Properties of ion exchangers

With ion exchangers, a large number of abbreviations are in use some more common 

TABLE 12.1 Some abbreviations used with ion exchangers 

All these functional groups can be bound on organic resins such as styrene-divinylbenzene or on silica (however, note the limited chemical stability of silica-based bonded phases as described in Section 7.5). The ligand density, which is identical with the maximum ion exchange capacity, is ca. 3 meq (milliequivalents) per gram on S-DVB and ca. 1 meq per gram on silica. However, silica has a higher density, therefore the capacities per volume unit of the HPLC column are similar for both types. 

With ion exchangers, a large number of abbreviations are in use some more common ones are listed in Table 12.1. Note that the first four abbreviations denote the type of exchanger where the other ones are related to its functional group. 

All these functional groups can be bound on organic resins such as styrene-divinylbenzene or on silica (however, note the limited chemical stability of 

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Hydraulic properties, of ion-exchange resins, 74 399 403 Hydraulic retention time (HRT), in biological waste treatment, 25 829 Hydraulic scales, 26 229-230 Hydraulic-settling classifiers, 22 275 Hydrazide(s), 70 504 73 573-576... 

Physical properties of ion-exchange resins (Perry and Green, 1999)... 

In the homogeneous mechanism, the reaction is assumed to start by protonation of one of the reactants, either ester (mechanisms denoted as Aac1 and Aac2 [397,398]) or, less frequently, alcohol (mechanism Aal1). It seems likely that protonation of reactants is an important step in esterification catalysed by ion exchangers, too. This follows from all that has been said above about the effect of the acidic properties of ion exchangers on their catalytic activity and is further supported by the effect of the dielectric constant of solvents (Fig. 18), which indicates that the reaction mechanism involves a positive ion and a dipolar molecule [454]. 

TABLE 15.4. Properties of Ion-Exchange Materials (a) Physical Properties... 

The most desired properties of ion-exchange membranes are high permselectivity, low electrical resistance, good mechanical and form stability, and high chemical and thermal stability. In addition to these properties bipolar membranes should have high catalytic water dissociation rates. 

Earlier discussion introduced the concept of using the characteristic truncated octahedral elements of the sodalite framework to explain the molecular architecture of the synthetic zeolites X and Y (see Section. 2.4.3). There are other structural correlations that can be drawn between felspathoids and zeolites, for example, that the cancrinite cage (11-hedron) is a face-sharing element seen in the LTL, ERI, OFF, and EOS frameworks. Furthermore, in nature, salt ion pairs are contained in felspathoid minerals and when these are removed the residual framework exhibits the zeolitic properties of ion exchange and reversible water loss. Other similarities arise in that zeolites can imbibe salt ion pairs, and isotypic structures... 

Guan GQ, Kusakabe K, and Morooka S. Synthesis and permeation properties of ion-exchanged ETS-4 tubular membranes. Micropor Mesopor Mater 2001 50 109-120. 

Kusakabe K, Kuroda T, Uchino K, Hasegawa Y, and Morooka S. Gas permeation properties of ion-exchanged faujasite-type zeolite membranes AIChE J 1999 45(6) 1220-1226. 

Kunst B and Lovrecek B. Electrochemical properties of ion-exchange membrane junctions. Croat. Chem. Acta 1962 34 219-225. 

Strongly functional cation and anion e.xchange resins when hydrated (swollen) dis.s K iute (ionize) giving an internal electrolyte which is undetectable externally unless ion exchange occurs. This fundamental property of ion exchange resins is easily demonstrated using coloured acid-base indicators. 

Gregor and Pepper and their co-workers have carried out detailed studies on the swelling properties of ion exchange resins from which the following general conclusions may be drawn ... 

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