Bioethanol

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Bioethanol is an alternative fuel (alcohol) to gasoline, from natural sources (no petroleum). 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.^[1] 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,^[2] 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. ^[3] 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.

<math>C_6 H_{12} O_{6(aqueous)} \rightarrow \; 2 C_2 H_6 O_{(aqueous)} + 2 CO_{2(gas)}</math>

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)^[4]

<math>2 C_2 H_6 O_{(aq)} + 6O_{2(g)} \rightarrow \; 4 CO_{2(g)} + 6 H_2 O_{(l)} + heat</math>

Photosynthesis reaction: 6 CO_2(g) + 6 H₂O_(L) + photons → C₆H₁₂O_6(aq) + 6 O_2(g)

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.^[5]

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.^[6] 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.^[7] Petroleum derived ethanol (synthetic ethanol) is chemically identical to bio-ethanol and can be differentiated only by radiocarbon dating.^[8]

Production

Ethanol can be produced in different ways, using a variety of feedstocks.^[9] 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.^[10][11]

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.^[12] Thus sugarcane nets 7/.34 or about or 20 times as much energy as corn. (corn produces an additional 0.33 units of energy in the form of high-protein livestock feed).

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.^[13] When compared to gasoline, ethanol releases less greenhouse gas.^[14][15]

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.^[16]

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 (so no extra methanol/petrol/etc. is needed to render it undrinkable for duty purposes). However, benzene is a powerful carcinogen and so will probably be illegal for this purpose soon.

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.^[17]

Technology

Ethanol in vehicles

Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors and airplanes. The V-2 rocket used ethanol fuel since Germany had an inadequate supply of petroleum-derived fuels like kerosene.

Current ethanol engines are mildly modified gasoline engines with a few adjustments required to operate reliably, such as the use of various seals made of "Viton" rubber, as opposed the common "Butyl"-based rubber seals, to overcome the corrosive effect due to the alcohol content of the ethanol fuel. Also there is a necessary water-separator system because of atmospheric humidity contaminating vented fuel tanks. Vehicles using gasoline/ethanol engines are often referred to as "Flex-Fuel" or "Dual-Fuel" in the marketplace.

Fuel system design must be compatible with the percent of ethanol permitted. All current (2006) production spark ignition vehicles in the United States are designed to be compatible with up to 10% ethanol. Every gasoline-powered vehicle in Brazil (since 1993) is designed to be compatible with up to 25% ethanol. Pure ethanol reacts with or dissolves certain rubber and plastic materials and must not be used in fuel systems that are not designed for it.

Pure ethanol has a much higher octane rating (116 AKI, 129 RON) than ordinary gasoline (86/87 AKI, 91/92 RON), allowing higher compression ratio and different spark timing for improved performance.^[18] To change a pure-gasoline-fueled car into a pure-ethanol-fueled car, larger carburetor jets (about 30-40% larger by area), or fuel injectors are needed. (Methanol requires an even larger increase in area, to roughly 50% larger.)

Engines using fuel with from 30% to 100% ethanol need a cold-starting system for reliable starting at temperatures below 13 °C (55 °F) and to meet EPA emissions standards.

Ethanol engines and power output

Ethanol consumption in an engine is approximately 34% higher than that of gasoline (the BTUs per gallon are 34% lower), but higher compression ratios in an ethanol-only engine allow for increased power output. In general, ethanol-powered engines were tuned to give similar power and torque output than gasoline-powered ones. For example, a 2001 Fiat Mille, 1 liter gasoline type C engine had 57 HP/8,2 mkgf outputs (and 9,5:1 compression ratio), while the 1 liter hydrated ethanol engine had 61HP/8,1 mkgf (and 11,4:1 compression ratio) tuning.^[19] However, in some older engines, differences of up to 10 HP were not uncommon. This was the case of the 1988 1.6/S Chevrolet Chevette engines: the ethanol-powered engine had a 82/12,8/12:1 configuration, the gas engine had a much lower, 73/12,6/8,5:1 configuration.^[20] The same happened with Volkswagen Passat TS 1,6 liters (1982, ethanol) and Passat LS 1,6 liters (1983, gasoline), which had 98(raw)/13,3(raw)/10,8:1 versus 88(raw)/13,3(raw)/8,3:1 respectively.^[21]

Since ethanol-powered engines were phased out in favor of flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For example, a 2006/2007 Volkswagen Polo 1.6 Total Flex tops 101 HP when running on gas, or 103 HP with ethanol.^[22]

Higher compression rates would allow for dramatically increased power output (this is the arrangement now used in "Indy" racing cars). 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.

When it is desireable to have a dual-fuel vehicle that can run on either gasoline or Ethanol, and the power output when using Ethanol needs to be equal or greater than when running on gasoline, it is possible to increase the effective compression ratio on-demand with a turbocharger that incorporates an electronically-controlled wastegate. In this scenario a modest compression ratio with a low level of boost would allow the use of gasoline. A higher level of turbo boost would increase the real compression ratio when using ethanol or a mixture of ethanol and gas, with the level of boost being based on the readout from fuel octane sensors.

