Heterogeneous–homogeneous interactions in catalytic microchannel reactors

Abstract

AbstractMicromachining of chemical reactors enables the manufacture of microchannel reactors with unsually large surface‐to‐volume ratios. This can strongly affect the coupling between heterogeneous (wall) reactions and homogeneous (gas‐phase) reactions, ultimately leading to a complete quenching of homogeneous reactions. Using a 2D boundary‐layer model coupled with detailed reaction kinetics for surface and gas‐phase reactions, we investigate the ignition behavior of hydrogen/air mixtures in a Pt‐coated microchannel. The influence of temperature, pressure, reactor diameter, and fuel‐to‐air ratio is studied. We find that a purely kinetic radical scavenging by the catalytic surface can indeed result in a complete suppression of gas‐phase reactions. However, the attainability of “intrinsic safety” in microchannel reactors is strongly dependent on a fine interplay between homogeneous and heterogeneous reaction pathways in the individual reaction system. In particular, the strong dependency of homogeneous reactions on pressure leads to a breakdown of intrinsic reactor safety at sufficiently high reactor pressure. A generalized equation for the boundary of safe reactor operation is derived for the current reaction system. © 2006 American Institute of Chemical Engineers AIChE J, 2006