Stability and performance of catalytic microreactors: Simulations of propane catalytic combustion on Pt

A pseudo-two-dimensional (2D) model is developed to analyze the operation of platinum-catalyzed microburners for lean propane-air combustion. Comparison with computational fluid dynamics (CFD) simulations reveals that the transverse heat and mass transfer is reasonably captured using constant values of Nusselt and Sherwood numbers in the pseudo-2D model. The model also reasonably captures the axial variations in temperatures observed experimentally in a microburner with a 300 mu m gap size. It is found that the transverse beat and mass transport strongly depend on the inlet flow rate and the thermal conductivity of the burner solid structure. The microburner is surface reaction limited at very low velocities and mass transfer limited at high velocities. At intermediate range of velocities (preferred range of reactor operation), mass transfer affects the microburner performance strongly at low wall conductivities, whereas transverse heat transfer affects stability under most conditions and has a greater influence at high wall conductivities. At sufficiently low flow rates, complete fuel conversion occurs and reactor size has a slight effect on operation (conversion and temperature). For fast flows, propane conversion strongly depends on residence time; for a reactor with gap size of 600 mu m, a residence time higher than 6 ms is required to prevent propane breakthrough. The effect of reactor size on stability depends on whether the residence time or flow rate is kept constant as the size varies. Comparisons to homogeneous burners are also presented. (c) 2007 Elsevier Ltd. All rights reserved.