Envision the airport tarmac on a hot sunny day, where heat and jet exhaust make the air shimmer. According to the Air Transport Action Group, the aviation industry is responsible for about two percent of human-caused carbon dioxide emissions around the world. While not a large percentage at this time, aviation is a rapidly growing greenhouse gas source and air travel demand is expected to jump 100% in the next 20 years.
This greenhouse gas challenge is generating increased interest in alternative jet fuels that cost less and that burn significantly cleaner, and in particular in biomass fuels derived from plant materials. To this end, teams of scientists are developing fuels based on oil-rich feedstocks including algae and other sources, some of which have been proven in test flights.
At the University of Illinois Champaign campus, a group of researchers has been targeting sugarcane as a potential feedstock for jet fuel. Sugarcane is already the most productive plant in the world. According to the team, it is already been in use in Brazil for alcohol-based fuel for decades. The group, composed of professors Steven P. Long, Vijay Singh, and postdoctoral researcher Deepak Kumar, cite that ethanol from sugarcane yields 25% more energy than the amount used during the production process, and that it reduces greenhouse gas emissions by 12 percent compared to fossil fuels.
The team wondered if it could increase sugarcane’s natural oil production and use the oil to produce biodiesel, which can yield 93 percent more energy and reduces emissions by 41 percent compared to fossil fuels.
The idea was met with skepticism by industry colleagues — in fact the team said that others thought they were crazy. Sugarcane plants contain just 0.05 percent oil, which is far too little to convert to biodiesel. Many plant scientists theorized that increasing the amount of oil to even 1 percent would be toxic to the plant. However, their computer models predicted that they could increase oil production to 20 percent.
With support from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-e), the researchers launched a research project called Plants Engineered to Replace Oil in Sugarcane and Sorghum, or PETROSS, in 2012. Since then, through genetic engineering they have increased production of oil and fatty acids to achieve 12 percent oil in the leaves of sugarcane.
Now they are working to achieve 20 percent oil – the theoretical limit, according to their computer models, targeting this oil accumulation to the stem of the plant, where it is more accessible than in the leaves. Their preliminary research has shown that even as the engineered plants produce more oil, they continue to produce sugar. They call these engineered plants lipidcane.
In a recent study they found that use of this engineered sugarcane could yield more than 2,500 liters of bio-jet fuel per acre of land. They say that in simple terms, “this means that a Boeing 747 could fly for 10 hours on bio-jet fuel produced on just 54 acres of land. Compared to two competing plant sources, soybeans and jatropha, lipidcane would produce about 15 and 13 times as much jet fuel per unit of land, respectively.”
Lipidcane offers many advantages for farmers and the environment. The group calculates that growing lipidcane containing 20 percent oil would be five times more profitable per acre than soybeans, the main feedstock currently used to make biodiesel in the United States, and twice as profitable per acre as corn.
To be sustainable, bio-jet fuel must also be economical to process and have high production yields that minimize use of arable land. They estimate that compared to soybeans, lipidcane containing 5 percent oil could produce four times more jet fuel per acre of land. Lipidcane with 20 percent oil could produce more than 15 times more jet fuel per acre.
And lipidcane offers other energy benefits. The plant parts left over after juice extraction, known as bagasse, can be burned to produce steam and electricity. According to their analysis, this would generate more than enough electricity to power the biorefinery, so surplus power could be sold back to the grid, displacing electricity produced from fossil fuels – a practice already used in some plants in Brazil to produce ethanol from sugarcane.
Sugarcane thrives on marginal land that is not suited to many food crops. Currently it is grown mainly in Brazil, India and China. The researchers are also engineering lipidcane to be more cold-tolerant so that it can be raised more widely, particularly in the southeastern United States on underutilized land.
According to the scientists, if the US devoted 23 million acres in the southeastern United States to lipidcane with 20 percent oil, they estimate that this crop could produce 65 percent of the U.S. jet fuel supply. “Presently, in current dollars, that fuel would cost airlines US$5.31 per gallon, which is less than bio-jet fuel produced from algae or other oil crops such as soybeans, canola or palm oil,” they say in an article published in the The Conversation.
Lipidcane could also be grown in Brazil and other tropical areas. As the scientists recently reported in Nature Climate Change, significantly expanding sugarcane or lipidcane production in Brazil could reduce current global carbon dioxide emissions by up to 5.6 percent. This could be accomplished without impinging on areas that the Brazilian government has designated as environmentally sensitive, such as rainforest.