Highly selective methanation by the use of a microchannel reactor

The successful application of a microchannel reactor to reduce the CO content by methanation in a model gas mixture containing CO, CO2, O-2 and H-2 can be shown. Microchannels coated with a RU/SiO2 and a Ru/Al2O3 catalyst were used at standard residence times of about 300 ms. The methanation allowed to remove CO almost completely from the gas flow at a temperature of 300 degrees C using a Ru/SiO2 catalyst. Although oxygen was added to the feed, the CH4-selectivity was still 95% at temperatures of 350 degrees C using the Ru/SiO2 catalyst. It can be shown, that the CO conversion is higher at temperatures between 140 and 200 degrees C under oxidizing conditions because CO can be converted to CO2. For temperatures from 200 to 320 degrees C the amount of oxidized H2 increases more than the amount of oxidized CO and consumes most of the O-2. In parallel, CO methanation is increasing temporarily up to 250 degrees C with increasing temperature maybe due to formation of Run+ sites so that the CH4 space time yield by CO methanation is also higher than that by CO2 methanation. At temperatures between 250 and 300 degrees C a local minimum in methane formation from CO methanation is determined which might be attributed to a considerable decrease in Run+ sites by oxygen consumption. The CH4 space time yield by CO methanation clearly decreases with H2O co-feed compared to the same conditions but without water over the reaction temperature range examined. If CO (in a mixture of CO and CO2) has to be converted over a Ru/SiO2-catalyst by methanation a sufficient amount Of 02 has to be added and temperature has to be controlled precisely. Because of the inner dimensions and the enhanced heat transfer coefficients of the microchannel reactor the latter demand can be met very easily. Temperature ranges can be controlled precisely, which is important to maximize the ratio of CH4 space time yield by CO to CO2 methanation. The experiments demonstrate that the microchannel reactor is an excellent tool for studying the reaction network of methanation of CO in presence of oxygen, CO2 and hydrogen without heat transfer limitation. (c) 2005 Elsevier B.V. All rights reserved.