Selectivity of ion exchange resins

Table 2. Selectivity of ion Exchange Resins in Order of Decreasing Preference.

Selectivity of ion-exchange resins in decreasing order of preference... 

The general characteristics of ion-exchange resin have been presente by Preuss and Kunin (P12) with special emphasis on those used fo uranium recovery. In the selection of ion-exchange resins for use in an ... 

By using countercurrent columns the two-temperature concept becomes more acceptable since the selectivity of ion-exchange resins may be changed by varying such process conditions as solution concentration, solution pH, the composition of solvent, and the presence of complexing reagents. 

Describe the factors that affect the selectivity of ion exchange resins,... 

Taking into account high capacity and selectivity of ion exchange resins for different dyes, they seem to be proper materials for dyes sorption from textile effluents. Applicability of the anion exchange resins in the removal of acid, reactive, direct dyes widely used in the textile industry, from aqueous solutions and wastewaters, was confirmed in some papers [2,15, 20, 23, 25-28]. 

Nature of ion exchange resin. The absorption of ions will depend upon the nature of the functional groups in the resin. It will also depend upon the degree of cross-linking as the degree of cross-linking is increased, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially. 

The first fractionation of urinary ampholytes in this way was carried out by Boulanger et al. (BIO) in 1952 with the use of ion-exchange resins. They had designed this procedure previously for the fractionation of ampholytes in blood serum (B8). According to this method, deproteinized urine was subjected to a double initial procedure aiming at the separation of low-molecular weight substances from macro-molecular ones. One of the methods consisted of the fractionation of urinary constituents by means of dialysis, the second was based on the selective precipitation of urinary ampholytes with cadmium hydroxide, which, as had previously been demonstrated, permits separation of the bulk of amino acids from polypeptides precipitated under these circumstances. Three fractions, i.e., the undialyzable part of urine, the dialyzed fraction, and the so-called cadmium precipitate were analyzed subsequently. 

Fig. 40. 2-D slice through a 3-D RARE image of a fixed bed of ion-exchange resin. The image has an isotropic resolution of 97.7 pm x 97.7 pm x 97.7 pm. The image slice in which the local volumes are located for the volume-selective spectroscopy study is identified. The image was acquired by saturating the bed with pure methanol. r2-contrast was exploited in the data acquisition so that signal was acquired only from the methanol in the inter-particle space. Reprinted from reference (84 with permission of Springer Science and Business Media.

The following sections will focus on the properties of ion-exchange resins, selection of experimental conditions, and applications of ion-exchange chromatography. 

In adsorption chromatography the mobile phase is usually a liquid and the stationary phase is a finely-divided solid adsorbent (liquid-solid chromatography). Separation here depends on the selective adsorption of the components of a mixture on the surface of the solid. Separations based on gas-solid chromatographic processes are of limited application to organic mixtures. The use of ion-exchange resins as the solid phase constitutes a special example of liquid-solid chromatography in which electrostatic forces augment the relatively weak adsorption forces. 

KF as the best basic reagents and towards DMF as the best solvent. An accurate determination of yields and purity of 9.73 in all reaction vessels selected entry 43 (TEA-DMF) as the best compromise for step a, Fig. 9.29. A similar optimization was performed for the f-butyl ester hydrolysis (step b, Fig. 9.29), creating the 39-member reaction library L19 by permutations of acidic reagents and solvents, and addition of adjuvants (Fig. 9.30). The screening outcome (Table 9.3) highlighted the poor performances of ion-exchange resins (no reaction) and TFA (unclean product) to prepare 9.74, and selected entry 7 (HCl/EtOAc) as the best reaction conditions to obtain clean 9.74 (CSA (camphor sulfonic acid) actually performed slightly better, but the reaction work-up was less automation friendly). The whole manual optimization process required three to four days, and the best reaction conditions were used directly to produce a 590-member discrete library, which met the >75% purity cutoff (78). 

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