Ion-exchange structures

Light filters for colorimeters, see Filters, optical Limiting cathode potential 509 see also Controlled potential electro-analysis Linear regression 145 Lion intoximeter 747 Liquid amalgams applications of, 412 apparatus for reductions, 413 general discussion, 412 reductions with, (T) 413 zinc amalgam, 413 Liquid ion exchangers structure, 204 uses, 204, 560... 

Additionally, ion-exchanged structures can be tied to SiC>2 as in [(EtO)3Si(CH2)3PBu3]+. It is also possible to synthesize a complex such as (Ph3P)2R2P-4(CH2)x Si(OR)3RhCl which, upon hydrogenolysis, yields a silica-supported rhodium catalyst. 

In contrast to the stabilization of monovalent exchange cations in zeolites the structural aspects of stabilization of multivalent metal exchange cations are not quite clear. For example, the ion exchange position for bivalent metal cations should be formed by two lattice Al atoms. According to the traditional point of view the aluminum distribution over zeolite lattice is predominantly stochastic. It creates a variety of mutual localization of two nearest lattice Al atoms and results in a number of possible ion exchange structures for the bivalent cation stabilization. On the other hand, it is evident that structural peculiarities of bivalent metal cations stabilization influence the adsorption ability and catalytic reactivity of the cation. 

J. R. Millar, Some Aspects of Ion Exchanger Structure and Synthesis, in Kunstharz lonenaustauscher Akademie Berlin (1970). Sulfonated copolymer with two interpenetrating polymer networks. Ion exchange properties. Swelling properties. 

The ion-exchange structure may support anionic or cationic exchange. Williams and McMurray [133] showed that release of organic anions from hydrotalcite pigments in poly(vinyl butyrate) coatings could inhibit filiform corrosion with... 

As an adjective applied to metals base represents the opposite of noble, i.e. a base metal would be attacked by mineral acids, base exchange An old term used to describe the capacity of soils, zeolites, clays, etc. to exchange their cations (Na, K, Ca ) for an equivalent of other cations without undergoing structural change. An example of the general process of ion exchange. ... 

A tremendous variety of structures is known, and some of the three-dimensional network ones are porous enough to show the same type of swelling phenomena as the layer structures—and also ion exchange behavior. The zeolites fall in this last category and have been studied extensively, both as ion exchangers and as gas adsorbents (e.g.. Refs. 185 and 186). As an example, Goulding and Talibudeen have reported on isotherms and calorimetric heats of Ca -K exchange for several aluminosilicates [187]. 

Alternatively the ion exchanger may be a synthetic polymer, for example a sulphonated polystyrene, where the negative charges are carried on the —SO3 ends, and the interlocking structure is built up by cross-linking between the carbon atoms of the chain. The important property of any such solid is that the negative charge is static—a part of the solid—whilst the positive ions can move from their positions. Suppose, for example, that the positive ions are... 

Structures of styrene, divinylbenzene, and a styrene-divinylbenzene co-polymer modified for use as an ion-exchange resin. The ion-exchange sites, indicated by R, are mostly in the para position and are not necessarily bound to all styrene units. 

Structure Modification. Several types of stmctural defects or variants can occur which figure in adsorption and catalysis (/) surface defects due to termination of the crystal surface and hydrolysis of surface cations (2) stmctural defects due to imperfect stacking of the secondary units, which may result in blocked channels (J) ionic species, eg, OH , AIO 2, Na", SiO , may be left stranded in the stmcture during synthesis (4) the cation form, acting as the salt of a weak acid, hydrolyzes in aqueous suspension to produce free hydroxide and cations in solution and (5) hydroxyl groups in place of metal cations may be introduced by ammonium ion exchange, followed by thermal deammoniation. 

Polymer-based, synthetic ion-exchangers known as resins are available commercially in gel type or truly porous forms. Gel-type resins are not porous in the usual sense of the word, since their structure depends upon swelhng in the solvent in which they are immersed. Removal of the solvent usually results in a collapse of the three-dimensional structure, and no significant surface area or pore diameter can be defined by the ordinaiy techniques available for truly porous materials. In their swollen state, gel-type resins approximate a true molecular-scale solution. Thus, we can identify an internal porosity p only in terms of the equilibrium uptake of water or other liquid. When crosslinked polymers are used as the support matrix, the internal porosity so defined varies in inverse proportion to the degree of crosslinkiug, with swelhng and therefore porosity typically being more... 

Low-molecular-weight products, generally secondary metabolites such as alcohols, carboxyhc and an iino acids, antibiotics, and vitamins, can be recovered using many of the standard operations such as liquid-hquid extraction, adsorption and ion-exchange, described elsewhere in this handbook. Proteins require special attention, however, as they are sufficiently more complex, their function depending on the integrity of a delicate three-dimensional tertiaiy structure that can be disrupted if the protein is not handled correctly. For this reason, this section focuses primarily on protein separations. Cell separations, as a necessary part of the downstrean i processing sequence, are also covered. 

Clinoptilolite is microporous crystalline solid with well-defined structure, which have great potential for a number of applications in various fields, such as adsorption, separation, ion-exchange and catalysis. 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

Ion exchange on an acid column yields the crystalline dihydrate" H4P2O6.2H2O which is actually the hydroxonium salt of the dihydrogen hypophosphate anion [H30lJl(II0)P(0)2--P(0)2(0H)] " it is isostructural with the corresponding ammonium salt for which X-ray diffraction studies establish the staggered structure shown. 

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