Winter 2007
In This Issue:
Focus On Energy
The Biomass Approach to Energy Independence
The cover article for the October 2006 issue of Consumer Reports may call it “The Ethanol Myth,” but there are many in the agricultural and energy communities who have a vision of fields of fast-growing, energy-rich grasses and low-value corn stover rescuing family farms and bringing sustainability and energy independence to the nation.
Fields of corn stover could become energy crops, providing extra income for small farms.
Corn-based ethanol is already being mixed with gasoline in the U.S. to improve combustion, replacing around 3% of automobile fuel. But calculations of the energy cost to produce ethanol are highly disputed, with some studies showing a small net energy gain for corn-based ethanol and others a net energy loss, meaning more energy is used to plant, fertilize, harvest and process the corn than is returned when the fuel is used. And because fossil fuels are generally burned to produce ethanol, the benefits in greenhouse gas reductions are small. Critics of biofuels are also concerned about redirecting a global food source, corn, to the production of fuel.
Cellulosic biomass – the fibrous, largely inedible portion of plant matter – has potential to overcome the objections to corn-based ethanol. By using fast-growing plants such as switchgrass and hybrid poplar, which can be grown in more marginal soil than corn and without the fertilizer that corn requires, biofuels would net a much higher energy gain without diverting food-growing acreage to energy production. Other potential sources for biofuel include forest residue and corn stover, the stalks and inedible parts of the corn plant, both of which can be gathered with little additional energy cost. It is estimated that over 1 billion tons of biomass is available annually nationwide.
Biofuels such as this biodiesel made from corn are under intensive study at Penn State.
Within the recently formed Penn State Biomass Energy Center, research is underway to make biomass an affordable and sustainable replacement for a significant portion of fossil energy. Led by Director Tom Richard from the Department of Agricultural and Biological Engineering, the Biomass Energy Center engages with every aspect of biomass as a fuel source, from the genetic improvement of the feedstock, widespread implementation in agriculture, and the processing of biomass, to materials characterization and the economics of biofuels.
Wall-loosening proteins
One of the researchers taking part in the Biomass Energy Center is biologist Daniel Cosgrove. It was in Cosgrove's lab a decade ago that a new group of proteins named expansins was discovered that allows plant cell walls to expand as the plant grows. These “wall-loosening” proteins could resolve the major limitation on current biomass-to-biofuel processing – the high cost of breaking down the tough fibers.
According to Cosgrove, the best current strategy for converting cellulosic biomass to transportation fuel calls for treating biomass with enzymes to break it down to simple sugars, which are then fermented to make ethanol or related alcohols for fuel. The high cost of the enzymes can add from 30 to 50 cents per gallon of fuel, although new types of enzymes may reduce the cost to 20 cents or less per gallon.
Daniel Cosgrove explains the nanostructure of cellulose.
Holding a model of the plant-wall structure, Cosgrove explained why cellulose is so difficult to break down: “First,” he said, “the sugar molecules are hooked up end to end to make a long strand. Then they are hydrogen bonded laterally into a sheet. Those sheets are then packed into layers to make a microfibril.” The enzymes have to break down the microfibril one layer at a time.
The dimensions of the cells are something on the order of 2 to 4 nanometers in size – the perfect thing for materials science to be involved with, he pointed out. “This is the material in which most of the organic carbon is found on this planet and that DOE wants to convert back into simple sugars and then into ethanol. This is the most abundant biomass on the planet.”
In the course of studying expansins, Cosgrove's team found that the proteins have the ability to speed the breakdown of cellulose material into sugars. The expansins strip off the hydrogen binders so the layers can be pulled apart to allow the enzymes to act on all of the layers of material at once.
Cosgrove believes there is a potential commercial use for these novel plant proteins in making biofuels. One possibility would be to make expansin proteins in much the same way that chemical engineers make enzymes. That is, ferment a fungi such as aspergillus that can grow large amounts of proteins. Then add these proteins to large vats where expansins and enzymes incubate together with biomass to break down the cellulose. Another possibility would be to use genetic engineering methods to get theplant to produce expansins just as it's about to be harvested so the protein would be ready to break down the cell walls.
“The Department of Energy is funding this biomass renewable energy to the tune of hundreds of millions of dollars,” Cosgrove said. “That is only part of the interest. A lot of other agencies as well as energy companies are interested in the area of biomass. The vision is that a substantial part of the nations energy will come from plant sources and that will replace petroleum and coal energy sources. There are downsides to fossil fuels: politically in the case of petroleum, which comes from unstable regions of the world, and environmentally for both coal and petroleum, because of burning the carbon and putting it into the atmosphere and accelerating global climate change.”
Expansins, cell wall loosening plant proteins, were first discovered by Cosgrove and his team.
As a concerned citizen, as well as a scientist paying attention to developments in his field, Cosgrove is interested in how farms could be made more profitable to help keep family farming alive. Bioenergy crops are one way that farmers can grow products with economic value.
“Around here, you notice, they leave a lot of the corn stubble in the field, so they're talking about using that residue, which is a large fraction of the material that the corn plant makes. You know that we harvest just the seeds, but the rest of the plant could potentially be harvested for energy purposes. A lot of this doesn't get used for anything.”
In prairie regions where the soil is too marginal for corn, bioenergy crops could replace low-level uses, such as foraging. The University of Nebraska is very interested in bioenergy crops to help support the state's farmers, Cosgrove remarked.
“This whole business of bioenergy fuels is very complicated politically. Some people think of it as farm supports, and certainly the bio ethanol that is produced right now is all produced from corn starch. This is viewed partly as an energy issue and partly as a farm support issue. Any time when you get into talking about billions of tons of biomass and billions of dollars of commodities, you are no long in the science, or not only in the science. You're now also involving all sorts of political and social issues. For every person who is for it, you're going to find people against it, for one reason or another. Any issue will have pros and cons, who are the winners and who are the losers. I'm not sure I know yet.”
You can find out more about the Penn State Biomass Energy Center on the Web at http://www.bioenergy.psu.edu
Dr. Cosgrove is Holder of the Eberly Family Chair in Biology at Penn State and is a member of the National Academy of Sciences. His discovery of the expansin gene family has been called a major breakthrough in plant biology. He can be contacted at Validate to view address - Send Email via form.
