Ethanol

Introduction

Ethanol—also known as drinking, ethyl, or grain alcohol—is a compound of carbon, hydrogen, and oxygen (C₂H₅OH) that can be burned as a fuel. Ethanol can be refined from petroleum, but its interest as an alternative energy source depends on the fact that it can be produced biologically. Yeast cells ingest sugars and excrete ethanol. The sugars can be extracted from kernels of grain, grapes, sugarcane, or other plant materials. Ethanol can be added to gasoline to substitute for some of it or to raise its octane or make it burn more cleanly.

Ethanol can also be burned by itself in specially designed engines. In the United States and Brazil, ethanol production is subsidized by the government in an effort to reduce national reliance on imported oil. The U.S. ethanol program, which relies on corn, is particularly controversial. There is a wide scientific consensus that little more energy, if any, is extracted from burning corn ethanol than is required to produce it. Defenders of corn ethanol argue that ethanol's energy balance is at least positive, and will be much better when methods are perfected for producing ethanol from cellulose, a more abundant plant material. There is also disagreement about whether ethanol contributes less to climate change than do equal amounts of fossil fuel.

Historical Background and Scientific Foundations

The use of ethanol as a fuel goes back to the early days of the internal combustion engine. Henry Ford (1863– 1947), the first person to apply assembly-line techniques to manufacturing cars, stated that ethanol was “the fuel of the future.” Ford even had the Model T, the first car to be marketed to millions of middle-class consumers, designed so that it could run either on gasoline or ethanol. Germany and France had few oil wells and hoped to increase their energy independence by promoting ethanol as a motor fuel. There was debate about which fuel was superior, gasoline or ethanol. In Europe in the late 1890s and early 1900s, a number of road races were held between vehicles burning pure gasoline, pure ethanol, or various blends of the two. In 1906, a third of the heavy locomotives built by the Deutz Gas works in Germany burned pure ethanol and a tenth of the automobile engines built by Otto Gas Engine Works in Philadelphia, Pennsylvania, burned pure ethanol.

Ethanol was eclipsed, however, by gasoline. One reason was that gasoline has 1.5 times as much energy per gallon as ethanol, so a gasoline-powered car can go farther on a tank of fuel. Efforts were made to revive ethanol in the 1920s and 1930s, with a blend of 90% gasoline and 10% ethanol being offered at many gas stations. At that time, ethanol was proposed not primarily as a substitute for gasoline, but as an antiknock additive. Knocking is the annoying sound caused by premature ignition of fuel in an engine's cylinders, which lowers efficiency.

However, the use of a highly toxic (but profitable) lead compound, tetraethyl lead, was successfully promoted by the companies Du Pont and General Motors starting in the early 1920s. About 7 million tons (6.3 million metric tons) of lead were added to the environment in the United States in the twentieth century as the result of using tetraethyl lead instead of ethanol as an antiknock additive. Lead was phased out by law in the United States from 1973 to 1996. Phaseout was completed in Japan in 1980 and in most European countries by the late 1990s. Leaded gasoline is still used in much of the developing world.

The Arab oil embargo of 1973 created awareness in many countries of their dependence on imported oil, and ethanol was advocated as a solution. The U.S. Energy Tax Act of 1978 lifted the $.04/gallon federal excise tax on gasoline blends containing at least 10% ethanol, and in the following decades other tax incentives were created to encourage the U.S. ethanol industry, including a $.54/ gallon tariff on imported ethanol, still in effect as of late 2007. By 2005, 1.6 billion bushels of corn, about 14% of

the U.S. crop, was being used to produce some 3 billion gallons (11.3 billion liters) of ethanol per year.

The U.S. ethanol industry began especially rapid growth after the Energy Policy Act of 2005, which mandated that 7.5 billion gallons (28.4 billion liters) of U.S. gasoline consumption, about 5%, come from renewable sources by 2012. This refers primarily to ethanol, with comparatively tiny contributions from biodiesel.

