Biodiesel: A New Way of Turning Plants into Fuel
June 7, 2005
By Sam Jaffe
Eco-dreamers have long hoped for a way to drive around without contributing
to global warming, but the slow pace of progress in alternative fuel technologies
has kept that vision from materializing. Now, a promising new process,
designed by researchers at the University of Wisconsin and outlined in
a paper that appeared in the journal Science on June 2, could be a significant
step toward turning that dream into a reality.
The paper details a new way to produce biodiesel fuel, which
is made out of plant matter. Traditional biodiesel refining uses only
the fatty acids of a plant, which typically make up less than 10 percent
of the mass of dried plants. Rather than converting only the fat, this
new method promises to turn all of the dried plant material, including
roots, stems, leaves, and fruit, into biodiesel or heat energy.
Ethanol, the most popular and commercial biofuel, has long been refined
out of plant matter, but it requires the costly, energy-intensive step
of distilling every molecule of water out of the solution. In contrast,
the new biodiesel process is based on aqueous phase reactions, which don't
need to go through the expensive distillation phase.
"The biggest advance we have to offer is the lack of that distillation
process," says George Huber, one of the paper's authors and a graduate
student at the University of Wisconsin who will soon be teaching at the
University of Massachusetts at Amherst. "That means that our process
is exothermic." In other words, it doesn't need a lot of extra energy.
And that's important, because the largest cost in the current biofuel
refining process is energy.
The new method is divided into four parts. First, a stream of processed
biomass consisting of water and sugars is fed over a nickel-tin catalyst
to strip off some of its hydrogen atoms. Then the stream is treated with
acids that take out most of the water. The resulting "goo" is
then transported over a solid base catalyst, which forms it into long
carbon chains, called alkanes. Finally, those alkanes are run through
a platinum-silica-alumina catalyst at high temperatures, while the hydrogen
from the first step is fed into the reactor. The resulting liquid has
almost the exact same chemical structure as traditionally refined biodiesel
and burns the same way in diesel engines. And the only byproducts are
water and heat.
If the process can be scaled up to industrial levels, it could be a major
step toward the creation of a transportation fuel that is relatively clean
burning, doesn't contribute to global warming, and provides U.S. farmers
with billions of dollars of new income.
According to Bill Jones, Chairman of the Board of Pacific Ethanol, a
leading biofuel company, the oil industry currently views the emerging
bio-fuels industry with fear, rather than acceptance.
"But eventually they'll come around," he says. "They'll
understand that this isn't just competition, it's a whole new market for
them to get into."
He points out that the Brazilian petroleum industry also resisted government
attempts to promote biofuels, but it is now a big supporter -- more than
half of Brazil's oil imports have been replaced with biofuels (see the
Technology Review April cover story on world-changing ideas).
Others don't need to be convinced, though. Charles Wyman, a distinguished
professor at Dartmouth College in Hanover NH, whose specialty is the biological
conversion of cellulosic biomass to ethanol and other products, says this
new methodology could give biodiesel a fighting chance to succeed in the
commercial marketplace by allowing manufacturers to make either ethanol
or biodiesel fuel.
"Once you break down all the sugars in the plant material, the only
option we had before was to make ethanol," Wyman says. "This
presents more options."
In the future, a single manufacturing center, after refining the biomass
into sugars, could make biodiesel or ethanol, depending on market demand.
However, Wyman also points out that the economic battle hasn't necessarily
"In the end it's the price at the gas station where these technologies
win or lose, not in the laboratory," he says.
To insure that both biodiesel and ethanol become more competitive in
the marketplace, Wyman says that a key breakthrough is needed to make
diesel fuel or other products such as ethanol competitively from sugars.
According to him, advances in this area could beat wholesale gasoline
And some believe that breakthrough is on the horizon. Advancements in
the last two years in enzyme technology by the National Renewable Energy
Laboratories and private companies such as Iogen and Novozymes have substantially
reduced the costs of cellulose transformation, which is tantalizingly
close to making the whole system economically competitive with cheap gas.
The new process being developed by James Dumesic, professor of chemical
and biological engineering at the University of Wisconsin, and Huber will
help to reduce those costs by limiting the amount of waste, since any
type of plant matter can be fed into their system. Unlike current ethanol
refineries, which can work only with high-glucose content materials such
as corn, the biodiesel fuel generated by this process uses the cellulose,
roots, and stems of any plant.
That means the waste biomass of America's vast agriculture industry --
everything from corn stover (the stems and leaves of the plant) to peanut
shells and fallen leaves -- can be used. A recent U.S. Department of Agriculture
study (see Notebook) estimated that more than 1.3 billion tons of such
waste is produced every year. If all of it were turned into biodiesel,
it would provide enough fuel to replace one-third of the petroleum consumed
in the United States. Furthermore, turning currently unused farmland into
grassland to be harvested for biodiesel production would easily account
for the other two-thirds of petroleum needs.
That, of course, means another beneficiary of such a transformation would
be family farmers, according to Pacific Ethanol's Jones. Ethanol refineries
owned by cooperatives of farmers already supply the bulk of U.S. ethanol
production, and biodiesel refineries could be modeled on the same program.
Honing this new process, though, is only the first step in the very long
process of transforming the country to a biodiesel nation. For that to
happen, the entire U.S. commercial car fleet would have to switch from
internal combustion engines to diesel ones, of course; but the move might
be attractive, since the new engines would cause less pollution (biodiesel
vehicles would produce far fewer pollutants like sulfur and nitrogen oxides.)
Such a sea-change in the U.S. transportation infrastructure won't happen
quickly. More likely, biodiesel production will start slowly, then ramp
up to an industrial scale, if it's competitive with diesel and gasoline.
Still, Huber thinks that his team has taken a major step toward harnessing
one of the world's most-prevalent, yet least-utilized energy resources.
"If this is a success," he says, "I can say that I helped
to convert our biomass resources to fuel our transportation system."
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