Dynamics of Transversal Hot Zones in Shallow Packed-Bed Reactors†

Infrared thermography was used to study the evolution and dynamics of hot zones on the top of a shallow packed-bed reactor (10 cm in diameter), packed with spherical catalyst pellets (Pd/Al2O3). The test reaction, the atmospheric oxidation of carbon monoxide, was run under conditions for which steady-state multiplicity exists. Slow cooling of the vessel housing the reactor close to its extinction temperature shifted the reactor from a fully ignited state to one with a hot region, separated by a sharp temperature front from the adjacent colder region (ΔT = 75 °C for a feed of 6 vol % CO). The hot zone exhibited one of three qualitatively different motions:  a breathing motion, an antiphase (standing wave) motion, or a hopping motion. In breathing motion, a the sharp temperature front moved back-and-forth. The breathing frequency increased upon cooling of the reactor. In antiphase motion, the hot zone moved rapidly and periodically from one side of the reactor to the other. In hopping motion, the hot zone r...