Modeling of the transient sorption and diffusion processes in microporous materials at low pressure

Abstract

Using pulse-response experiments in an ultra-high vacuum reactor system the adsorption and diffusion behavior of gases in microporous materials can be determined. In a TAP-like system, called Multitrack, the adsorption of gases on zeolites and microporous carbons has been measured. This paper discusses the experimental procedures and the modeling to obtain the relevant sorption and diffusion parameters. Although this technique is macroscopic, contrary to other macroscopic methods such as thermogravimetrical and chromatographic techniques, the diffusivities obtained are in agreement with those determined using microscopic techniques such as NMR. The model used for the description of the measurements is discussed, together with some model simplifications that can be made for special experimental conditions. Possible extensions to the model are also discussed. Finally, the sensitivity of the method towards parameters like sorption strength, diffusion rates, particles size and occupancy range is discussed.