Misplaced Pages

Revision as of 19:16, 29 March 2007

Ethanol fuel is an alternative to gasoline. It can be combined with gasoline in any concentration up to pure ethanol (E100). Anhydrous ethanol, that is, ethanol with at most 1% water, can be blended with gasoline in varying quantities to reduce consumption of petroleum fuels and in attempts to reduce air pollution. Worldwide automotive ethanol capabilities vary widely and most spark-ignited gasoline style engines will operate well with mixtures of 10% ethanol (E10).

In Brazil, ethanol-powered and flexible-fuel vehicles are manufactured to be capable of operation by burning hydrated ethanol, an azeotrope of ethanol (around 93% v/v) and water (7%). Hydrated ethanol may also be mixed with gasoline in flexible fuel vehicles but a minimum amount of ethanol (granted by legally regulated gasoline type C) is required to avoid problems with the mixture. A few flexible-fuel systems, like Hi-Flex, used by Renault Clio and Fiat Siena, can also run with pure gasoline.

Ethanol is increasingly used as an oxygenate additive for standard gasoline, as a replacement for methyl t-butyl ether (MTBE), the latter chemical being difficult to retrieve from groundwater and soil contamination. At a 10% mixture, ethanol reduces the likelihood of engine knock, by raising the octane rating. The use of 10% ethanol gasoline is mandated in some cities where the possibility of harmful levels of auto emissions are possible, especially during the winter months. Ethanol can be used to power fuel cells, and also as a feed chemical in the transesterification process for biodiesel.

Ethanol can be mass-produced by fermentation of sugar or by hydration of ethylene from petroleum and other sources. Current interest in ethanol lies in production derived from crops (bio-ethanol), and there's discussion about whether it is a sustainable energy resource that may offer environmental and long-term economic advantages over fossil fuels, like gasoline or diesel. It is readily obtained from the starch or sugar in a wide variety of crops. Ethanol fuel production depends on availability of land area, soil, water, and sunlight.

In 2004, around 42 billion liters of ethanol were produced in the world, most of it being for use in cars. Brazil produced around 16.4 billion liters and used 2.7 million hectares of land area for this production (4.5% of the Brazilian land area used for crop production in 2005. Of this, around 12.4 billion liters were produced as fuel for ethanol-powered vehicles in the domestic market.

Overview

Chemistry

During ethanol fermentation, glucose is evolved into ethanol and carbon dioxide.

${\displaystyle C_{6}H_{12}O_{6(aqueous)}\rightarrow \;2C_{2}H_{6}O_{(aqueous)}+2CO_{2(gas)}}$

The reaction of burning ethanol is almost identical to burning hydrocarbons in gasoline. Ethanol reacts with oxygen to produce carbon dioxide, water, and heat: (trace quantities of other pollutants such as ozone, carbon monoxide, nitric oxide are also produced)

${\displaystyle 2C_{2}H_{6}O_{(aq)}+6O_{2(g)}\rightarrow \;4CO_{2(g)}+6H_{2}O_{(l)}+heat}$

It can be seen from these equations that the law of conservation of energy still holds true.

Sources

Bioethanol is obtained from the conversion of carbon based feedstock. Agricultural feedstocks are considered renewable because they get energy from the sun using photosynthesis. Ethanol can be produced from a variety of feedstocks such as sugar cane, bagasse, miscanthus, sugar beet, sorghum, grain sorghum, switchgrass, barley, hemp, kenaf, potatoes, sweet potatoes, cassava, sunflower, fruit, molasses, whey or skim milk, corn, stover, grain, wheat, wood, paper, straw, cotton, other biomass, as well as many types of cellulose waste. As of 2006, production is primarily from sugarcane, maize (corn) and sugar beets - and also as of 2006, technology does not exist that makes it economically competitive to produce ethanol from cellulosic feedstock.

Four countries have developed bioethanol fuel programs: Brazil, Colombia, China and the United States.

