Cation exchange rates

Kennedy VC, Brown TC (1965) Experiments with a sodium ion electrode as a mean to studying cation exchange rate. Clays Clay Minerals 13 351-352 Khachikian C, Harmon TC (2000) Nonaqueous phase liquid dissolution in porous media Current state of knowledge and research needs. Trans Porous Media 38 3-28 Kookana RS, Aylmore LAG (1993) Retention and release of diquat and paraquat herbicides in soils. Austral J Soil Res 31 97-109... 

Enthalpies and entropies of complexation have been measured for complexes of 12,13 (105), 135) and 29, 30 (127) Cation exchange rates have been determined for complexes of ligands 15 (137,138) and 30 (106, 127). 

Combining the data on complexation selectivity (section IV.5.) and cation exchange rates (section IV.8.), it appears that flexible ligands, capable of undergoing conformational changes on complexation, should be able to form fast exchanging complexes while retaining sufficient stability and selectivity. 

In addition to specific carrier features, a number of external factors may also have marked effects on transport rates. The nature of the membrane phase (in particular for liquid or supported liquid [6.10b] membranes) influences the distribution equilibria as well as the stability and selectivity of the complex in the membrane and the cation exchange rates at the interfaces. The nature of the coextracted anion affects transport via a (cationic complex-anion) pair (Fig. 10) simply by modifying the amount of salt extracted into the membrane this amount decreases with higher hydration energy and lower lipophilicity of the anion (for example, chloride compared with picrate). The concentration of salt in the aqueous phase will, of course, affect the amount extracted into the membrane and therefore the transport rates (for illustrations of these effects see for instance [6.1]). 

Kennedy, V. C., and Brown, T. C. (1965). Experiments with a sodium-ion electrode as a means of studying cation exchange rates. Clays Clay Miner. 13, 351-352. 

Examples of pressure drop variation for new resin as a function of flow rate and water temperature are shown in Eigure 5 for a standard styrenic strong acid cation exchanger. The lower pressure drop at the higher temperature is a reflection of water viscosity. 

Eig. 5. Pressure drop as affected by resin type, flow rate, and temperature, where A, B, and C, correspond respectively to acryUc strong base anion exchanger (Amberlite IRA-458), styrenic strong base anion exchanger (Amberlite IRA-402), and styrenic strong acid cation exchanger (Amberlite IR-120), all at 4°C. D represents styrenic strong acid cation resin (Amberlite IR-120) at 50°C (14). To convert kg/(cm -m) to lb/(in. -ft), multiply by 4.33 to convert... 

When strong acid cation exchangers are used in the Na" form and strong base anion exchangers are used in the CL form, they are regenerated with a 10% sodium chloride [7647-14-5], NaCl, solution. Other concentrations may be used, perhaps with some adjustment in flow rate. 

Esterification. Extensive commercial use is made of primary amyl acetate, a mixture of 1-pentyl acetate [28-63-7] and 2-metliylbutyl acetate [53496-15-4]. Esterifications with acetic acid are generally conducted in the Hquid phase in the presence of a strong acid catalyst such as sulfuric acid (34). Increased reaction rates are reported when esterifications are carried out in the presence of heteropoly acids supported on macroreticular cation-exchange resins (35) and 2eohte (36) catalysts in a heterogeneous process. Judging from the many patents issued in recent years, there appears to be considerable effort underway to find an appropriate soHd catalyst for a reactive distillation esterification process to avoid the product removal difficulties of the conventional process. 

The hydrogen-deuterium exchange rates for 1,2-dimethylpyrazolium cation (protons 3 and 5 exchange faster than proton 4 Section 4.04.2.1.7(iii)) have been examined theoretically within the framework of the CNDO/2 approximation (73T3469). The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 

Example 8 Estimation of Rate Coejficient Estimate the rate coefficient for flow of a 0.01-M water solution of NaCl through a bed of cation exchange particles in hydrogen form with e = 0.4. The superficial velocity is 0.2 cm/s and the temperature is 25 C. The particles are 600 im in diameter, and the diffusion coefficient of sodium ion is 1.2 X 10 cmVs in solution and 9.4 X 10 cmVs inside the particles (of. Table 16-8). The bulk density is 0.7 g dry resin/cnd of bed, and the capacity of the resin is 4.9 mequiv/g dry resin. The mass action eqiiihbrium constant is 1.5. 

