Ion-exchangers applications

The applications of zeolites can be divided into tliree major categories ion exchange, adsorjDtion and catalysis. The largest amount of zeolites is used in ion exchange applications while tire largest value is derived from catalytic applications [1, 33]. 

Most HPLC applications involving biomolecules utilize aqueous mobile phases. Critical parameters include both ionic strength and pH. Common solutes include TRIS, sodium phosphate, sodium acetate, and sodium chloride. Slightly alkaline pHs are preferable, for stability reasons. Specific examples of mobile phases include 50 mM TRIS, 25 mM KC1, and 5 mM MgCl2 (pH 7.2) for nucleotides, and 50 mM NaH2P04 (pH 7.0) and 20 mMTRIS and 0.1 M sodium acetate (pH 7.5) for both peptides and amino acids. All of these mobile phases are suitable for reverse phase or ion exchange applications. 

K. Stambert, Construction-Technological Problems of Ion Exchange Applications, Berlin, Akad-Verlag (1970) CA... 

Ion exchange resembles adsorption in that solid particles are used and regeneration is necessary. However, a chemical reaction is involved. In water softening, a typical ion-exchange application, an organic or inorganic polymer in its sodium form removes calcium ions by exchanging calcium for sodium. 

The cations on the as-made pillared clays are protons. The ion-exchange capacity of the original clay is preserved in the hnal pillared clay. Hence, PILCs can have very large ion-exchange capacities, for example, 140 meq/g for the Arizona montmorillonite. The high ion-exchange capacities of PILCs are potentially useful for ion exchange applications. 

Another ion-exchange application of natural zeolites is the removal of radioactive ions from waste-water [7,17,18,20,57,70,71], Chabazite, clinoptilolite, and mordenite selectively exchange radioactive Cs+ and Sr2+ from solutions [5,7,17,18,20,57,70,71], In addition, the high temperature, because of the activity of these radionuclides, and the effect of gamma radiation do not affect the performance of natural zeolites, which is the case for organic ion-exchange resins [72],... 

Dr. T.L Thomas participated in the earliest research on adsorption/desorption kinetics, air separation, pressure swing adsorption systems, liquid phase separations, and ion exchange applications. He directed many of the application studies between 1955 and 1959. 

Other major products of suspension processes include expandable polystyrene, where a volatile hydrocarbon is diffused into the polymer beads, and spherical divinylbenzene-based beads for chromatographie and ion-exchange applications. PVC is different from most other suspension proeess polymers in that it is produced by precipitation polymerization, as described earlier. 

A more complex field of ion-exchange application is associated with the separation of mixtures of substances that react similarly with ion-exchange resins. In this case the separation is based on differences in resin selectivity toward the mixture s components. These differences are characterized by the magnitude of the equilibrium separation coefficient which can be represented for a pair of ions as follows ... 

Practically every type of separation that has been done by the column technique can also be carried out by thin-layer chromatography. Several papers and reviews were published on the various aspects of the technique. In addition to the books on chromatography [17,26-301, an overview of ion-exchange application of TLC was presented by Devenyi and Kalasz 311. Recent results on the separation of enantiomers have been reviewed by Mack, Hauck and Herbert (32.33) (enantiomer. separation on an RP-18 plate, impregnated with copper salt and proline derivative as chiral selectors) and Lepri, Coas and Desideri, using a microcrystalline triacetylcellulose stationary phase, or modified beta-cyclodextrins in the mobile phase 134.35). 

The disadvantages of zeolites over resins for conventional ion exchange applications arise largely from their irregular physical form, friability, slower kinetics, and most importantly their chemical... 

The particle size has a significant effect on the hydraulics of an ion-exchange column. In about half of all ion-exchange applications, the design is based on hydraulic rather than chemical limitations (the allowable pressure drop dictates the smallest particle size used)... 

Examples of major ion-exchange applications are listed in Table 13.2-1, The fields of water treatment, effineal treat mam, and pollution control ate predominant and there heve been many recent advnaces. For example, the partial demineralization of brackish water using the Siimherm process has been developed in Australia and this is probably one of the most innovative developments in recent yarns. Important applications in the fields of medicine, pharmacology, chemical processing, catalysis, and analytical techniques are also mentioned. The remainder of this suction describes some important applications in detail. 

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