Surface Diffusion of Adsorbed Molecules in Porous Media:  Monolayer, Multilayer, and Capillary Condensation Regimes

Choi, Jeong-Gil; D., D.; D., H.

doi:10.1021/ie010195z

Cited by 245 publications

(190 citation statements)

References 135 publications

(314 reference statements)

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“…Diffusion of OCS in the adsorbed phase can theoretically occur and can be described in a similar fashion to other trace gases (e.g. see Choi et al (2001) for ozone). However we will neglect such a diffusion flux in the adsorbed phase because it is expected to be orders of magnitude smaller than in the two other phases.…”

Section: Diffusive Fluxesmentioning

confidence: 99%

A new mechanistic framework to predict OCS fluxes from soils

Ogée¹,

et al. 2016

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Abstract.Estimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO 2 cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic gross primary productivity (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO 2 hydration during photosynthesis. However soils also exchange OCS with the atmosphere, which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere, but empirical results, once upscaled to the global scale, indicate that OCS consumption by soils dominates OCS emission and its contribution to the atmospheric budget is large, at about one third of the OCS uptake by vegetation, also with a large uncertainty. Here, we propose a new mechanistic model of the exchange of OCS between soils and the atmosphere that builds on our knowledge of soil CA activity from CO 2 oxygen isotopes. In this model the OCS soil budget is described by a first-order reaction-diffusion-production equation, assuming that the hydrolysis of OCS by CA is total and irreversible. Using this model we are able to explain the observed presence of an optimum temperature for soil OCS uptake and show how this optimum can shift to cooler temperatures in the presence of soil OCS emission. Our model can also explain the observed optimum with soil moisture content previously described in the literature as a result of diffusional constraints on OCS hydrolysis. These diffusional constraints are also responsible for the response of OCS uptake to soil weight and depth observed previously. In order to simulate the exact OCS uptake rates and patterns observed on several soils collected from a range of biomes, different CA activities had to be invoked in each soil type, coherent with expected physiological levels of CA in soil microbes and with CA activities derived from CO 2 isotope exchange measurements, given the differences in affinity of CA for both trace gases. Our model can be used to help upscale laboratory measurements to the plot or the region. Several suggestions are given for future experiments in order to test the model further and allow a better constraint on the large-scale OCS fluxes from both oxic and anoxic soils.

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Section: Diffusive Fluxesmentioning

confidence: 99%

A new mechanistic framework to predict OCS fluxes from soils

Ogée¹,

et al. 2016

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“…It has been reported that surface diffusion of most organic fluids in typical porous materials is reduced by roughly an order of magnitude from that of the pure liquid. 19,20 Since the diffusion of pure methanol 21 is 1.6 × 10 −9 m 2 /s, this is expected to be on the order of 10 −10 m 2 /s . This reduction can be largely attributed to the geometrical form factor often represented by the phenomenological relation known as Archie's Law.…”

Section: Theorymentioning

confidence: 99%

Enhanced self-diffusion of adsorbed methanol in silica aerogel

Lee

Mounce

et al. 2014

Phys. Rev. B

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Molecular transport of a two-component system of liquid and vapor in a porous medium can be anomalously increased owing to fast exchange between the two phases. 1 We have investigated this phenomenon measuring the self-diffusion coefficient of methanol adsorbed in a 98% porosity aerogel using nuclear magnetic resonance (NMR) field gradient techniques. We found enhancement of several orders of magnitude from which we determined the ballistic mean-free-path in the vapor phase. We have grown globally uniform anisotropic aerogels and applied the diffusion measurements to characterize the anisotropy. Our results are important for understanding the novel properties of superfluid 3 He confined within an aerogel framework and for application to other physical systems.

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“…Experimental studies have shown that surface diffusion contributes significantly to the total diffusive flux in both mesoporous and microporous systems [2,3]. There are examples where the surface diffusion accounts for more than 50% of the total mass flow rate [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…Today, there are basically three different approaches in modeling surface diffusion; mechanistic (hopping) model, random walk (Fick's law) model and hydrodynamic (slip) model [4,6]. Fick's law approach is the most widespread in use [4,6] and assumes that the gaseous and the surface fluxes are independent of each other [6].…”

Section: Introductionmentioning

confidence: 99%

An alternative procedure for modeling of Knudsen flow and surface diffusion

Argönül¹,

Keil²

2008

Per. Pol. Chem. Eng.

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An alternative procedure for the calculation of impingement rate distribution and simultaneously the transmission probability in pores under Knudsen diffusion conditions is introduced. It is based on a combination of the finite difference method and a projection approach. Pore entrance and exit effects, and the influence of the pore length on diffusive fluxes are investigated. Later on, it is applied for a simultaneous Knudsen and surface flow system. In the model, the equation system is built without the independent flow and adsorption-desorption equilibrium assumptions. For the conditions investigated, the results indicate that if the surface flow rate is substantial, the independent flow and adsorption equilibrium assumptions become improper estimates for the behaviour of the system. The surface and gas flow rates, the impingement rate distribution and the surface coverage behave much more complex than the characteristics found with such assumptions. KeywordsKnudsen flow · surface diffusion · equilibrium assumption · cylindrical pore · projection approach Acknowledgement One of the authors would like to thank to Mr. Erkan Aksoy and Mr. Denis Chaykin for their comments concerning mathematical calculations.

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Surface Diffusion of Adsorbed Molecules in Porous Media: Monolayer, Multilayer, and Capillary Condensation Regimes

Abstract: This review provides an overview of surface diffusion and capillary condensate flow in porous media. Emphasis has been placed on the distinction between purely surface diffusion, multilayer surface diffusion, and capillary condensate flow.

Cited by 245 publications

References 135 publications

A new mechanistic framework to predict OCS fluxes from soils

A new mechanistic framework to predict OCS fluxes from soils

Enhanced self-diffusion of adsorbed methanol in silica aerogel

An alternative procedure for modeling of Knudsen flow and surface diffusion

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