidic catalysts in chemical reactions as acid ion-exchang by dissociation of water cannot successfully compete with the potassium and sodium ions for the exchange sites. By the method of this invention, hydrogen ions are madetoexchangesuccessfullybycontactingazeolitecon ers and as acidic adsorbents. For example, hydrogen ion-exchangedzeoliteX (describedandclaimedinpend 15 tainingsilvercationswithanaqueoussolutioncontaining ing application Serial No. 400,389 now US. Patent 2,882, 244) has been found to adsorb ozone from an ozone oxygengasmixtureat——78°C. Weightloadingsof8-10 weight~percent ozone were obtained as compared to 7 20 (3) only cations which permit hydrogen ions in the weight-percent adsorba'ble on silica gel under the same conditions. Atthislowtemperaturetheadsorbedozone wasonlyveryslowlydecomposed. However,athigher temperatures such as 0° C., the zeolite e?ects a rapid de compositionoftheozone. Thisisafurtheradvantagein 25 that when the hydrogen ion-exchanged zeolite is used to store ozone, any inadvertent temperature rise, instead of causing release of dangerously reactive ozone, evolves aqueous solution to compete successfully for at least a part of the exchange sites in the zeolitic crystal frame work. Hydrogenionsaretherebyexchangedinthesolu tion for at least a part of the Silver cations, and the latter are precipitated. Cations that permit substantial successful competition by hydrogen ion are cations which, because of their size, energy, or concentration, or combination of these factors, exchange with the exchangeable cations of the zeolite normal oxygen gas. Variousmethodsarepresentlyavailableforhydrogen 30 onlywithdifficulty,sothattheydonoteifec'tivelybarex ion-exchanging crystalline zeolites. Leaching the zeo lites with water gives a slight amount of hydrogen ion exchange. However, more thorough hydrogen ion-ex change can be achieved by treating the zeolite with an aqueousacidsolution. Solutionsofhigheraciditytend35 zeolite,analcite,withabouttentimesitsweightofsilver to provide greater hydrogen exchange but also tend to destroy the zeolitic crystal structure. An alternative method for providing hydrogen-exchanged zeolite is to ammonium ion-exchange the zeolite and decompose the ammonium ions and drive o? volatile ammonia, thereby leavingahydrogen-exchangedzeolite. Again,however, the crystal structure is at least partially destroyed. It is an object of this invention to provide a method for hydrogen ion-exchanging crystalline zeolites wherein the crystal structure is retained by the exchanged product. Other objects will be apparent from the disclosure. Zeolites are hydrated aluminosilicates having the gen eral formula expressed in terms of oxides as follows: M2OzAlzOazxSiOzzyHaO nitrate, and heating the mixture at about 220° C. to 230° C. in an open beaker in an electrically heated furnace for about four hours. This process was repeated, and the resultant mixture was cooled to room temperature, immersed in water to dissolve the impurities, ?ltered, washed and air-dried. ‘Part of this silver analcite was treated with a solution of tetraethyl ammonium iodide; tests indicated that about 60 percent of the silver ion had been replaced by hydro gen ion, and that substantially no teraethyl ammonium ion was exchanged. The exchange proceeded according to theequation: exchange was promoted by the low solubility of silver iodide. The remainder of the silver analcite was treated with worksofSiO.,andA104tetrahedron. Theterahedraare55 asolutionofcesiumchloride(47.5mg.CsClto10ml. wherein“M”representsatleastonemetal,and 12 its valence. Zeolites consist basically of three-dimensional frame cross-linked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and siliconatomsisequaltotwo. Theelectrovalenceofthe H2O) sothatthemolarratioofsilveranalcitetocesium chloridewas0.76. Themixturewasheatedoverawater bath for 18 hours, and the precipitated silver chloride removed by ?ltering the reaction mixture and leaching the tetrahedra containing aluminum is balanced by the in clusion in the crystal of a cation. One cation may be 60 residue ‘with cold, concentrated ammonium hydroxide. exchangedforanotherbyion-exchangetechniques. The spaces between the tetrahedra are occupied by water mole cules‘priortodehydration. Not all cations will cation-exchange with the zeolites. Some cations are too large to enter the zeolitic crystal 65 framework. That is, the maximum dimension of the minimum projected cross-section of the cation is large enough to hinder entrance of that cation into the pores of the zeolite. Other cations possess too little energy to enter the structure; some cations already present in the structure tend to repel the entering cations. It may be seen that competition exists between cations This procedure was repeated four times with fresh aque ouscesiumchloride. Theanalcitewasrinsed,driedand chemically analyzed. About 6.1 percent hydrogen-ex changehadoccurred. Theequationfortheexchangeis: A synthetic zeolite, sodium zeolite A (described and claimed in pending application Serial No. 400,388, now US. Patent 2,822,243), was silver ion-exchanged as fol lows: 35 grams of sodium zeolite A were treated with a solution consisting of 34 grams of silver nitrate, 0.85 gram of sodium nitrate in 200 milliliters of water at room temperaturefor30minutes. Thezeolitewasthen?ltered (1) hydrogen ions in a concentration not substantially greater than the hydrogen ion concentration of water, (2) anions which form precipitates with the silver cations and changewithhydrogenions. The method of this invention will be more clearly un derstood by the following examples. Silver analcite was prepared by grinding the natural if 50 wherein“Z”representsanalcite. Theextentofhydrogen



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