Binder, Thomas

Chmelik, Christian

Kärger, Jörg

Ruthven, Douglas M.

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The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and ApplicationMass-transfer of binary mixtures in DDR single crystalsTomas Binder1∗, Christian Chmelik1, Jo¨rg Ka¨rger1, Douglas M. Ruthven21Department of Interface Physics, Universita¨t Leipzig, Leipzig, Germany2Chemical and Biological Engineering, University of Maine, Orono, USA∗tomas@uni-leipzig.deFor the first time, micro imaging by interference microscopy (IFM) is applied for studying uptakeand release of guest molecules in nanoporous host material for investigating the adsorption of gasmixtures and for correlating the thus observed behavior with corresponding single-component sorptionexperiments. Combining the advantages of high spatial and temporal resolution in the order of 0.45 µmand 15 s, respectively, this promising approach results in time-dependent two-dimensional profiles ofthe intra-crystalline sorbate concentration of the single crystal under study [1, 2, 3]. However, with thelack of differentiation of different species present inside the microporous framework only certain typesof experiments seems feasible, notably when the mixture consists of species with large differences inthe rate of mass transport under the confinement of the channels, cages and windows of e.g. zeoliteZSM-58, which is well known from previous IFM studies [4].Figure 1: IFM mixture experiments are enabled by several orders of magnitude difference in the single-componentdiffusion rates of e.g. CO2 and ethane leading to apparent instantaneous uptake of CO2 and much a slowersorption process for ethane. When provided as a 1:1 gas mixture of ptotal = 400 mbar, CO2 reaches a quasi-equilibrium at about 30% IFM signal (shaded area) followed by additional and much slower ethane adsorption.Hence, influences of the presence of CO2 on the diffusivity of ethane can be examined.We report the results obtained with the host-guest-system CO2 and ethane in ZSM-58 together withtheir single-component equivalent. The experiments could be carried out as true mixture adsorptionIFM measurements benefitting from the huge difference of the diffusion coefficients of the two species.The almost instantaneous increase of IFM signal equally distributed throughout the whole crystal cantherefore be correlated with the very fast uptake of CO2, see shaded area in Fig. 1, with the ethaneadsorption starting shortly afterwards.References[1] C. Chmelik, L. Heinke, R. Valiullin, J. Ka¨rger: A new view of diffusion in nanoporous materials.Chem. Ing. Tech. 82, 779–804 (2010)[2] C. Chmelik, J. Ka¨rger: In situ study on molecular diffusion phenomena in nanoporous catalyticsolids. Chem. Soc. Rev. 39, 4864–4884 (2010)[3] J. Ka¨rger, D.M. Ruthven, D.N. Theodorou: Diffusion in nanoporous materials. Wiley (2012)[4] T. Binder, F. Hibbe, C. Chmelik, J. Ka¨rger, A. Martinez-Joaristi, J. Gascon, F. Kapteijn,D. Ruthven: Micro-imaging of transient guest profiles in nanoporous host systems of cylindri-cal symmetry. J. Chem. Phys. 137, 164704 (2012)

Mass-transfer of binary mixtures in DDR single crystals

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Mass-transfer of binary mixtures in DDR single crystals

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