Moving transversal hot zones in adiabatic, shallow packed-bed reactors



Transversal hot zones have been observed in industrial and laboratory packed-bed reactors. Yet, previous modeling attempts failed to predict them without making the unrealistic assumption that the transversal heat dispersion exceeds that of the reactants. It is shown that the formation of transversal hot zones in a uniformly active catalytic reactor is strongly dependent on the reaction kinetics. For example, transversal spatiotemporal concentration and temperature patterns can be predicted to form in a shallow adiabatic packed-bed reactor using realistic parameters for a catalytic reaction, the rate of which may oscillate under constant ambient conditions. Various experimentally tested rate expressions, such as those describing the oxidation of CO, exhibit this feature. A large number of different types of stable, transversal patterns may form for a sufficiently large reactor diameter, most of which do not exhibit azimuthal symmetry. Surprisingly, the time-averaged effluent reactant concentration and the period of the different spatiotemporal patterns are rather similar and close to those obtained under a uniform oscillating state. A systematic procedure is presented for finding the initial conditions leading to formation of the different patterns. Numerical simulations show that, because of their homoclinic features, the spatiotemporal patterns have a long period (order of hours), in agreement with various reported laboratory experiments. © 2005 American Institute of Chemical Engineers AIChE J, 2006