Ethylene is a highly important commodity chemical used to produce a variety of products including polyethylene and ethylene oxide. Due to the significant fraction of ethane in shale gas, it has become an attractive feedstock for ethylene production. Currently the main process to produce ethylene is through steam cracking. In this process, ethane is diluted with steam and fed into reactor tubes where it is converted into ethylene, hydrogen and other hydrocarbon products. Although ethane cracking is a well-established commercial process, it faces a number of challenges: it is energy intensive, has significant CO2/NOx emissions, equilibrium limited single pass ethane conversion and the need for periodic coke burn off. Oxidative dehydrogenation (ODH) represents an alternative method that can potentially address the limitations in steam cracking. In ODH, ethane is partially oxidized into ethylene and water. Unlike steam cracking, ODH is exothermic and not equilibrium limited, which can result in higher single-pass conversion, lower energy consumption, and lower CO2/NOx emissions. However, ODH requires gaseous oxygen to be co-fed with ethane, which imposes additional safety requirements and air separation systems for oxygen generation are capital and energy intensive. We proposed a chemical-looping based ODH (CL-ODH) system that can address these issues. In this system, a metal oxide based redox catalyst is used to provide its active lattice oxygen for the ODH reaction. The depleted redox catalyst is subsequently oxidized in air, regenerating the catalyst and releasing heat. This scheme removes the need for oxygen separation, potentially making the operation safer and more selective. In the ODH step of the CL-ODH system, there may still be a need to supply heat since the reduction of the redox catalyst, which is generally endothermic, can lead to overall endothermicity despite the combustion of hydrogen. In this work, we report the performance of mixed Fe-Mn oxide redox catalysts for CL-ODH. Simultaneous TGA/DSC measurements showed that by adjusting the Fe to Mn molar ratio, the heat of reduction of the redox catalyst could be adjusted so that the overall reaction was exothermic. Reaction testing showed that the addition of a sodium tungstate promoter led to high yields of ethylene and other unsaturated hydrocarbons. Further characterization techniques including XRD and XPS were used to evaluate the redox catalysts before and after reaction testing.

Iron-manganese oxide redox catalysts for chemical looping: Oxidative dehydrogenation of ethane

2019 Spring National Meeting

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