About 5% (in 2003) of the ethanol produced in the world is actually a petroleum product. It is made by the catalytic hydration of ethylene with sulfuric acid as the catalyst. It can also be obtained via ethylene or acetylene, from calcium carbide, coal, oil gas, and other sources. Two million tons of petroleum-derived ethanol are produced annually. The principal suppliers are plants in the United States, Europe, and South Africa. Petroleum derived ethanol (synthetic ethanol) is chemically identical to bio-ethanol and can be differentiated only by radiocarbon dating.

Production

Ethanol can be produced in different ways, using a variety of feedstocks. Brazil uses sugarcane as primary feedstock. For information on Brazil's method of ethanol production, see ethanol fuel in Brazil. More than 90% of the ethanol produced in the U.S. comes from corn (see Renewable Fuels Association's list of United States ethanol plants).

Crops with higher yields of energy, such as switchgrass and sugar cane, are more effective in producing ethanol than corn. Ethanol can also be produced from sweet sorghum, a dryland crop that uses much less water than sugarcane, does not require a tropical climate and produces food and fodder in addition to fuel. Sweet sorghum cultivar improvement and cultivation is emphasized in India.

Basic steps for dry mill production of ethanol from corn are: refining into starch, liquification and saccharification (hydrolysis of starch into glucose), yeast fermentation, distillation, dehydration (required for blending with gasoline), and denaturing (optional).

Ethanol is produced by yeast fermentation of the sugar extracted from sugarcane or sugar beets. Subsequent processing is the same as for ethanol from corn. Production of ethanol from sugarcane (sugarcane requires a tropical climate to grow productively) returns about 8 units of energy for each unit expended compared to corn which only returns about 1.34 units of fuel energy for each unit of energy expended.

Carbon dioxide, a potentially harmful greenhouse gas, is emitted during fermentation. However, the net effect is offset by the uptake of carbon gases by the plants grown to produce ethanol. When compared to gasoline, ethanol releases less greenhouse gas.

For the ethanol to be usable as a fuel, water must be removed. Most of the water is removed by distillation, but the purity is limited to 95-96% due to the formation of a low-boiling water-ethanol azeotrope. The 96% m/m (93% v/v) ethanol, 4% m/m (7% v/v) water mixture may be used as a fuel, and it's called hydrated ethyl alcohol fuel (álcool etílico hidratado combustível, or AEHC in Portuguese). In 2006/2007, an estimated 17 billion liters (4.5 billion gallons) of hydrated ethyl alcohol fuel will be produced, to be used in ethanol powered vehicles.

For blending with gasoline, purity of 99.5 to 99.9% is required, depending on temperature, to avoid separation. Currently, the most widely used purification method is a physical absorption process using molecular sieves. Another method, azeotropic distillation, is achieved by adding the hydrocarbon benzene which also denatures the ethanol (to render it undrinkable for duty purposes).

Ethanol is not typically transported by pipeline for three reasons. Current production levels will not support a dedicated pipeline. The costs of building and maintaining a pipeline from Midwestern United States to either coast are prohibitive. Any water which penetrates the pipeline will be absorbed by the ethanol, diluting the mixture.

Technology

Ethanol-based engines

Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors and airplanes. Ethanol consumption in an engine is approximately 15-24% higher than that of gasoline (the BTUs per gallon are 15-24% lower), but higher compression ratios in an ethanol-only engine allow for increased power output, and better fuel economy. In general, ethanol-powered engines are tuned to give similar power and torque output to gasoline-powered engines. In flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For maximum use of ethanol's benefits, a compression ratio of nearly 15:1 should be used, which would render that engine unsuitable for gasoline usage. When ethanol fuel availability increases to the point where high-compression ethanol-only vehicles are practical, the fuel efficiency of such engines should be the same or greater than current gasoline engines.

A 2004 MIT study , and paper published by the Society of Automotive Engineers, present the possibility of a definite advance over hybrid electric cars' cost-efficiency by using a high-output turbocharger in combination with continuous dual-fuel direct injection of pure alcohol and pure gasoline in any ratio up to 100% of either. Each fuel is stored separately, probably with a much smaller tank for alcohol, the peak cost-efficiency being calculated to occur at approximately 30% alcohol mix, at maximum engine power.