Brazil began an ambitious ethanol program in 1975 in response to the oil shock of 1973. By 2007, most automotive fuel sold in Brazil contained 70% gasoline and 30% ethanol; about 4 million cars were burning pure ethanol; and most new vehicles contained “flexible-fuel” engines that could burn pure gasoline, pure ethanol, or any blend. Brazil's ethanol is produced not from corn but from sugarcane, which contains more sugar per ton and is therefore a more efficient feedstock for ethanol production. Large volumes of sugarcane are not grown in the United States.

One of the most commonly voiced criticisms of the U.S. corn-ethanol program is that as much, or almost as much, fossil-fuel energy is needed to produce a gallon of ethanol as can be obtained by burning it. Most recent scientific studies support this view. One reason for the poor energy balance of corn ethanol is that only a tiny fraction of the corn plant—the sugar in the kernels—is turned into alcohol. The rest consists of the woody material lignocellulose (cellulose bound with lignin), which cannot be digested by yeast to produce ethanol.

Research on ways to ferment cellulose to produce ethanol has been conducted for decades. Methods proposed include genetically engineered yeast or bacteria, enzymes, or chemicals to liberate sugars from cellulose so that yeast can digest them. As of 2007, very little ethanol was produced from cellulosic fermentation (also called lignocellulosic fermentation), as no process yet affordable compared to either fossil fuels or sugar ethanol. Many experts state that if the process is perfected, it will significantly improve the energy balance of ethanol. Others disagree, claiming that the energy balance even of cellulosic fermentation is negative. The different claims are based on different listings or accountings of all the energy inputs required for the process.

Impacts and Issues

Brazilian Program

Brazil's large ethanol program has been deemed a success by many observers. But it also has its critics, who argue that it has depended on cheap labor, in some cases even slave labor, and that the conversion of large areas of land to single-crop agriculture to support ethanol production is damaging society. For example, in 2007, more than a thousand workers kept as virtual slaves by Para Pastoril e Agricola SA, one of Brazil's largest ethanol producers, were liberated by a Brazilian government raid. Many Brazilian cane workers, harvesting with 8-14 tons (7.2-12.7 metric tons) of sugarcane apiece each day with machetes, are kept in permanent debt and are not free to leave. As some harvesting machines are introduced, supervisors demand even larger harvests from the hand laborers. Seasonal jobs, concentration of land ownership in the hands of large corporations, deforestation to make room for plantations, and other problems are also cited.

Corn Ethanol

As mentioned earlier, corn ethanol has been accused of producing no significant energy. The U.S. Department of Agriculture claims an energy ratio of 1.34, that is, it says that for 1 unit of fossil-fuel energy invested, corn ethanol yields 1.34 units of energy. Most studies, however, agree that the gain is smaller, or that energy is actually lost. Although any plant, when burned, simply returns carbon to the atmosphere that it extracted from the atmosphere, and so makes no net contribution to climate change, in practice the use of fossil fuels to raise and process corn does add carbon dioxide to the atmosphere. Corn ethanol, gallon for gallon, presently contributes about as much to climate change as gasoline.

Critics also point to the fact that modern agribusiness is a destructive industry, leading to the rapid erosion of irreplaceable soil. Even if ethanol yielded an energy profit, these critics say, it would only be a means of mining the soil, which is a non-renewable resource. Some agricultural scientists have also argued that the removal of roots, husks, and stalks from fields to make cellulosic ethanol would accelerate erosion and bleed soil fertility. Such materials slow erosion and aid the penetration of the soil by rainwater.

Critics of ethanol also claim that it puts arable land at the service of the automobile, against which the poor and hungry of the world must then compete for food. In 2007 the New York Times reported that soaring food prices, driven partly by sharply rising demand for corn ethanol, had caused U.S. foreign food-aid dollars to buy less than half the food they bought in 2000.

The official government position is that ethanol will help U.S. farmers, produce cleaner air, and reduce U.S. dependence on foreign oil. As of 2007, this position is supported by leaders of both the Republican and Democratic parties.

