Short contact time catalytic wall reactors

Short contact time reactors are attractive for the high throughput they offer in reactors much smaller than their traditional counterparts. While they usually operate adiabatically due to the difficulty in removing heat at short contact times, efficient heat exchange in such reactors can be achieved by placing a heat source and a heat sink very close to each other, such as on opposite sides of a thin wall. This eliminates the resistance to heat transfer in the thermal boundary layers, leading to higher heat transfer rates, which results in reactor residence times that can be as short as a few milliseconds. This is the concept behind the coupled short contact time catalytic wall reactors discussed in this thesis, which aims to build and understand a system that transfers the heat released by an exothermic reaction efficiently to an endothermic reaction.;A coupled catalytic wall reactor that enabled efficient heat exchange between exothermic catalytic methane combustion and endothermic homogeneous ethane dehydrogenation in a concentric tube configuration was built. A parallel plate reactor in which exothermic methane combustion on platinum and endothermic methane steam reforming on rhodium occurred on walls in alternate channels was also built. Preheat passes that enabled heat exchange between the hot combustion products and the cold combustion inlet gases to increase temperature upstream and decrease it downstream were added on the combustion side in both these configurations.;The endothermic channel length in the two-pass co-current parallel plate reactor was also extended, with a platinum-ceria wall coating on the extended region to further reduce downstream temperatures and promote the water-gas shift reaction. This reactor gave downstream temperatures as low as 200°C, and produced H2/CO ratios as high as 42/1 with a residence time of ∼300 milliseconds at a steam/methane ratio of 4/1. The extended reactor shows tremendous potential for producing high H2/CO ratio product streams suitable for preferential oxidation and subsequent use in fuel cells in a scalable configuration.;Detailed simulations of both the concentric tube and the parallel plate configurations were performed to understand the role of heat and mass transfer in these systems.