The estimated cost advantage is calculated at 4.6:1 return on the cost of alcohol used, in gasoline costs saved, when the alcohol is used primarily as an octane modifier and is otherwise conserved. With the cost of new equipment factored in the data gives a 3:1 improvement in payback over hybrid, and 4:1 over turbo-diesel (comparing consumer investment yield only). In addition, the danger of water absorption into pre-mixed gasoline and supply issues of multiple mix ratios can be addressed by this system.

Ethanol fuel mixtures

To avoid engine stall, the fuel must exist as a single phase. The fraction of water that an ethanol-gasoline fuel can contain without phase separation increases with the percent of ethanol. This is shown for 25 C (77 F) in a gasoline-ethanol-water phase diagram, Fig 13 of . This shows, for example, that E30 can have up to about 2% water. If there is more than about 71% ethanol, the remainder can be any proportion of water or gasoline and phase separation will not occur. However, the fuel mileage declines directly with water content. The increased solubility of water with higher ethanol content permits E30 and hydrated ethanol to be put in the same tank since any combination of them always results in a single phase. Somewhat less water is tolerated at lower temperatures. For E10 it is about 0.5% v/v at 70 F and decreases to about 0.23% v/v at -30 F as shown in Figure 1 of .

In many countries cars are mandated to run on mixtures of ethanol. Brazil requires cars be suitable for a 25% ethanol blend, and has required various mixtures between 22% and 25% ethanol, as of October 2006 23% is required. The United States allows up to 10% blends, and some states require this (or a smaller amount) in all gasoline sold. Other countries have adopted their own requirements.

Beginning with the model year 1999, an increasing number of vehicles in the world are manufactured with engines which can run on any fuel from 0% ethanol up to 100% ethanol without modification. Many cars and light trucks (a class containing minivans, SUVs and pickup trucks) are designed to be flexible-fuel vehicles (also called dual-fuel vehicles). Their engine systems contain alcohol sensors in the fuel and/or oxygen sensors in the exhaust that provide input to the engine control computer to adjust the fuel injection to achieve stochiometric (no residual fuel or free oxygen in the exhaust) air-to-fuel ratio for any fuel mix. The engine control computer can also adjust (advance) the ignition timing to achieve a higher output without pre-ignition when higher alcohol percentages are present in the fuel being burned.

However E-85 fuel distribution's fate rests mainly with the Service stations owed by oil companies, as they control a large majority of fuel stations. Because they are hesitant to substitute their own product for someone else's (farmers and investors), they only allow ethanol blended in small amounts with gasoline, for the longevity of their own product, and to degraded the validity of E-85 fuel.

Fuel Economy

For 2006 vehicles with flexible fuel engines, fuel economy (measured as miles per gallon (MPG), or liters per 100 km) is directly proportional to energy content. Ethanol contains approx. 15-24% less energy per gallon than gasoline, and therefore will result in a 34% reduction in miles per gallon. For E10 (10% ethanol and 90% gasoline), the effect is small (~3%) when compared to conventional gasoline, and even smaller (1-2%) when compared to oxygenated and reformulated blends. However, for E85 (85% ethanol), the effect becomes significant. E85 will produce lower mileage than gasoline, and will require more frequent refueling. Actual performance may vary depending on the vehicle. The EPA-rated mileage of current USA flex-fuel vehicles should be considered when making price comparisons, but it must be noted that E85 is a high performance fuel and should be compared to premium.

Environment

Energy balance

For ethanol to contribute significantly to transportation fuel needs, it would need to have a positive net energy balance and the U.S. Department of Energy has concluded that it does, stating in a recent report "the net energy balance of making fuel ethanol from corn grain is 1.34; that is, for every unit of energy that goes into growing corn and turning it into ethanol, we get back about one-third more energy as automotive fuel." The report also indicates that using a crop with a higher sugar content than corn, such as sugar beets, would result in production with a much higher positive net energy balance.

Some scientists argue that the energy balance is negative when all factors are considered. Professors Tad Patzek and David Pimentel are the most well-known academics to make this argument. These arguments have been challenged in a report from the U.S. Department of Energy as being based on decades-old data and not considering recent advances in production or the use of more efficient source crops for ethanol fermentation. In January 2006, the Journal Science published a study from U.C. Berkeley which concluded that ethanol does have a positive net energy balance, but noted that corn based ethanol has " ... greenhouse gas emissions similar to those of gasoline".

