(688f) Intensification of Ethylene Production By Chemical Looping Oxidative Dehydrogenation through Exergy Loss Minimization

The production of ethylene is one of the most energy and carbon intensive processes among commodity chemicals. Recently, we reported a chemical looping approach to oxidative dehydrogenation of ethane (CL-ODH), where a metal oxide redox catalyst is used to supply oxygen to convert ethane to ethylene and water. The redox catalyst is subsequently circulated into a separate reactor were the lattice oxygen is regenerated in air. In addition to experimental data showing excellent ethylene yield and selectivity, our process modeling of the CL-ODH systems project up to 81% fuel savings with respect to ethane steam cracking, which is the standard industrial process for ethylene production. These projected large energy savings are surprising given the high thermal efficiencies reported for steam cracking reactors/furnaces (~95%) owing to decades of industrial research and optimization to improve cracking plant efficiency. The net cracking reaction, in which ethane decomposes into ethylene and hydrogen, is very endothermic and requires high temperatures (>1000 °C). However, a large amount of energy is recovered in the form of high temperature steam, for power generation, and hydrogen, for use as fuel-gas or as a chemical feedstock. The high thermal efficiencies of cracking, the loss of hydrogen and the practical reactor limitations of conventional ethane and oxygen co-feed ODH has led to some industrial skepticism about the ability of ethane-ODH to intensify ethylene production. However, our AspenPlus modeling studies using experimental redox catalyst results indicate that significant energy savings and CO₂ emission reductions can be achieved through CL-ODH even when hydrogen is fully credited.

We present experimental and modeling data of a robust redox catalyst for use in circulating fluidized beds that supports the viability of the CL-ODH system. We also present extensive process modeling of exergy (exploitable energy) loss in cracking and CL-ODH process to identify the sources of the energy savings in CL-ODH. We show that CL-ODH can reduce the exergy loss of ethylene production by over 4 GJ/tonne High Value Products and reduce CO₂ emissions by up to 87%. We identify multiple locations where CL-ODH reduces the exergy destruction when compared with the high (1^st law) efficiency steam crackers. It is shown that the in-situ combustion of hydrogen and inherent heat integration of circulating fluidized ODH reactors offer significant exergy advantages over cracking furnaces.