Here's the Earth's recipe for petroleum: Take plants. Add pressure and heat. Bake for hundreds of millions of years.
Today, companies are racing to cook the same products, but they want to do it in hours or days.
Converting crops, plant residue and even trash to fuels avoids unleashing the fossil carbon buried millennia ago. More importantly, experts say, "biogasoline," renewable diesel and clean jet fuel would not face the major infrastructure barriers that have limited the expansion of ethanol use, or, for that matter, electric cars.
The holy grail is a renewable fuel that no one can tell is renewable. Its price would be similar to that of a barrel of oil. It would be dropped into existing pipelines, refineries and vehicle engines that already process millions of barrels of petroleum a day.
It is clear to experts that ethanol, whether produced from corn or cellulosic feed, is not that fuel. Unlike gasoline, ethanol mixes with water, produces about a third less energy to the gallon, and also burns differently. As a result, typical car engines and refueling stations would need to be changed to massively increase its use. And today, trains, not pipelines, are needed to move ethanol from the Midwest to the nation's coasts.
"This is a must-do type of situation. Ethanol has been very important in establishing a very large market, but it can only go so far," said Andy Aden, a senior research engineer at the Department of Energy's National Renewable Energy Laboratory.
Big oil backers, such as Chevron Corp. and Royal Dutch Shell PLC, have taken note, investing in and funding the research of companies and scientists working to step up their technologies from the lab to the commercial scale.
'No clear winner, yet'
"There's no clear winner that's coming yet. Almost everybody is facing the same challenges. Almost all of the ideas are scientifically sound," said Caroline Taylor, a bioenergy analyst with the Energy Bioscience Institute, a collaboration of two universities, DOE's Lawrence Berkeley National Laboratory, and BP PLC, which has invested $500 million.
As with cellulosic ethanol, the difficulty is the scaling up. That's when all of the little costs become big ones. That's when problems no one even noticed in a test tube arise. "What will make the winner is who can adapt to that," said Taylor.
The absence of a clear front-runner isn't from lack of trying. Dozens of companies are adopting nearly as many approaches, according to Michael McAdams, executive director of the Advanced Biofuels Coalition, which represents many of the companies.
Take Virent Energy Systems Inc., one early leader. Since starting up the company seven years ago, founder and chief technology officer Randy Cortright has worked to convert a range of sugar molecules into petroleum products and other chemicals in a process called aqueous phase reforming. The company uses a chemical catalyst in a refining process that is conceptually similar to how fuel refiners operate today, which Cortright said is a big advantage and does not waste a lot of energy.
Virent aims to eventually produce fuels competitive with crude oil priced at $60 a barrel and is now building a pilot plant in Madison, Wis., that will turn corn and sugar beet into 10,000 gallons of fuel a year, with hopes of getting to the full 100-million-gallon-a-year production scale by 2015.
The main challenges, said Cortright, will be to improve on their yields when converting sugar to gasoline and to ensure a low-cost feedstock. For that reason, Virent will have an early focus on traditional crops, like corn, beets and sugarcane, in both Brazil and the United States.
As with ethanol, cellulosic feed, such as corncobs or grasses, will cost more until it's cheaper to break down these materials into simple sugars. Cortright said, however, that for Virent's process, the needed treatments will be simpler and less costly.
Designing bugs to do the work
Other companies are also using catalysts, but in different ways. One, said Aden, uses extreme heat to first gasify biomass into a mixture of carbon monoxide and hydrogen. Then catalysts help convert the "syngas" into fuel, whether that is ethanol or hydrocarbons. Taylor said that a major problem with gasification is the energy costs of heating up the biomass.
Pyrolysis, also involving heat and catalysts, is another approach, but the bio-oil it produces is, right now, not high quality, Aden said.
Another approach is to use biology. Many companies are working with bugs, such as yeast, E.coli bacteria and algae. While many organisms are capable of fermenting sugars into alcohols, it's a much harder trick to get them to churn out pure petroleum. But recent advances in genetic engineering have allowed scientists to change that.
Amyris Biotechnologies Inc., for example, has programmed yeast strains to convert sugar into hydrocarbons similar to diesel and jet fuel. Earlier this year, U.S. EPA certified the company's fuels to be blended up to 50 percent with traditional diesel, and Amyris has now opened pilot plants in California and Brazil.
Neil Renninger, the company's co-founder and chief technology officer, said it is looking to first expand into existing sugarcane ethanol mills in Brazil, where it will be able to ferment sugars more cheaply because it will not have to separate its fuel from water. He said the company would be able to also use existing corn ethanol infrastructure in the United States.
Turning algae into 'green' crude
Algae is another popular organism. When Harrison Dillon, president of Solazyme Inc., co-founded his company in 2003, he spent two years trying to make biodiesel from algae grown in ponds, an approach many other companies are still pursuing. Dillon said he quickly realized it could take years to bring the cost down, with no clear path to doing that. Instead of having algae photosynthesize basking in the sun, he turned to engineering them to eat up biomass and, in big dark steel fermentation vats, turn out a "green" crude oil which could be further refined to a product of choice.
But Solazyme faces challenges similar to many others. "Our biggest cost is feedstock, just like the biggest cost for a refinery is the crude oil coming off the supertanker," said Dillon, who also predicts the company will bring its price down to $60 to 80 a barrel in the next two to three years.
Overall, a limitation of biological approaches, said Taylor, is that they have to deal with inhibitors and toxins that are produced in the process and can slow down or even kill the organisms that are the fuel factories.
Meanwhile, as companies are striving to bring their costs down and secure financing to scale their technologies up, McAdams said he is concerned that the federal government isn't doing enough to help them.
A 2007 energy law provides massive incentives for biofuels, slowly ramping up "advanced biofuels" mandates to 21 billion gallons a year by 2022, 16 billion of which will be cellulosic ethanol.
"The law decided to try to pick winners. Why didn't [the government] just call it 21-billion-gallon pool and call it a day?" McAdams wondered.