Commercial cation exchanger based

Microorganisms of family Actinoplanacease (by fermentation) Commercial cation exchanger based on polystyrene with a degree of crosslinking 3-4%... 

In the 1970s, DuPont developed a polymer based on PFSA called Nafion that not only showed a two-fold increase in the specific conductivity of the membrane but also extended its lifetime (10 -10 hours). This soon became a standard for PEFC and remains so today. The Dow Chemical Company and Asahi Chemical Company synthesised advanced PFSA membranes with shorter side chains and a higher ratio of SO3H to CF2 groups (Costamagna and Srinivasan, 2001). Table 1.7 (adapted from Smitha et al., 2005) provides a comparison of some commercial cation exchange membranes (CEMs). 

Ion Exchange. Crystalline molecular sieve ion exchangers do not foUow the typical rules and patterns exhibited by organic and other inorganic ion exchangers. Many provide combinations of selectivity, capacity, and stability superior to the more common cation exchangers. Their commercial utilization has been based on these unique properties (59). 

This i>aper describes two broad types of intercalation conpomds which are based on graphite on the one hand and sheet aluminosilicate (clay) hosts on the other. Taken together these provide a rich veiriety of examples of heterogeneously catalysed reactions. Appropriately cation exchanged clays, for example, act as efficient catalysts for a number of commercially important proton catalysed reactions (10-13) (see Table I). Graphite intercalates, whilst also capable of... 

One of the technically and commercially most important cation-exchange membranes developed in recent years is based on perfluorocarbon polymers. Membranes of this type have extreme chemical and thermal stability and they are the key component in the chlorine-alkaline electrolysis as well as in most of today s fuel cells. They are prepared by copolymerization of tetrafluoroethylene with perfluorovinylether having a carboxylic or sulfonic acid group at the end of a side chain. There are several variations of a general basic structure commercially available today [11]. The various preparation techniques are described in detail in the patent literature. 

Ion-exchange polymeric resins are the most important types of exchangers currently in use [113-123], The first, totally organic ion-exchange resin was synthesized in 1935 by Adams and Holmer, when they produced a phenol-formaldehyde cation-exchange resin and an amine-formaldehyde anion-exchange resin, both obtained with the help of condensation polymerization reactions [113], In 1944, D Alelio synthesized styrene-based polymeric resins, which could be modified to obtain both cationic- and anionic-exchange resins. The majority of the resins commercially applied currently are of this type, for example, Amberlite IR-20, Lewatit S-100, Permutit Q, Duolite, C-20, Dowex-50, and Nalcite HCR. 

Ordinary anion and cation ion-exchange resins are of limited use for the analytical concentration of trace elements from water, because of their lack of selectivity. This is especially so with strong electrolytes such as seawater. In this case the major ions sodium, magnesium, calcium and strontium, are retained preferentially. However, the recent advent of commercial chelating resins based mainly on iminodiacetic acid-substituted cross-linked polystyrene, makes it possible to concentrate trace elements from waters. In consequence, a number of researchers have used chelating resins for trace-metal preconcentration from seawater and natural waters. 

The development in the field of cation-exchange and anion-exchange resins have been discussed mainly on the basis of the monomers used for the synthesis of polymer matrices. Many of the chemical systems studied do not appear to be of commercial significance at first sight. Nevertheless, enough scope exists in designing novel syn-thesis/modification based on such systems so as to render them more useful and economically viable. 

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