Exchangeable cations anions

Pure water for use in the laboratory can be obtained from tap water (hard or soft) by distillation if water of great purity is required, distillation must be carried out in special apparatus, usually made of quartz, not glass or metal precautions must be taken to avoid any spray getting into the distillate. Water which is sufficiently pure for most laboratory purposes can, however, be obtained by passing tap water through cation-exchangers and anion-exchangers as described above, when the water is deionised . 

Polymeric resins [81133-25-7], widely used in the food and pharmaceutical industries as cation—anion exchangers for the... 

Ion exchange is a process in which cations or anions in a Hquid are exchanged with cations or anions on a soHd sorbent. Cations are interchanged with other cations, anions are exchanged with other anions, and electroneutraUty is maintained in both the Hquid and soHd phases. The process is reversible, which allows extended use of the sorbent resin before replacement is necessary. 

Example 2 Calculation of Variance In mixed-hed deionization of a solution of a single salt, there are 8 concentration variables 2 each for cation, anion, hydrogen, and hydroxide. There are 6 connecting relations 2 for ion exchange and 1 for neutralization equilibrium, and 2 ion-exchanger and 1 solution electroneiitrahty relations. The variance is therefore 8 — 6 = 2. 

It has been shown that the effects found are caused by specific solvation of both the PhAA ionogenic and other polar groups by the plasticizers used, as well as by the influence of ion-exchangers nature on the PhAA cations-anionic sites complex formation constants. 

Variances in resin performance and capacities can be expected from normal annual attrition rates of ion-exchange resins. Typical attrition losses that can be expected include (1) Strong cation resin 3 percent per year for three years or 1,000,000 gals/ cu.ft (2) Strong anion resin 25 percent per year for two years or 1,000,000 gals/ cu.ft (3) Weak cation/anion 10 percent per year for two years or 750,000 gals/ cu. ft. A steady falloff of resin-exchange capacity is a matter of concern to the operator and is due to several conditions ... 

Provision of pretreatment The initial fill volume and MU supply is almost always pretreated in some manner. Because of the large volume of water in these systems, even low-hardness waters can produce sufficient quantities of calcium carbonate scale to severely impede heat transfer thus, for MTHW pretreatment, the use of ion-exchange softeners is the norm. For HTHW, some form of demineralization such as reverse osmosis (RO) or deionization by cation-anion exchange is typically preferred. 

CATION/ ANION type Resin Notes Total Wet Exchange Capacity meq/ml Max. Open Temp °F Swelling e.g. Na H... 

The BX converts all cations to sodium and the desilicizer exchanges all anions, including silica, for hydroxyl ions, thus effectively changing the treated water into a dilute caustic solution. This is normally a suitable proposition for boiler MU because the FW pH level typically required at these presssures is 8.5 to 9.5. A schematic layout of this type of plant is shown in Figure 9.3b. 

Figure 35. Schematic representation of the reversible variation of volume associated with the electrochemical switching of polypyrrole. Changes in free volume are mainly due to two effects electrostatic repulsions between fixed positive charges and exchange of cations, anions, and solvent molecules between the polymer and the solution. (Reprinted from T. F. Otero, H.-J. Grande, and J. Rodriguez, J. Phys. Chem. 101, 3688, 1997, Figs. 1, 3,6, 7, 13. Copyright 1997. Reprinted with the permission of the American Chemical Society.)...

Exchange diffusion systems are present in the membrane for exchange of anions against OH ions and cations against H ions. Such systems are necessary for uptake and output of ionized metaboUtes while preserv-... 

Coordination isomers occur when complex cations and complex anions are present and ligands are exchanged between anions and cations, for example ... 

Glucose hydrogenation to sorbitol was carried out on 40 wt% aqueous solution at 100°C, under 80 bar H2-pressure, in the presence of Ru/ACC catalysts prepared by cationic exchange and anionic impregnation. The hydrogenation of 10 wt% aqueous glucosone solution was conducted at 80°C under 80 bar H2-pressure on 2.5 wt%Pd/ACC catalyst in the presence of small amounts of NaHC03 added to increase the pH of reaction medium. Reaction kinetics was followed by HPLC and GC analysis of the reaction medium at different time intervals. 

In this scheme, a counter ion Y", attached to the R+ group on the resin, is exchanged for another anion X" from solution. To exchange cations, we need a structure with exchange sites that are negatively charged, and associated positive counter ions ... 

Liquid ion-exchangers have been discussed in the section on solvent extraction (p. 65). They can be used in column form by coating them on to a solid support such as cellulose powder or Kel-F (polytrifluorochloroethylene). Tris-n-octylamine (TNOA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) behave as strong-base and strong-acid exchangers for anions and cations respectively. 

Hoffmann, E. K. (1982). Anion exchange and anion-cation co-transport systems in mammalian cells, Phil. Trans. R. Soc. Lond. B, 299, 519-535. 

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