Diffusion in carbon molecular sieves

Kinetic data are reported for sorption of O-2, N-2, Ar, CH4 and CO2 in Bergbau-Forschung carbon molecular sieve. It is shown that for O-2, N-2 and Ar the data are consistent with internal diffusion control whereas the data for CH4 are consistent with surface resistance control. CO2 shows a transition from surface rate control at lower temperatures to diffusion control at higher temperatures. The data (particularly for CO2) are consistent with a dual resistance model. The relative importance of the two resistances depends on the ratio of their time constants which is affected by changes in temperatures or pressure as well as by subtle differences in sample pre-treatment.