Cation and anion exchange

The point at which two polymeric chains are joined together by a cross-linker such as divinylbenzene, or sites where tertiary hydrogens are located in the stmcture, are other locations for oxidative attack. In both cation- and anion-exchange resins, oxidative attack results in the removal of cross-linking. 

Ton-exchange systems vary from simple one-column units, as used in water softening, to numerous arrays of cation and anion exchangers which are dependent upon the appHcation, quaHty of effluent required, and design parameters. An Hlustration of some of these systems, as used in the production of deionized (demineralized) water, is presented in Figure 7. 

Demineralizers are often used to treat raw makeup water or condensate where high purity is required, such as in large central station boHers that operate at high steam pressures. Demineralizers employ a combination of cation and anion exchange to remove additional material, including sodium and ammonium cations. VirtuaHy aH salt anions, such as bicarbonate, sulfate, and chloride, are removed and replaced by hydroxide ions in the demineralizer. 

TABLE 16-7 Equilibrium Constants for Polystyrene DVB Cation and Anion Exchangers... 

Amberlite MB-1 cation- and anion-exchange resin, and allowing to crystallise. [Benesch, Lardy and Benesch J Biol Chem 216 663 1955.] Also crystd from MeOH or EtOH, and dried under vacuum at room temperature. 

In mixed-bed units, both the cation and the anion resins are mixed together thoroughly in the same vessel by compressed air. The cation and the anion resins being next to each other constitute an infinite number of cation and anion exchangers. The effluent quality obtainable from a well-designed and operated mixed-bed exchanger will readily produce demineralized water of conductivity less than 0.5 mmho and silica less than 10 ppb. 

The synthesis of ionic liquids can generally be split into two sections the formation of the desired cation, and anion exchange where necessary to form the desired product (demonstrated for ammonium salts in Scheme 2.1-1). 

Water-soluble pAANa anionic polymer interacts with ions through cation and anion exchange mechanisms. 

Numerous types of both cation and anion exchange resins have been prepared, but only a few can be mentioned here. Cation exchange resins include that prepared by the copolymerisation of methacrylic acid (E) with glycol... 

Ammonia-free water may be prepared in a conductivity-water still, or by means of a column charged with a mixed cation and anion exchange resin (e.g. Permutit Bio-Deminrolit or Amberiite MB-1), or as follows. Redistil 500 mL of distilled water in a Pyrex apparatus from a solution containing 1 g potassium permanganate and lg anhydrous sodium carbonate reject the first 100 mL portion of the distillate and then collect about 300 mL. 

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

For chemical and electrostatic reasons, some ions are bound more strongly than others. Polyvalent cations are much more strongly bound than univalent cations the same holds for anions. Thus, when a solution containing Ca ions (hard water) is passed through a cation exchanger which is present in its Na or H+ form, the Ca ions are held back in it and the Na or H+ ions leave instead. Similarly, an anion exchanger in the OH form will retain Cl or SO ions from the solution. By a cation and anion exchanger in series, the former in the H+ and the latter in the OH... 

Feibush, B. and Santasania, C. T., Hydrophilic shielding of hydrophobic, cation- and anion-exchange phases for separation of small analytes direct injection of biological fluids onto high performance chromatographic columns, /. Chromatogr., 544, 41, 1991. 

Air Filter wet ashed in HNO3/HF, purified with cation and anion exchange columns and electrodeposition a -Spectroscopy No data No data Knab1979... 

Extract of Kentucky 31 tall fescue was prepared by soaking 75 g fresh fescue leaves for 24 hours in 500 ml of distilled water. The extract was filtered and fractionated through cation and anion exchange columns according to the procedure described by Williams (6), Boland (7 ) and Boland and Garner (8). The extract was first... 

The adsorbent should have a high affinity and capacity for the enzyme and it should not absorb the reaction product or enzyme inhibitors. Among the materials used the more popular are cation and anion exchange resins, activated charcoal, silica gel, alumina, control pore glasses and ceramics. 

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