Scott et al. [12] provided some experimental evidence supporting equation (27). The mixture contained uracil, hypoxanthine, guanine and cytosine, each present in the mobile phase at a concentration of 14 mg/1. The column employed was Im long, 1.5 mm I.D., packed with a pellicular cation exchange resin and operated at a flow rate of 0.3 ml/min. 

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

The slower rate of hydrolysis of alkyl substituted esters in the presence of the cation exchange resin can be explained by the assumption that the alkyl groups interfere more in the formation of the intermediate complex on the resin surface than in the homogeneous system. The efficiency of the resin q was less than unity... 

J mol ). This is additional evidence in favor of rate limitation by inner diffusion. However, the same reaction in the presence of Dowex-50, which has a more open three-dimensional network, gave an activation energy of 44800 J mol , and closely similar values were obtained for the hydrolysis of ethyl acetate [29] and dimethyl seb-acate [30]. The activation energy for the hydrolysis of ethyl acetate on a macroreticular sulphonated cationic exchanger [93] is 3566 J mol . For the hydrolysis of ethyl formate in a binary system, the isocomposition activation energy (Ec) [28,92] tends to decrease as the solvent content increases, while for solutions of the same dielectric constant, the iso-dielectric activation energy (Ed) increases as the dielectric constant of the solvent increases (Table 6). 

The rate of hydrolysis of sarin on Dowex-50 cation exchange resin is insensitive to the stirring rate. However, with a more active catalyst (Amberlite-IRA 400), the rate constant at 20°C was 5.3, 7.5, and 8.5 h at 60,800 and 1000 revolutions/min , respectively, suggesting that film diffusion was the rate-limiting. step. Thus, the mechanism of the rate-limiting step depends on the nature of the catalyst [34]. 

Fig. 3. Cation-exchange chromatography of protein standards. Column poly(aspartic acid) Vydac (10 pm), 20 x 0.46 cm. Sample 25 pi containing 12.5 pg of ovalbumin and 25 pg each of the other proteins in the weak buffer. Flow rate 1 ml/min. Weak buffer 0.05 mol/1 potassium phosphate, pH 6.0. Strong buffer same +0.6 mol/1 sodium chloride Elution 80-min linear gradient, 0-100% strong buffer. Peaks a = ovalbumin, b = bacitracin, c = myoglobin, d = chymotrypsinogen A, e = cytochrom C (reduced), / = ribonuclease A, g = cytochrome C (oxidised), h = lysozyme. The cytochrome C peaks were identified by oxidation with potassium ferricyanide and reduction with sodium dithionite [47]...

Fig. 11a. Fractionation of (/) chymotrypsinogen A, (2) cytochrome C and (3) lysozyme on strong cation exchangers, a) Support Fractogel TSK 650(s)SP (conventional type) sample, 1 mg each flow rate, 1 ml/min column size, 150 x 10 mm T.D. Solvent A = 0.02 mol/1 phosphate, pH 6.0 solvent B = A + 1 mol/1 NaCl gradient, 0-10 min, 0% B 10-70 min, 0-100% B. b) Support Fractogel EMD 650(s)SO( — (tentacle type) conditions as in (a) [78]...

It is believed that clay minerals promote organic reactions via an acid catalysis [2a]. They are often activated by doping with transition metals to enrich the number of Lewis-acid sites by cationic exchange [4]. Alternative radical pathways have also been proposed [5] in agreement with the observation that clay-catalyzed Diels-Alder reactions are accelerated in the presence of radical sources [6], Montmorillonite K-10 doped with Fe(III) efficiently catalyzes the Diels-Alder reaction of cyclopentadiene (1) with methyl vinyl ketone at room temperature [7] (Table 4.1). In water the diastereoselectivity is higher than in organic media in the absence of clay the cycloaddition proceeds at a much slower rate. 

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