Hot zones formation and dynamics in long adiabatic packed-bed reactors

Transversal ( normal to the flow direction) hot zones have been reported to form in packed-bed reactors. While hot zones may form due to local nonuniformities in the local activity or porosity, they may form also in a strictly uniform reactor for certain classes of reaction kinetics. For example, they are predicted to form in an adiabatic packed-bed reactor using realistic parameters when the catalytic reaction rate oscillates under some constant ambient conditions. Qualitatively different hot zones may form in the bed for the same set of parameters. A systematic procedure is outlined to predict the set of parameters for which such spatiotemporal temperature patterns may form. Dynamic simulations of a 2-D long packed-bed reactor model ( one that ignores the azimuthal dependence) reveal the existence of complex periodic motions ( period-2, -4, -8) as well as chaos. The transversal features of these periodic motions resemble those of several transversal modes predicted by the linear stability analysis. Spatial snapshots of the chaotic motion strongly suggest that it was caused by modulation and juxtaposition among motions corresponding to different modes.