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

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 gas es on zeolites and microporous carbons has been measured. This paper discus ses the experimental procedures and the modeling to obtain the relevant sor ption and diffusion parameters. Although this technique is macroscopic, con trary to other macroscopic methods such as thermogravimetrical and chromato graphic 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 sim plifications that can be made for special experimental conditions. Possible extensions to the model are also discussed. Finally, the sensitivity of th e method towards parameters like sorption strength, diffusion rates, partic les size and occupancy range is discussed. (C)1999 Elsevier Science B.V. Al l rights reserved.