title: Uphill diffusion and overshooting in the adsorption of binary mixtures in nanoporous solids.
abstract: Under certain conditions, during binary mixture adsorption in nanoporous hosts, the concentration of one component may temporarily exceed its equilibrium value. This implies that, in contrast to Fick's Law, molecules must diffuse in the direction of increasing rather than decreasing concentration. Although this phenomenon of 'overshooting' has been observed previously, it is only recently, using microimaging techniques, that diffusive fluxes in the interior of nanoporous materials have become accessible to direct observation. Here we report the application of interference microscopy to monitor 'uphill' fluxes, covering the entire period of overshooting from initiation until final equilibration. It is shown that the evolution of the profiles can be adequately predicted from the single-component diffusivities together with the binary adsorption equilibrium data. The guest molecules studied (carbon dioxide, ethane and propene) and the host material (ZSM-58 or DDR) are of practical interest in relation to the development of kinetically selective adsorption separation processes.
authors.affiliation: Faculty of Physics and Earth Sciences, University of Leipzig, Linnéstraße 5, 04103 Leipzig, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lauerer
authors.affiliation: Faculty of Physics and Earth Sciences, University of Leipzig, Linnéstraße 5, 04103 Leipzig, Germany.
authors.forename: Tomas
authors.initials: T
authors.lastname: Binder
authors.affiliation: Faculty of Physics and Earth Sciences, University of Leipzig, Linnéstraße 5, 04103 Leipzig, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Chmelik
authors.affiliation: Department of Mathematics, University of Leipzig, Augustusplatz 10/11, 04109 Leipzig, Germany.
authors.forename: Erich
authors.initials: E
authors.lastname: Miersemann
authors.affiliation: Faculty of Physics and Earth Sciences, University of Leipzig, Linnéstraße 5, 04103 Leipzig, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Haase
authors.affiliation: Department of Chemical and Biological Engineering, University of Maine, 5737 Jenness Hall, Orono, Maine 04469, USA.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Ruthven
authors.affiliation: Faculty of Physics and Earth Sciences, University of Leipzig, Linnéstraße 5, 04103 Leipzig, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Kärger