Cation-exchange techniques, stability

Cation-exchange techniques, stability constant determination of Pu sulfate... 

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. 

The kinetics and dynamics of crvptate formation (75-80) have been studied by various relaxation techniques (70-75) (for example, using temperature-jump and ultrasonic methods) and stopped-flow spectrophotometry (82), as well as by variable-temperature multinuclear NMR methods (59, 61, 62). The dynamics of cryptate formation are best interpreted in terms of a simple complexation-decomplexation exchange mechanism, and some representative data have been listed in Table III (16). The high stability of cryptate complexes (see Section III,D) may be directly related to their slow rates of decomplexation. Indeed the stability sequence of cryptates follows the trend in rates of decomplexation, and the enhanced stability of the dipositive cryptates may be related to their slowness of decomplexation when compared to the alkali metal complexes (80). The rate of decomplexation of Li" from [2.2.1] in pyridine was found to be 104 times faster than from [2.1.1], because of the looser fit of Li in [2.2.1] and the greater flexibility of this cryptand (81). At low pH, cation dissociation apparently... 

Ion chromatography (1C) allows the separation of substances in the form of ions, chiefly in aqueous solutions. Mobile phases used in the technique contain relatively large amounts of salts stabilizing the pH and determining the sequence of analyte retention. They enable the separation of only cations or only anions the ions that are not separated by a selected phase (cationic or anionic) are eluted in the column dead volume. As the next step, they can be loaded into appropriate ion-exchange columns in the second chromatographic dimension [148]. 

Beneficial Modification of HC-SCR DeNO Catalysts to Improve Hydro-thermal Stability. - Impairment of the hydrothermal durability of HC-SCR catalysts, particularly metal-exchanged zeolites which are of interest in high-temperature deNOx applications, can be either prevented or at least reduced by selecting appropriate parent zeolite structure, employing suitable preparation technique, modifying physicochemical properties, and adding subsequent cation. The former two approaches have been extensively described in the previous section and the other ones will be mainly discussed. 

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