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in Wiley InterScience (www.interscience.wiley.com).Recent analysis revealed that a pseudohomogeneous model of a uniformly active, adiabatic packed bed reactor can predict formation of stable hot zones in the crosssection of the reactor if the kinetic rate expression can lead to isothermal rate oscillations. This prediction was confirmed by simulations of CO oxidation. We show that hot zone formation in a shallow reactor can be predicted also for C 2 H 4 hydrogenation, the kinetic model of which is structurally different from that of CO oxidation. Qualitatively different spatiotemporal temperature patterns may form under the same operating conditions. Their number increases as the reactor diameter is increased. An increase in the reactor diameter increases the time constant of the transversal heat dispersion and decreases the temperature synchronization among points on the same reactor crosssection. The interaction and conjugation among qualitatively different moving temperature patterns can lead to formation of complex motions.

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The evolution and motions of transversal hot zones on the top of a shallow packed bed reactor, in which the atmospheric oxidation of either propylene or its mixture with CO took place, were studied using infrared thermography. The hot regions were separated by a sharp temperature front from the adjacent colder region (ΔT ∼ 50 °C). The period of the oscillations of mixtures of propylene and carbon monoxide was about 20 times shorter than those of CO and about 2 times shorter than those of propylene. This indicates that the frequency of the hot zone motions is affected mainly by the kinetics of the catalytic reaction and the strength of adsorption of the organic reactants and not by the properties of the bed and/or the flow through it. The mixture of the two reactants led to the formation of a moving hot spot over a much wider range than that of either reaction, and under operating conditions for which neither one of the two reactions led to formation of hot regions. The experiments seem to confirm the prediction by Viswanathan and Luss (Viswanathan, G. A.; Luss, D. AIChE. J. 2006, 52, 705−717), that transversal hot zones are likely to form in a shallow packed bed reactor for reactions whose rates may exhibit oscillatory behavior.