Primary Source Connection

The following journal article outlines biomass ethanol's potential to aid in reduction of greenhouse gas emissions, but does not discuss many of the potential drawbacks and limitations of ethanol use. While supporters of ethanol note its clean-burning potential and renewable source, critics assert that current production methods (including those of industrialized farming) require large amounts of petroleum, reducing biomass ethanol's “green” potential. The author here notes that researchers are working to develop greener ethanol production technologies, and that biomass ethanol faces several challenges before becoming a significant petroleum alternative.

BIOMASS ETHANOL: TECHNICAL PROGRESS, OPPORTUNITIES, AND COMMERCIAL CHALLENGES

No other sustainable option for production osf transportation fuels can match ethanol made from lignocellulosic biomass with respect to its dramatic environmental, economic, strategic, and infrastructure advantages. Substantial progress has been made in advancing biomass ethanol (bioethanol) production technology to the point that it now has commercial potential, and several firms are engaged in the demanding task of introducing first-of-a-kind technology into the marketplace to make bioethanol a reality in existing fuel-blending markets. Opportunities have also been defined to further reduce the cost of bioethanol production so it is competitive without tax incentives.

WORDS TO KNOW

BIODIESEL: A fuel made from a combination of plant and animal fat. It can be safely mixed with petro diesel.

CELLULOSIC FERMENTATION: Digestion of high-cellulose plant materials (e.g., wood chips, grasses) by bacteria that have been bred or genetically engineered for that purpose. The useful product is ethanol, which can be burned as a fuel. Cellulosic fermentation is one way of producing cellulosic ethanol.

ENERGY POLICY ACT OF 2005: U.S. federal law passed in 2005 that offers tens of billions of dollars of subsidies and loan guarantees for energy technologies it categorizes as “clean,” including renewables, some forms of coal-burning, and nuclear power. Most commentators believed that the majority of the loan guarantees authorized by the act would go to the nuclear industry.

FOSSIL FUEL: Fuel formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

LIGNOCELLULOSE: Any of several substances making up woody cell walls in plants, consisting of cellulose mixed with lignin (both organic polymers). Digestion of lignocellulose to produce ethanol is a sought-after technology for producing biofuel.

This chapter provides a brief review of the key factors that drive interest in producing ethanol from biomass sources such as agricultural (e.g., sugar cane bagasse) and forestry (e.g., wood trimmings) residues, significant fractions of municipal solid waste (e.g., waste paper and yard waste), and herbaceous (e.g., switchgrass) and woody (e.g., poplar) crops. Next, a state-of-the-art bioethanol process is outlined, followed by an economic pro forma analysis to provide a sense of the important cost drivers. Against this backdrop, progress made in advancing bioethanol technology is reviewed to define the key accomplishments made possible through sustained research and development. Then two important areas meriting much greater emphasis are outlined. The first is in developing a solid technical foundation built on fundamental principles to help overcome the barriers that impede introduction of first-of-a-kind technology into the marketplace. The second is in aggressively funding research to advance bioethanol technology to the point at which it can be competitive as a pure fuel in the open marketplace. Hopefully, this chapter will provide a better appreciation of how bioethanol production technology has been improved and the vast potential it has for continued advancements and large-scale benefits…

Greenhouse Gas Reductions

Perhaps the most unique attribute of bioethanol is very low greenhouse gas emissions, particularly when compared with the emissions from other liquid transportation fuel options. Because nonfermentable and unconverted solids left after making ethanol can be burned or gasified to provide all of the heat and power to run the process, no fossil fuel is projected to be required to operate the conversion plant for mature technology. In addition, many lignocellulosic crops require low levels of fertilizer and cultivation, thereby minimizing energy inputs for biomass production. The result is that most of the carbon dioxide released for ethanol production and use in a cradle-to-grave (often called a full-fuel-cycle) analysis is recaptured to grow new biomass to replace that harvested, and the net release of carbon dioxide is low. If credit is taken for export of excess electricity produced by the bioethanol plant and that electricity is assumed to displace generation by fossil fuels such as coal, it can be shown that more carbon dioxide can be taken up than is produced.

