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Significance of pressure gradients in porous materials: Part III. Effect of pressure gradients on the effectiveness of porous catalysts
Author(s) -
Otani Seiya,
Wakao Noriaki,
Smith J. M.
Publication year - 1965
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690110315
Subject(s) - pellet , diffusion , catalysis , knudsen diffusion , porosity , knudsen number , mass transfer , chemistry , chemical engineering , pressure gradient , surface diffusion , capillary action , thermodynamics , materials science , chromatography , composite material , organic chemistry , adsorption , mechanics , physics , engineering
The effect of a change in moles, due to reaction, on the effectiveness of a catalytic reaction is analyzed by calculating the concentration profile along a capillary whose wall surface acts as a catalyst and within a spherical, porous, catalyst pellet. The effectiveness factor E is influenced most when the diffusion is predominately of the bulk type and none at all for Knudsen diffusion. For an increase in moles, the diffusion of reactant into the pellet is suppressed because of the opposing pressure gradient. The result is a decrease in E . Application to a typical bidisperse catalyst pellet such as alumina indicates that the reduction in E due to an increase in moles is not likely to be large. The effect can be important only if the change in moles exceeds 1 or 2, and the pellet is of the low‐density type with large macropores. In contrast the pressure gradient is large only when mass transfer is by the Knudsen process.