Future Fuels

Rome was not built in a day, and modern gasoline did not show up overnight. It took decades of refining and discovery to perfect the blends and design ever-better engines to suit the fuel. How long it will take to meet global aspirations for clean, sustainable, widely available transportation fuels made from plants remains an open question.

But over the past few years biofuels research and technology—spurred by government support and private investment—are picking up speed even as new ideas of what’s possible are expanding.

Those ideas are coming from every facet of the biofuel production chain -- from farm to fuel tank. Researchers are grappling with how best to use and process the Earth’s tremendous wealth of biomass -- whether it be with enzymes, yeast, bacteria or some other way -- to make cellulosic ethanol, liquid fuel made from the stems, leaves and woody parts of plants.

At the same time, fuel scientists around the world are working to create entirely new biofuels to mimic gasoline, diesel, and jet fuel so that they can be dropped easily into existing engines, tanks, and pipelines.

All of this is happening as world-wide attention and, at times, scrutiny grows. Today, 36 countries mandate the use of biofuels for transportation. Most require only modest amounts of traditional ethanol made primarily from corn and sugarcane to be blended with gasoline or biofuels blended with diesel. But some, led by the United States and the European Union, have put fuel standards in place for the coming decade that that are driving biofuel advances.

These advanced biofuels will not only need to be produced at large scale, they will need to be competitively priced, and they will need to reduce greenhouse gas emissions. Further, the raw plant materials from which biofuels are made—the feedstock—will need to avoid competing with food crops for land and water.

To develop new biofuels, global energy giants (including BP, Chevron, Exxon, and Shell) are investing hundreds of millions of dollars in partnerships with leading research universities to resolve fundamental issues of science. The largest of its kind, the Energy Biosciences Institute, is a partnership among the University of California, Berkeley; the University of Illinois at Urbana-Champaign; Lawrence Berkeley National Laboratory; and BP, with BP providing $500 million over 10 years to the effort.

At the same time a host of new biotech firms, many headquartered in the San Francisco Bay Area, are emerging, joining forces with established energy companies or backed by venture capital. This new kind of biofuel company is moving fast to take the newest science from the lab straight to the consumer.

“I see these technologies getting ready to come into the market,” says Mike McAdams, president of the Advanced Biofuels Association, which comprises companies working on new biofuels. “In the next 24 months you’re going to see butanol, you’re going to see renewable diesel, you’re going to see renewable jet fuel.”

Which fuels for the future?

One of the leaders in fuel innovation is Jay Keasling, a University of California, Berkeley chemical and bioengineering professor, and head of the Joint Bioenergy Institute. Located in the San Francisco Bay Area and modeled like an entrepreneurial start-up, JBEI is one of three Department of Energy research centers charged with accelerating research and development into advanced biofuels as part of the government’s mandate to produce 21 billion gallons of advanced biofuels for transportation by 2022.

Dr. Jay Keasling/Credit: JBEI

Keasling’s specialty is synthetic biology, the ability to design and build biological systems for a specific purpose. For biofuels, by changing the basic DNA codes of the yeasts and bacteria that ferment sugar into alcohol, Keasling and his team hope to control the kind of chemicals that come out. So rather than ethanol, he can teach a microbe to produce perhaps a new form of biodiesel or, say, an iso-octane, a component of gasoline which is used to calibrate fuel performance standards.

Keasling, who grew up on his family corn and soybean farm in Nebraska, points out that 1.3 billion tons of biomass lie fallow every year, as much energy as 100 billion gallons of advanced biofuels a year. The key, he says, is that the new bio-sourced fuel must look and act like the petroleum-based fuels of today.

“What are the fuels of the future that will be most effective? Gasoline and diesel. They don’t have to be petroleum derived, but they will be gasoline and diesel,” he says. “We’re trying to mimic as much of the petroleum- derived fuels as we can so that you don’t have to compromise when you drive up to the pump."

