(216a) Internal and External Diffusional Effects on the Selectivity of C2 Products in Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) is an attractive route for the direct conversion of methane into value added chemicals. The highly exothermic feature of OCM system leads to complex ignition-extinction behavior that depends on both operating conditions and design parameters. Experimentally observed hysteresis behavior in lab-scale reactors motivated the investigation of the feasibility of autothermal operation for OCM. In steady-state autothermal operation, there is no heat addition to the reactor and there is no intentional heat removal by cooling through reactor walls. The existence of multiple steady-states, and in particular an ignited high temperature (conversion) state is essential for autothermal operation with low feed temperatures or space times. High temperature ignited steady-state can be attained either by reactor scale back-mixing of heat or by interphase gradients leading to particle level ignition. The present work examines the impact of operating variables (space time, methane to oxygen ratio and feed temperature), inter and intra-phase diffusion and bed level heat and mass dispersion on the ignition-extinction behavior and C₂ product selectivity in catalytic OCM reactors.