Chmelik, Christian

Ito, Taro

Kortunov, Pavel

Kärger, Jörg

Rakoczy, Rainer Albert

Ruthven, Douglas M.

Traa, Yvonne

Vasenkov, Sergey

Weitkamp, Jens

English

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 Time- and Spatially-Resolved Study of Methanol Sorption in Ferrierite Crystals using Interference and IR Microscopy Pavel Kortunov1, Christian Chmelik1, Jörg Kärger1, Rainer Albert Rakoczy2, Douglas M. Ruthven3, Yvonne Traa2, Sergey Vasenkov1, Jens Weitkamp2,  Taro Ito4 1Universität Leipzig, Fakultät für Physik und Geowissenschaften, Linnéstr. 5, D-04103 Leipzig, Germany; 2Universität Stuttgart, Institut für Technische Chemie, Pfaffenwaldring 55, D-70550 Stuttgart, Germany; 3University of Maine, Department of Chem. Engineering, 5737 Jenness Hall Orono, Maine 04469-5737, USA; 4Tamai Environment System, Zenibako 3-chome, 524-11 Otaru 047-0261, Japan. E-Mail: kortunov@physik.uni-leipzig.de 1. Introduction The present work is devoted to the study of sorption kinetics of methanol in the Ferrierite crystals using the Interference Microscopy (IFM) and the IR Microscopy (IRM) techniques. These techniques provide a possibility to image the adsorbate distribution within a single crystal during the sorption process: Transient intracrystalline profiles reflect the distribution of molecular concentration inside the crystal at a certain time. The integration of such profiles over the entire crystal dimension results in the sorption rates. The determination of the relevant information on the system under study from the data on sorption kinetics has already been thoroughly discussed in the literature. In the present work, we show that the spatially resolved kind of experiments provide additional information about the sorption process. 2. Experimental The two-dimensional concentration profiles inside the Ferrierite crystal (fig.1a) with a high spatial resolution (of about 0.5 μm) were measured using IFM [1]. Gaseous methanol was used as an adsorbate, which at different vapour pressures was brought into contact with the Ferrierite crystals. The data for more than twenty single Ferrierite crystals (similar to that in fig. 1a) were obtained and used for the data analysis [2]. It is worth noting that the local concentration of adsorbate molecules in the crystal can also be measured using IR microscopy [3]. 3. Results and Conclusion Adsorption/desorption concentration profiles and kinetics were analyzed in the frame of three theoretical models: the surface resistance model, the diffusion resistance model and the surface and diffusion resistance model [4]. It was found that the data on sorption kinetics (Fig.1b) can be well described by either model within the experimental precision. At the same time, the spatially resolved data (the concentration profiles in Fig.1c) are satisfactorily described only within the surface and diffusion resistance model. The diffusion coefficient D of methanol in 8-ring channels of the Ferrierite crystals and the surface mass-transfer coefficient α were determined according to this model. © 2005, P. Kortunov The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and ApplicationDiffusion Fundamentals 2 (2005) 96.1 - 96.2 1     Fig. 1. Shape of the ferrierite crystal and 2D-concentration profiles for the entire crystal for the large pressure step (0→80 mbar) (a), experimental adsorption and desorption curves plotted in semi-logarithmic scales (b) and adsorption concentration profiles in the y-direction (c) near the edge of the crystal (z = 2 μm) for the pressure  steps  5 → 10  and  10 → 5 mbar at certain times measured by interference microscopy. Also the theoretical curves calculated using the surface resistance model and the surface and diffusion resistance model are shown.  References [1]   J. Kärger, U. Schemmert and S. Vasenkov, Adsorption Science and Technology, Proc. 2nd Pacific Conf. On Adsorption, (2000) 324-328. D.D. Do ed. World Scientific, Singapore. [2]   W. M. Meier and D.H. Olson, Atlas of Zeolite Structure Types, p. 98. Third Edition, Butterworth-Heinemann (1992).  [3]   M. Hermann, W. Niessen and H.G. Karge, Stud. Surf. Sci. Catal. 94 (1995) 131-138.  [4]   J. Crank, Mathematics of Diffusion. Oxford University Press, London, (1956).  Diffusion Fundamentals 2 (2005) 96.1 - 96.2 2

Time- and spatially-resolved study of methanol sorption in ferrierite crystals using interference and IR microscopy

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Time- and spatially-resolved study of methanol sorption in ferrierite crystals using interference and IR microscopy

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