Chemical Looping –Oxidative Dehydrogenation for the Green Production of Ethylene

Ethylene is an important precursor for a variety of materials used today. The traditional method for ethylene production, i.e. steam cracking of hydrocarbons, is highly energy intensive due to the endothermic nature of the reaction, the high process temperatures, and heavy separation loads for downstream purification. The generation of the energy necessary for this process leads to an annual emission of over 150 million tonnes of CO₂ worldwide. Oxidative dehydrogenation of ethane (ODH) has been investigated as a potentially more efficient approach. In ODH, ethane is partially oxidized into ethylene and water. The oxidation of hydrogen makes the ODH reaction exothermic, thereby reducing fuel needs while overcoming the equilibrium limitations for cracking reactions. However, to allow economical product separation, conventional ODH schemes require the use of pure oxygen co-fed with ethane. The oxygen generation, which uses cryogenic air separation systems, are capital and energy intensive.

We propose a chemical-looping ODH (CL-ODH) approach that can address these issues. In this scheme, a metal oxide based redox catalyst provides oxygen for the ODH reaction from its lattice. The oxygen depleted redox catalyst is subsequently oxidized in air, regenerating the catalyst and releasing the heat needed for the process. In this work we show proof of concept and characterization data for a model CL-ODH redox catalyst. Additionally, we report the results of a process modeling study based upon preliminary reaction data. It is shown that an active CL-ODH catalyst can be made based upon a doped Mg₆MnO₈ system. Simulations indicate that CL-ODH has the potential to reduce CO₂ and NO_x emissions by over 80%, and that system is projected to be more energy efficient than steam cracking even when the fuel value of byproducts is considered.