Ethanol fuel

For other forms of alternative energy, see energy development.

Information on pump, California.

Ethanol fuel is ethanol (ethyl alcohol), the same type of alcohol found in alcoholic beverages. It can be used as a fuel, mainly as a biofuel alternative to gasoline, and is widely used in cars in Brazil.

Anhydrous ethanol, that is, ethanol with at most 1% water, the same alcohol as found in alcoholic beverages, can be blended with gasoline in varying quantities up to pure ethanol (E100), and most spark-ignited gasoline style engines will operate well with mixtures of 10% ethanol (E10). Most cars on the road today in the U.S. can run on blends of up to 10% ethanol, and the use of 10% ethanol gasoline is mandated in some cities where harmful levels of auto emissions are possible.

Ethanol can be mass-produced by fermentation of sugar or by hydration of ethylene from petroleum and other sources. Current interest in ethanol mainly lies in bio-ethanol, produced from the starch or sugar in a wide variety of crops, but there has been considerable debate about how useful bio-ethanol will be in replacing fossil fuels in vehicles. Concerns relate to the large amount of arable land required for crops, as well as the energy and pollution balance of the whole cycle of ethanol production. Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns.

According to the International Energy Agency, cellulosic ethanol could allow ethanol fuels to play a much bigger role in the future than previously thought. Cellulosic ethanol can be made from plant matter composed primarily of inedible cellulose fibers that form the stems and branches of most plants. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be produced in many regions of the United States.

In the U.S., there is potential to expand the market for ethanol fuels beyond the farm states where they have been most popular to date. Flex-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, should also help to expand the U.S. market.

Chemistry

In this 3-d diagram of ethanol, the lines represent single bonds.

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

C₆H₁₂O₆ → 2C₂H₆O + 2CO₂

During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat: (other air pollutants are also produced when ethanol is burned in the atmosphere rather than in pure oxygen)

2C₂H₆O + 6O₂ → 4CO₂ + 6H₂O + heat

Together, these two equations add up to the following:

C₆H₁₂O₆ + 6O₂ → 2CO₂ + 4CO₂ + 6H₂O + heat

This is the reverse of the photosynthesis reaction, which shows that the three reactions completely cancel each other out, only converting light into heat without leaving any byproducts:

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

Sources

Main article: Energy crop

Sugar cane harvest

Cornfield in South Africa

Switchgrass

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.

Bioethanol is obtained from the conversion of carbon based feedstock. Agricultural feedstocks are considered renewable because they get energy from the sun using photosynthesis, provided that all minerals, required for growth (such as nitrogen and phosphorus), are returned to the land. 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, corn, stover, grain, wheat, straw, cotton, other biomass, as well as many types of cellulose waste and harvestings, whichever has the best well-to-wheel assesment.

Production Process

The basic steps for large scale production of ethanol are: microbial (yeast) fermentation of sugars, distillation, dehydration (required unless distillation is done repeatedly), and denaturing (optional). Prior to fermentation, some crops require saccharification or hydrolysis into carbohydrates. Saccharification of cellulose is called cellulolysis (see cellulosic ethanol). Other pre-production steps can be necessary for certain crops like corn which requires refinement into starch and liquification.[16]

Fermentation

Main article: Ethanol fermentation

Ethanol is produced by microbial fermentation of the sugar. 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 greenhouse gas, is emitted during fermentation and combustion. However, this is cancelled out by the greater uptake of carbon dioxide by the plants as they grow to produce the biomass. When compared to gasoline, depending on the production method, ethanol releases less or even no greenhouse gases.

Distillation

Ethanol plant in West Burlington, Iowa

Ethanol plant in Sertãozinho, Brazil.

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.

Dehydration

Currently, the most widely used purification method is a physical absorption process using a molecular sieve, for example, ZEOCHEM Z3-03 (a special 3A molecular sieve for EtOH dehydration). Another method, azeotropic distillation, is achieved by adding the hydrocarbon benzene which also denatures the ethanol (to render it undrinkable for duty purposes). A third method involves use of calcium oxide as a desiccant.

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 (E100) consumption in an engine is approximately 34% higher than that of gasoline (the energy per volume unit is 34% lower). However, higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than would be obtained with the lower compression ratio. In general, ethanol-only engines are tuned to give slightly better 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 much higher compression ratio 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, in energy terms, that is, a larger volume of ethanol is still required to produce the same energy, since the energy content is lower, than that of gasoline.

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

Further information: Common 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 [17]. 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 [18].

