Dynamics of Transversal Hot Zones in a Shallow Packed Bed Reactor during Oxidation of Mixtures of C₃H₆ and CO

Abstract

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.

Reactor diameter impact on hot zone dynamics in an adiabatic packed bed reactor

“…Marwaha and Luss9 showed that various 2‐dimensional temperature patterns may form on the surface of a thin, hollow cylindrical catalytic reactor used to carry out an oscillatory reaction. Sundarram and Luss24 conducted two reactions in the same shallow packed‐bed reactor. These experiments showed that the dynamics of the hot zones were mainly influenced by the reaction kinetics and not by the transport parameters.…”

Transversal Hot Zones Formation in Catalytic Packed-Bed Reactors

“…It is experimentally difficult to isolate the impact of individual rate processes. Sundarram and Luss observed striking differences in the pattern dynamics during the oxidation of a single reactant (either CO or propylene) and of a mixture (CO and propylene) in the same reactor. For example, using the reactants mixture the frequency of the oscillations was 20 times higher than when using only CO and twice higher than when the feed contained only propylene.…”

“…(III) Range of vessel temperature over which nonuniform states existed at different flow rates for single reactant feed (CO or C 3 H 6 ) and for mixture (CO + C 3 H 6 ). Adapted with permission from ref . Copyright 2007 American Chemical Society.…”

Wall Temperature Modulates Transversal Spatiotemporal Pattern Selection in Shallow, Nonadiabatic Packed-Bed Reactors

“…18 While breathing, antiphase and rotating patterns with large periods have been reported to form in shallow reactors during CO oxidation, 19,20 similar nonuniform states were observed during oxidation of propylene with periods of oscillation 10 times shorter. 16 Lack of a suitable noninvasive, in situ technique for accurate local temperature measurement 21 in a large commercial reactor limits the ability to detect formation of hot zones deep inside a PBR and to understand their characteristics. However, mathematical modeling provides an alternative approach to systematically predict and analyze hot zone formation and dynamics.…”

“…Using infrared imaging configured appropriately on various model lab- and bench-scale packed-bed reactors such as a radial flow reactor, thin cylindrical shell reactor, shallow PBRs, or catalytic glass fiber cloth, spatiotemporal patterns on top of or curved surface of the reactor have been detected experimentally for exothermic reactions such as CO oxidation, ,, simultaneous ethylene and acetylene hydrogenation, oxidation of a mixture of propylene and CO, and oxidative coupling of methane . For a detailed review of these, see Luss and Sheintuch .…”