Ethanol fuel mixtures

Template:See details 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 [1]. 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 [2].

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. Because of this requirement it is speculated that all cars can run blends up to about 30% (so that manufactures do not have to stock parts incompatible with ethanol next to parts compatible), but it is not known if this is true.

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.

Fuel Economy

Case in point, a 2003 Chevrolet Tahoe FFV running on gasoline gets 15 mpg on the highway, while getting 13 mpg on E85 on the highway (real-world experience). This is a much better scenario than the EPA estimates would indicate, but many people consider the EPA data to be suspect. In reality this is about a 15-20% decrease in mpg, not the 34% aforementioned. Some part of this must be the result of the 15% gasoline blended in, the other cause is unknown to me (higher horsepower and more efficient burning?). The lower price of E85 in relation to gasoline, and the current Illinois tax rebate of $450, make the use of E85 economically superior to using gasoline. There is also a fair point below about comparing E85 to premium gasoline, not regular. This makes E85 an even more economically attractive fuel.

For the EPA-rated mileage of current USA flex-fuel vehicles, see.^[27]

This reduced fuel economy 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. For USA price comparisons, see.^[28]

Some researchers are working to increase fuel efficiency by optimizing engines for ethanol-based fuels. Ethanol's higher octane allows an increase of an engine's compression ratio for increased thermal efficiency.^[29] In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19.5 with fuels ranging from neat ethanol to E50. Thermal efficiency up to approximately that for a diesel was achieved.^[30] This would result in the MPG of a dedicated ethanol vehicle to be about the same as one burning gasoline. There are currently no commercially-available vehicles that make significant use of ethanol-optimizing technologies, but this may change in the future.

Environment

Energy balance

Template:Main article 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."^[31] 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^[32] 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.^[33] 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".^[34]

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.^[35]

Petroleum gasoline only returns 0.8 units of energy for each unit put into it, while corn ethanol returns 1.3 units. Therefore, corn ethanol is more energy friendly than gasoline. Biomass ethanol is several times greater than corn ethanol, many times greater than gasoline.

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:

C₂H₅OH + 3 O₂ → 2 CO₂ + 3 H₂O + heat

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.^[36] If all bioethanol-production energy came from non-fossil sources the use of bioethanol as a fuel would add no greenhouse gas.^[37]

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.^[38] 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.^[39]

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.

Environmentalists have objections to many modern farming practices, including some practices useful for making bioethanol more competitive ("factory farming"). If more third-world land were to be converted to agriculture to feed ethanol fuel demand, there is the possibility of trading today's automotive pollution for tomorrow's farm pollution.

- There is some potential that through irresponsible farming methods some rainforest areas could be cleared to make land available for growing crops for commercial commodities such as palm oil for the generation of biodiesels.^[40]

Effects of ethanol on food consumption patterns

The below two paragraphs are in dispute. Most corn tortillas are made from white corn, not the yellow field corn used for corn ethanol. There was a significant drought that caused a decreased supply of white corn in Mexico, and the Mexican government was slow to import more white corn. This caused the price of corn tortillas to increase. Similarly, if peanut butter prices went up it should not be blamed on a shortage of pecans. They may have similarities, but they do not result in the same product. Also, sweet corn is not used for ethanol, should there be a shortage and increased price of this human food in the future. Even a Washington Post article can have its untruths, should research methods or sources be faulty. Below is the disputed tortilla information:

Central American countries feel that their culture and diet are under attack due to price pressures on corn, which are being diverted from consumption to fuel production.^[41]

The production of Ethanol from corn has been driving up the price of corn creating cost problems for tortilla makers in Mexico. The Mexican Government is attempting to reduce the fears of both producers and consumers over how to best control the rising price of the centuries-old dietary staple.

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.

Using current farming and production methods, ethanol from corn may not be sustainable as a replacement for fossil fuels. The amount of energy needed to produce it is a concern, especially if that energy is derived from fossil sources. One study critical of ethanol assumes massive use of pesticides and fertilizers, which consume fossil fuels and damage the farming environment. Moreover, the amount of ethanol that could be produced from corn or sugarcane, given the amount of farmland that is available, is likely limited to an amount below what would be needed to replace global petroleum consumption.

Replacement of fossil energy

Only about 5% of the fossil energy required to produce bioethanol from corn in the United States is obtained from nonUS petroleum.^[42] 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 nonUS 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

Some economists have argued that using bioalcohol as a petroleum substitute is economically infeasible (and environmentally inappropriate) because the energy required to grow and process the corn used as fuel is greater than the amount ultimately produced. They argue that government programs that mandate the use of bioalcohol are agricultural subsidies. The United States Department of Energy, however, finds that for every unit of energy put towards ethanol production, 1.3 units are returned.^[43] Another study found that corn-grain ethanol produced 1.25 units of energy per unit put in.^[44]

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.