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.

File:Gas x álcool - 70%.svg

Hydrated ethanol × gasoline type C price table for use in Brazil

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

All vehicles have a fuel economy (measured as miles per gallon -MPG- , or liters per 100 km) that is directly proportional to energy content. Ethanol contains approx. 34% 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.

Ethanol fuel use by country

The top five ethanol producers in 2005 were Brazil (4.35 billion gallons per year), the United States (4.3 billion gallons per year), China (530 MMgy), the European Union (250 MMgy) and India (80 MMgy). Brazil and the United States accounted for 90 percent of all ethanol production. Also, it should be noted that the United States, now producing at a rate of about 4.6 billion gallons per year, is widely considered the world’s largest ethanol producer. Strong incentives, coupled with other industry development initiatives, are giving rise to fledgling ethanol industries in countries such as Thailand, the Philippines, Columbia, the Dominican Republic and Malawi. Nevertheless, ethanol hasn't yet made much of a dent in world oil consumption.

Brazil

Main article: Ethanol fuel in Brazil

Gasoline on the left, alcohol on the right at a filling station in Brazil

Brazil has one of the largest bio-fuel programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a result of this, together with the exploitation of domestic deep water oil sources, Brazil, which years ago had to import a large share of the petroleum needed for domestic consumption, recently reached complete self-sufficiency in oil.

Brazil produced around 16.4 billion liters of ethanol in 2004 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. In Brazil, ethanol-powered and flexible-fuel vehicles are manufactured for operation with hydrated ethanol, an azeotrope of ethanol (around 93% v/v) and water (7%).

Production and use of ethanol has been stimulated through: (1) low-interest loans for the construction of ethanol distilleries; (2) guaranteed purchase of ethanol by the state-owned oil company at a reasonable price; (3) retail pricing of neat ethanol so it is competitive if not slightly favorable to the gasoline-ethanol blend; and (4) tax incentives provided during the 1980s to stimulate the purchase of neat ethanol vehicles.

Guaranteed purchase and price regulation were ended some years ago, with relatively positive results. In addition to these other policies, ethanol producers in the state of Sao Paulo established a research and technology transfer center that has been effective in improving sugar cane and ethanol yields.

United States

A Ford Taurus "fueled by clean burning ethanol" owned by New York City.

Main article: Ethanol fuel in the United States

Most cars on the road today in the U.S. can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, DaimlerChrysler, and GM are among the automobile companies that sell “flexible-fuel” cars, trucks, and minivans that can use gasoline and ethanol blends ranging from pure gasoline up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on U.S. roads.

There is potential to expand the market for ethanol fuels beyond the farm states where they have been most popular to date. Flex-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, should also help to expand the U.S. market.

It should also be noted that the growing ethanol and biodiesel industries are providing jobs in plant construction, operations, and maintenance, mostly in rural communities. According to the Renewable Fuels Association, the ethanol industry created almost 154,000 U.S. jobs in 2005 alone, boosting household income by $5.7 billion. It also contributed about $3.5 billion in tax revenues at the local, state, and federal levels.

Sweden

Main article: Ethanol fuel in Sweden

All Swedish gas stations are required by an act of parliament to offer at least one alternative fuel, and every fifth car in Stockholm now drives at least partially on alternative fuels, mostly ethanol.

Stockholm will introduce a fleet of Swedish-made electric hybrid buses in its public transport system on a trial basis in 2008. These buses will use ethanol-powered internal-combustion engines and electric motors. The vehicles’ diesel engines will use ethanol.

Australia

Main article: Ethanol fuel in Australia

Legislation imposes a 10% cap on the concentration of fuel ethanol blends. Blends of 90% unleaded petrol and 10% fuel ethanol are commonly referred to as E10. E10 is available through service stations operating under the BP, Caltex, Shell and United brands as well as those of a number of smaller independents. Not surprisingly, E10 is most widely available closer to the sources of production in Queensland and New South Wales. E10 is most commonly blended with 91 RON "regular unleaded" fuel. There is a requirement that retailers label blends containing fuel ethanol on the dispenser.

China

China is promoting ethanol-based fuel on a pilot basis in five cities in its central and northeastern region, a move designed to create a new market for its surplus grain and reduce consumption of petroleum. The cities include Zhengzhou, Luoyang and Nanyang in central China's Henan province, and Harbin and Zhaodong in Heilongjiang province, northeast China. Under the program, Henan will promote ethanol-based fuel across the province by the end of this year. Officials say the move is of great importance in helping to stabilize grain prices, raise farmers' income and reducing petrol- induced air pollution.

