Clean Ethylene process created by U.S. Energy Dept.

It has been a hope for some time that simple (in concept), scientifically elegant, radical solutions will emerge from laboratories to clean out greenhouse gas emissions from industrial processes. To a large extent, current technologies tend to be aimed at capturing and cleaning the noxious gases after they have been produced in the main application process and the "cleansing" result is often comparative and only "cleaner" in comparison to the established process.

Nanotechnology has been championed as a source of ultimate solutions but has so far not produced a pollution-free silver bullet. Billions are being invested in the quest for clean coal generation and sequestration of gases and various forms of renewable, green energy sources. These technologies do not posses a zero pollution audit profile and many of the processes do not provide the output of product in the volumes and form required. Where there is fire there is still smoke.

The scientists at the U.S. Department of Energy's Argonne National Laboratory may just have come up with a scientifically elegant and effective way to take the pollution out of ethylene production by going into the heart of the production process. Under the leadership of senior ceramist Balu Balachandran, the research team has devised a high-temperature membrane that can produce ethylene from an ethane stream by removing pure hydrogen. "This is a clean energy-efficient way of producing a chemical that before required methods that were expensive and wasteful and also emitted a great deal of pollution," Balachandran said.

Ethylene is the world's most commonly produced organic compound of which 75 million tons produced annually worldwide result in the production of millions of tons of greenhouse gas emissions.

Argonne's new membrane lets only hydrogen pass through it, so the ethane stream does not come into contact with atmospheric oxygen and nitrogen, preventing the creation of a miasma of greenhouse gases (nitrogen oxide, carbon dioxide and carbon monoxide). These gases are associated with the traditional production of ethylene by pyrolysis, in which ethane is exposed to jets of hot steam. The elegant bit of the new technique when compared with pyrolysis, which requires the constant input of heat, is that the hydrogen transport membrane produces the fuel needed in order to drive the reaction. By using air on one side of the membrane, the already-transported hydrogen can react with oxygen to provide energy. "By using this membrane, we essentially enable the reaction to feed itself. The heat is produced where it is needed," Balachandran said.

He said the new membrane reactor also performs an additional chemical trick. By constantly removing hydrogen from the stream, the membrane alters the ratio of reactants to products, enabling the reaction to make more ethylene than it theoretically could have before reaching equilibrium. "We are essentially confusing or cheating the thermodynamic limit. The membrane reactor thinks, 'Hey I haven't reached equilibrium yet, let me take this reaction forward,' " he said.

The team, including chemists Stephen Dorris, Tae Lee, Chris Marshall and Charles Scouton, designed the experiment to prove the membrane's capability to produce ethylene. But now Balachandran hopes to extend the project by pairing with an industrial partner who could produce the membranes commercially. He adds that since the membrane reduces the number of steps required to produce ethylene, the technology could enable the chemical to be produced more cheaply.

The work was funded by the Energy Department's Industrial Technology Program in its Office of Energy Efficiency and Renewable Energy. The results of the research are expected to be presented at the 2008 Clean Technology conference in Boston, Massachusetts, in June.

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