Comparison among structured and packed-bed reactors for the catalytic partial oxidation of CH4 at short contact times

Three types of catalyst support (foams, honeycomb monoliths with square channels and spheres with approximately equal values of specific geometric surface av) were examined and compared by simulation with a 1D, dynamic heterogeneous mathematical model for application to the autothermal partial oxidation of methane. Both cold start-up and steady-state behaviours were investigated. It was found that mass and, particularly, heat transfer properties markedly affect the reactor behaviour, both at start up and at steady state. Thus, the choice of the catalyst support can lead to greatly different reactor performances. Concerning the reactor start-up, simulations revealed that better interphase heat transport properties and lower bed heat capacity are useful to minimize the total start-up time; on the other hand, more favourable transport properties reduce the maximum flow rate which allows to achieve and maintain an ignited steady state. At steady state, oxygen conversion is strictly governed by interphase mass transfer, while methane conversion depends on a more complex, mixed chemical-diffusional regime.