Douglas M Ruthven

Publications of Douglas M Ruthven

• Monitoring Molecular Mass Transfer in Cation-Free Nanoporous Host-Crystals of Type AlPO-LTA.

  Authors: Florian Hibbe, Jürgen Caro, Christian Chmelik, Aisheng Huang, Tom Kirchner, Douglas M Ruthven, Rustem Valiullin, Jörg Kärger

  Journal of the American Chemical Society. 04/2012;

  Micro-Imaging is employed to monitor the evolution of intracrystalline guest profiles during molecular ad- and desorption in cation-free zeolites AlPO-LTA. The measurements are shown to provideMicro-Imaging is employed to monitor the evolution of intracrystalline guest profiles during molecular ad- and desorption in cation-free zeolites AlPO-LTA. The measurements are shown to provide direct evidence on the rate of intracrystalline diffusion and surface permeation and their interrelation. Complemented by PFG NMR and integral IR measurements, a comprehensive overview of the diffusivities of light hydrocarbons in this important type of host materials is provided.

• Nanoporous glass as a model system for a consistency check of the different techniques of diffusion measurement.

  Authors: Christian Chmelik, Dirk Enke, Petrik Galvosas, Oliver Gobin, Andreas Jentys, Hervé Jobic, Jörg Kärger, Cordula B Krause, Jens Kullmann, Johannes Lercher, Sergej Naumov, Douglas M Ruthven, Tobias Titze

  Chemphyschem : a European journal of chemical physics and physical chemistry. 03/2011; 12(6):1130-4.

  The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of aThe remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their differing influence due to the differing diffusion path lengths covered by the different measuring techniques. We report diffusion measurements with nanoporous glasses where the existence of such resistances could be avoided. Molecular propagation over diffusion path lengths from hundreds of nanometers up to millimeters was thus found to be controlled by a uniform mechanism, appearing in coinciding results of microscopic and macroscopic diffusion measurement.

• The nature of surface barriers on nanoporous solids explored by microimaging of transient guest distributions.

  Authors: Florian Hibbe, Christian Chmelik, Lars Heinke, Sanhita Pramanik, Jing Li, Douglas M Ruthven, Despina Tzoulaki, Jörg Kärger

  Journal of the American Chemical Society. 02/2011; 133(9):2804-7.

  Nanoporous solids are attractive materials for energetically efficient and environmentally friendly catalytic and adsorption separation processes. Although the performance of such materials isNanoporous solids are attractive materials for energetically efficient and environmentally friendly catalytic and adsorption separation processes. Although the performance of such materials is largely dependent on their molecular transport properties, our fundamental understanding of these phenomena is far from complete. This is particularly true for the mechanisms that control the penetration rate through the outer surface of these materials (commonly referred to as surface barriers). Recent detailed sorption rate measurements with Zn(tbip) crystals have greatly enhanced our basic understanding of such processes. Surface resistance in this material has been shown to arise from the complete blockage of most of the pore entrances on the outer surface, while the transport resistance of the remaining open pores is negligibly small. More generally, the revealed correlation between intracrystalline diffusion and surface permeation provides a new view of the nature of transport resistances in nanoporous materials acting in addition to the diffusion resistance of the regular pore network, leading to a rational explanation of the discrepancy which is often observed between microscopic and macroscopic diffusion measurements.

• Combining macroscopic and microscopic diffusion studies in zeolites using NMR techniques.

  Authors: Krzysztof Banas, Federico Brandani, Douglas M Ruthven, Frank Stallmach, Jörg Kärger

  Magnetic resonance imaging. 03/2005; 23(2):227-32.

