D. Leung et al., DIFFUSION LIMITATION EFFECTS IN THE WASHCOAT OF A CATALYTIC MONOLITH REACTOR, Canadian journal of chemical engineering, 74(1), 1996, pp. 94-103
In monolith reactors with catalytic washcoat, intraphase diffusion eff
ects have often been underestimated. This paper presents numerical sim
ulations of diffusion/reaction in the washcoat of a catalytic monolith
reactor. The problem is solved in two dimensions for the washcoat geo
metry obtained in a 1-mm square monolith channel, as revealed by scann
ing electron microscopy. For the oxidation of carbon monoxide, propane
or methane diffusion limitation can be substantial at typical operati
ng conditions. The two-dimensional solution is compared to a one-dimen
sional approximation. The latter approximation for the real washcoat i
s valid provided that the characteristic length is selected carefully.
This value is different from the characteristic length of the two-dim
ensional washcoat. The characteristic length of a two-dimensional geom
etry is not sufficient in itself to describe all washcoat geometries.
It is predicted that the application of a diffusion barrier of 4-6 mu
m of inactive washcoat may be used to lower the rate of reaction in th
e inlet region of the monolith reactor.