Ideally, these so called “drop-in” fuels would be compatible with today’s refining and distribution networks, thus being just as useful in a next-generation hybrid as a 1967 Mustang hardtop.

Others, though, are looking toward new kinds of fuels altogether. Researchers at the Massachusetts Institute of Technology and other organizations are retrofitting bugs to create biobutanol, a fuel that to this point has not been in the market. The potential for butanol is exciting because it appears to have all the benefits of ethanol without the drawbacks. Ethanol is corrosive, tends to pick up unwanted water, and lacks the power of petroleum. Butanol is non-corrosive, repels water, and has as much punch as jet fuel.

The MIT team, like many others, is trying to find a life form that can create this new fuel. Their microbe of choice is a bacterium that has been used in the past to clean up oil spills. Engineering a microbe that can create butanol is just the start, though.

Because butanol is toxic to microorganisms, it will collect and kill the very creatures that created it. So the team, led by professor Anthony Sinskey, has been trying to create bacteria that not only synthesize a novel fuel but are immune to it.

Not everyone is convinced, though.

“We welcome new entrants into the market—all fuels to replace petroleum are good—but I think it’s going to be difficult for a molecule to compete with ethanol, just on a cost basis,” says Jeff Broin, CEO of POET, a well-established ethanol producer. POET has an ethanol plant that produces ethanol from corn stover (the plant material left over after harvesting) for a competitive $2.35 a gallon.

Converting biomass into sugars

Regardless of the kind of biofuel you want to produce, you must start with the same component—sugar. And in the case of cellulosic fuels, that means turning the fibrous, pulpy plant material into usable sugar. For companies like POET, this breakdown (or pre-treatment as it’s called) is the most expensive step. Scientists say the best way to break down fibrous cellulose and lignin is the same way that nature does it – with enzymes. Enzymes are natural catalysts that kick-start chemical changes.

“One of the big problems is the cost of enzymes,” says Chris Somerville, UC Berkeley professor and head of the Energy Biosciences Institute. “Right now it’s estimated to cost somewhere between 50 cents and a dollar per gallon of fuel just for the enzymes that convert the biomass into sugars.”

With such a big price tag, enzymes are now seen as the major impediment to cost-effective biofuels and labs around the world are working to find cheaper alternatives. Much has been made recently about exotic and creative places in nature to hunt for new enzymes. Researchers, for example, have picked apart animals like termites looking for the ability to spin straw into sugary gold. Scientists make frequent trips to the rainforests of Puerto Rico, which are said to have the most aggressive and dynamic decomposition properties in the world (the theory being nothing breaks down cellulose like a rainforest).

Cow rumen, which -- as anyone who has stepped in a cow pie knows -- is expert at breaking down grass fiber. It's a well-studied source of enzymes, yet EBI researcher Eddy Rubin found a staggering 27,000 new enzymes that play a role in biomass breakdown there.

Yet we don’t really even have a good sense  of the useful enzymes in our backyard. Take the cow rumen, which—as anyone who has stepped in a cow pie knows—is expert at breaking down grass fiber. It’s a well-studied source of enzymes, yet EBI researcher Eddy Rubin recently found a staggering 27,000 new enzymes that play a role in biomass breakdown after sifting through 280 billion base pairs of DNA from the hundreds of microorganisms that inhabit cow rumen.

Essentially, a single cow’s rumen increased the world’s enzyme library by 30 percent. Bruce Dale at Michigan State University agrees it’s important to look for new exciting enzymes at the far corners of the Earth.

However, he says many of the same gains can be made by tweaking the mixtures of what is already in regular use.

“Commercial enzymes that most people have used in laboratories are mixtures. And they are actually quite undefined mixtures and haven’t really been optimized,” Dale says.
Breaking down cellulose is more complicated than putting grass clippings and wood chips with a generic bottle marked “enzyme” in a machine and setting it to spin cycle. Different enzymes work on different plants and even on different parts of the same plant. In addition, enzymes seem to work differently when they are mixed with other enzymes in an industrial setting.

