U.S. Ethanol - Field of Dreams?
The December 7 issue of Nature contained an interesting article on U.S. biofuel production (subscription only). As I'm sure many of you are aware, corn - from which ethanol is made - is a fairly inefficient source of energy. It's high in starch, which is easy to convert to ethanol, but much of the corn plant's energy goes to producing structural materials such as stalk which are harder to break down. Estimates vary, but the energy output may only be twice the amount of energy it takes to produce the ethanol.
The cellulose and hemicellulose which make up the stalks and also make up most biomass which could be converted to ethanol require pretreatment with acids, peroxides and ammonia, often along with mechanical shredding or pressing of the material. Following that step comes the use of enzymes to produce fermentable sugars. Interestingly, one of the companies concentrating on these enzymes got it's start distressing denim for jeans.
Some other plants, including a variety of prairie grasses, may be more energy-rich than corn. A number of researchers are studying the viability of these other resources.
The article wraps up with a brief discussion of butanol as an alternative to ethanol. Ethanol is corrosive, volatile and has a tendency to pick up water, making it difficult to transport. Butanol is a four-carbon alcohol which contains a higher energy per gallon than ethanol and can be shipped through existing pipelines.
The large companies who are working on these biofuels have some pretty familiar names - BP and DuPont are working with British Sugar to adapt an ethanol fermentation facility in East Anglia to produce Butanol. And BP has announced it will invest $500 million over 10 years to fund an Energy Biosciences Institute at a major academic center.
Comments (3)
Good information! Thanks Laura.
Time to do a little research on Butanol.
I've often wondered why US companies focus on corn as an Ethanol source when countries such as Brazil have had much better success with sugar cane. Without a whole lot of research, I'm guessing it may have to do with the growing conditions required for Sugar Cane. If it requires warmer and longer growing seasons that corn, then there's an obvious reason.
Posted by Greg Simmons | December 18, 2006 3:20 PM
Greg - Sugarcane is a tropical crop, one which requires a wet season and a dry season. I know it's grown in parts of Hawaii and in parts of South Texas, Louisiana and Florida. Here's a link to a map of the harvested acres in 2002. http://www.nass.usda.gov/research/atlas02/Crops/Field%20Crops%20Harvested/Sugarcane%20for%20Sugar,%20Harvested%20Acres.gif
Corn is obviously far more abundant in this country than sugarcane, and unfortunately there's probably some political motivation for promoting corn ethanol as well.
It seems to me it makes more sense in this country to use sugar beets, which are much more widely grown. http://www.geo.msu.edu/geo333/sugarbeets.html
The East Anglia facility mentioned in the Nature article is converting sugar beets into butanol.
Posted by Laura Hannon | December 19, 2006 10:43 AM
Thank for the clarification. Not being horticulturally gifted like my wife, I'm oblivious to the needs of different plants.
I would agree on the political motivation behind corn use. I wonder if some of these same farms could convert to sugar beets and still have some political muscle?
Posted by Greg Simmons | December 19, 2006 11:28 AM