Comments on "Diffusion in a mesoporous silica membrane: Validity of the Knudsen diffusion model" by Ruthven, D.M., et al., Chem. Eng. Sci. 64 (2009) 3201-3203

Bhatia, Suresh K. and Nicholson, David (2010) Comments on "Diffusion in a mesoporous silica membrane: Validity of the Knudsen diffusion model" by Ruthven, D.M., et al., Chem. Eng. Sci. 64 (2009) 3201-3203. Chemical Engineering Science, 65 15: 4519-4520. doi:10.1016/j.ces.2010.04.031

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Author Bhatia, Suresh K.
Nicholson, David
Title Comments on "Diffusion in a mesoporous silica membrane: Validity of the Knudsen diffusion model" by Ruthven, D.M., et al., Chem. Eng. Sci. 64 (2009) 3201-3203
Journal name Chemical Engineering Science   Check publisher's open access policy
ISSN 0009-2509
1873-4405
Publication date 2010-08-01
Sub-type Letter to editor, brief commentary or brief communication
DOI 10.1016/j.ces.2010.04.031
Volume 65
Issue 15
Start page 4519
End page 4520
Total pages 2
Editor A. T. Bell
Place of publication London, U.K.
Publisher Pergamon Press/Elsevier
Language eng
Subject 0904 Chemical Engineering
C1
Formatted abstract
From all accounts the conclusion is inescapable that the Knudsen equation overestimates the diffusivity, and the problem of unrealistically high tortuosities it leads to is only exacerbated by consideration of adsorption or partially specular reflection without considering the effect of the forcefield on the diffusion. Dispersive interactions reduce in significance relative to the kinetic energy at high temperatures or in very wide pores, and only under this condition is Ruthven et al.’s stout defence of the Knudsen equation likely to hold. How high a temperature or how wide a pore is sufficient must vary from system to system.

The conclusion that the diffusivity predicted by the Knudsen expression is too large does have a potential impact on the approach to the design of adsorbents, membranes and reactors. However, in the latter case the temperatures are typically much higher than ambient, and the error in the Knudsen expression may not necessarily be large, but that would depend on a case by case basis. For adsorption and membrane transport, where the temperatures are closer to ambient, significant differences may generally be expected, and should indeed be accounted for.
© 2010 Elsevier Ltd. All rights reserved
Keyword Transport
Nanopores
Diameter
Fluids
Q-Index Code CX
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Letter to editor, brief commentary or brief communication
Collections: School of Chemical Engineering Publications
Non HERDC
 
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Citation counts: TR Web of Science Citation Count  Cited 16 times in Thomson Reuters Web of Science Article | Citations
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Created: Sun, 27 Jun 2010, 00:08:54 EST