Environment

Energy balance

Main article: Ethanol fuel energy balance

All biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented and burned. All of these steps require resources and an infrastructure.

Opponents of corn ethanol production in the U.S. often quote the 2005 paper of David Pimentel, a retired Entomologist, and Tadeusz Patzek, a Geological Engineer from Berkeley. Both have been exceptionally critical of ethanol and other biofuels. Their studies contend that ethanol, and biofuels in general, are "energy negative", meaning they take more energy to produce than is contained in the final product.

A 2006 report by the U.S. Department Agriculture compared the methodologies used by a number of researchers on this subject and found that the majority of research showed that the energy balance for ethanol is positive. In fact, a large number of recent studies, including a 2006 article in the prestigious journal Science offer the consensus opinion that fuels like ethanol are energy positive. Furthermore, it should be pointed out that fossil fuels also require significant energy inputs which have seldom been accounted for in the past.

It is also important to note that ethanol is not the only product created during production, and the energy content of the by-products must also be considered. Corn is typically 66% starch and the remaining 33% is not fermented. This unfermented component is called distillers grain, which is high in fats and proteins, and makes good animal feed.

In Brazil where sugar cane is used, the yield is higher, and conversion to ethanol is somewhat more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further.

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 net 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.

Manufacture

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. Smog causing pollutants are also increased by using ethanol fuel in comparison to gasoline.

Greenhouse gas abatement

Corn ethanol has received much support on environmental grounds primarily because of its role in reducing greenhouse gas emissions. However, the evidence for this claim is mixed.

A recent ten-year forecast of ethanol production by the USDA places 2017 corn ethanol production at 12 billion gallons and growing at only 2% per year. This estimate, together with a parameter publishing in the Proceedings of the National Academy of Sciences (PNAS), indicates that this near-maximum level of ethanol production will abate GHG emissions by 0.13% (~1/10 of 1%) of current US GHG emissions. However, this does not hold for all greenhouse gases. Another study has suggested that replacement of 100% petroleum fuel with E85 (a fuel mixture comprised of 85% ethanol and 15% petroleum) would significantly increase ozone levels, thereby increasing photochemical smog and aggravating medical problems such as asthma.[19][20]

This value reflects increases in corn acreage and the use of 30% of the corn crop for ethanol. It also apparently takes into account anticipated improvements in corn yields and ethanol production. The PNAS value is a 12% reduction in greenhouse gas emission relative to the "net emissions of production and combustion of an energetically equivalent amount of gasoline."

The January 2006 Science article from UC Berkeley's ERG, estimated this parameter to be 13% after reviewing a large number of studies. However, in a correction to that article releases shortly after publication, they reduce the estimated value to 7.4%. None of the other values needed to complete the calculation are controversial.

GREET model maintained by Argonne National Labs in Chicago has produced a series of publications on GHG abatement through ethanol. The latest of the studies is [21]

Land use

Large-scale 'energy farming', necessary to produce agricultural alcohol, requires substantial amounts of cultivated land. Some have claimed that land is acquired through deforestation, while others have observed that areas currently supporting forests are usually not suitable for growing any sort of crops. Related concerns have been raised regarding a decline in soil fertility due to reduction of organic matter, a decrease in water availability and quality, an increase in the use of pesticides and fertilizers, and potential dislocation of local communities.

As demand for ethanol fuel increases, food crops are replaced by fuel crops, driving food supply down and food prices up. Growing demand for ethanol in the United States has increased corn prices by 50% in Mexico. Average barley prices in the United States rose 17% from January to June 2007 to the highest in 11 years. Prices for all grain crops trend upward, reflecting a progressive increase in farming acreage devoted to corn for the production of produce ethanol fuel.

Prices for U.S. corn-based products, including animal feed, also rise. This translates to higher prices for animal products like chicken, beef, and cheese. June 2007 cheese prices rose to $2 per pound on average, increasing 65% over the same period in 2006. As milk prices in the United States, approached $4.00 per gallon, many American restaurant franchises announced price increases for their products to compensate for rising food costs.