Note that these reports refer to the use of corn (largely in America where corn is subsidised) to produce bioethanol. In Brazil where sugar cane is used, the yield is higher, and conversion of corn to ethanol is far higher in terms of energy efficiency. Biotechnology may improve the energy gain of bioethanol.

Air pollution

Compared with conventional unleaded gasoline, ethanol is a particulate-free burning fuel source that combusts cleanly with oxygen to form carbon dioxide and water. The Clean Air Act requires the addition of oxygenates to reduce carbon monoxide emissions in the United States. The additive MTBE is currently being phased out due to ground water contamination, hence ethanol becomes an attractive alternative additive.

Use of ethanol, produced from current (2006) methods, emits a similar amount of carbon dioxide but less carbon monoxide than gasoline. If all bioethanol-production energy came from non-fossil sources the use of bioethanol as a fuel would add no greenhouse gas.

In considering the potential for pollution reduction with ethanol, however, it is equally important to consider the potential for environmental contamination stemming from the manufacture of ethanol. In 2002, monitoring of ethanol plants revealed that they released VOCs (volatile organic compounds) at a higher rate than had previously been disclosed. The Environmental Protection Agency (EPA) subsequently reached settlement with Archer Daniels Midland and Cargill, two of the largest producers of ethanol, to reduce emission of these VOCs. VOCs are produced when fermented corn mash is dried for sale as a supplement for livestock feed. Devices known as thermal oxidizers or catalytic oxidizers can be attached to the plants to burn off the hazardous gases.

Effects of ethanol on agriculture

One result of increased use of ethanol is increased demand for the feedstocks. Large-scale production of agricultural alcohol may require substantial amounts of cultivable land with fertile soils and water. This may lead to environmental damage such as deforestation or decline of soil fertility due to reduction of organic matter.

However, the proposed use of switchgrass and miscanthus as a feedstock has the benefit of actually building up topsoil, fixing carbon, and greatly reducing fertilizer inputs. Additionally, these crops would grow many years before being tilled under, saving more pollution and runoff compared to conventional tillage practices.

Renewable resource

Ethanol is considered "renewable" because it is primarily the result of conversion of the sun's energy into usable energy. Creation of ethanol starts with photosynthesis causing the feedstocks such as switchgrass, sugar cane, or corn to grow. These feedstocks are processed into ethanol (see production). However, Brazil is the only country in the world where farming and production of ethanol is a profitable and widespread substitute for gasoline, since the energy balance of Brazilian sugar-cane-derived ethanol produced to fossil fuels used is supposedly over 800%.

However, Corn Ethanol may very well become a viable and energy efficient commodity in the future. With the advent and promotion of cheaper non-petroleum fertilizers and herbicides. Increased corn acreage and conservation from new techniques of farming. Farming equipment and machinery that runs on E85. Renewable sources of electricity for power and transport. The discovery of new and better Enzymes for chemical processing. New more efficient and cost effective production processes and manufacturing methods being developed with higher yields. The creation of Corn Ethanol could very well become a much more energy efficient and cost effective process and leaving lesser environmental footprint. These technologies are under development and progressing, and could together easily increase the energy balance of corn Ethanol to 500%.

Current, first generation processes for the production of ethanol from corn use only a small part of the corn plant: the corn kernels are taken from the corn plant and only the starch, which represents about 50% of the dry kernel mass, is transformed into ethanol. Two types of second generation processes are under development. The first type uses enzymes to convert the plant cellulose into ethanol while the second type uses pyrolysis to convert the whole plant to either a liquid bio-oil or a syngas. Second generation processes can also be used with plants such as grasses, wood or agricultural waste material such as straw.

Replacement of fossil energy

Only about 5% of the fossil energy required to produce bioethanol from corn in the United States is obtained from non-US petroleum. Current (2006) United States production methods obtain the rest of the fossil energy from domestic coal and natural gas. Even if the energy balance were negative, US production involves mostly domestic fuels such as natural gas and coal so the need for non-US petroleum would be reduced. Developed regions like the United States and Europe, and increasingly the developing nations of Asia, mainly India and China, consume much more petroleum and natural gas than they extract from their territory, becoming dependent upon foreign suppliers as a result.

