Zeolites calcium form

Hopkins (161) found that a steady decrease in n-heptane cracking activity occurred over La- and Ca-exchanged Y zeolites as the catalyst calcination temperature was increased from 350° to 650°C. The lanthanum form was about twice as active as the calcium form. Reduction in activity with increasing activation temperature was attributed to removal of acidic framework hydroxyl sites as dehydration becomes more extensive. The greater activity of La—Y with respect to the calcium form was thought to result from the greater hydrolysis tendency of lanthanum ion, which would require more extensive dehydration to result in the same concentration of acidic OH groups as found on Ca—Y. 

We postulated that In the calcium form pure LSX should have about a 20% Increase In N2 capacity due to the Increased number of accessible calcium Ions. Figure 7 Illustrates a typical faujaslte structure Including the location of selected accessible and Inaccessible cation sites. The accessible cation content Increases 1n CaLSX. Standard CaX zeolite (S1/A1 = 1.25) has 43 calcium Ions per unit cell, whereas LSX has 48. In standard dehydrated CaX, 16 of the calcium Ions are In N2-1naccess1ble (site I) positions.(18) Assuming that the same siting occurs In LSX, there are 32 N2 accessible calcium Ions 1n LSX, compared to only 27 In a standard X. This results 1n an 18.5% Increase In the number of accessible cations. This Increase has a direct effect on the N2 equilibrium capacity which for pure LSX showed a 20% Increase over conventional X zeolites. Furthermore, compared to commercially available X adsorbents which all contain binders, the self-bound LSX adsorbents do not have any binder to "dilute" the active component and lower the gas capacity. 

Furthermore, the products from n-decane cracking were exclusively unbranched. In contrast, cracking the same feed over amorphous silica-alumina or the calcium form of the zeolite gave branched products (Table 10.1). This implied that not only was there selectivity for the shape of molecules that could access the reactive site, but also for those that departed. The eventual finding for... 

CO. The alternative assumption (i) did not lead to such a coincidence of calculated and measured isotopic separations. A comparison of the band profiles observed with CO on the calcium forms (asymmetric profile) and on sodium forms (symmetric profile) of the zeolites suggested that in the case of calcium-exchanged A- and X-type zeolites the rotation of the CO molecules is significantly hindered, which resulted in the observed one strong band and two shoulders on both sides. Thus, the three absorptions in the case of CO/Na-A were interpreted as indicating the R, Q and P branches, i.e., free rotation. The spectrum of... 

The choice of antiblocking additive depends on the polymer, the desired film quality, and whether there is a pigment. Several inorganic substances are used, including synthetic amorphous precipitated silica, diatomaceous earths, nepheline syenite, calcined clay, coated calcium carbonate, magnesium carbonate, magnesium sulphate, mica, talc and various zeolites. Calcium carbonate particles are approximately spherical, but silica ones are irregular mica forms sheets and talc is plate-like. 

Type 5A (five angstroms). Molecular sieve is the calcium form of the zeolite. Type 5A adsorbs molecules having a critical diameter of less than five angstroms (e.g., methanol, ethane, propane). Type 5A sieves can be used to separate normal paraffins from branched-chain and/cyclic hydrocarbons through a selective adsorption process. 

The product, NaA, is a white crystalline solid with a crystal density of 1.27 cm. Its crystals are normally l-2pm in diameter and have cubic symmetry. A typically unit cell formula is Na,2[(A102)i2(Si02)i2] 27H20 the sodium ions are readily exchanged in aqueous solution by cations such as calcium or potassium. In the sodium form, after dehydration at 350-400° in vacuo, zeolite A will sorb about 0.25 g H2O per gram of ash (at room temperature, 4 torr), but it will not sorb hexane. In the dehydrated calcium form, 0.27 g H2O per gram (4 torr) and 0.145 g hexane (10 torr) per gram are sorbed, but benzene is not. The X-ray diffraction pattern of NaA is as follows ... 

