Ignition–extinction analysis of catalytic reactor models

A detailed analysis of the ignition–extinction and hysteresis behavior of the two widely used catalytic reactor models (packed-bed and monolith) for the case of a single exothermic reaction is presented. First, limiting models are used to determine the minimum adiabatic temperature rise and/or catalyst activity needed to observe hysteresis behavior. Next, explicit expressions are provided for estimating the feed temperature or space time at ignition (light-off) and extinction (blow-out) as a function of the adiabatic temperature rise (or inlet concentration of limiting reactant), effective thermal conductivity, time and length scales (reactor, tube/channel diameter, effective diffusion length and pore size), catalyst activity (or dilution) and heat loss. It is shown that various limiting reactor models such as the thin-bed, long-bed, lumped thermal, adiabatic and strongly cooled cases that are defined in terms of various inter- and intraphase heat and mass dispersion time scales can be used to derive scaling relations that are useful in predicting the ignition/extinction loci for both laboratory scale (with heat exchange) and large scale (near adiabatic) reactors.