Kinetic limit of C_2 hydrocarbons yield at gas-phase oxidative coupling of methane

摘要

Oxidative coupling of methane into ethane and ethylene (OCM) is believed to be one of the most promising routes for methane conversion into more valuable products. Usually OCM is accomplished at atmospheric pressure and temperatures T=900-1200K with a use of catalysts. However, the highest yields of C_2 hydrocarbons that were reached so far are less the 25-30 percent due to a sharp decrease in selectivity of formation of C_2 hydrocarbons with the rise of oxygen content in reacting mixture. These yields are insufficient for the practical realisation of this technology. Many efforts to find appropriate catalysts to improve the process were made recently. According to the widely accepted mechanism of catalytic OCM, interaction of oxygen with surface of the catalyst leads to active centres, which dissociate molecules of methane to hydrogen atom and methyl radical. The formation of C_2 hydrocarbons takes place in subsequent gas-phase reactions. Such a mechanism of catalytic OCM may be compared with the gas-phase OCM mechanism with additional source of methyl radicals.