Biofuels
Biofuels are liquid transportation fuels made from plant matter instead of petroleum. Ethanol and biodiesel — the primary biofuels today — can be blended with or directly substitute for gasoline and diesel, respectively. Biofuels reduce air toxics emissions, greenhouse gas buildup, dependence on imported oil, and trade deficits, and support agricultural and rural economies.
Unlike gasoline and diesel, biofuels contain oxygen. Therefore, adding biofuels to petroleum products causes the fuel to combust more completely and reduces air pollution. Also, when fossil fuels such as petroleum are burned, they release carbon dioxide that was captured by plants billions of years ago. This release contributes to the buildup of greenhouse gases that may cause global warming. Carbon dioxide release from burning biofuels, however, is balanced by the carbon dioxide capture by the recent growth of the plant material they are made from. Depending on how much fossil energy is used to grow and process the biomass feedstock, this results in substantially reduced net greenhouse gas emissions.
Ethanol
Ethanol, also known as ethyl alcohol or grain alcohol, can be used either as an alternative fuel or as an octane-boosting, pollution-reducing additive to gasoline.
Ethanol From Grain
Ethanol from Grain (chiefly the starch in kernels of field corn) is the primary means of current ethanol production in the United States. Ethanol is the same clear, colorless, flammable liquid that has been produced as a beverage from time immemorial. Ethanol can be used either as an alternative fuel (usually with 15% gasoline, E85 requires slight engine modification) or as an octane-boosting, pollution-reducing additive to gasoline (usually 8%-10%).. Most of that ethanol is made by fermenting the starch in kernels of field corn, by an industrial version of beverage production. In the future, ethanol could be used as a fuel to power fuel cells.
In Brazil, the world's largest producer of ethanol, sugar made from sugarcane is the primary feedstock. In the United States, the second-largest producer and user of fuel ethanol, the primary feedstock is the starch in kernels of field corn (otherwise predominantly used as animal feed). Other current feedstocks include milo, wheat starch, potato waste, cheese whey, and beverage waste, but any starch or sugar source can be used. The Renewable Fuels Association, a trade association for ethanol producers, is a good source of additional information.
Advanced Bioethanol Technology
Advanced Bioethanol Technology allows fuel ethanol to also be made from cellulosic (plant fiber) biomass, such as agricultural forestry residues, industrial waste, material in municipal solid waste, and trees and grasses.
Corn and other starches and sugars are only a small fraction of biomass, the wide range of plant and plant-derived waste materials. Cellulose and hemicellulose, the two main components of plants —and the ones that give plants their structure — are also made of sugars, but those sugars are tied together in long chains. Advanced bioethanol technology can break those chains down into their component sugars and then ferment them to ethanol. U.S. Department of Energy (DOE) Biofuels Program scientists and engineers are at the forefront of bioethanol technology research. This technology turns ordinary low-value plant materials such as corn stalks, sawdust, or waste paper into fuel ethanol. To help improve this technology and prepare it for commercial operation, the DOE researchers and their industrial partners use the DOE Bioethanol Pilot Plant, a fully integrated biomass-to-ethanol production facility that can turn as much as one ton per day of corn stalks or other plant material into transportation fuel.
Using advanced bioethanol technology to produce fuel ethanol from cellulose and hemicellulose opens up a vast resource to supplement grain ethanol production. Forest residues, urban wastes, agricultural residues, mill residues, and energy crops have been estimated to be able to supply more than 500 mill dry tons of biomass, enough to make more than 50 billion gallons of ethanol (equivalent to 33 billion gallons of gasoline) or about one quarter the current U.S. consumption of gasoline. Corn stover (corn stalks and husks) and wheat straw alone could be made into 10-15 billion gallons of ethanol.
Modern fuel ethanol technology is highly sophisticated and efficient, but the basic process is similar to that of making alcoholic beverages. Most fuel ethanol is biologically produced by using an enzyme to convert starch to sugar and a yeast to ferment sugar to ethanol.
Of U.S. corn ethanol production, about 25% is in wet-mill plants and 75% in dry-mill plants. The former are typically large operations that produce ethanol along with a slate of food industry products such as corn oil, corn syrup, and corn sugar. The latter are typically smaller facilities that produce ethanol as a primary product with a high-protein animal feed known as distillers dried grains as a coproduct.
Used as an additive, ethanol requires no engine modification. Because it contains oxygen, fuel with ethanol added burns more completely, -particularly in older or high-mileage vehicles, and reduces carbon monoxide and other toxic emissions. Ethanol additive also boosts octane to avoid engine knocking (about 3 octane points for 10% blend). Use as an alternative fuel — typically with 15% gasoline to aid cold-weather starting (E85) — requires minor modifications including redesigned oxygen sensors and different seals in the fuel system. E85 flexible-fuel vehicles qualify as alternative fuel vehicles, and several auto manufacturers offer models that can use E85 at the same cost as gasoline-only models. Because ethanol contains about one-third less energy per gallon than gasoline, E85 vehicles will get fewer miles per gallon.
