It Might Just Happen
An interdisciplinary approach could unlock the secrets of cellulosic biofuels.
The scientific challenge is straightforward. If the U.S. hopes to realize significant reductions in both the volume of imported petroleum and the level of carbon emissions, a portion of the solution will involve a substantial increase in the use of biofuels by the domestic automobile industry. The willingness of Americans to embrace biofuels, and the subsequent economic transformation in a variety of industrial sectors, will depend in large measure on whether researchers at Oak Ridge National Laboratory can find a way to produce cellulosic ethanol at a cost that is competitive with that of gasoline.
At the midway point of a five-year mission to revolutionize the production of biofuels, ORNL's BioEnergy Science Center (BESC) has made considerable progress toward overcoming several fundamental scientific roadblocks. One key to this progress is BESC's unprecedented coalition of industrial, academic and government partners that has made possible an interdisciplinary approach to research and development. Associate Laboratory Director for Biological and Environmental Sciences Martin Keller has the daunting task of coordinating the partners and integrating a variety of laboratory research functions as diverse as land use planning, biomass conversion and the linkage of biobased products, such as lignin carbon fiber, to biofuel production. Prior to his promotion in February 2010 to associate lab director, Keller served as the director of BESC. The center's new director is Paul Gilna, who has assumed the role of managing the multifaceted system of partnerships and collaborative research efforts for the Department of Energy. Keller is quick to point out that because the problems addressed at the center are both interconnected and broad in scope, BESC's research efforts, by definition, must be interdisciplinary. While the center's research targets are guided by DOE, Keller and Gilna are working to leverage BESC's capabilities with other bioenergy projects across ORNL.
Sustainable crops
The first consideration for any bioenergy production effort is the sustainability of the "feedstocks," or crops, on which the process relies. "If we look back at what happened when corn-based ethanol became popular," Keller says, "few researchers paid enough attention to issues of sustainability." He stresses that the practical limits of feedstock production, land use changes, environmental impacts and the effect of feedstock production on the price of food need to be resolved before America can establish a sustainable biofuels industry. "The questions we ask now will have an impact on the project's ultimate success," he says.
If large-scale biofuel production can be established and sustained, Keller envisions an economy in which as much as 30 percent of the energy required for transportation would come from biofuels. He also anticipates that a significant percentage of the steel used in cars could be replaced by lightweight carbon fiber, a biomass byproduct. Keller says answers to a number of fundamental sustainability questions were provided by the "Billionton Study," which concluded that the U.S. could produce a tremendous volume of biomass. "We now need to go a step further and determine in what specific areas we can grow these crops, which crops should be grown where and whether these feedstocks will require a change in our agricultural practices. All of these questions are being considered by ORNL's Center for BioEnergy Sustainability."
Better plants, better enzymes
As they sort through sustainability issues, BESC scientists are also investigating "recalcitrance," the most intractable problem facing the biofuels process.
Recalcitrance is the term researchers use to describe the difficulty of extracting the sugars stored in the stalks, branches, and stems of plants. Producing biofuels involves converting plant material into accessible sugars and then fermenting those sugars into biofuels, such as ethanol.
"Nature made plants extremely resistant to this process," Keller explains. "The complexity of the conversion process is the primary reason the biofuels industry has not taken off." The three major components of biomass are cellulose, hemicellulose, and lignin. BESC researchers are searching for both a cost-effective way to separate the lignin from the cellulose and hemicelluloses and an equally effective way to digest cellulose and hemicellulose into sugars and ferment them into biofuels. Keller says that BESC scientists are trying to understand, at the biochemical and genetic levels, why biomass is so hard to digest. Once they unlock this door, the equally important challenge will be to identify or engineer new enzymes and microbes to make the digestion process cost effective.
