Long-Range Water Transport and Self-Diffusion in Zeolite 4A Powder Beds

Dynamics of water intercalation fronts in a nano-layered synthetic silicate: A synchrotron X-ray scattering study

“…This is suggested both by our observation of traces of mixed-intercalation states over 5 h ahead of the intercalation front, and by other studies on comparable systems [16,17]. The expected low gradient in the vapor concentration is in contrast to the observed ''sharpness'' of the intercalation front after $19 h, which suggests that the platelet intercalation front does not follow the diffusion gradient of vapor in the pore space.…”

“…To our knowledge, it is the first time that Wide Angle X-ray Scattering is used as a local probe to study transport at the macroscale. Previous studies of such transport processes have relied on NMR techniques [16,17]. A comparison with what was observed in those studies was one of the initial motivations of the present study.…”

Applications of NMR tomography to mass transfer studies

“…Virtually no sodium is present in the vicinity of the water front; sodium falls far short of the water front, being adsorbed into the pore space. It was recognised that the profiles obtained using the 23 Na NMR signals correspond to the sodium ions present in solution, whereas the concentration of the adsorbed sodium can be found from the adsorption isotherm measured in that study. The results obtained for sodium cannot be described by the diffusion equation in the C(x/t 1/2 ) coordinates even assuming that the equilibrium local concentration of the adsorbed sodium (determined from the adsorption isotherm) is reached following an exponential dependence some time after the beginning of the process rather than instantaneously.…”

“…When exponential adsorption isotherm is used, the D value increases as the water content increases and can be represented as the sum of a constant and an exponential term. 21,23 Analogous experiments were carried out at different temperatures for two contacting layers comprised of 3 mm zeolite 4A granules with different initial water content. 23 Simulation of the results obtained showed that a decrease in the water content and an increase in temperature make the role of intragranular transport more significant.…”

“…21,23 Analogous experiments were carried out at different temperatures for two contacting layers comprised of 3 mm zeolite 4A granules with different initial water content. 23 Simulation of the results obtained showed that a decrease in the water content and an increase in temperature make the role of intragranular transport more significant. Equilibration of two contacting layers saturated with the light and heavy water occurs at a high vapour pressure and much faster, while the apparent (constant) diffusion coefficients of the adsorbed water and water vapour are somewhat higher than the corresponding values obtained in the equilibration experiments with a water-saturated layer contacting a dry layer.…”