Industrial bioscience company Amyris and energy giant Total have begun to market a so-called drop-in jet fuel containing a 10-percent mix of renewable farnesane under a newly revised ASTM standard, the companies announced on June 16. Amyris and Total have worked closely on approval of the new fuel with Boeing, which, according to the airframer’s managing director of environmental strategy and integration, Julie Felgar, wants to see biofuel account for a 1-percent share of the total jet fuel supply within 10 years.
The ASTM standard involved an “end-to-end” evaluation program to verify and ensure the compatibility of the renewable jet fuel product with aircraft and engine components and systems. According to Amyris amd Total, the fuel’s favorable properties include a low freezing point, high thermostability and high net heat of combustion. The Brazilian fuels regulator, ANP, has indicated it will include the fuel as an option among the other alternative aviation fuels already allowed in the national specification.
“Aviation needs regional as well as global biofuel solutions depending on what feedstocks and processing methods are available,” said Felgar. “The Amyris/Total fuel pathway will be important in the near term in Brazil, where Gol Airlines, Amyris and Boeing are part of the Brazilian Biojetfuel Platform, a stakeholder-led plan to create a sustainable aviation biofuel industry in Brazil.”
The process developed by Amyris involves the use of yeasts to convert plant sugars into a hydrocarbon molecule that, with additional processing, becomes farnesane, an aviation biofuel that can be blended directly with Jet A. The processing method—namely, the direct fermentation of sugar—allows for a 10-percent blend rate, said Felgar.
In the United Arab Emirates, Etihad Airways, Total and Boeing collaborate on a similar stakeholder effort to develop a biofuel supply chain called BioJet Abu Dhabi. Etihad and Boeing also work with Abu Dhabi’s Masdar Institute on research into halophyte-based biofuel.
Etihad flew a demonstration flight in a Boeing 777 in January using the Amyris/Total fuel, which at the time hadn’t gained approval for commercial use. That test proved highly valuable because the Abu Dhabi partners could use the same processing method with halophytes.
“Plants called halophytes show even more promise than we expected as a source of renewable fuel for jets and other vehicles,” said Dr. Alejandro Rios, director of the Masdar Institute-affiliated Sustainable Bioenergy Research Consortium (SBRC). “The UAE has become a leader in researching desert land and seawater to grow sustainable biofuel feedstocks, which has potential applications in other parts of the world.”
Felgar said the use of biofuels could reduce net carbon emissions by 50 to 80 percent on a gallon per gallon basis per flight, due largely to the ability of the plants used to absorb carbon dioxide from the atmosphere through photosynthesis during their growth cycle.
“These plants rely on the CO2 in the atmosphere to grow, so they’re also pulling it out. The lifecycle assessment on halophytes in particular is very good,” she noted.
Challenges associated with plant-based biofuels, of course, include cost and a limited sustainable feedstock. Last year the U.S. government qualified sustainable aviation biofuel for tax credits, a move Felgar said helped cut prices substantially. It also increased the economic viability of a product called green diesel, which Boeing found is chemically similar to approved aviation biofuel. Boeing seeks ASTM approval this year for use of green diesel in commercial airplanes. Green diesel, which comes from such materials as recycled animal fat, used cooking oil and inedible corn oil, would be blended directly with traditional jet fuel at a ratio of as much as 50 percent.
Without government incentives, green diesel costs roughly $5 a gallon, while with the incentives the cost falls to about $3 per gallon—virtually on par with traditional jet-A.