Carbon-dioxide emissions from jets are a growing environmental concern. In the United States, about 12 percent of carbon-dioxide emissions come from jet fuel, a rate that is expected to rise as air travel increases. In addition, fuel prices have more than doubled from 2000 to 2006, boosting airline operating costs and making airlines increasingly desperate for a more price-stable alternative.

But designing less-polluting new jet fuels is a challenge. Such a fuel must have a freezing point low enough to withstand high-altitude temperatures and an energy density high enough to allow planes to fly long routes without added weight–two requirements that take currently available biofuels out of the running. Ethanol has a low energy content and other problematic properties, and biodiesel’s freezing point is too high.

A new biofuel under development by Amyris Biotechnologies, a startup based in Emeryville, CA, could fill that hole. The company’s approach is to engineer the metabolic system of microorganisms to create a variety of specialized hydrocarbons. To date, the company has successfully created microbes that can pump out the precursor for a crucial malaria drug called artemisinin. (See “Cheaper Malaria Drugs.”) Spurred by interest from the British megaconglomerate Virgin, which has recently launched a fuel division, Amyris has put a new focus on a cost-competitive jet fuel. Amyris scientists say they can now produce hydrocarbons with properties that rival the current jet-fuel industry standard, a kerosene-based product known as jet-A. The microbial factories ferment sugar to produce hydrocarbons, a process that has significantly less impact on global warming than traditional fuel production.

Amyris CEO John Melo, formerly president of U.S. Fuels Operations for British Petroleum, talks with TR about the company’s progress.

Technology Review: Why is Virgin so interested in alternative jet fuels?

John Melo: Carbon taxes are coming into play for air travel in Europe, and they are concerned that this is the beginning of a trend that, if it took hold, would significantly take away profit from airlines. In addition, fuel is such a big driver of profit contribution to airlines, they see having an alternative as a critical issue for the future of air travel. Demand growth for jet fuel is about three times the demand growth of gasoline.

We had not given jet fuels a lot of thought until Virgin approached us towards the end of last year. They had learned about what we were doing and wanted to explore if our technology could be used for jet fuel. The fact that no one else was addressing the problem in a sustainable way focused us on the problem. We realized we could make a big impact if we developed a fuel with zero sum carbon emissions.

TR: Developing a new jet fuel has considerable challenges. How did Amyris approach the problem?

JM: We started with the current standard for jets, called jet-A. We asked ourselves if we could generate a fuel with more energy than jet-A and a colder freezing point, which would enable flight over the poles.

We identified a molecule that we believed our core technology could make, and then set out to design microbes to make that product. Now we’ve been able to make it efficiently enough that we believe it would allow us to make a jet-A equivalent with better properties on energy and freezing point with a $40 barrel cost equivalent by 2010 or 2011.

TR: How difficult will it be to get to that point?

JM: In our first project on artemisinin, we had to generate a million-fold improvement in yield. Using that base technology platform, we now need to generate a three- to four-fold improvement on top of that. That would take us to a point where it is cost competitive with fossil fuel.

TR: Does your fuel have better properties than current jet fuel?

JM: The freezing point is -57 ºC, compared to -40 ºC for jet-A. In the lab, we see a higher energy density than jet-A. But I’d rather set an expectation that we’ll be equivalent to jet-A.

TR: How will Amyris fit the new product into existing infrastructure?

JM: We foresee selling our fuels as blends. With ethanol, many infrastructures limit blending to 10 percent. We want to give people the level of blending they see as most reasonable, depending on economics and geography. If consumers want a lower carbon footprint, they should be able to get a 100 percent product.

We’re also trying to be pragmatic. I don’t think we can deliver the volumes the world will need for transportation fuels in the short term, so we’re creating fuels that can be blended.

TR: Regulatory hurdles to certify a jet fuel are high. Have you started that process yet?

JM: Our approach is to participate in a consortium, like the one Boeing has pulled together with Virgin and General Electric. [In April, Boeing, Virgin Atlantic, and GE Aviation announced an environmental partnership.] The consortium is trying to pool resources and technological talent to identify these products and get them to certification. It would like to start testing a viable renewable jet fuel next year.

The consortium brings to the table a clear understanding of the best attributes of a fuel blend, as well as access to labs and financial resources to support the certification process. We’re not yet part of that, but we’re looking into it.