Steam reforming of methane and water-gas shift in catalytic wall reactors

Catalytic wall reactors permit high heat-transfer rates between exothermic and endothermic reactions taking place catalytically on opposite sides of a thin wall, because they eliminate resistance to heat transfer in thermal boundary layers, thus making them compact and efficient. A parallel plate catalytic wall reactor was built in which exothermic methane combustion on platinum and endothermic methane steam reforming on rhodium occurred on walls in alternate channels. This reactor gave 95% conversion of methane to synthesis gas with a residence time of similar to 70 ms at a steam/methane ratio of 1/1 with a thermal efficiency of similar to 60 %. A preheat pass was added on the combustion side that enabled heat exchange between hot combustion products and cold combustion inlet gases to increase temperature upstream and decrease it downstream. This two-pass reactor gave H-2/CO ratios of similar to 14/1 with a residence time of similar to 170 ms at a steamlmethane ratio of 1/1. To increase the H-2/CO ratio, the endothermic channel length was also extended, with a platinum-ceria wall coating on the extended region to further reduce downstream temperatures and promote water-gas shift. This reactor gave downstream temperatures as low as 200degreesC, and produced H-2/CO ratios as high as 4/1 with a residence time of similar to 300 ms at a steamlmethane ratio of 4/1. The extended reactor shows good potential for producing high H-2/CO ratio product streams suitable for preferential oxidation and subsequent use in fuel cells in a scalable configuration.