Research and criticisms

Economics

The United States Department of Energy, finds that for every unit of energy put towards ethanol production, 1.3 units are returned. Another study found that corn-grain ethanol produced 1.25 units of energy per unit put in. Distillers grains are a by-product of the transformation of corn kernels into ethanol (about 0.8 kg per liter of ethanol); burning the distillers grains to generate energy dramatically improves the energy efficiency, so that half of the energy in the ethanol comes from the solar energy absorbed by the corn plant and half comes from fossil fuels.

As yields improve or different feedstocks are introduced, ethanol production may become more economically feasible in the US. Currently, research on improving ethanol yields from each unit of corn is underway using biotechnology. By utilizing hybrids designed specifically with higher extractable starch levels, the energy balance is dramatically improved. Also, as long as oil prices remain high, the economical use of other feedstocks, such as cellulose, become viable. By-products such as straw or wood chips can be converted to ethanol. Fast growing species like switchgrass can be grown on land not suitable for other cash crops and yield high levels of ethanol per acre.

Yields of common crops associated with ethanol production

Source: Petroleum Club (with permission)

Ethanol from algae

Similar to the research done on biodiesel, making ethanol from algae has the higher potential production efficiency, and unlike more complex organisms, the time it takes to improve energy output for algae is much shorter.

In 2006-2-23, Veridium Corporation announced the technology to convert exhaust carbon dioxide from the fermentation stage of ethanol production facilities back into new ethanol and biodiesel. The bioreactor process is based on a new strain of iron-loving blue-green algae discovered thriving in a hot stream at Yellowstone National Park.

In 2006-11-14, US Patent Office approved Patent 7135308, a process for the production of ethanol by harvesting starch-accumulating filament-forming or colony-forming algae to form a biomass, initiating cellular decay of the biomass in a dark and anaerobic environment, fermenting the biomass in the presence of a yeast, and the isolating the ethanol produced.

Problems

Some of the problems experienced with ethanol include:

• Ethanol-based fuels are not compatible with some fuel system components. Examples of extreme corrosion of ferrous components, the formation of salt deposits, jelly-like deposits on fuel strainer screens, and internal separation of portions of rubber fuel tanks have been observed in some vehicles using ethanol fuels.
• The use of ethanol-based fuels can negatively affect electric fuel pumps by increasing internal wear and undesirable spark generation.
• E-85 is not compatible with capacitance fuel level gauging indicators and may cause erroneous fuel quantity indications in vehicles that employ that system.
• E-85 pumps are not widely available. In several Midwestern states, especially Minnesota, it has become much more available, and the price has become very attractive compared to gasoline. The trend is increasingly positive for conversion to E85 pumps, but it needs to occur much more quickly to serve the general public in any significant way.

Notes

1. http://www.eia.doe.gov/pub/oil_gas/petroleum/data_publications/monthly_oxygenate_report/current/pdf/819mhilt.pdf
2. Template:Pt icon http://www.inee.org.br/down_loads/eventos/PERSPECTIVAS%20DA%20PRODUCAO%20%20RJ%20NOV05.ppt
3. Template:Pt icon http://www.nipeunicamp.org.br/proalcool/Palestras/16/Antonio%20de%20Padua%20Rodrigues.ppt
4. Heat of Combustion of Fuels
5. energy.gov, newsitem 3804
6. meti.go.jp file g30819b40j
7. (grainscouncil.com, Biofuels_study 268 kB pdf, footnote, p 6)
8. ethanolproducer.com, article 2077
9. http://ethanol.org/howethanol.html
10. nariphaltan.virtuallave.net - sorghum
11. nariphaltan.vurtuallave.net - rural ethanol
12. iea.org, biofuels2004.pdf
13. oregon.gov, biomass forum
14. (pdf) (Wang et al 1999)
15. (pdf) (Wang 2002)
16. globo.com notice
17. agmrc.org, ethanol pipeline
18. MIT Study
19. SAE Paper 2001-01-2901
20. DOE FAQ
21. Energy.gov site
22. Alternative Fuel Efficiencies in Miles per Gallon
23. EPA Info
24. EPA Mileage
25. http://www1.eere.energy.gov/biomass/net_energy_balance.html DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use
26. http://www.news.cornell.edu/stories/July05/ethanol.toocostly.ssl.html
27. http://www1.eere.energy.gov/biomass/net_energy_balance.html DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use
28. http://rael.berkeley.edu/ebamm/: ERG Biofuel Analysis Meta-Model
29. Bioethanol needs biotech now
30. ethanol.org, Science Journal January 2006
31. biomasschpethanol.umn.edu paper
32. CBS News
33. Kononova, M. M. Soil Organic Matter, Its Nature, Its role in Soil Formation and in Soil Fertility, 1961
34. ethanol.org, Science Journal January 2006
35. http://www1.eere.energy.gov/biomass/net_energy_balance.html
36. Hill, Jason (2006). "Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels". Proceedings of the National Academy of Sciences. 103 (30): 11206–10. doi:10.1073/pnas.0604600103. Retrieved 2007-01-24. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
37. [http://www.treehugger.com/files/2006/03/veridian_corp_e.php Veridium Patents Yellowstone Algae-Fed Bioreactor to Capture Ethanol Plant CO2 Emissions]
38. US patent 7135308

