What if you could make biofuels without using plants? Or oil without extracting anything from the ground?
That's been the goal of the U.S. Department of Energy's "electrofuels" program, a $48 million research effort involving 14 separate projects that is wrapping up this year.
Instead of relying on corn, sugar cane, or other plants to collect the sun's energy, electrofuels researchers use microorganisms.
And instead of harvesting plants and other biomass and converting them into biofuels like ethanol, electrofuels researchers are genetically engineering microorganisms that, as one researcher put it, "poop out" chemicals that can burn directly in your gas tank.
"That's exactly what they do," said Eric Toone, a professor of chemistry and biochemistry who is now back at Duke University in North Carolina, after spending two years helping to administer the U.S. Department of Energy's four-year-old ARPA-e program. (See related: "Storage, Biofuel Lead $156 Million in Energy Research Grants.")
The Advanced Research Projects Agency-Energy program, modeled after the Pentagon's long-running Defense Advanced Research Projects Agency (DARPA) program to support innovative military systems research, is an effort to inject support into "high-risk, high-payoff" research on energy. The fledgling research into electrofuels, which the agency says offers the possibility of generating alternative transportation fuels ten times more efficiently than current biofuel production methods, was a perfect fit for ARPA-e. (See related: "Quiz: What You Don't Know About Biofuels.")
"It's the first fundamentally new way to think about biofuels in a long time," Toone said.
Just Add CO2 and Electricity
To produce electrofuels, researchers feed carbon dioxide to microorganisms, and run an electrical current through the tank in which they are grown.
Electrofuels microbes are derived from exotic bacteria that live underground or in other places (such as geothermal springs) where photosynthesis doesn't occur.
In the wild, these organisms survive by "eating" electrons derived from minerals in the surrounding soil. But in the lab, their genes are transferred to other bacteria that can more easily be grown in vats hooked up to a power grid that can provide the needed electricity.
If the power source is solar, the outcome is an alternative to photosynthesis—the process by which green plants harness sunlight.
Conventional biofuel production, such as the refining of ethanol from corn or sugar cane, has successfully displaced about 10 percent of the motor gasoline in the United States and at times, depending on price, about 50 percent of the gas in Brazil. But biofuels also are controversial for a variety of reasons, including that they divert grain and land from food production. (See related story: "Water Demand for Energy to Double by 2035.")
The process of making biofuel from plants is also inherently inefficient.
Even the best energy crops, Toone said, can produce only about ten tons of dry biomass per acre per year. That sounds like a lot, but it's actually not. "If you go back and say, 'What does that represent as a fraction of the total solar radiation that fell on that acre of land in a year?' it's less than one percent," Toone said. (See related: "A Rainforest Advocate Taps the Energy of the Sugar Palm.")
Electrofuels offer an entirely new way to harvest the sun's energy—one that might be considerably more efficient. Not to mention that they don't require farmland, tractors, fertilizer, or irrigation water.
But that's only half the process. Rather than using the sun's energy to grow and produce biomass for conversion into ethanol or other biofuels, electrofuels bacteria have been further modified to produce chemicals that can be used as fuel.
"The advantage of the electrofuels approach is that it's all very direct and highly efficient," said Derek Lovley, a microbiologist at the University of Massachusetts whose lab was one of the 14 to work under the ARPA-e grants. "And you don't need arable land to grow plants. You can basically do it anywhere there's electricity. You basically have much higher efficiency, much less water usage, and much less environmental degradation."
Also useful is the fact that the fuels can be designed to be much more practical than the ethanol that is currently the primary focus of U.S. biofuels production.
"We're focusing on butanol," said Lovley.
Butanol is another fuel alcohol, but with a molecule about twice as large as ethanol.
It's a far better fuel than ethanol, Lovley said, describing it as a "drop-in gasoline substitute"—meaning that it can be used directly in the gas tanks of today's automobiles. (See related: "Whisky a Go Go: Can Scotland's Distillery Waste Boost Biofuels?") Although more and more flexible-fuel vehicles are being sold in the United States—and they dominate the market in Brazil-the vast majority of U.S. cars are not designed to run on large amounts of ethanol. Ethanol is typically blended as a 10 percent additive to a mix that is 90 percent conventional gasoline to meet the requirements of automobiles; this so-called "blend wall" is one of the barriers hindering wider biofuels use in the United States.
Butanol, on the other hand "can be used as a sole fuel," Lovley said. "More importantly, it can be stored and distributed in existing pipelines. You can't do that with ethanol because ethanol absorbs water."
Another possible end product, said Toone, is isooctane (the chemical that is the basis of "octane" ratings for gasoline).
Plastics Before Gasoline?
The electrofuels process can be used to make things other than fuel. Robert Kelly, a chemical engineer at North Carolina State University and Michael Adams of the University of Georgia have engineered a strain of Pyrococcus (a microorganism that normally lives in near-boiling-point hot springs) to make a compound called 3-hydroxyproprionic acid from carbon dioxide and hydrogen (the latter of which can be produced via electricity or other environmentally friendly methods).
3-Hydroxyproprionic acid isn't a fuel, but it's an important intermediate for making plastics—"one of the top 12 industrial chemical building blocks," Kelly and Adams wrote in a paper describing their new organism in the March 25 edition of Proceedings of the National Academy of Sciences.
Because such compounds can be sold at a higher price than fuels, Lovley said, they might be the first commercial realization of the electrofuels program.
"Fuel is the hardest market to compete in because you're competing against gasoline and oil," he said.
The stark economics mean there's a possibility that this advanced energy research will lead to a different way of making plastics before it yields a better way of fueling vehicles. But because chemicals made this way could substitute for fossil fuels currently used in petrochemical production, this byproduct of the electrofuels program still helps attain that program's green objectives, say the program's advocates.
Electrofuels research, however, is still in its infancy. "At the end of three years of funding, we know it works," Toone said. "We can build [the needed biochemical] pathways into these organisms and grow them on electrons. Can we scale to competitive costs at meaningful volumes? There's certainly quite a bit of promise, but we're not far enough along" to know.
ARPA-e is not designed to support energy research projects indefinitely, but to provide seed money that attracts private investment, potentially on a much larger scale. The agency recently tallied 17 of its projects that had attracted over $450 million in private sector follow-on funding after ARPA-e's initial investment of approximately $70 million. Two of them, one at OBX Biotechnologies of Boulder, Colorado, and another at the University of California, Los Angeles, were electrofuels projects.
Pamela Silver, a synthetic biologist at Harvard Medical School, who has worked with bioengineering microbes to make octanol, notes that it's still a long way from lab experiments to commercial production.
"Scale-up is still going to [require a] pilot plant," she said.
Even then, large-scale fuel production might still encounter technical limitations on how much current can be passed through any given vat of microorganisms.
Still, she said, electrofuels offer a novel way of energy production. "[That] makes it inherently attractive."
This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.