Exchange compositions

The aim of the present work was optimization of synthesis of SG -polymeric cation exchanger composite films by sol-gel technology in the presence of non-ionic surfactants and their application for detenuination of Zn (II) as phenanthrolinate (Phen) complex. 

Mass exchange composite curves, 20 740 Mass exchange network (MEN), 20 738, 739... 

A large body of experimental research exists concerning two-component ion exchangers, whose behavior is described by Eq. 5.1 or 5.2.5 These systems thus exhibit binary ion exchange equilibria. The central problem in applying chemical thermodynamics to them is to derive equations that permit the calculation of and the activity coefficients of the two adsorbate species.6 Several approaches have been taken to solve this problem, each of which reflects a particular notion of how exchanger composition data can be utilized most effectively to calculate thermodynamic quantities. 

One conceptually simple approach is to express all binary ion exchange reactions as combinations of the special case of Eq. 4.3, in which the species Q is deleted and SR = SR, with the possibility that more than 1 mol of SR may combine with adsorptive ions to form the adsorbate species. This approach portrays ion adsorption formally as a complexation reaction and builds ion exchange reactions as combinations of these reactions.7 Since the adsorbate species may be formed from both cations and anions (cf. Eq. 4.3), ion exchange reactions involving charged complexes [e.g., CaCT(aq) as well as monatomic ions [e.g., Na (aq)J can be described. If the further simplification is made that adsorbate species activity coefficients do not depend on exchanger composition, then equilibrium spccialion calculations can be performed exactly as described... 

Thus measurements of as a function of EB in a binary exchange system are sufficient to calculate the adsorbate species activity coefficients at any exchanger composition. 

In a multicomponent ion exchange system, the reactions between exchanging ions still can be expressed as in Eqs. 5.1 and 5.2, which are binary processes, but the description of exchanger composition in terms of mole or charge fractions requires a generalization of expressions like Eq. 5.12 ... 

Fig. 5.3. Three pathways of integration for Eq. 5.43, shown in a ternary exchanger composition diagram, for Na-Ca-Mg exchange reactions on montmorillonite. Note that integration path c, a binary pathway from Na- to Ca-montmorillonite, is simply the bottom edge of the ternary diagram.

For any pair of cations, we have two equivalent exchangeable fractions—Pi and P2. These two parameters are related through their exchange coefficient, Ki 2. They must also satisfy the condition Pi + P2 = 1. Then, from these two conditions. Pi and P2 are determined. If the CEC is known, their exchange compositions can be calculated. This principle can be extended to more than two cations. 

M. Hepel, X. M. Zhang, R. Stephenson, S. Perkins, Use of electrochemical quartz crystal microbalance technique to track electrochemiccJly assisted removal of heavy metals from aqueous solutions by cation-exchange composite polypyrrole-modified electrodes. Microchem J 1997, 56 (1), 79-92. 

Ibrahim NA (1992) New cation exchange composite based upon cellulose/melamine form-aldehyde/citric acid reaction products. J Appl Polym Sci 46 829-834... 

Synthetic fibres with ion-exchange properties were obtained from tapes extruded from polystyrene or its mixtures with polyethylene or polypropylene, by chlorosulfonation by chlorosulfonic acid for cross-linking, followed by treatment with aniline. Ion-exchange composite spun fibres have also been synthesized from a thermoplastic polymer and an aromatic vinyl polymer by immersion of the drawn fibres in chlorosulfonic acid at 20 °C, followed by treatment with dichloromethane, methanol and 10% sodium hydroxide, and drying to yield fibres with an ion-exchange capacity of 2.1 mequiv.g" . ... 

Lu, W., Lu, D., Liu, J., Li, C., Guan, R. (2007) Preparation and characterization of sulfonated poly(phenylene oxide) proton exchange composite membrane doped with phosphosilicate gels. Polymers for Advanced Technologies, 18, 200-206. 

Yan, X. Wang, Y. He, G. Hu, Z. Wu, X. Du, L., Hydroxide exchange composite membrane based on soluble quatemized polyetherimide for potential applications in fuel cells. International Journal of Hydrogen Energy 2013, 38(19), 7964-7972. 

The selectivity of a particular molecular sieve for a given ion as a function of exchanger composition is normally measured fi om an ion exchange isotherm, which is an isonormal [45], isothermal and reversible plot of equilibrium distributions of ions between the solution and zeohte phases. It is emphasised that it is only vahd to calculate selectivity coeffidents, and derived thermodynamic data, from isotherms which are reversible (that is, the forward and reverse isotherms coindde within experimental uncertainty). The types of isotherms. 

Thermodynamic Parameters, Non-Ideality and the Prediction of Exchange Compositions... 

Two points should be noted from Eq. (12). First, the magnitude of Dab depends strongly on the composition of the exchanger not only because it is a direct function of ionic concentrations, but also because it is a function of both and D b, which we have already noted vary with exchanger composition [45]. Secondly, Dab is a function of the non-ideaUty of the zeolite [data for which can be obtained, as we saw earUer, from the activity coefficients described in Eq. (10)]. One may expect therefore that to describe adequately the kinetic behaviour of even a binary exchange process in a molecular sieve would be a very compHcat-ed task. 

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