  In this study the zero length column (ZLC) technique is extended to the case where the decay of the adsorbed phase concentration is observed directly by nuclear magnetic resonance (NMR). AnIn this study the zero length column (ZLC) technique is extended to the case where the decay of the adsorbed phase concentration is observed directly by nuclear magnetic resonance (NMR). An adsorption-desorption apparatus compatible with a 400-MHz NMR spectrometer was developed. It operates with nitrogen or helium as the inert purge gas. The column of the adsorbent material is placed in the sensitive region of the superconducting magnet and the rf coil of the NMR spectrometer. The time scales of the adsorption and desorption processes depend on concentration, temperature and crystal shape and are found to be in the range of 1-10 min. From the desorption branch, the non-equilibrium ZLC-NMR measurements yield intracrystalline diffusion coefficients in the range of 10(-13) to 10(-11) m2/s for different alkanes in silicalite-1. These values are always found to be smaller than the values measured by pulsed field gradient NMR under equilibrium condition indicating that there must be additional transport resistance at the external surface of these silicalite-1 zeolite crystals.

• The use of higher moments to extract transport data from chromatographic adsorption experiments

  Authors: Hugh A. Boniface, Douglas M. Ruthven

  Chemical Engineering Science.

  A chromatographic method based on analysis of the first four moments of the response peak has been developed and applied to the analysis of experimental data for the sorption of some light gases onA chromatographic method based on analysis of the first four moments of the response peak has been developed and applied to the analysis of experimental data for the sorption of some light gases on several zeolitic adsorbents. Axial dispersion, intra-particle diffusivities and adsorption equilibrium were found using this method and were shown to be consistent with the values derived by other methods of analysis. The proposed methods provides a significant improvement over methods of analysis that use only the first and second moments because the quantity of data necessary to derive the model parameters is reduced.

• Measurement of diffusion in porous solids by zero length column (ZLC) methods

  Authors: Douglas M. Ruthven, Stefano Brandani

  Membrane Science and Technology.

  The measurement of diffusion in zeolite crystals and pellets by the Zero Length Column (ZLC) method is reviewed, including the extension of this technique to self-diffusion, counter-diffusion andThe measurement of diffusion in zeolite crystals and pellets by the Zero Length Column (ZLC) method is reviewed, including the extension of this technique to self-diffusion, counter-diffusion and liquid phase measurements.

• Diffusion in a mesoporous silica membrane: Validity of the Knudsen diffusion model

  Authors: Douglas M. Ruthven, W.J. DeSisto, S. Higgins

  Chemical Engineering Science.

  Experimental permeance data for several light gases in a mesoporous silica membrane are analyzed in detail and shown to conform closely to the Knudsen diffusion model. The results of this study doExperimental permeance data for several light gases in a mesoporous silica membrane are analyzed in detail and shown to conform closely to the Knudsen diffusion model. The results of this study do not support the conclusions drawn from recent molecular simulations concerning the inadequacy of the Knudsen model.

• A new experimental technique for measurement of intracrystalline diffusivity

  Authors: Mladen Eic, Douglas M. Ruthven

  Zeolites.

  A new experimental technique has been developed for measuring the intracrystalline diffusivities of strongly adsorbed species by following chromatographically the desorption curve for a small sampleA new experimental technique has been developed for measuring the intracrystalline diffusivities of strongly adsorbed species by following chromatographically the desorption curve for a small sample of zeolite, saturated at a low concentration level. Results obtained by this method for o-xylene in 50-μm and 100-μm NaX crystals are self-consistent and in good agreement with previously determined gravimetric values.

• Chromatographic adsorption with sinusoidal input

  Authors: Hugh A. Boniface, Douglas M. Ruthven

  Chemical Engineering Science.

  A chromatographic method based on a steady state sinusoidally varying input concentration has been developed and applied to the analysis of experimental data for some selected weakly adsorbingA chromatographic method based on a steady state sinusoidally varying input concentration has been developed and applied to the analysis of experimental data for some selected weakly adsorbing systems. Axial dispersion coefficients, zeolitic diffusivities and adsorption equilibrium constants determined by this method were shown to be consistent with the values derived by other methods of analysis. The proposed method is an improvement over pulse or step input chromatography in certain systems because simpler, less accurate measurements are required from experiments and the modelling process is mathematically less complicated.