Governors' Biofuels Coalition

“We’ve learned a lot of basic science about the role that lignin plays in plants and how it interacts with other components that the plant also synthesizes,” said Paul Gilna, director at Oak Ridge’s BioEnergy Science Center. “That information can be put to use — instead of getting away from it, how do we make it useful?”

Until now, lignin has been mostly viewed as a hindrance in biofuels production, and most science has revolved around how to make it easier to extract sugars from its grip. Biofuels companies have burned off — or plan to burn off — excess lignin at the end of production processes for power and because there’s been nothing better to do with it.

But scientists who have studied lignin for years say it’s time to think about lignin for its own potential value, rather than as a waste product that needs to be addressed in biofuel production.

In a paper published last week in Science, researchers laid out their vision for the future of lignin and biofuels production. The industry is at a “tipping point,” they said, with three major cellulosic biofuel companies planning to bring plants online this year.

“Our first desire was to crawl. The next desire was to stand up and walk, and then to run,” said Art Ragauskas, the article’s lead author and a researcher at Georgia Tech. “Clearly if you’re a cellulosic ethanol company, the first desire is to make ethanol at a competitive price. Now you have this bioprocess stream. The next question is what do you do with that?”

Ragauskas has been studying lignin since the early 1990s. The concept of burning off lignin came from the pulp and paper industry, he said, which has been using the excess plant material for years as a source of heat and electricity.

But biofuel plants don’t require as much lignin for power as pulp and paper mills. In general, plants generate 60 percent more lignin than is needed to meet internal energy uses. The lignin that goes through a biofuels process also comes out the other end with fewer chemical changes than in a pulp and paper mill, opening up the potential for new uses.

Researchers see carbon fiber as one of the most exciting potential uses for lignin. Carbon fiber, a strong and lightweight material made of carbon atoms, is most commonly used in the aircraft and sporting goods industries.

Until now, the market for carbon fiber has been restricted partly because of the cost. The global market is still less than 100,000 tons a year, compared to the steel market of 1.5 billion tons a year. Put another way, if Ford had made its F150 out of carbon fiber, the automaker would use up the world’s total supply of carbon fiber.

But the market has the potential to grow as automakers and airlines seek lighter-weight materials to increase efficiency. And lignin could one day make carbon fiber cheaper.

While lignin will never be the basis for any structural elements in a plane or car, lignin-based carbon fiber could work well in interior spaces and in applications that are not directly essential for safety, said Cliff Eberle, a mechanical engineer at Oak Ridge.

“I do not think you’ll ever see a lignin carbon fiber ever used in the primary structure in an aircraft,” Eberle said.

Where it could potentially be used instead, he said, are “seats, luggage bins, luggage carts, clips, lots of stuff.”

Next: genetic engineering

The roadmap published in Science identifies genetic engineering as one of the most important tools going forward for creating useful lignin.

The goal of research is to create forms of lignin that can be easily broken down in the front end of the biofuels process yet that are engineered for valuable uses at the back end.

“We’re looking at: Can you even do plant genetics that will allow you to tailor the lignin either by selecting existing plants or designing plants,” Eberle said. “Can you have designer trees that will give you the lignin you want?”

Gilna said that Oak Ridge has seen increased interest from industry over the last few years in its research into lignin.

POET-DSM Advanced Biofuels, a joint venture spearheaded by the nation’s largest ethanol producer, is actively looking at alternatives for its lignin, according to Steve Hartig, the company’s general manager for licensing.

POET-DSM is planning to open one of the nation’s first large-scale cellulosic ethanol plants, a 25-million-gallon plant in Iowa that will use corn residues collected from nearby fields, within a few weeks. It will at first burn the lignin off to produce power for both the cellulosic facility and a co-located conventional ethanol plant, Hartig said.

“If we look over time, burning it is not a bad thing to do, but we’re certainly aggressive in assessing technologies for other ways to do it,” Hartig said.

Hartig said that the company is eyeing carbon fiber and various petrochemical feedstocks. But carbon fiber applications would have to be driven by greater demand from industries such as the aviation and automobile sectors themselves, he said, given that about one month’s worth of lignin from POET-DSM’s plant would about equal the whole world’s current demand for carbon fiber.

DuPont also plans to open a large-scale cellulosic ethanol plant in Iowa before the end of the year and, like POET-DSM, plans to burn off lignin for energy. Jan Koninckx, global business director for biofuels at DuPont, said that that company had always had a plan to develop more value from lignin.

But DuPont is first aiming for agricultural uses, such as mulch, potting soil, disposable potting plants and fertilizer components, Koninckx said. DuPont hopes to roll out those products within the next few years, he said.

“They’re products that we make out of the agricultural residue that is left on the field today that is not used. All the same positives that we shared with people about cellulosic ethanol apply just the same to this,” he said. “They’re renewable, fully sustainable and made out of carbon that was in the sky.”