Abstract
The catalytic activation of CH4 by limited amounts of O2 produces a mixture of synthesis gas (CO, H2) and light hydrocarbons (C2Hx), the relative amounts of each depending on catalyst type and process conditions. Using an elementary reaction mechanism for the oxidative coupling of methane (OCM) on a La2O3/CeO2 catalyst derived from the literature, this study replaces the activating O2 with moist H2O2 vapor to reduce synthesis gas production while improving C2Hx yields and selectivities. As the H2O2 content of the activating oxidant rises, more of the CH4 conversion occurs in the gas phase instead of with the catalytic surface. In a packed bed reactor (PBR), the use of H2O2 allows the PBR “light-off” to occur using a lower feed temperature. In exchange for a small decline in CH4 conversion, C2Hx selectivity increases while synthesis gas production drops. In a continuous stirred tank reactor (CSTR), H2O2 improves C2Hx over synthesis gas across a wider range of feed temperatures than is possible with the PBR. This suggests the CSTR will likely reduce OCM preheating requirements.
Highlights
The expanded use of hydraulic fracturing has resulted in the venting and flaring of large volumes of hydrocarbons, especially natural gas
An intermediate direct approach is the oxidative coupling of methane (OCM) that uses a very small amount of O2 to activate the CH4 while limiting the coke formation
We discuss whether the replacement of O2 by H2 O2 allows for a lowering of the overall packed bed reactor (PBR) feed temperature, which would be an energy and cost saving
Summary
The expanded use of hydraulic fracturing has resulted in the venting and flaring of large volumes of hydrocarbons, especially natural gas. An intermediate direct approach is the oxidative coupling of methane (OCM) that uses a very small amount of O2 to activate the CH4 while limiting the coke formation. A competition between COx and C2+ Hx formation occurs in this window This suggests that reactor configuration and temperature will be critical for OCM reactor design. The desired C2+ Hx products are more susceptible to oxidation than the reactant CH4 This can occur via gas phase O2 or surface oxygen species [7,13]. An alternate or supplementary oxidant that might be less aggressive toward C2+ Hx by reducing surface oxygen species while still activating the CH4 is the OH gas phase radical. Gas phase hydroxyl radicals can be formed from the gas phase decomposition of co-fed
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