So researchers working with Dale at the Great Lakes Bioenergy Center have been working to trim superfluous enzymes out of the mix. It turns out that oftentimes much of the enzyme mix is going to waste. By simply adjusting the existing mixtures, the team has managed to cut by 75 percent the amount of enzymes used in breaking down the feedstock grass Miscanthus.

But there may be other solutions beyond finding the sleekest mixture of enzymes. What if the plant could break itself down, rather than stubbornly forcing humans to do it with expensive cocktails? Perhaps the most innovative approach to enzyme use means not adding them to the cocktail at all.

Agrivida, a Boston-based biotech start-up hopes to essentially outsource the breakdown of the plant—to the plant itself.

Plants, after all, are life forms and with modern genetics there is no reason they can’t be created pre-loaded with enzymes. The problem is that a plant that creates its own corrosive enzyme would obviously wither and die.

“You don’t want to put a xylanase or a cellulase into a plant and have it chew up the cell walls while it’s trying to grow. We’ve actually done that, and you get all these stunted plants,” says Agrivida founder and president R. Michael Raab. “It’s almost like they’re melting while they’re growing.”

That’s where a new tool, called an intein, comes in. An intein is a removable segment of protein that keeps the rest of the protein from working, like an internal “mute” button. Here’s how it could work: You insert an intein into cellulase to mute the corrosive properties of the protein and the plant grows. When the plant is harvested for conversion into sugar, a simple trigger—like heating it—would remove the intein. The cellulase would reassemble and, like some kind of microscopic saboteur, start liquidating cells.

This technology is very new. Inteins were only discovered in 1987 and even then it took a while for some scientists to believe they were real. “People recognized RNA splicing and transcription but had never seen protein splicing before,” Raab says. “It’s pretty cool.”

Using a single enzyme, Raab and his team have also cut the need for added enzymes in corn stover by 75 percent. He says when they start mixing several enzymes into one plant, that number may jump above 90 percent.

Zeroing in on the feedstocks

Of course, the type of fuel and how to prepare it is pointless without a massive and steady source of plant material.

“Feedstocks is a huge issue,” says JBEI’s Keasling. “We are not going to ship biomass all over. It’s too bulky. We’re going to ship it about 30 miles, maybe less.”
That means that a feedstock needs to grow near the processing plant. Many species are under investigation and the list continues to grow.

The ideal feedstock, in addition to its energy benefits, would grow where food crops struggle and wouldn’t tax local water resources or demand expensive and polluting fertilizers. The National Resource Defense Council, for example, supports biofuels but has adopted the mantra “not all biofuels are created equal” to highlight the importance of using only sustainable feedstocks.

Giant biomass-generating perennial grasses including switchgrass and Miscanthus areamong the front-runners for temperate climates. Low-sugar varieties of sugarcane and Napier grass are favored in tropical climates with adequate rainfall. Fast growing poplar and eucalyptus trees, Jatropha for biodiesel, and even agave and bull kelp are among many that offer potential in various parts of the world.

No silver bullet—not a problem

In the end, of course, no one can predict with certainty how next-generation biofuelswill succeed or to what extent they will challenge petroleum’s dominance. More and more the sense is that that there will not—and perhaps even should not—be a silver-bullet solution.

Eric Toone, the deputy director for technology at the Department of Energy’s ARPA-Eprogram, says whether a company is growing energy crops or focused on breaking down the cellulose or synthesizing it into fuel, the most important part is that they be able to work with each other and be be interchangeable. “These pieces are modular. Exactly like Legos, so you can mix and match,” says Toone.

Toone says we don’t know what the game-changer will be. “The tool box we have today is so much bigger than what we had even just a few years ago,” he says. The only certainty, he adds, is that fuel production in the future will be a diversified endeavor.


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