Biodiesel
Biodiesel, made from animal fat or vegetable oil, is a renewable pollution-reducing alternative to petroleum diesel. It is made by transforming animal fat or vegetable oil with alcohol, and can be directly substituted for diesel either as neat fuel (B100) or as an oxygenate additive (typically 20%—B20). B20 earns credits for alternative fuel use under the Energy Policy Act of 1992, the only fuel that does not require purchase of new vehicles. In Europe, the largest producer and user of biodiesel, the fuel is usually made from rapeseed (canola) oil. In the United States, the second largest producer and user of biodiesel, the fuel is usually made from soybean oil or recycled restaurant grease. The National Biodiesel Board, a trade association for biodiesel producers is a good source of additional information.
Soybean oil and recycled restaurant cooking oil are in surplus, and biodiesel production uses only a small portion of each, so there is no resource constraint.
Esters are compounds of alcohol and organic acids. Fatty acid methyl ester, commonly known as biodiesel, is made by bonding methanol to animal fat or vegetable oil. The process is relatively straightforward, but must consistently achieve prescribed standards to minimize the risk of damaging expensive diesel engines.
Because it is oxygenated, biodiesel dramatically reduces air toxins, carbon monoxide, soot, small particles, and hydrocarbon emissions by 50% or more, reducing the cancer-risk contribution of diesel up to 90% with pure biodiesel. Air quality benefits are roughly proportional for diesel/biodiesel mixtures. Biodiesel's superior lubricity helps reduce engine wear, even as a small percentage additive.
The most common use of biodiesel is as B20: -20% biodiesel, 80% diesel. It requires no engine modifications. Because it gels at higher temperatures than petroleum diesel, however, pure biodiesel requires special management in cold climates. Biodiesel contains slightly less energy than petroleum diesel, but it is denser, so fuel economy tends to fall 7% for every 10% biodiesel in a fuel blend.
Methanol
Methanol, also known as wood alcohol, can be made thermochemically from biomass, but is now usually made from natural gas or coal. Research on biomass methanol has waned, because making ethanol from cellulosic material now shows greater promise.
Markets for Biofuels
Biofuels such as ethanol made from corn and biodiesel made from soybeans help support American agriculture. Advanced bioethanol technology will also provide a market for dedicated energy crops such as fast-growing trees for ethanol production.
There are two basic markets for biofuels: the fuel additive market and the alternative fuel market. The fuel additive market reduces carbon monoxide emissions, reduces chemical emissions that lead to smog formation, and provides a substitute for methyl tertiary butyl ether (MTBE).
The Clean Air Act Amendments of 1990 mandated the sale of oxygenated fuels in regions with unhealthy levels of carbon monoxide, a poisonous gas that interferes with the ability of blood to transport oxygen. Ethanol can help offset carbon monoxide emissions. Most regions use blends of 8%-10% ethanol in their gasoline to comply.
For smog or ozone, the Clean Air Act Amendments also direct regions severely failing to meet standards for ground-level ozone—a strong oxidant that causes respiratory problems and the main pollutant we usually associate with "smog"—to use reformulated gasoline (RFG). The EPA required RFG to contain an oxygenate as a specification of these standards. Although ethanol is widely used in the Midwest, fuel manufacturers have predominantly used MTBE, a petroleum-derived oxygenate, and approximately 25% of gasoline today contains MTBE as an additive. As a result of surface and groundwater contamination, however, many states have moved to phase out the use of MTBE. Nontoxic and biodegradable, ethanol can directly and easily replace MTBE use and could be added to all U.S. gasoline. The replacement of MTBE as an oxygenate will substantially increase demand for ethanol as an additive.
Currently, the ethanol industry is responsible for approximately 200,000 jobs. In 2004, 81 plants produced a total of 3.41 billion gallons of ethanol, still less than 2% of total automotive fuel use but enough to be an additive for one in eight gallons of gasoline.
Ethanol production creates domestic jobs in plant construction, operation, maintenance, and support in the communities where it is produced. Growth in the ethanol industry offers potential for overall economic development and additional employment in smaller and agricultural communities. The U.S. Department of Agriculture estimates that a 100 million gallon ethanol production facility can create 2,250 local jobs for a single community.
The Alternative Fuels Data Center's Alternative Fuels Price Report has current price information for ethanol, biodiesel and other alternative fuels.
Visit the U.S. Department of Energy's Biomass Program for more information.