The impact of bioethanol on greenhouse gas emissions can be particularly significant because the transportation sector is a major contributor to greenhouse gas emissions, accounting for about one-third of the total. As part of a Presidential Advisory Committee on reducing greenhouse gas emissions from personal vehicles, a survey of experts in the field clearly showed that most alternatives to petroleum (e.g., hydrogen production from solar energy) required significant changes in the transportation infrastructure to be implemented, whereas others that could be more readily used (e.g., methanol production from coal or natural gas) would have little impact on reduction of greenhouse gas emissions. On the other hand, ethanol is a versatile liquid fuel, currently produced from corn and other starch crops, that is blended with ~10% of the gasoline in the United States and is widely accepted by vehicle manufacturers and users. Vehicles that use high-level ethanol blends (e.g., in E85, a blend of 85% ethanol in gasoline) are now being introduced throughout the United States. In addition, bioethanol production technology could be commercialized in a few years and would not require extended time frames to be applied. Overall, the evidence suggests that the best choice from the coupled perspectives of greenhouse gas reduction, integration into the existing infrastructure, and rapid implementation is the production of ethanol from lignocellulosic biomass.

Although surveys show that Americans are concerned about the prospects of global climate change, the issue has not received broad political support, perhaps owing to the influence of special-interest groups. On the other hand, much of Europe, Canada, and other countries are actively seeking to reduce greenhouse gas emissions. Ironically, much more attention has been focused on developing bioethanol technology in the United States, whereas other countries have only recently shown interest in the area. Thus, there is tremendous potential for application of U.S. technology in many other regions of the world, benefiting all concerned…

Conclusions

Biomass ethanol is a versatile fuel and fuel additive that can provide exceptional environmental, economic, and strategic benefits of global proportions. Bioethanol can play a particularly powerful role in the quest to reduce greenhouse gas emissions that will be difficult for any other transportation fuel options to match. Because of the widespread abundance of biomass, bioethanol can also be invaluable for meeting the growing international demand for fuels by developing nations as well as enhancing the energy security of developed countries. Furthermore, conversion of waste materials to ethanol provides an important disposal option as new regulations restrict historical approaches. It also is important to note that bioethanol is among the few options available for sustainable production of liquid fuels. Finally, although gasoline is continually being reformulated to reduce its environmental impact, ethanol has favorable properties that can provide air and water quality attributes comparable, if not superior, to gasoline and can provide particular benefits when used as a pure fuel in properly optimized engines and ultimately fuel cells.

Tremendous progress has been made in reducing the cost of enzymatic-based technology for bioethanol production, with current estimated costs showing the technology to be potentially competitive now, particularly for niche markets. A key to these advances has been in achieving higher yields, faster rates, and greater concentrations of ethanol through improved pretreatment technology, development of better cellulase enzymes, and synergistic combination of cellulose hydrolysis and

fermentation steps that make progress in overcoming the natural recalcitrance of biomass. Genetic engineering of bacteria so that they ferment the diverse range of sugars in lignocellulosic materials to ethanol with high yields is a milestone achievement essential to economic success.

Although progress has been impressive, the cost of bioethanol production must be reduced further if it is to be competitive without special tax incentives on a large scale for the fuel market. Because enzyme-based systems can build off the emerging achievements of biotechnology, they show particular promise for further cost reductions, and sensitivity studies, process modeling, and macroscopic economic analyses reveal that there are no fundamental barriers to advancing the technology. Cost estimates reveal that pretreatment is a particularly expensive step, both directly and indirectly. From a technology perspective, the sensitivity studies clearly show that ethanol yield is a strong economic driver, and there are significant gains from improving the yields of all process steps. It is important that even greater cost reductions can result from improving pretreatment and biological-conversion process configurations. In fact, specific advanced pretreatment and bioprocessing configurations based on continued progress in overcoming the recalcitrance of biomass have been identified that would reduce the cost of bioethanol production to levels that it can compete in a nonsubsidized market. However, even though the advanced pretreatment configuration chosen significantly reduces cost, it would represent about two-thirds of an overall advanced design scenario, suggesting that further improvements beyond those envisioned should be sought, with tremendous impact. This result also implies that emphasis on novel pretreatment technology with extremely low-cost potential is badly needed instead of pursuing relatively minor improvements over dilute sulfuric-acid approaches, and such advances will probably best come through improving our knowledge of how pretreatment works. Interestingly, although feedstock cost reductions are constrained to levels that will have moderate impact for large-scale bioethanol production, more productive and less expensive biomass would make it feasible to feed larger plants that realize significant economies of scale.

