Highly selective methanation by the use of a microchannel reactor

Abstract

The successful application of a microchannel reactor to reduce the CO content by methanation in a model gas mixture containing CO, CO 2, O 2 and H 2 can be shown. Microchannels coated with a Ru/SiO 2 and a Ru/Al 2O 3 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 °C using a Ru/SiO 2 catalyst. Although oxygen was added to the feed, the CH 4-selectivity was still 95% at temperatures of 350 °C using the Ru/SiO 2 catalyst. It can be shown, that the CO conversion is higher at temperatures between 140 and 200 °C under oxidizing conditions because CO can be converted to CO 2. For temperatures from 200 to 320 °C the amount of oxidized H 2 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 °C with increasing temperature maybe due to formation of Ru n+ sites so that the CH 4 space time yield by CO methanation is also higher than that by CO 2 methanation. At temperatures between 250 and 300 °C a local minimum in methane formation from CO methanation is determined which might be attributed to a considerable decrease in Ru n+ sites by oxygen consumption. The CH 4 space time yield by CO methanation clearly decreases with H 2O co-feed compared to the same conditions but without water over the reaction temperature range examined. If CO (in a mixture of CO and CO 2) has to be converted over a Ru/SiO 2-catalyst by methanation a sufficient amount of O 2 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 CH 4 space time yield by CO to CO 2 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, CO 2 and hydrogen without heat transfer limitation.