A comparative simulation study on oxidative coupling of methane in fixed-bed and membrane reactors

Oxidative coupling of methane (OCM) on a conventional fixed-bed reactor (FBR) and a ceramic dense membrane reactor (DMR) packed with Li/MgO catalyst is analyzed using plug-flow reactor models. The validity of OCM kinetic equations employed in the modeling is confirmed by excellent agreement between the simulation and experimental data for OCM on FBR. For FBR, a high methane to oxygen feed ratio favors the OCM reaction, with a low C-2 yield because of insufficient oxygen supply. The highest C-2 yield achieved with a feed mixture consisting of 70% methane and 30% oxygen is 20.7% at a selectivity of 53% and operating temperature of 750 degrees C. The C-2 yield and selectivity increase slightly at a higher operating temperature. The optimal feed ratio does not change with temperature. DMR is made of a mixed-conducting ceramic membrane tube packed with an OCM catalyst. The membrane tube separates the methane and oxygen feed. The oxygen concentration in the DMR is much lower and more uniform than that in the FBR because of the different reactant feeding mode and logarithemic dependence of oxygen flux on oxygen partial pressures of the dense ceramic membrane. This results in a significantly increased C-2 selectivity and yield for the DMR as compared to the FBR.