Making Jet Fuel From Sea Water?
The U.S. Navy could soon be sailing through an ocean of jet fuel
if new research proves economical.
By extracting dissolved carbon dioxide from seawater and combining
it with hydrogen stripped from water molecules, Navy chemists
hope to one day secure a cheap and steady fuel source for its
fleet of jets.
"The U.S. Navy is surrounded by seawater and the Navy needs
jet fuel," said Robert Dorner, a scientist at the Naval Research
Laboratory in Washington, D.C. who works on the technology.
"In the seawater you have CO2 and you have hydrogen. The
question is how do you convert that into jet fuel."
The answer, according to Dorner, is a modified version of the
chemical reaction known as the Fischer-Tropsch process.
Typically Fischer-Tropsch starts with carbon monoxide and hydrogen
and, using metal catalysts and heat, ends with a mixture of methane,
waxes and synthesis gas (syngas), which can then produce fuel
Fischer-Tropsch is expensive and energy-intensive, which often
limits its usefulness. One of the few times it has proven economical
was using solid coal to produce liquid fuel for World War II Germany.
Instead of coal, Dorner and his colleagues want to use the carbon
dioxide dissolved in seawater (140 times the amount found in the
atmosphere) and hydrogen stripped from water as the base materials
for the reaction.
They also want to change the metal catalysts, switching from
cobalt, which produces mostly methane, to iron, which drops methane
production by 70 percent and increases the amount of syngas produced.
Producing syngas instead of methane more efficiently is significant,
but it's not jet fuel. One additional step is necessary to get
jet fuel. During the next few weeks Dorner and his colleagues
will take the final step, turning syngas into actual jet fuel.
The results of those experiments will help determine whether
or not their modified version of the Fischer-Tropsch process is
economical for the U.S. Navy.
"It's still a very energy-intensive process," said
Dorner. "A lot of work remains to be done. We haven't even
really looked at building an actual pilot plant yet."
Assuming the process is economical, Dorner doesn't expect every
aircraft carrier in the fleet will be equipped with the technology.
Instead the various pumps and energy sources required to turn
seawater into jet fuel would be installed on a separate ship that
uses the heat difference in the water column to help power the
reaction, although this is speculation, says Dorner.
The economics of turning seawater into jet fuel still need to
be demonstrated, said Jean-Michel Lavoie, a scientist at Sherbrooke
University in Quebec, Canada. But, he adds, the idea is appealing
because it doesn't use drinkable water and there are massive amounts
of raw materials to work with.
With cheap oil still readily available, especially in the United
States, it probably won't be practical for several years.
"But one thing is for sure," says Lavoie. "The
idea of using seawater as a medium for CO2 transportation is a
good one and could be beneficial both on the energy as well as
environmental point of view."
January 19, 2010