In the United States, ethanol has long been associated with corn. But as ethanol production has expanded rapidly, that perception will have to change.
While food prices rose 4.9 percent in 2007, corn ethanol production rose from 5 billion gallons to 7 billion. This has been a cause for alarm, triggering worries about inflation in the United States and concerns about the ethics of using food crops for fuel. Also, new ethanol mandates under the 2007 Energy Act require more ethanol than can be produced from corn in the United States. So while ethanol in the United States will come almost entirely from corn in the near-term, long-term ethanol will have to be made from a variety of fibrous feedstocks.
Cellulose, essentially any kind of plant fiber, is available all over the country. By comparison, corn cultivation and current ethanol production is primarily in agricultural regions in the Midwest. Consequently, ethanol plants could be located all across America and near coastal cities, alleviating the problem of transporting ethanol from the Midwest. (Ethanol is corrosive and absorbs water, making it difficult to transport in pipelines. And barge and rail capacity to transport ethanol is expensive and constrained. Ethanol is already the number one hazardous material shipped by rail in the United States.)
Cellulose can be harvested from a variety of sources. The main ones being developed are:
- Corn stover, the cobs, stalks, and husks left over from harvesting corn
- Wood pulp, either from existing pulp mills or through harvesting eastern hardwood forests
- Prairie switchgrass
- Leftover construction materials
- Municipal waste.
While some studies have shown that making ethanol from corn consumes more petroleum than it saves (though a majority of studies now show a positive energy balance), cellulosic ethanol is much more efficient. Taking cellulose from plants that grow natively, such as switchgrass and poplar trees, doesn't require fertilizer--sparing the use of petroleum to transport and spread. Using waste materials such as corn stover, wood pulp, or trash can be even more efficient, and have the positive effect of putting waste materials to work.
Depending on the raw materials, cellulosic ethanol could be more expensive than corn ethanol, though it could eventually become cheaper.
Researchers are developing two main processes for refining ethanol from fiber. Both use specially bred enzymes to break down the fibrous material into sugar for refining into ethanol. These enzymes, however, add about $1 a gallon to the cost of refining ethanol from fiber, relative to corn.
The traditional conversion process is to pre-treat the raw fibrous material to soften it, then break it down with enzymes into sugar. Biotech companies such as Rochester, New York-based Genencor and Danish company Novozymes are developing such processes for various woody feedstocks. Novozymes says it will have a commercial plant producing cellulosic ethanol in three years. One company, SunEthanol, of Hadley, Massachusetts, says it can shortcut such processes by using enzymes that make ethanol directly, rather than sugar.
Another process is being developed by a Warrenville, Illinois, company, Coskata, which claims it can use feedstocks such as municipal and construction waste. In its process the waste is heated to turn it into gas (specifically syngas, which is a mixture of hydrogen, carbon dioxide, and carbon monoxide), then special enzymes convert the gas into ethanol. (Read: GM invests in cellulosic ethanol )
Now these companies are beginning to look beyond ethanol as a motor fuel to using it as a supply to make fabric and plastics, and other industrial uses.
So far, much of this cellulosic technology is either unproven or too expensive. But like many biotechnology processes, prices are coming down. New machinery would have to be developed to harvest trees and other feedstocks for this purpose. But the supply of fuel could be almost endless, as it is renewable within our national borders.
In the 19th century and into the beginning of the 20th, almost all energy came from renewable, biological sources. And Henry Ford built the Model T to run on ethanol. Now it looks certain that more cars will return to renewable fuel sources in the future.
Learn more about alternative fuels in our fuel economy special section.