North Carolina State University develops biofuels for jet airplanes

Biofuels for aviation have received a lot of attention lately, not in the least because the single biggest cost-factor for an airline consists of fuel costs. The airline industry is also a major contributor to greenhouse gas emissions.

The search for alternatives for petroluem-based kerosene and jet-fuel has so far resulted in a breakthrough in Brazil, where a biofuel company is cooperating with Boeing and NASA (earlier post) and as well as in Argentina, where the airforce has been testing biofuels mixed with jet-fuel ('bio-kerosene') (earlier post), whereas the U.S. Air Force has been experimenting with synthetic fuels, which can be made from biomass (earlier post). The University of North Dakota recently received a US$5 million grant to develop military bio-jet fuels (earlier post). And an airline moghul, like Sir Richard Branson, has repeatedly hinted at a future in which aviation biofuels will become viable on a large scale (earlier post).

Serious research challenges remain, though, because aviation biofuels need to have special properties, such as a high energy density and properties that allow them to be used at high altitudes and under very cold conditions, and in jet engines. Ordinary biodiesel won't do.

North Carolina State University engineers have now announced they have developed a biofuel technology that has the potential to turn virtually any fat source into fuel to power jet airplanes.

The technology – called 'Centia', derived from the Latin 'crudus potentia' or 'green power' in Latin – is '100 percent green', as no petroleum-derived products are added to the process. Centia can also be used to make additives for cold-weather biodiesel fuels and holds the potential to fuel automobiles that currently run on gasoline.

The Centia process (see picture, click to enlarge) comprises the four following steps:

1. high temperatures and high water pressure strips off the free fatty acids from the accumulated feedstock of oils and fats, or triglycerides.
2. the free fatty acids are decarboxylated in a reactor to perform; that is, carbon dioxide is taken off the free fatty acids. The result consists of alkanes, or straight-chain hydrocarbons of either 15 or 17 carbon atoms, depending on the feedstock.
3. the straight chains are boken down 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; this process can be controlled to elicit exactly the type of fuel desired.
4. Finally, in a last step the crude fuel is refined further to obtain the desired properties, even though the basic building blocks of the particular fuel are not changed.

Interestingly, the process makes use of glycerol (or glycerine), a by-product from bio-diesel production and from the Centia process, which is burned off to provide heat and power for the various steps involved, making the refining operations efficient:
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NC State received provisional patents to use the process to convert fats into jet fuel or additives for cold-weather biodiesel fuels. The technology has been licensed by Diversified Energy Corp., a privately held Arizona company specializing in the development of advanced alternative and renewable energy technologies and projects.

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.

When it comes to the availability of feedstocks, Roberts adds that “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.”