When the permanent hardness salt CaS04 passes through the bed, calcium zeolite (CaZ) and sodium sulfate (Na2S04 ) are formed, which are then flushed away. 

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

The coagulant sodium aluminate (NaA102) is strongly caustic (contributing hydroxide alkalinity to the BW) and reacts with calcium and magnesium salts and any silica present to form a zeolite sludge of calcium-magnesium-aluminum silcate. 

Several different possible zeolite structures may result, and if the sodium content is too high, calcium and magnesium are excluded and a hard zeolite scale of sodium-aluminum silicate preferentially forms. If only calcium is present, calcium-aluminum silicate zeolite forms, also as a hard scale. If only magnesium is present in solution, it forms the flocculant magnesium aluminate, MgAl204. 

The formation of heavy carbonaceous compounds in 5A calcium exchanged zeolites depends on the calcium content. These zeolites are able to protonated ammonia molecules in ammonium ions. This Bronsted acidity results from the presence of CaOH+ species which are formed by water dissociation on Ca2+ ions and have an IR signature at 3515 cm"1. 

The process is best shown by example. Suppose that we wish to balance the reaction by which calcium clinoptilolite (CaAl2Siio024 8H2O), a zeolite mineral, reacts to form muscovite [KAl3Si30io(OH)2] and quartz (Si02). We choose to write the reaction in terms of the aqueous species Ca++, K+, and OH-. 

The zeolite group of minerals provides further examples of defect structures. These are complex aluminosilicates, the crystals of which have a rigid framework of Al, Si, and O atoms in which there are continuous channels water molecules may enter or leave the crystals by way of these channels, the amount of water in the crystals being variable (W. K. Taylor, 1930, 1934). (In normal hydrates the structure collapses when water is removed, a new structure being formed.) A simple substance in which the same thing occurs is calcium sulphate subhydrate CaS04.0-fH20 (Bunn, 1941). 

In the physical separation process, a molecular sieve adsorbent is used as in the Union Carbide Olefins Siv process (88—90). Linear butenes are selectively adsorbed, and the isobutylene effluent is distilled to obtain a polymer-grade product. The adsorbent is a synthetic zeolite, Type 5A in the calcium cation exchanged form (91). UOP also offers an adsorption process, the Sorbutene process (92). The UOP process utilizes a liquid B—B stream, and uses a proprietary rotary valve containing multiple ports, which direct the flow of liquid to various sections of the adsorber (93,94). The cis- and trans-isomers are... 

Physicochemical properties of L zeolites and of clinoptilolite were studied by adsorption, chromatographic, spectral, and ther-mogravimetric methods. The sodium form of L zeolite is characterized by better adsorption with respect to water and benzene vapor and by higher retention volumes of C C hydrocarbons and CO than potassium and cesium forms. The activation energy of dehydration determined by the thermogravimetric method decreases on going from the sodium to cesium form of L zeolite. When calcium is replaced by potassium ions in clinoptilolite, the latter shows a decreased adsorption with respect to water vapor. The infrared spectra of the L zeolite at different levels of hydration show the existence of several types of water with different bond characters and arrangements in the lattice. 

Zeolite A. The structure of zeolite A contains two types of voids (1) the a cage, 11.4 A in diameter, and (2) the P cage (or sodalite unit), 6.6 A in diameter (7). Table I compares experimentally determined pore volumes of zeolite A with the void volume as calculated from the structure (no influence of cations considered). Since the sodium zeolite A does not adsorb normal paraffins, data are included for the calcium-exchanged form. Also shown in column 5 is the void fraction, Vi, as calculated by... 

In these experiments, synthetic zeolites of the faujasite-type without binding substance were used. Calcium and nickel-calcium samples in ionic form were obtained by ion exchange under conditions ensuring stability of the crystal structure (5). Platinum addition was carried out by ion exchange with Pt(NH3)6Cl4 (6). 

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