(710d) Kinetic Measurements on Hierarchical Zeolites Using the Zero Length Column

The Zero Length Column (ZLC) technique, first introduced for diffusion measurements in zeolites [1], has been under continuous development in the past three decades proving to be an essential tool for the investigation of kinetic and equilibrium properties of novel adsorbents. The very small size of the column offers several key advantages compared to other experimental methods. Foremost, the small sample quantity required greatly reduces the synthesis costs of the materials and allows rapid testing of prototype materials. In additionheat resistances and external mass transfer resistances can be neglected and axial dispersion is maximised and as a result, the dynamic response of the ZLC corresponds to that of a perfectly mixed isothermal cell.

Here we present the use of the ZLC for the study of the adsorption kinetics of three hierarchical and the parent Y zeolite. We will show how the novel experimental approach, based on the choice of the most appropriate probe molecule, mesitylene, and the combination of full and partial loading experiments, allows to measure accurately the kinetics of the different zeolites using less than 1 mg of sample. Results show how different synthesis routes lead to different prevailing mass transport mechanisms. The use of the partial loading experiment is used to characterise the combined diffusion and surface resistance mechanisms as well as demonstrate if the system follows a pure diffusion model.

Of the samples tested, one is shown to result in adsorption rates that are four times faster than the parent sample, while one is shown to give slower mass transport kinetics, indicating that simply producing hierarchical materials does not necessarily result in improvements in the mass transport properties and that combining the synthesys process with screening using the ZLC technique can be very effective.

[1] Eic M. and Ruthven D.M. A New Experimental Technique for Measurement of Intracrystalline Diffusivity (1988), 8, 40-45