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Ethylene has a vast number of uses in all aspects of industry. Farmers
and horticulturalists use it as a plant hormone to promote flowering
and ripening, especially in bananas. Doctors and surgeons have also
long used ethylene as an anesthetic, while ethylene-based polymers can
be found in everything from freezer bags to fiberglass.
Because the new membrane lets only hydrogen pass through it, 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 � associated with
the traditional production of ethylene by pyrolysis, in which ethane
is exposed to jets of hot steam. The world�s ethylene producers
manufacture more than 75 million metric tons of ethylene per year,
causing millions of metric tons� worth of greenhouse gas emissions.
Unlike pyrolysis, which requires the constant input of heat, the
hydrogen transport membrane (HTM) 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,� Balachandran said. �The heat is produced where it is needed.�
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 that it theoretically could have before reaching equilibrium.
�We are essentially confusing or cheating the thermodynamic limit,�
Balachandran said. �The membrane reactor thinks: �hey, I haven�t
reached equilibrium yet, let me take this reaction forward.��
While Balachandran�s team, which included chemists Stephen Dorris, Tae
Lee, Chris Marshall and Charles Scouton, designed this experiment
merely to prove the membrane�s capability to produce ethylene, he
hopes to extend the project by pairing with an industrial partner who
would produce the membranes commercially. Since the membrane reduces
the number of steps required to produce ethylene, the technology could
enable the chemical to be produced more cheaply, he said.
The results of the research are expected to be presented at the 2008
Clean Technology conference in Boston in June. The work was funded by
the Department of Energy's Industrial Technology Program, which
resides within its Office of Energy Efficiency & Renewable Energy.
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