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Hindrance Factor Expression for Diffusion in Random Mesoporous Adsorbents Obtained from Pore-Scale Simulations in Physical Reconstructions
journal contribution
posted on 2018-02-07, 00:00 authored by Stefan-Johannes Reich, Artur Svidrytski, Dzmitry Hlushkou, Daniela Stoeckel, Christian Kübel, Alexandra Höltzel, Ulrich TallarekHindered
diffusion of solutes is the rate-limiting step in many
processes for which random porous media play a central role as providers
of adsorbing or reactive interfaces. The key to an optimized layout
of these processes is the knowledge of the overall diffusive hindrance
factor H(λ) = Deff,H(λ)/Dm, which quantifies the degree
to which diffusion through a material (represented by the effective
diffusion coefficient Deff,H) is hindered
compared with diffusion in the bulk liquid (represented by Dm) in dependence of λ, the ratio of solute
size to mean pore size. To arrive at an adequate hindrance factor
expression for random mesoporous silica, we use electron tomography
to physically reconstruct the mesopore space of three macro-mesoporous
silica monoliths. The samples share the same general mesopore shape
and topology at varied mean feature size, as established by morphological
analysis, and serve as realistic models in pore-scale simulations
of hindered diffusion. From a large set of Deff,H(λ) values for 0 ≤ λ ≤ 0.9,
we derive a quantitative expression for H(λ)
that captures the morphological evolution (in dependence of λ)
and allows a prediction of the extent of hindered diffusion from material
properties. We propose the expression for structures of similar morphology
as the investigated samples, which potentially encompasses all mesoporous
silica materials obtained through sol–gel processing.
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Physical Reconstructions Hindered diffusionsolute sizePore-Scale Simulationsmacro-mesoporous silica monolithsHindrance Factor Expressionmaterial propertiessamples sharehindrance factor expressionmesoporous silica materialsfeature sizeD mreactive interfacespore sizerate-limiting stepmesopore spacemesoporous silicamesopore shapeoptimized layoutuse electron tomographyeffpore-scale simulationsRandom Mesoporous Adsorbents Obtained
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