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Dr. William Roberts, professor of mechanical and
aerospace engineering and director of the Applied Energy Research
Laboratory at NC State, developed the biofuels process with NC State’s
Dr. Henry Lamb, associate professor of chemical and biomolecular
engineering; Dr. Larry Stikeleather, professor of biological and
agricultural engineering; and Tim Turner of Turner Engineering in
Carrboro, N.C.
Roberts says that besides being "100 percent green,"
the new technology has some key advantages over other biofuel projects.
"We can take virtually any lipid-based feedstock,
or raw material with a fat source – including what is perceived as
low-quality feedstock like cooking grease – and turn it into virtually
any fuel," Roberts says. "Using low-quality feedstock is typically 30
percent less costly than using corn or canola oils to make fuel. And
we’re not competing directly with the food supply, like ethanol-based
fuels that are made from corn."
The fuel created by the new process also burns
cleaner, so it’s better for the environment, Roberts says. There is no
soot or particulate matter associated with fuel from fats.
Further, Roberts says, the Centia™ process puts to
use what other biodiesel processes throw away. Converting feedstock
into fuel produces a low-value commodity – glycerol – as a by-product.
Rather than discarding glycerol as waste like most biodiesel plants
do, the NC State engineers’ process burns glycerol cleanly and
efficiently to provide some of the process’ requisite high
temperatures.
"Instead of composting the glycerol as waste, we
use it as an integral part of the fuel-making process," Roberts said.
It really does take a rocket scientist to make jet
fuel, especially out of oils or agricultural crops, Roberts says. The
physical and chemical properties of traditional biodiesel fuels –
their combustion characteristics and viscosity, for example – don’t
match the stringent requirements required of jet fuels, making
biodiesel unacceptable for the task.
"Jet fuel travels at 25,000 to 35,000 feet where
temperatures can reach 70 degrees below zero Fahrenheit, so it needs
to flow better in cold temperatures," Roberts says.
The Centia™ process comprises four steps, Roberts
explains. First, the engineers use high temperatures and high water
pressure to strip off the so-called free fatty acids from the
accumulated feedstock of oils and fats, or triglycerides. Next, the
engineers place the free fatty acids in a reactor to perform the
decarboxylation step; that is, carbon dioxide is taken off the free
fatty acids. Depending on the feedstock used, the scientists are left
with alkanes, or straight-chain hydrocarbons of either 15 or 17 carbon
atoms.
"After these first two steps, which are always the
same no matter which fuel you want, we can make any fuel we want to
make," Roberts says. "In the last two steps, we can change the recipe
based on the fuel output desired."
In the last two steps, the engineers break up the
straight chains into molecules with branches, making them more compact
and changing their chemical and physical characteristics. Jet fuel and
biodiesel fuel require a mixture of molecules with between 10 and 14
carbon atoms, while gasoline requires only eight carbon atoms, so the
engineers can control the process to elicit exactly the type of fuel
they desire.
Finally, the engineers make some other chemical
tweaks to create the desired fuel. Also, the glycerol by-product is
burned off to provide heat for the various processes involved.
"We produce one-and-a-half billion gallons of
animal fats annually, which is about half of the amount of vegetable
oil produced yearly," Roberts said. "Animal fats are harder to work
with, but cheaper. Last year, for the first time ever, fuel costs in
the aviation industry exceeded labor costs. We think the aviation
industry is keen on finding alternatives to petroleum-based jet fuel." |
