Facts of the Matter
Realizing ethanol's energy potential takes effort
WE HAVE heard that adding ethanol to gasoline will lower prices, and it seems like a good idea on the surface.
But looking deeper reveals quite a bit more complexity.
Ethanol is primarily produced by fermentation, although there are other methods.
Fermentation is an anaerobic metabolic process used by yeast to extract energy from sugar, producing carbon dioxide in the process. The result contains only a small percentage of ethanol because, above a certain concentration, it poisons the yeast and kills the culture.
To further refine ethanol, fractional distillation is required.
Because ethanol boils at a lower temperature than water, the vapor obtained from boiling an ethanol-water mixture has a higher percentage of alcohol than the liquid mixture.
Successively evaporating and condensing the mixture produces an ever higher concentration of ethanol.
Fractional distillation can concentrate ethanol only to about a 96 percent concentration. The mixture of 96 percent ethanol and 4 percent water is an azeotrope that boils at 173 degrees Fahrenheit.
An azeotrope is a liquid mixture whose vapor has the same composition as the liquid. This means that you cannot change the composition of that liquid at its azeotropic composition by simple boiling.
The presence of even 4 percent of water in ethanol destroys its desirability as a fuel when mixed with gasoline. To be mixed with gasoline for a fuel, ethanol must be purified to at least 99.5 percent to keep the water from separating and interfering with combustion.
Sugar is not the only natural product that can yield ethanol by fermentation.
Cellulose is a complex carbohydrate made from polymers (long chains) of sugar molecules that can produce ethanol by fermentation. Until recently, the cost of cellulose enzymes that could render the cellulose into a fermentable form was prohibitive.
Since 2004, cellulose-based ethanol has been produced commercially in Canada. The Canadian government is the primary consumer, and the U.S. Department of Energy has invested millions of dollars toward making this a more commercially viable and profitable industry.
Although ethanol is a good, high-energy liquid fuel, it cannot be used in pure form as a substitute for gasoline without modification of fuel injection systems and cold starting systems for winter climates. Most modern cars can easily run on up to a 30 percent mixture without modification.
In Brazil there has been a significant reduction in oil consumption since ethanol-burning cars were introduced during the oil crisis of the 1970s. In the 1980s more than 90 percent of cars were ethanol-only, but the fad petered out when oil prices fell in the early 1990s. Since then the demand has changed with market fluctuations of gasoline and ethanol prices. In 2005, 80 percent of cars sold in Brazil were dual-fuel, compared with only 17 percent the previous year.
The use of ethanol as a fuel replaces about 40 percent of the gasoline consumed, but the effect on the overall oil consumption by the country is smaller. Brazil is a major oil producer, but it still must still import oil due to demands for other petroleum byproducts such as diesel fuel and lubricants, which cannot be produced by biomass.
Gas in Brazil now costs the equivalent of $4.69 a gallon. Pure ethanol, taxed at slightly lower levels and cheaper to produce, goes for about $3.59 a gallon.
Brazil increased the energy efficiency of its ethanol, produced from sugar cane, in several ways.
Only 30 percent of the energy in sugar cane is in the sugar. Thirty-five percent is in the leaves and stems (which are often left in the field), and 35 percent is in bagasse, the fibrous material left over from pressing the cane.
Using bagasse to provide heat for distillation and electricity to run the processing plants makes many Brazilian ethanol plants energy self-sufficient. Some even sell electricity to the grid.
There are no U.S. locations where sugar cane can be grown as economically as in Brazil, which is entirely in the tropics. The best U.S. crop for producing ethanol is corn.
For an average efficiency corn farm and an average efficiency ethanol plant, the energy output-input ratio is about 1.35-to-1.
At $60 a barrel, the cost of the raw material required to produce a gallon of gasoline is $1.43.
The energy density of ethanol is only 64 percent that of gasoline, so it takes 1.5 times the amount of ethanol to produce the same energy as gasoline.
The 2004 average cost of producing a gallon of ethanol was $1.34 a gallon. Multiplying this by 1.5 (the energy density factor) makes the equivalent price of ethanol per gallon $2.
Another way to look at the cost benefit of ethanol is to look at the numbers a different way.
Making 4 gallons of ethanol requires the energy in 3 gallons of ethanol (4/3 = 1.33). So you must make 4 gallons of ethanol to save 1 gallon of gas.
But ethanol has less energy per gallon, so to save 1 gallon of gas, you must make 6 gallons (4 x 1.5) of ethanol.
Federal tax exemption keeps ethanol economically competitive with petroleum fuel products. With the subsidy due to expire in 2008, the future of ethanol might depend on whether it can compete with crude oil on its own merits.
To become energy independent, we would have to grow corn on every square inch of the U.S., including Alaska, and then half that much again.
To meet President Bush's goal of ethanol providing 30 percent of energy, corn would cover 50 percent of the United States.
If the Department of Energy meets its goals, production costs for ethanol could be reduced by 60 cents per gallon by 2015 with cellulosic conversion technology, which would allow for a wider variety of biomass to be used for ethanol production.
An alternative to ethanol, currently in production at a commercial facility, produces oil from biowaste by thermal conversion, mimicking the process by which Earth has created petroleum.
The company, called Changing World Technologies, uses high temperature and pressure processing to produce oil from virtually anything that contains carbon: slaughterhouse waste, municipal sewerage, old tires or plastic. About 300 tons of biowaste can make 500 barrels of oil.
The byproducts of this emergent technology are high-grade fertilizer and water clean enough to discharge into a municipal waste-water system.
Although still in the development stage, this technology shows promise for producing oil from biowaste.
None of these technologies will solve the environmental, social and geopolitical problems of the oil economy, but until the continuing dream of controlled fusion becomes reality, it might be the best we can do.
Richard Brill, professor of science at Honolulu Community College (honolulu.hawaii.edu~rickb
), teaches earth and physical science and investigates life and the universe. His column is published on the first and third Sundays of every month. E-mail questions and comments to email@example.com
picks up where your high school science teacher left off. He is a professor of science at Honolulu Community College, where he teaches earth and physical science and investigates life and the universe. He can be reached by e-mail at firstname.lastname@example.org