Dynamics of flow and diffusion of adsorbing gases in Al2O3 and Pd-Al2O3 pellets

A nonisobaric pulse-response technique was proposed for the simultaneous analysis of flow and diffusion of adsorbing tracers in porous solids. Relative contributions of viscous flow, Knudsen flow, surface flow, and effective diffusion of adsorbing (hydrogen and carbon dioxide) and inert (helium) tracers in alumina and Pd-alumina pellets were evaluated. Hydrogen permeability was shown to increase by Pd impregnation into alumina, due to the contribution of surface flow, especially at low temperatures. The tortuosity factor, corresponding to the viscous and Knudsen flow, was found to be less than the tortuosity factors evaluated from effective diffusivities obtained from isobaric pulse-response experiments.