Synthetic ion exchangers

G. H. Osborn, Synthetic Ion Exchangers, 2nd ed.. Chapman and Hall, London, 1961. 

PhenoHc-based resins have almost disappeared. A few other resin types are available commercially but have not made a significant impact. Inorganic materials retain importance in a number of areas where synthetic organic ion-exchange resins are not normally used. Only the latter are discussed here. This article places emphasis on the styrenic and acryHc resins that are made as small beads. Other forms of synthetic ion-exchange materials such as membranes, papers, fibers (qv), foams (qv), and Hquid extractants are not included (see Extraction, liquid-liquid Membrane technology Paper.). 

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... 

Truly porous, synthetic ion exchangers are also available. These materials retain their porosity even after removal of the solvent and have measurable surface areas and pore size. The term macroreticular is commonly used for resins prepared from a phase separation technique, where the polymer matrix is prepared with the addition of a hq-uid that is a good solvent for the monomers, but in which the polymer is insoluble. Matrices prepared in this way usually have the appearance of a conglomerate of gel-type microspheres held together to... 

Ion-exchange Resins. An ion-exchange resin is made up of particles of an insoluble elastic hydrocarbon network to which is attached a large number of ionisable groups. Materials commonly used comprise synthetic ion-exchange resins made, for example, by crosslinking polystyrene to which has been attached non-... 

Although the phenomenon of ion-exchange has been appreciated for many years, it was the development, by D Alelio in 1942, of synthetic ion-exchange media based on the polystyrene resins that extended the use of ion-exchange as an analytical tool. 

In the broad use of the word polymer, ion-containing polymers are ubiquitous. They include inorganic substances such as silicate and borosilicate glasses discussed in Chapter 4, most biopolymers, solvent-swollen synthetic ion exchangers and some synthetic structural polymers. With few exceptions, these exhibit the characteristic feature of an electrolyte, ion mobility. In this chapter we consider the group of synthetic... 

Synthetic ion-exchange organic polymers are often network polyelectrolytes. 

Shrinking core model The shrinking core model has been derived for noncatalytic solid-fluid reactions (Levenspiel, 1972). However, it has been successfully used for specific ion-exchange systems—those using synthetic ion exchangers, mainly chelating resins (Cortina et al, 1998 Juang, 1999). 

Electro-osmotic oscillation (first observed by Teorell [1]—[4] in a laboratory set-up devised to mimic nerve excitation) may likely represent a common source of oscillations in various natural or synthetic electrokinetic systems such as solid microporous filters, synthetic ion-exchange membranes or their biological counterparts. The original experimental set-up, which contained all essential elements to look for when the electro-osmotic oscillations are suspected in a natural system, is schematically as follows. 

B. A. Adams and E. L. Holmes developed the first synthetic ion-exchange resins in 1935. Resins are relatively hard, amorphous organic solids. Gels are relatively soft. 

Ion-exchange packing materials are traditionally formed from the emulsion copolymerisation of styrene and divinylbenzene, the latter polymer is used to provide cross linking and thus increase the rigidity of the beads. Ionic functional groups are chemically bonded to this backbone. Pellicular silica-based packing materials may also be used which are then coated with a synthetic ion-exchange resin but these tend to have comparatively less sample capacity. 

Table 2.5 Functional Groups on Typical Synthetic Ion-Exchange Materials3...

The concentration was measured by comparing against a container (% = 0) having no zeolite, where the ammonium concentration in this container was taken as C [%] = 100%. A similar test was carried out in the aquaculture experimental station in Manzanillo, Cuba [85], Even though natural zeolites are inexpensive, it has limited NH4 removal capacity and cannot be easily regenerated when exhausted therefore, synthetic ion-exchange resins have been proposed for NH4 removal [79],... 

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