Modeling study in two-dimensional mathematical model of oxidative coupling of methane in fixed bed and membrane reactor

Abstract

The oxidative coupling of methane (OCM) in a fixed bed reactor (FBR) and a membrane reactor (MR) were studied by two-dimensional numerical simulations. In FBR, a suitable catalyst was selected by comparing between Li/MgO, La2O3/CaO and Na-W-Mn/SiO2 catalysts. The simulation results indicated that Na-W-Mn/SiO2 catalyst offers the best performances. Different operating conditions, such as temperature, CH4/O2 ratio and GHSV were studied. Increasing operating temperature resulted in increasing of CH4 conversion but decreasing C2 selectivity. However, the effects of CH4/O2 ratio and GHSV showed the contrary results. In MR, the suitable membranes were selected by comparing between porous Membranox, a dense BSCFO and LSGFO membrane. Simulation results indicated that BSCFO membrane offers the best performances. Various operating conditions, such as methane flow rate, air flow rate and temperature have influences on performance of OCM reaction. Increasing operating temperature resulted in increasing of CH4 conversion and decreasing of C2 selectivity. Moreover, increasing of methane feed flow rate resulted in lower CH4 conversion but increased C2 selectivity. The effect of air flow rate showed the contrary results. When comparing the performance between FBR and MR, it was found that the yield of MR was higher than FBR. The temperature profiles of FBR and MR revealed that significant hot spot temperature was observed for the FBR unlike that of the MR. Optimum dimension of MR was 0.018 m diameter and 0.2 m length. The best performance was found at GHSV of 38904.54 h-1 and temperature of 1073 K, offering CH4 conversion of 43.713 %, C2 selectivity of 61.352 % and C2 yield of 26.82 %.