Chemical looping as a reactor concept for the oxidative coupling of methane over the MnxOy-Na2WO4/SiO2 catalyst, benefits and limitation

The chemical looping concept (CLC) has been implemented to suppress the formation of COx in an oxidative coupling of methane (OCM) reactor under a wide range of conditions. In comparison to the normal co-feeding strategy, this technique resulted in an enhanced C-2 selectivity at the same methane conversions. Nevertheless, the obtained yield never exceeded 25% which is still lower than the minimum value needed for industrializing OCM. The CLC was applied in mechanistic studies to investigate the consecutive reaction of the main products of OCM, i.e. ethane and ethene. The performance of the reaction of C-2 components at 750 degrees C in the chemical looping reactor was compared with that obtained in the co-feeding experiments. The effect of the surface adsorbed oxygen species on the reaction of both ethane and ethene was investigated. The results of these experiments reveal that some of the mechanistic assumptions about the OCM reaction are not compatible with the nature of MnxOy-Na2WO4/SiO2, one of the most stable and best performing catalysts known for this reaction. The yield limitation is shown to be inherent to the catalyst. However, this limitation should be solvable through the modified process concept aiming at the production of ethane in a separated first step.