Direct Injection of Hydrogen Peroxide for Selective Homogeneous Conversion of Methane into Higher Hydrocarbons

Abstract

The impact of direct H₂O₂ injection on the selective CH₄ coupling reaction at high temperatures was investigated both experimentally and by kinetic modeling to provide insight into the reaction mechanism of the catalytic oxidative coupling of methane (OCM). H₂O₂ injection transforms CH₄ into C₂H₆ and C₂H₄ at high selectivity, confirming the effectiveness of the involvement of H₂O₂ by generating OH radicals in OCM. For carbon oxides, there was only CO formation without CO₂ at CH₄ conversions at or below 10%, as expected from the pure contribution of the gas phase. These results were consistent with simulation results using kinetic modeling of gas-phase elementary reactions. Rate of production (ROP) analysis suggests that OH radicals formed from H₂O₂ decomposition were responsible for the high selectivity toward C₂ products. The major loss of C₂ selectivity and CH₄ conversion is due to HO₂ radicals, a secondary product in H₂O₂ decomposition. The HO₂ radicals were found to both oxidize CH₃ radicals and neutralize OH radicals. The kinetic model consistently overpredicted the CH₄ conversion and C₂ selectivity over the experimental results, which can be attributed to the radical quenching and overoxidation reaction on the surface of the quartz tube reactor. The findings in this work help create a better understanding of the requirements of selective C₂ formation under OCM conditions.