It is important to remember, however, that for each unit of energy put into a gallon of gasoline, only 0.8 units are returned. Therefore corn ethanol has a 50-60% increased energy gain over gasoline.

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.^[45]

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.^[46]

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.
• E-85 fuel still contains a 15% gasoline component. Greater environmental benefits could be achieved without the gasoline.
• E-85 fuel distribution's fate rests mainly with the Big Oil interests, as they control the majority of fuel stations. Why would they want to substitute their own product for someone else's (farmers and investors)? They prefer to allow ethanol blended in small amounts with gasoline, for the longevity of their own product, and to denigrate the validity of E-85 fuel.^{[citation needed]}||}}

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. ↑ http://www.ethanol.org/autoracing.html
19. ↑ http://noticias.vrum.com.br/veiculos_ig/template_interna_noticias,id_noticias=20367&id_sessoes=160/template_interna_noticias.shtml
20. ↑ http://www.chevetteiroscuritiba.com.br/motor.htm
21. ↑ http://www2.uol.com.br/bestcars/classicos/passat-5.htm
22. ↑ http://www2.uol.com.br/interpressmotor/lancamento/item14863.shl
23. ↑ http://www.eia.doe.gov/cneaf/alternate/page/faq.html#12
24. ↑ http://www.eere.energy.gov/afdc/progs/ddown.cgi?afdc/FAQ/5/0/0
25. ↑ http://www.eia.doe.gov/cneaf/solar.renewables/alt_trans_fuel/attf.pdf#page=39 "Alternative Fuel Efficiencies in Miles per Gallon"
26. ↑ http://www.epa.gov/orcdizux/rfgecon.htm
27. ↑ http://www.fueleconomy.gov/feg/byfueltype.htm
28. ↑ http://www.eere.energy.gov/afdc/resources/pricereport/price_report.html
29. ↑ washington.edu, course, Oct. 22 v2
30. ↑ http://www.epa.gov/otaq/presentations/epa-fev-isaf-no55.pdf (pdf)
31. ↑ http://www1.eere.energy.gov/biomass/net_energy_balance.html DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use
32. ↑ http://www.news.cornell.edu/stories/July05/ethanol.toocostly.ssl.html
33. ↑ http://www1.eere.energy.gov/biomass/net_energy_balance.html DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use
34. ↑ http://rael.berkeley.edu/ebamm/: ERG Biofuel Analysis Meta-Model
35. ↑ Bioethanol needs biotech now
36. ↑ ethanol.org, Science Journal January 2006
37. ↑ biomasschpethanol.umn.edu paper
38. ↑ http://www.cbsnews.com/stories/2002/05/03/tech/main508006.shtml
39. ↑ Kononova, M. M. Soil Organic Matter, Its Nature, Its role in Soil Formation and in Soil Fertility, 1961
40. ↑ http://www.dft.gov.uk/stellent/groups/dft_roads/documents/page/dft_roads_028393-04.hcsp
41. ↑ http://www.washingtonpost.com/wp-dyn/content/article/2007/01/26/AR2007012601896_pf.html
42. ↑ ethanol.org, Science Journal January 2006
43. ↑ http://www1.eere.energy.gov/biomass/net_energy_balance.html
44. ↑ {{#if:Hill |{{#if: |[[{{{authorlink}}}|{{#if: Hill |Hill{{#if: Jason |, Jason }} |{{{author}}} }}]] |{{#if:Hill |Hill{{#if: Jason |, Jason }} |{{{author}}} }} }} }}{{#if:Hill |{{#if:Nelson, Erik; Tilman, David; Polasky, Stephen; and Tiffany, Douglas |, Nelson, Erik; Tilman, David; Polasky, Stephen; and Tiffany, Douglas }} }}{{#if: | ({{{date}}}) |{{#if:2006 |{{#if:July 25 | (July 25 2006) | (2006) }} }} }}{{#if:Hill2006 |. }}{{#if:http://www.pnas.org/cgi/content/abstract/103/30/11206 |[http://www.pnas.org/cgi/content/abstract/103/30/11206 | }} {{#if: |“|"}}Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels{{#if: |”|"}}{{#if:http://www.pnas.org/cgi/content/abstract/103/30/11206 |] | }}{{#if: | ({{{format}}}) }}{{#if:Proceedings of the National Academy of Sciences |. Proceedings of the National Academy of Sciences }}{{#if:103 | 103 }}{{#if:30 | (30) }}{{#if:11206-10 |: 11206-10 }}{{#if: | . DOI:{{{doi}}} }}{{#if:Template:Doi |. Template:Doi }}{{#if:2007-01-24 |. Retrieved on 2007-01-24 }}.
45. ↑ [http://www.treehugger.com/files/2006/03/veridian_corp_e.php Veridium Patents Yellowstone Algae-Fed Bioreactor to Capture Ethanol Plant CO2 Emissions]
46. ↑ US patent 7135308

See also

Categories: Pages needing cleanup | Articles with unsourced statements | Biofuels | Biotechnology products | Fuels | Ethanol fuel | Alternative propulsion