The 7 Most Promising Aviation Biofuels

A decade after their first flight, biofuels have yet to clean up aviation. But seven are best poised to scale when they do make meaningful penetration, according to a panel of experts who convened this month in Abu Dhabi.
"We really need to focus on the feedstocks that are cheapest and most abundant," said Jeff Skeer, a senior program officer for the International Renewable Energy Agency. "And I think there’s a lot out there, not just from the carbon waste streams and woody waste streams but even also from energy crops. There’s a lot of interesting developments in carbohydrate crops lately."
Should biofuels come into wide use, airlines are likely to have an array of sources to choose from, Skeer said, depending on where aircraft land.
"There's something for everyone," Skeer said. "One of these crop options grows almost everywhere, and where nothing is grown you've got the industrial plants producing carbon dioxide, so we should have plenty of feedstock.”
According to Skeer and other panelists at the Atlantic Council's Global Energy Forum, these seven feedstocks are best poised to scale:
1 Dwarf Saltwort
In the coastal deserts of Abu Dhabi, Boeing and Etihad Airways have teamed up to grow Salicornia bigelovii, an edible succulent native to the Caribbean and the southern U.S. The plant grows in brackish water, fertilized by shrimp and tilapia that can be killed and eaten. The tender tips of the saltwort are also an edible vegetable, and the plant produces an abundance of oil seeds that can be used to make biofuel.
"It’s all about fitting a feedstock to the environment that we’re in," said Linden Coppell, Etihad's sustainability manager. "We knew we couldn’t do anything that needed arable land—we didn’t have any. We knew we couldn’t do anything that needed fresh water. There’s very little amounts of fresh water available."
A preliminary, independent analysis of the saltwort experiment found the biofuel produces 38 to 68 percent less greenhouse gas emissions than fossil jet fuel.
"It could be an excellent option that we hadn’t been thinking about," Skeer said. Other options:
2 Energy Cane
Energy cane is from the sugar-cane family but genetically optimized to produce more fiber than sucrose.
"Sugar cane is already a high-yielding crop in terms of land use," Skeer said, but it won't grow everywhere, which is why "I think that different options will be good for different places."
3 Waste Gas
Biofuels made from waste avoid the controversies that have dogged energy crops—that they compete with food for land, raise food prices, encourage deforestation, said Jennifer Holmgren, the CEO of LanzaTech, an Illinois company that uses microbes to produce liquid fuels from waste gases and residues.
"One of the things that waste allows you to do is to use carbon that's already been used before," she said. "You're using carbon that's already had a first purpose and you're using it for a second purpose so you're not growing it on purpose, you're not utilizing land, you're not utilizing water, you're not utilizing any fertilizer or anything else.
LanzaTech calculated its processes could make 30 billion gallons of ethanol per year just from the waste gases from steel production.
4 Lumber Waste
Much of the wood that remains when logs are trimmed into planks goes to paper mills.
"A lot of that is going to paper," Skeer said. "With the electronic age you might be needing less paper, and more of that might be available for using to upgrade to jet fuel."
5 Logging Waste
"You’ve got the tops and branches and you’ve got the trunks, which are pretty much all left in the forest because they’re only worth one-eighth as much as the standard logs," Skeer said. "It’s just not worth it to take it out, but you could, there’s plenty there if you just get the logistics in place."
Loggers are already hauling logs out of the forest, he added. They just need an incentive to extract more cuts of wood, and the industry needs to reduce the cost of converting those to fuel.
6 Municipal Solid Waste
Analysts studied the biofuel potential of Europe's wastes in 2015 and concluded the conversion of municipal solid waste has the highest potential for avoiding greenhouse gas emissions.
"Municipal solid waste was found to deliver the highest greenhouse gas savings of all, well in excess of 100 per cent due to the possibility of avoiding decomposition to methane in landfill sites," according to Wasted, a report commissioned by a coalition of environmental groups and technology companies.
A 2016 study found that cities could save money by converting wastes to biofuels and the resulting fuel could compete with fossil fuels in the U.S. and Germany.
7 Palm Oil
"Palm oil has a very bad reputation, justifiably so," Skeer said. "It has this terrible history of destroying rainforests in Indonesia. But it’s a very high yielding crop, and … it’s possible to grow palm oil sustainably, if you don’t grow it in a rain forest, if you grow it on an existing farm, if you get certifications and things right, it might be worth considering."
Despite these promising feedstocks, biofuels have had little penetration so far, said David Hitchcock, who moderated the panel and who just completed a paper on aviation biofuels for the Atlantic Council.
Read why aviation biofuels haven't scaled, and what's next.