Bifurcation Analysis of Catalytic Monoliths with Nonuniform Catalyst Loading

Abstract

A one-dimensional two-phase model with position-dependent heat- and mass-transfer coefficients and a nonuniform catalyst distribution along the channel is used to present a complete steady-state bifurcation analysis of a catalytic monolith for the case of an exothermic first-order reaction when the feed temperature is taken as the bifurcation variable. It is found that, for typical operating conditions, washcoat diffusion and the species Lewis number have the largest influence on the light-off boundary (in the sense that the metal loading needed to obtain an ignition point in the bifurcation diagram of exit cup-mixing conversion versus inlet fluid temperature varies by a factor of 100 or more as these parameters are varied), followed by solid conduction (factor of 50), nonuniform catalyst distribution (factor of 10), and channel geometry (factor of 5). A nonuniform catalyst distribution with three zones of catalyst loading (with high activity in the middle zone) appears to be the best configuration considering important factors such as the exit fluid conversion, inlet fluid temperature required for ignition, fouling, and transient time required for the monolith to attain the mass-transfer-controlled regime.