With an annual production capacity of over 150 million tons, ethylene is one of the most important building blocks in the chemical industry. State-of-the-art ethylene production processes are based on thermal cracking of aliphatic hydrocarbons in the presence of steam. Such cracking processes have multiple drawbacks including high energy consumption, coke formation, and significant CO2 and NOx emissions. To address such challenges, we proposed a chemical looping oxidative dehydrogenation (CL-ODH) process to convert ethane into ethylene in a two-step, cyclic redox scheme. In this process, lattice oxygen in a metal oxide based redox catalyst is used to combust the hydrogen formed in ethane dehydrogenation, thereby enhancing ethylene formation while retarding coke formation. The oxygen-deprived redox catalyst is subsequently regenerated with air, releasing heat. We estimate over 80% reduction in energy consumption and pollutant emission can be realized. In the current study, we report alkali metal promoted, manganese-containing mixed metal oxides for CL-ODH of ethane. The effects of supports and promoters are evaluated and the underlying mechanisms are investigated. Among the redox catalysts investigated, sodium tungstate promoted Mg6MnO8 was the most effective, showing an ethane conversion of 76.5% and ethylene selectivity of 89.2%. The resultant ethylene yield (68.2%) is 38.9% higher than thermal cracking. Temperature programmed reaction (TPR) with ethane indicated that un-promoted Mg6MnO8 combusts ethane at a relatively low temperature (650°C) in a nonselective manner. Addition of sodium tungstate promoters inhibits ethane activation on the oxide surface, rendering a parallel homogeneous thermal cracking and heterogeneous selective hydrogen combustion scheme. XPS analysis indicates the presence of tungsten stabilizes sodium concentration on the surface. Moreover, the presence of promoter significantly suppresses the surface Mn4+ coverage, which contributes to the inhibition of electrophilic surface oxygen species and the significantly enhanced ethylene selectivity. In addition to the model catalyst studies, long-term cyclic performances, attrition resistance, and fluidization properties of a Mn-based redox catalyst with improved physical and chemical properties are also reported. ASPEN Plus® simulation of the proposed CL-ODH process and its comparisons with the conventional stream cracking process is also discussed.

Mn-containing mixed metal oxides for chemical looping oxidative dehydrogenation of ethane

253rd National Meeting (2017)

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