Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 x 105 h-1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.