Novel Membrane Technology for Green Ethylene Production
Dehydrogenation1: This image is an electron micrograph of the Argonne catalytic membrane (side view). By decreasing the thickness and the overall hydrogen flux, researchers have dramatically improved the overall reactivity.
Dehydrogenation2: Schematic diagram of the Argonne catalytic membrane for low temperature conversion of paraffins to olefins. Deep oxidation (CO2) is avoided since the hydrocarbon and the oxygen never come in contact.
Ethylene is currently produced by pyrolysis of ethane in the presence of steam. This reaction requires substantial energy input, and the equilibrium conversion is thermodynamically limited. The reaction also produces significant amounts of greenhouse gases (CO and CO2) because of the direct contact between carbon and steam. Argonne has demonstrated a new way to make ethylene via ethane dehydrogenation using a dense hydrogen transport membrane (HTM) to drive the unfavorable equilibrium conversion. Preliminary experiments show that the new approach can produce ethylene yields well above existing pyrolysis technology and also significantly above the thermodynamic equilibrium limit, while completely eliminating the production of greenhouse gases.Description
With Argonne’s 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 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%, but Argonne has shown that an ethylene yield of 69% with a selectivity of 88% can be obtained under the same conditions. Coking was not a problem in runs extending over several weeks.
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. With the Argonne 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.Benefits
- Simplifies overall product purification and processing schemes
- Results in greater energy efficiency
- Completely eliminates greenhouse gases from the reactor section
- Lowers the cost of the “back end” purification train, which accounts for about 70% of the capital cost of a conventional ethylene production unit
- Chemical industry
- Polyethylene manufacturing
- Petroleum industry
|Title and Abstract||
Hydrogen transport membranes for dehydrogenation reactions
A method of converting C.sub.2 and/or higher alkanes to olefins by contacting a feedstock containing C.sub.2 and/or higher alkanes with a first surface of a metal composite membrane of a sintered homogenous mixture of an Al oxide or stabilized or partially stabilized Zr oxide ceramic powder and a metal powder of one or more of Pd, Nb, V, Zr, Ta and/or alloys or mixtures thereof. The alkanes dehydrogenate to olefins by contact with the first surface with substantially only atomic hydrogen from the dehydrogenation of the alkanes passing through the metal composite membrane. Apparatus for effecting the conversion and separation is also disclosed.
|Argonne National Laboratory||02/12/2008
|Development Stage||Availability||Published||Last Updated|
|Prototype - Proof of concept has been demonstrated in laboratory experiments.||Available - The green ethylene technology is available for licensing. Argonne welcomes contact from companies interested in developing this technology for commercial application.||04/05/2011||04/05/2011|