In the quest for better biofuel feedstocks, BESC scientists are also developing microbes with unique capabilities to break down biomass into its component sugars. "We know that if we cut down a tree in the forest, it will lie on the ground and eventually decay and disappear," Keller says. "The tree will ultimately be digested; it just takes a long time. In a similar way, our goal with biomass is to accelerate this process." To gain a more detailed understanding of exactly how plants are deconstructed by microbes, BESC researchers are designing computer simulations of plant cell wall structures. Their goal is to determine where and how to make genetic modifications to these structures that would render them easier to digest. "BESC is bringing together an unprecedented consortium of 20 institutions and the collective resources of molecular biologists, biochemists and computer scientists to overcome this fundamental problem of recalcitrance," Keller says.
Broadening the research base
Another major focus within BESC's biofuels program is integrating biological studies focused on creating better plants and enzymes with research being done by chemical and materials scientists on separating various constituents within the biofuels production process and catalyzing the chemical reactions. Keller says ORNL benefits from a history of effective separation technologies research. "By bringing the laboratory's separations scientists into the collaboration, we have been able to apply their knowledge and experience to the challenges posed by bioenergy." The collaboration plays a critical role in increasing the pace of BESC's efforts to combine the pretreatment of biomass and the separation of its key components, such as cellulose and hemicellulose, into a single, continuous process.
The laboratory also has considerable expertise in catalysis, a process that involves starting or accelerating chemical reactions. One area in which this expertise is being applied is biofuels fermentation. Ideally, BESC will eventually be able to produce not just ethanol, but also other biofuels that are more compatible with America's current fuel supply. To accomplish this, researchers will need to do one of two things. They must either modify the microorganisms to enable them to ferment sugars into fuels with longer-chain carbon molecules or devise a chemical means of converting the ethanol produced by these organisms to higher hydrocarbons—or a combination of both techniques. Understanding the chemical pathways by which these higher hydrocarbons can be produced is critical to success. "This scientific challenge explains why we are integrating catalysis specialists into the research process," Keller says. "Traditionally, scientists in different disciplines might have investigated the problem from isolated bubbles. Our success has come in part from bringing people together across disciplines."
As additional biofuels are developed, Keller is accessing the resources of the National Transportation Research Center, where ORNL researchers are testing various biofuel blends to determine emission and efficiency performance in a variety of engines. This capability will become increasingly important as biofuels are created that can be introduced directly into the current energy infrastructure. The center's researchers also model combustion, applying their findings to studies of biomass combustion for both gasification and power. Gasified biomass (or syngas) can be converted into fuels through catalysis or fermentation, yet another illustration of interdisciplinary research in the bioenergy arena.
Valuable leftovers
Lignin, or plant fiber, accounts for most of the leftover material after the sugars have been extracted from biomass. In a conventional biomass conversion process, this leftover fiber would be burned to create heat for other processes, such as producing steam used to generate electricity. This particular bioenergy byproduct, however, has a higher value potential. With funding from DOE's Office of Energy Efficiency and Renewable Energy, ORNL is promoting a more efficient approach that involves converting lignin, the biofuel byproduct, into carbon fiber for use in lightweight automotive and aircraft components. Keller predicts that if lignin could be used to create carbon-fiber components that are costcompetitive with steel, the material's low weight and high strength would quickly generate a market in an automobile industry constantly in search of better fuel mileage. "If we could replace a significant portion of the steel in a car with carbon fiber," Keller reasons, "the car would be much lighter, require less fuel, and, in turn, reduce the demand for imported oil. Fuel efficiency must go hand-in-hand with biofuels. We cannot simply replace one kind of fuel with another. In order to create a sustainable model, we have to deliver fuel efficiency, as well."
Bridging islands of science
Keller stresses that, while the pressure for breakthroughs in the field of biofuels production is undeniable, the keys to success are communication and cooperation across scientific disciplines and among organizations. The need is too pressing, the questions too broad and the problem too complex for any single group of scientists. "We're trying to get researchers to look at the problem of providing energy for transportation in an integrated way. If we want to succeed, if we hope to create a sustainable biofuels industry, we cannot remain islands of science. The only path forward is an integrated approach to addressing one of the most important scientific challenges of our lifetimes."