It is just as important to take the next step and commercialize bioethanol technology so that its tremendous benefits can be realized. However, because bioethanol plants must typically be large to be profitable, substantial capital outlay is required, and risk management is essential to attract investors to finance the introduction of first-of-a-kind technology. Although large pilot and perhaps even semi-works demonstration projects may be required to provide an adequate level of comfort, significantly more emphasis on developing solid fundamental principles for design of biomass processing operations would greatly reduce the tremendous costs and delays associated with technology scale-up. Building expert teams to work cooperatively to understand key bioethanol-processing steps in the context of applying and advancing the technology is the most effective approach to realize the low-cost potential of bioethanol and realize its benefits on a large scale. In the final analysis, researchers, research managers, program leaders, and funding authorities who have had the vision and courage to advance bioethanol technology to the point that it now has commercial potential need to facilitate advancing and applying the technology in the face of even greater challenges to achieve widespread impact. In addition, entrepreneurs, financiers, engineers, and contractors with equal vision and courage are needed to take the technology to its first commercial applications.

Charles E. Wyman

wyman, charles e. “biomass ethanol: technical progress, opportunities, and commercial challenges,” annual review of energy and the environment24 (1999):
189–226.

See Also Biofuel Impacts.

BIBLIOGRAPHY

Books

Worldwatch Institute. Biofuels for Transport: Global otential and Implications for Energy and Agriculture. London: Earthscan Publications, Ltd., 2007.

Periodicals

Dugger, Celia. “As Prices Soar, U.S. Food Aid Buys Less.” The New York Times (September 29, 2007).

Farrell, Alexander et al. “Ethanol Can Contribute to Energy and Environmental Goals.” Science 311 (2006): 506-508.

Krauss, Clifford. “Sudden Surplus Arises as Threat to Ethanol Boom.” The New York Times (September 30, 2007).

Pimentel, David. “Ethanol Fuels: Energy Balance, Economics, and Environmental Impacts Are Negative.” Natural Resources Research 12 (2007): 127-134.

Rosner, Hillary. “Cooking Up More Uses for the Leftovers of Biofuel Production.” The New York Times (August 8, 2007).

Sanderson, Katharine. “A Field in Ferment.” Nature 444 (2007).

Wald, Matthew L. “Is Ethanol for the Long Haul?” Scientific American (January 2007): 42-49.

Wyman, Charles E. “Biomass Ethanol: Technical Progress, Opportunities, and Commercial Challenges.” Annual Review of Energy and the Environment 24 (1999): 189-226.

Web Sites

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Friedemann, Alice. “Peak Soil: Why Cellulosic Ethanol, Biofuels are Unsustainable and a Threat to America.” CultureChange.org, April 10, 2007. <http://www.culturechange.org/cms/index.php?option=com_content&task=view&id=107&Itemid=1> (accessed October 26, 2007).

Kenfield, Isabella. “Brazil's Ethanol Plan Breeds Rural Poverty, Environmental Degradation.” Americas Program, Center for International Policy, March 6, 2007. < http://americas.irc-online.org/am/4049> (accessed October 26, 2007).

“‘Slave’ Labourers Freed in Brazil.” BBC News, July 3, 2007. < http://news.bbc.co.uk/2/hi/americas/6266712.stm> (accessed October 26, 2007).

Larry Gilman