See also

• Bioconversion of biomass to mixed alcohol fuels
• Biodiesel
• Biofuel
• Biomass
• Butanol from Clostridium acetobutylicum
• Butanol fuel
• Cellulosic ethanol
• Corn Ethanol
• Ethanol fuel in Brazil
• Ethanol fuel in Australia
• Ethanol fuel in the United States
• Hydrogen fuel
• Hydrogen vehicle
• Liquid fuels
• List of energy topics
• MTBE
• Oil crisis
• P-series fuels
• Sugarcane
• Timeline of alcohol fuel
• Vegetable oil economy

External links

• Ethanol from Sweet Sorghum:
• Ethanol fuel for rural households;
• U.S. Department of Energy: ethanol.
• Federal Aviation Administration: 10/27/06 Special Airworthiness Information Bulletin - Automobile gasoline containing alcohol (Ethanol or Methanol) is not allowed to be used in aircraft.
• National Pollutant Inventory - Ethanol fact sheet
• Farm Industry News: Hydrogen Corn Economy. Article about converting ethanol to hydrogen.
• Clean Fuels Development Coalition
• Pimentel: Ethanol - Inefficient Fuel and Debunking Pimentel: Ethanol - Efficient Fuel
• Henry Ford, Charles Kettering and the Fuel of the Future (history of ethanol)
• Renewable and Appropriate Energy Laboratory's survey article *Ethanol Can Contribute to Energy and Environmental Goals (.pdf format). Published in Science, January 27, 2006
• David Cohn, "Ethanol's New Cheap Trick", Seed Magazine" March 31, 2006
• DrivingEthanol.org
• e85 ethanol information
• Thermodynamics of the Corn-Ethanol Biofuel Cycle Tad W. Patzek, Department of Civil and Environmental Engineering, University of California, Berkeley
• Ethanol as Fuel: An Evironmental and Economic Analysis, Martin Turon, U.C. Berkeley, Chemical Engineering, November 25, 1998
• How far can you drive on a bushel of corn? Crunching the numbers on alternative fuels. Popular Mechanics May, 2006 issue
• Robert Rapier, "Ethanol Investing: Counterpoint", Financial Sense" June 23, 2006
• Digging into the Ethanol Debate Wall Street Journal Online, June 9, 2006. Summary of the production efficiency debate, with references.
• Biofuels: Think Outside The Barrel-- Google talk on ethanol by Vinod Khosla, a Silicon Valley billionaire (requires media player)
• Iowa State University - ISU Formula SAE E85 Run Racecar
• American Coalition for Ethanol
• Ethanol Generators
• Ethanol & Methanol - Article by Rob Rodriguez (ASE) on CDX eTextbook
• Ethanol: Myths and Realities

Template:Energy Transportation Template:Sustainability and energy development group

• Biofuels
• Biotechnology products
• Fuels
• Ethanol fuel
• Alternative propulsion