Browsing by Author "Klinowski, J."

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    Influence of Framework Charge Density on lon-exchange Properties of Zeolites
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Barrer, R. M.; Klinowski, J.
    Ion-exchange isotherms have been measured at 25 ’C for the high framework charge chabazite- typezeolite, K-Gl, and involving the cation pairs: K* F^Na*,Na* Li*, Na* f^ Cs*, Na* f^ Ca2*, Na* f^ Sr2*, and Na* f^ Ba2*. The results have been compared with those for an isostructural natural chabazite of lower charge density. The values of the thermodynamic equilibrium constants show that the larger ion is preferred by the zeolite of lower charge density. In terms of a solid state reaction involving exchange of ions between both zeolites, the standard free energy of exchange is negative if the larger ion goes from Gl to chabazite. All these results can be explained in terms of dielectric theory if the local dielectric constant in solution is greater than that in either zeolite, and if this constant is greater in a given cationic form of the zeolite of high charge density than in the corresponding form of the zeolite of lower charge density. The correctness of these assumptions for the zeolites was supported by measurements of the refractive indices. The exchanges involving caesium are incomplete in both Gl and the natural chabazite. The different limiting values for these two exchangers have been discussed in terms of steric, electrostatic and hydration effects. The pattern of exchange behaviour observed is consistent with that reported previously for the isostructural zeolites X and Y.
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    Ion Exchange Involving Several Groups of Homogeneous Sites
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Barrer, R. M.; Klinowski, J.
    Crystalline exchangers such as zeolites may contain more than one group of different exchange sites. The theoretical basis of these multi-site exchangers has therefore been examined. Overall exchange isotherms and selectivities have been expressed in terms of the properties of j different kinds of co-existent site. The resulting plots of log kc against equivalent cation fraction of the entering ion (Kielland plots) are complex, showing maxima, minima, inflection points and sigmoid shapes according to the properties of the several groups of sites. It is concluded that linear Kielland plots in such circumstances can at best only be approximations. Even where each group of sites behaves ideally the overall exchange isotherm can be strongly non-ideal. Where Kielland coefficients C1 are not zero for the overall isotherm, this isotherm may show maxima and minima (and hence limited solid solubility of the end members of the exchange), the criterion for which is a positive value of C1 which varies according to the valence of the exchanging ions. By an appropriate choice of quantities characterizing each of two groups of sites Kielland plots and isotherms were found, as an example, for chabazite which closely agreed with those determined experimentally.