A byproduct of biofuels production could produce a new opportunity for American industry.
Some projections indicate that within two decades U.S. production of fuel from biomass could exceed a billion gallons annually. If these predictions are accurate, simple arithmetic suggests that disposing of lignin, the primary byproduct of manufacturing biofuels, will present scientists with both a challenge and an opportunity. For every pound of sugar-yielding cellulose extracted from biomass, about half a pound of lignin remains. Rather than sending the waste material to landfills or burning it to heat buildings, researchers now advocate turning this waste into a variety of useful products. At a minimum, these new products could offset the cost of biofuels production. In the most optimistic scenario, creative uses for lignin could represent a transformational technology with virtually unlimited potential for American industry.
At ORNL, researchers are focused on converting lignin to carbon fiber. Materials scientist Fred Baker notes that ORNL's decade-old carbon fiber research program is driven by a simple objective: to find a way to produce carbon fiber at a low cost. The largest potential market for carbon fiber is the automotive industry. Researchers calculate that if carbon fiber could be produced and sold at a price comparable to that of the amount of steel it would replace, the weight of an average automobile could be reduced by as much as 60 percent. At present, the cost of carbon fiber is far from competitive. Suitable-quality fiber currently costs about $15 per pound. U.S. automotive industry spokespersons suggest carbon fiber would be substituted on a large scale if the price comes down to $5-$7 per pound, Baker says. "Carbon fiber is already used in some high-performance vehicles, but current costs remain prohibitive for the majority of domestic automobiles."
Baker explains that 50 percent of the cost of producing conventional carbon fiber is associated with the precursor material called polyacrylonitrile, a petroleum-based product. More than 90 percent of the 50,000 tons of carbon fiber produced annually worldwide is made from polyacrylonitrile. "That's the lowhanging fruit," he says. "If we can reduce the cost of material substantially by using lignin as a precursor, we can also reduce the cost of the finished product." In their effort to engineer a low-cost, lignin-based alternative, Baker and his colleagues examine every stage of the carbon fiber manufacturing process. They look for opportunities to save time and energy with a goal of saving money. "This is not blue-sky research," Baker emphasizes. "We have a specific purpose in mind. We are on track to produce a lignin-based carbon fiber for about $3.50 per pound, which could be sold commercially for about $5.50 per pound—well inside the target range." Targets notwithstanding, Baker concedes a number of engineering hurdles remain.
Baker estimates that he and his colleagues are about 60 to 70 percent of the way toward producing commercialgrade, lignin-based carbon fiber. "We know where we have fundamental issues to address," Baker says. Many of these challenges are related to the structural properties of the lignin, so his group has been working closely over the last year with ORNL's BioEnergy Science Center to implement ways of modifying these properties. Rather than employ the relatively expensive approach of chemically processing the lignin to optimize its structure for carbon-fiber production, Baker prefers to manipulate the chemistry of lignin at the source of production, in the plant. "Some researchers think the idea is far-fetched," he says, "but it's not. The process actually occurs every day in the forest products industry. The trees that are grown today to make paper are very different from the trees that were grown 50 years ago. Today's trees have been genetically engineered to provide the best cellulose fibers for paper production. We hope to do exactly the same for lignin. Optimizing the quality of the lignin in the tree or plant would be a much more efficient process."
While producing lightweight vehicle components is the group's primary goal, Baker's team has determined that carbon fiber can be used for a range of diverse applications. Carbon fiber reinforcement has been demonstrated to reduce cracking in the electrodes used in steel recycling operations. The team is about 80 percent of the way toward the goal of making a lignin-based product for this application. Researchers also are investigating the fiber for use in energy storage applications, such as increasing the surface area of supercapacitor electrodes. In a supercapacitor, surface area translates directly into electrical storage capacity. Ligninbased carbon electrodes can be structured to provide thousands of square meters of surface area within just one gram of material. These components have potential applications in several industries, including the next generation of charging systems for electric vehicles.
One of the more creative potential applications for carbon fiber involves using an electric vehicle's body panels as part of an energy storage system. Structural elements that could do double duty as electrical storage devices would be immensely helpful in overcoming the size and weight of batteries—currently one of the biggest drawbacks of electric vehicles. The ability to reduce the weight and expand the power of electric vehicles simultaneously would be another transformational step in transportation technology.
One indicator of confidence in ORNL's carbon materials research comes from the Department of Energy, which in the summer of 2010 awarded $34.7 million to ORNL for the construction of a Carbon Fiber Technology Center. Baker says the center will not only accelerate the pace of carbon fiber research but will also fill a long-standing need for small production runs of carbon fiber made from lignin and other precursors that are needed to bridge the gap between experimentation and commercial viability. "The world's leading automakers require a minimum of one ton of carbon fiber to begin basic testing on the manufacturing of carbon fiber car parts," he says. "To manufacture and test carbon fiber wind turbines, General Electric needs one ton for each blade, and they would rather have twice that much." The Carbon Fiber Technology Center will be able to meet research needs similar to these and will have the capacity to produce 25 tons of carbon fiber annually.
Both the new Carbon Fiber Technology Center and the range of applications to which carbon fiber technology is being applied speak volumes about the progress ORNL and the Department of Energy have made in the field of carbon materials research. The progress is even more impressive when one considers the role carbon fiber could play in increasing the commercial viability of biofuels and boosting the production of lighter-weight, fuel-efficient vehicles.
Becoming reflective, Baker looks at his research as being the beginning of something much larger. "The question regarding biorefineries has always been what to do with all the lignin when we start making vast amounts of biofuel? If we can learn how to turn a waste material into useful products that reduce the cost of biofuel, reduce our dependency on oil imports and spawn a new sustainable sector of American industry, then we are indeed talking about something special."