Ion exchange compounds

Zeohtes (qv), ion-exchange compounds, have been researched to some extent and have been proposed to improve NPN utilisation (25). However, no improvement in NPN utilisation was found with lambs fed seoHtes (26). 

Complexation is one of several ways to favorably enhance the physicochemical properties of pharmaceutical compounds. It may loosely be defined as the reversible association of a substrate and ligand to form a new species. Although the classification of complexes is somewhat arbitrary, the differentiation is usually based on the types of interactions and species involved, e.g., metal complexes, molecular complexes, inclusion complexes, and ion-exchange compounds. Cyclodextrins (CDs) are classic examples of compounds that form inclusion complexes. These complexes are formed when a guest molecule is partially or fully included inside a host molecule e.g., CD with no covalent bonding. When inclusion complexes are formed, the physicochemical parameters of the guest molecule are disguised or altered and improvements in the molecule s solubility, stability, taste, safety, bioavailability, etc., are commonly seen. 

Carbonates are examples of builders that precipitate out the calcium ions in the form of calcium carbonate. Precipitating builders can leave behind insoluble deposits on clothes and washing machine components. Aluminosilicates such as zeolites are ion exchange compounds they remove (predominantly) calcium and magnesium ions and exchange them with sodium ions. 

The first attempt to employ ion exchange for commercial purposes was in 1896 by F. Harm, a German agricultural chemist, to remove Na and from sugar beet juice. The first synthetic ion exchange compounds were aluminum silicates called zeolites and were available commercially about 1903. 

Figure 23-3. p. 271, shows a diagram of a portion of a natural inorganic ion exchange compound, sodalite. 

Heparinoids and Mucopolysaccharides as Complexes, Clathrates, Ion-Exchange Compounds... 

W. A. England, M. G. Cross, A. Hamnett, P. J. Wiseman and J. B. Goodenough, Fast Proton Conduction in Inorganic Ion Exchange Compounds, Solid State Ionics, 1 (1980) 231-49. 

Oscillometric or high-frequency titration was invented simultaneously and independently by Foreman and Crisp and also by Jensen and Parrak in 1946. Inorganic ion-selective heterogeneous membrane electrodes were introduced for electrometric titrations by Pungor in 1961 and those with neutral organic complexing or ion-exchange compounds by Simon in 1966. 

Liquid-membrane electrodes include classical ion-exchange, liquid ion-exchange, and electroneutral ionophore-based liquid monbrane electrodes. Of particular interest are systems where the ion-exchanging compounds are dissolved macrocyclic compounds that have a strong selectivity to alkali metals. The stability of the formed complexes in nonpolar solvents far exceeds that found in water and allows for the fabrication of membrane-free micropipettes where the nonpolar/water interface is the membrane. Unfortunately, this leads to higher resistance than that exhibited by crystalline micropipettes and requires the addition of lipophilic salt to the nonpolar solvent to decrease the pipette resistance. 

Sephadex A trade name for an insoluble hydrophilic substance prepared by cross-linking dextran, and used in gel filtration. It can also be linked to acidic or basic groups for ion exchange or to alkanes for the chromatography of lipophilic compounds. 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

See Adsorption, LIQUID separation Aluminum compounds, aluminum oxide (alumina) Carbon, activated carbon Ion exchange Molecular sieves Silicon... 

Physical Properties. Physical properties of importance include particle size, density, volume fraction of intraparticle and extraparticle voids when packed into adsorbent beds, strength, attrition resistance, and dustiness. These properties can be varied intentionally to tailor adsorbents to specific apphcations (See Adsorption liquid separation Aluminum compounds, aluminum oxide (alumna) Carbon, activated carbon Ion exchange Molecular sieves and Silicon compounds, synthetic inorganic silicates). 

These ethers readily copolymerize with tetrafluoroethylene and other fluoroalkenes to commercially significant plastics, elastomers, and ion-exchange resins such as Teflon PFA, Kalrez, andNafton (see Fluorine compounds organic-tethafluoroethylene-perfluorovinylETHERcopolya rs EuASTOPffiRS, SYNTHETIC-FLUOROCARBONELASTOTffiRS lONIC POLYTffiRS). 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

U02(C02) 3. The pregnant solution is concentrated and purified by ion exchange or solvent extraction, yielding a stripping solution of ca 50 kg/m U Og. Uranium is then precipitated chemically. Pure U Og is obtained by calcination (see Uraniumand URANIUM COMPOUNDS). 

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

The aqueous sodium naphthenate phase is decanted from the hydrocarbon phase and treated with acid to regenerate the cmde naphthenic acids. Sulfuric acid is used almost exclusively, for economic reasons. The wet cmde naphthenic acid phase separates and is decanted from the sodium sulfate brine. The volume of sodium sulfate brine produced from dilute sodium naphthenate solutions is significant, on the order of 10 L per L of cmde naphthenic acid. The brine contains some phenolic compounds and must be treated or disposed of in an environmentally sound manner. Sodium phenolates can be selectively neutralized using carbon dioxide and recovered before the sodium naphthenate is finally acidified with mineral acid (29). Recovery of naphthenic acid from aqueous sodium naphthenate solutions using ion-exchange resins has also been reported (30). 

The batch and fed-batch procedures are used for most commercial antibiotic fermentations. A typical batch fermentor may hold over 150,000 Hters. When a maximum yield of antibiotic is obtained, the fermentation broth is processed by purification procedures tailored for the specific antibiotic being produced. Nonpolar antibiotics are usually purified by solvent extraction procedures water-soluble compounds are commonly purified by ion-exchange methods. Chromatography procedures can readily provide high quaHty material, but for economic reasons chromatography steps are avoided if possible. 

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