(75b) Hydrogen Transport Membrane Technology for Ethylene Production

We have demonstrated in the laboratory a new way to make ethylene via ethane dehydrogenation using a dense hydrogen transport membrane (HTM) to drive the unfavorable equilibrium conversion. Preliminary laboratory experiments show that the new approach can afford ethylene yields significantly above the thermodynamic equilibrium limit, even at high ethane conversion, while eliminating production of greenhouse gases in the reactor section. Moreover, the new approach results in a much simpler product slate than that obtained from today's pyrolysis technology. This simpler product slate affords an opportunity to lower the cost of the ?back end? purification train. In addition to significant energy savings, feedstock and capital cost savings, and overall cost reduction are expected in this ethylene production.

In our approach, a disk-type dense ceramic/metal composite (cermet) membrane is used to produce ethylene by dehydrogenation of ethane at 850°C. The gas-transport membrane reactor combines a reversible chemical reaction (e.g., hydrogenation/dehydrogenation) with selective separation of one product species and leads to increased reactant conversion to the desired product. In an experiment ethane was passed over one side of the HTM membrane and air over the other side. The hydrogen produced by the dehydrogenation of ethane was removed and transported through the HTM to the air side. The air provided the driving force required for the transport of hydrogen through the HTM. The reaction between transported hydrogen and oxygen in air can provide the energy needed for the dehydrogenation reaction. At 850°C and 1-atm pressure, equilibrium conversion of ethane normally limits the ethylene yield to 64%, whereas in our experiment under the same conditions, we obtained an ethylene yield of 69% with a selectivity of 88%.

Further improved HTM materials will lower the temperature required for high conversion at a reasonable residence time, while the lower temperature will suppress unwanted side reactions and prolong membrane life. In our approach, oxygen does not contact the ethane/ethylene stream, so oxidation products are not formed. Consequently, higher selectivity to ethylene and fewer by-products can be achieved. Thus, the approach simplifies overall product purification and processing schemes, results in greater energy efficiency, and completely eliminates greenhouse gases from the reactor section. The results of our work will be discussed at this talk.

Work was supported by the U.S. Department of Energy, Office of Industrial Technologies Program, under Contract DE-AC02-06CH11357. The submitted manuscript has been created by Argonne National Laboratory, a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC, under Contract Number DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.