Measurement of Diffusion in Small Pore Zeolites to Improve Selectivity in Separation Processes

Abstract

The determination of mass transport coefficients is essential for the design of adsorption separation processes, especially for those driven by kinetic selectivity. In this chapter, a specific focus is given to the experimental measurements of adsorption kinetics in nanoporous zeolites. A selection of zero length column (ZLC) experiments on a series of zeolite Rho samples is presented to demonstrate the use of the ZLC technique to determine accurately the time constant of an adsorption process. The examples chosen examine the kinetic behaviour of complex materials characterised by severe hindering effect resulting in highly selective but very slow materials. In addition, the kinetic characterisation is complicated by the specific nature of Rho zeolites, which undergo structural change during the adsorption process. The discussion of the experimental methodology and the analysis of the results offer the opportunity to highlight some of the challenges related to the experimental determination of adsorption kinetics and discuss some of the best experimental practices. The contribution emphasises the importance of designing experimental methods addressing the needs of the inventors of novel materials: rapid and reliable measurements, small amount of sample required, rapid assessment of the performance and feedback for continuous improvement of the synthesis process and material development.