Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-13simulation results. In another study (Gosiewski et al., 2007b) the kinetics of homogeneouscombustion over a monolith was studied based on a simple, single-step reaction schemeleading to CO 2 and H 2 O. At that time, this scheme was regarded as satisfactory as the relevantexperiments did not show the presence of CO in the gaseous product. However, the problemof CO formation is by no means resolved, as some authors (Slepterev et al., 2007) clearlypoint out that the combustion of methane at comparable concentrations, at temperatures of upto 900 °C, may lead to temporary presence of substantial amounts of CO.The previous studies carried out on a monolith packing were thus extended ontocombustion in a free space. These studies were done in an empty cylindrical reactor (10 mm x210 mm), over a temperature range of 500 °C to 890 °C and for methane concentrations from0.5 vol.% to 1.4 vol.%; the flowrate of the feed gas was kept at 120 l/h. Since the reactionsmight potentially occur in the inlet and outlet tubes of the vessel, the gas velocity was chosensuch that the combustion only took place inside the reactor itself. The study corroboratesearlier results obtained elsewhere (Slepterev et al., 2007), that the combustion in a free space,over certain temperature ranges, occurs with the production of considerable amounts ofcarbon monoxide, and only at higher temperatures does it lead to carbon dioxide. It cantherefore be assumed that the oxidation of methane in this system is a consecutive reaction. Acomparison between methane combustion in a free space and the same process over amonolith reveals that the ignition temperatures for the mixture methane – air differconsiderably. This temperature is about 300 °C higher for the combustion in a free space(around 830 °C for the free-space oxidation and 530 °C for the monolith combustion). Theresults obtained so far have shown that the mechanism of the reaction strongly depends on theenvironment in which the combustion occurs. Furthermore, whereas the monolith combustionis a fairly stable process, the free-space oxidation is unstable and the results may be difficultto reproduce. We may theorize that the large surface area of the monolith channels may havea major effect upon the products of the combustion by activating oxidizing radicals. For thecombustion conditions investigated a number of hypothetical simplified reaction mechanismswere studied. The estimation of kinetic parameters for these mechanisms will be presentedtogether with a comprehensive analysis of the results thus obtained.References1. Gosiewski, K., Warmuzinski, K., Jaschik, M., Tanczyk, M., (2007a). Kinetics of thermal combustion of leanmethane–air mixtures in reverse flow reactors. Chemical and Process Engineering, 28, 335-345.2. Gosiewski, K., Matros, Y., Warmuzinski, K., Jaschik, M., Tanczyk, M., (2007b). Homogeneous vs. catalyticcombustion of lean methane-air mixtures in reverse-flow reactors. Chemical Engineering Science, in press.3. Slepterev, A.A., Salnikov, V.S., Tsyrulnikov, P.G., Noskov, A.S., Tomilov, V.N., Chumakova, N.A.,Zagoruiko A.N., (2007). Homogeneous high-temperature oxidation of methane. React. Kinet. Catal. Lett.,91(No 2), 273-282.51