4 results
Now showing1 - 4 of 4
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Transport in nanoporous materials including MOFs : the applicability of Fick’s laws(Wiley-VCH, 2015); ; ; ; Diffusion in nanoporous host-guest systems is often considered to be too complicated to comply with such “simple” relations as Fick’s first and second laws of diffusion. However, we show here that the microscopic techniques of diffusion measurement, notably the pulsed field gradient (PFG) technique of NMR and micro-imaging by interference microscopy (IFM) and IR microscopy (IRM), provide direct experimental evidence of the applicability of Fick’s laws to such systems. This remains true in many situations, even when the detailed mechanism is complex. The limitations of the diffusion model are also discussed with reference to the extensive literature of this subject.Publicationtype: Journal ArticleScopus© Citations 84 450 1449 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Transport at gas–zeolite interfaces probed by molecular simulations(2013-08); In this work, the so-called surface-barriers phenomenon is investigated for hydrocarbons entering siliceous zeolites. Using molecular simulation methods (transient and equilibrium molecular dynamics, Monte Carlo, reactive flux simulations) and comparison to experimental data from literature, conditions (systemic, thermodynamic, and chemical) were identified under which such barriers have significant impact on diffusion measurements.Publicationtype: Doctoral Thesis339 979 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Predicting local transport coefficients at solid-gas interfacesThe regular nanoporous structure make zeolite membranes attractive candidates for separating molecules on the basis of differences in transport rates (diffusion). Since improvements in synthesis have led to membranes as thin as several hundred nanometers by now, the slow transport in the boundary layer separating bulk gas and core of the nanoporous membrane is becoming increasingly important. Therefore, we investigate the predictability of the coefficient quantifying this local process – the surface permeability α – by means of a two-scale simulation approach. Methane tracer-release from the one-dimensional nanopores of an AFI-type zeolite is employed. Besides a pitfall in determining α on the basis of tracer exchange, we, importantly, present an accurate prediction of the surface permeability using readily available information from molecular simulations. Moreover, we show that the prediction is strongly influenced by the degree of detail with which the boundary region is modeled. It turns out that not accounting for the fact that molecules aiming to escape the host structure must indeed overcome two boundary regions yields too large a permeability by a factor of 1.7 to 3.3, depending on the temperature. Finally, our results have far-reaching implications for the design of future membrane applications.Publicationtype: Journal ArticleScopus© Citations 36 261 496 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Adsorption and diffusion in zeolites : the pitfall of isotypic crystal structures(Taylor & Francis, 2011-06-27); ; ; ; The influence of isotypic crystal structures on adsorption and diffusion of methane in all-silica LTA, SAS and ITE zeolites is studied. Results obtained with the experimental structures are compared with structure predictions and approximations that are commonly employed. The results indicate that diffusion coefficients are much more affected than Henry coefficients. In fact, orders of magnitude deviations in the diffusivity can be observed and a systematic parameter study finally gives rise to the correlation between structure sensitivity and diffusion-window size.Publicationtype: Journal ArticleScopus© Citations 13 330 470