NMR study of mass transfer in granulated molecular sieves

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Abstract
Nuclear magnetic resonance (NMR) tracer desorption technique in combination with the traditional pulsed field gradient technique is applied to measure directly intracrystalline and long‐range molecular transport, as well as molecular exchange rates, between the individual crystallites in granulated molecular sieves. It is found that the granulation process leads to the formation of transport resistances on the external surface of the crystallites, which may be dramatically enhanced during their technical application. As an example, for granulated zeolite NaCaA the enhancement of such surface barriers under hydrothermal conditions and under the influence of a hydrocarbon atmosphere is studied. Since both intra‐ and intercrystalline transport are found to remain practically unaffected by this treatment, changes in the overall transport behavior are caused by the enhanced transport resistance on the external surface of the zeolite crystallites.