THE MICROPORE FLOW OF H₂O AND D₂O THROUGH ACTIVATED CARBON RODS

Abstract

The flow rates of water adsorbed on activated charcoal have been measured a t temperatures between -24°C. and f35"C. and compared with the flow rate of adsorbed D?O a t 25OC. In earlier papers a formula was presented which describes the ~nicropore flow rate of adsorbed water as a laminar flow of liquid adsorbate under a high pressure gradient due to surface forces. Our results confirm this picture. From our flow data the relative viscosity of adsorbates can be calculated. Above 0°C. the viscosity of the adsorbate shows nearly the same temperature dependence as liquid water; below 0°C. the viscosity increases much Inore rapidly, but there is no sudden increase which could be ascribed to freezing of an appreciable fraction of the adsorbate a t any particular temperature. The greater temperature coefficient of the adsorbate viscosity is consistent with a viscous flow of liquid films over a solid surface which exerts attractive forces on the liquid. INTRODUCTIONI t has been well established (1, 3, 9) that in the absence of appreciable absorption, the flow of gases through active carbons is a viscous flow with slip through the macropore system. The flow rate may be described by the well-known equation From flow data for a gas such as helium the constants A and B can be evaluated and Equation [I] used to calculate flow rates of other gases of known viscosities a t various temperatures, provided that the gases are not strongly adsorbed.If a gas is strongly adsorbed the observed flow rates may be much higher than given by Equation [I]. Such increased flow rates have been attributed to flows through the micropore systems by ( a ) surface diffusion (2, 3, 4) and (b) laminar or viscous flow of liquid adsorbate. Previous work in this laboratory (8,9) indicates that in the case of our carbon the second of these alternative mechailisms is the dominating one when the quantity adsorbed is a t all large. 'Manuscript received M a y 17, 1956.

Dynamic, structured heterogeneity of water isotopes inside hillslopes

“…The location of these samples relative to the LMWL is characteristic of a nonequilibrium fractionation event, or, alternatively, may be due to mixing with an undefined source that has a strongly negative δ 18 O composition. Laboratory studies show that H 2 O flow rates are higher than D 2 O through micropores in carbon rods [ Huber et al ., ], and across a sulfanated polystyrene membrane [ Myagkov , ]. Additionally, fractionation due to filtration was measured as water passed through a 35% porosity montmorillonite disc [ Coplen and Hanshaw , ].…”

Multilayer Diffusion Behavior and the Swelling Effect of 1-Butene and Propylene in Dry AgNO3-doped Perfluorocarbon Type Ion-Exchange Membranes

“…Transport of gases or vapors through porous materials is governed by different mechanisms depending on the size of the pores. In macroporous materials ( d p > 50 nm), viscous flow and Knudsen diffusion occur in the absence of gas−solid interaction other than reflection of the gas molecules at the pore wall. , Whereas in mesoporous materials (2 nm < d p < 50 nm), the transport varies from diffusive in the dilute monolayer region with gas molecules experiencing an interaction with the pore wall , to hydrodynamic when the adsorbate is in the form of multimolecular layers or liquid condensate. − In microporous materials ( d p < 2 nm), it was shown that the size of the gas molecules and the specific molecule−wall interactions could lead to distinct differences in potential energy barriers and therefore transport rate. − However, the transport mechanism through amorphous microporous materials is still under discussion. The derivation of a multilayer diffusion equation is carried out below to interpret the transport mechanism of gases or vapors through microporous materials, assuming that the BET n-layer adsorption takes place and that the transport of the adsorbed molecules is controlled by the activated diffusion mechanism …”

Model Evaluation of Adsorbate Transport in Mesoporous Media in the Multilayer Adsorption Region

“…This is acceptable, with the proviso that κ c in eq 7 does not vary significantly with v s . On this basis, a simple result, equivalent to 9 and subject to the restriction that v s → 1, was derived by Flood et al In spite of this severe restriction, eq 9 is at the basis of the following formulation of J s in the multilayer adsorption region: ,,, Equation 10 follows from eqs 7 and 9 and states that the flux produced by the real liquid sorbate (which is inhomogeneously distributed in the pore space) is equivalent to the flux which would be observed (under otherwise identical conditions) if the pore space was saturated with a (imaginary) fluid of the same viscosity as the real sorbate but of higher molar volume V s = V L / v s and subject to a correspondingly lower hydrodynamic pressure gradient, as dictated 4 by the thermodynamic relation V s d p s = V L d p L .…”