Re. Hayes et St. Kolaczkowski, MASS AND HEAT-TRANSFER EFFECTS IN CATALYTIC MONOLITH REACTORS, Chemical Engineering Science, 49(21), 1994, pp. 3587-3599
Numerical simulations bf catalytic oxidation in monolith reactors are
performed in order to develop criteria for mass transfer limitation. A
two-dimensional finite-element simulator previously developed is used
to examine previously reported studies of propane and carbon monoxide
combustion in excess oxygen. The Sherwood and Nusselt numbers compute
d from the two-dimensional simulation results are compared to numbers
derived experimentally. The results from the simulations are much high
er than results which have been reported in the literature for experim
ental work. Simulation results agree well with numbers obtained analyt
ically and experimentally for non-reacting flow in circular tubes, and
also with other correlations for reacting flows based on numerical wo
rk. The reason for the discrepancy between experimental and simulated
results is explained. For first-order reactions, a dimensionless catal
ytic reaction number is proposed, which may be used to evaluate whethe
r or not the rate is mass transfer controlled. For the oxidation of CO
, multiple steady states are possible and the variation in Nusselt and
Sherwood numbers under transient conditions is discussed. The influen
ce of diffusion in a real monolith washcoat is also examined. In squar
e monolith channels of dimension 1 mm, low effectiveness factors are o
btained for temperatures above 700 K, and much of the catalyst is not
utilised. It is shown that care needs to be taken in the extension of
relatively low-temperature kinetic data to the elevated temperatures e
ncountered in real operating conditions.