Kinetic studies of the oxidative coupling of methane over the Mn/Na 2WO 4/SiO 2 catalyst

Abstract

Oxidative coupling of methane is a direct way to obtain C 2 hydrocarbon, and Mn-Na-W/SiO 2 catalyst is the most promising among all the catalysts. The 2%Mn/5%Na 2WO 4/SiO 2 catalyst was prepared by the incipient wetness impregnation method. A 7-step heterogeneous reaction model of the oxidative coupling of methane to C 2 hydrocarbons was conducted by co-feeding methane and oxygen at a total pressure of 1 bar over the catalyst. The kinetic measurements were carried out in a micro-catalytic fixed bed reactor. The kinetic data were obtained at the appropriate range of reaction conditions (4 kPa<PO 2 <20 kPa, 20 kPa<P CH 4 <80 kPa, 800 °C<T<900 °C). The proposed reaction kinetic scheme consists of three primary and four consecutive reaction steps. The conversions of hydrocarbons and carbon oxides were evaluated by applying Langmuir-Hinshelwood type rate equations. Power-law rate equation was applied only for the water-gas shift reaction. In addition, the effects of operating conditions on the reaction rate were studied. The proposed kinetic model can predict the conversion of methane and oxygen as well as the yield of C 2 hydrocarbons and carbon oxides with an average accuracy of ±15%.