Alternatively, cellulosic ethanol can be produced from any plant material, potentially doubling yields, in an effort to minimize conflict between food needs versus fuel needs. Instead of utilizing only the starch bi-products from grinding wheat and other crops, cellulosic ethanol production maximizes the use of all plant materials, including gluten. This approach would have a smaller carbon footprint because the amount of energy-intensive fertilisers and fungicides remain the same for higher output of useable material. While the enzyme technology for producing cellulosic ethanol is currently in developmental stages, it is not expected to be available for large-scale production in the near future. Moreover, the production of ethanol for fuel raises a number of land scarcity issues, regardless of what production method is employed. Many analysts suggest that biofuel strategies must be accompanied by fuel conservation restrictions.

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).

The environmental and economic benefits of non-cellulosic ethanol - including corn ethanol - have been heavily critiqued by many, including Brad Ewing of Environmental Economics & Sustainable Development and Lester R. Brown of Earth Policy Institute. The main criticism dwells on the increasing costs of corn for food as the demand for ethanol production increases. It remains to be seen if ethanol production can overcome these problems.

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 petroleum

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.

Alternatives

A switch to battery electric vehicles combined with solar power and nuclear power may be cheaper and less damaging to the environment. Vehicles directly powered from starches (via hydrogen release and fuel cells), such as corn starch, are also being considered, as their total system efficiency is almost three times higher than converting the starch to ethanol and burning it.[22]

Economics

The science of Economics is generally defined as the study of scarcity management. Absent scarcity and alternative uses of available resources, there is no economic problem. As such, the subject of economics involves the study of choices as they are affected by incentives and resources. Since land and agriculture have historically served the world as utilities for food production, many believe the alternative use of agricultural resources for ethanol fuel production imposes an artificial scarcity of food on a global scale.

Meanwhile, 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. 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.

Common crops associated with ethanol production

Note: U.S. motor gasoline consumption is 384.7 million gallons per day or 140 billion gallons per year. Total arable land in the U.S. is 460 million acres. Figures are for gross ethanol yield; they do not account for fuel used for crop production or ethanol processing.

Crop	Yield (gallons/acre) (per year?)	Greenhouse-gas savings (% vs. petrol)	Comments
Miscanthus	780	37 - 73	Low-input perrenial grass. Ethanol production depends on development of cellulosic technology.
Switchgrass	330 - 810	37 - 73	Low-input perrenial grass. Ethanol production depends on development of cellulosic technology. Breeding efforts underway to increase yields. Higher biomass production possible with mixed species of perennial grasses.
Poplar	400 - 640	51 - 100	Fast-growing tree. Ethanol production depends on development of cellulosic technology. Completion of genomic sequencing project will aid breeding efforts to increase yields.
Sugar cane	570 - 700	87 - 96	Ethanol being produced on a commercial scale using existing technology. Newer processing plants burn residues not used for ethanol to generate electricity. Only grows in tropical and subtropical climates.
Sweet sorghum	270 - 750	No data	Low-input annual grass. Ethanol production possible using existing technology. Grows in tropical and temperate climates, but highest ethanol yield estimates assume multiple crops per year (only possible in tropical climates). Does not store well. [23] [24] [25] [26]
Corn	330 - 420	10 - 20	High-input annual grass. Used as feedstock for most bioethanol produced in USA. Only kernals can be processed using available technology; development of commercial cellulosic technology would allow stover to be used and increase ethanol yield by 1,100 - 2,000 litres/ha.

Source (except sorghum): Nature 444 (Dec. 7, 2006): 670-654.

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.

Criticism and Controversy

Critics argue that ethanol is a fancy way of using solar power. The processing and production, as well as burning of ethanol would not significantly improve carbon emissions over the current use of gasoline. Instead, critics propose the widespread adoption of battery electric vehicles (zero emissions vehicles) combined with increased use of nuclear power and solar power.

Problems

• Ethanol-based fuels are not compatible with some fuel system components.
• Examples of extreme corrosion of ferrous components, and internal separation of portions of rubber fuel tanks have been observed in some vehicles using ethanol fuels.
• Formation of salt deposits, jelly-like deposits on fuel strainer screens
• Can negatively affect electric fuel pumps by increasing internal wear and undesirable spark generation.
• Is not compatible with capacitance fuel level gauging indicators and may cause erroneous fuel quantity indications in vehicles that employ that system.
• Not always compatible with marine craft, especially those that use fiberglass tanks.
• Decreases fuel-economy by 15-30%; this can be avoided using certain modifications that would, however, render the engine inoperable on regular petrol without the addition of an adjustable ECU, or use of multiple ECUs to run the engine on multiple fuel types.
• Support for biofuels could keep petroleum prices high in the USA (NY Times - [27])

See also

Alcohol fuel Biobutanol, a gasoline replacement. Bioconversion of biomass to mixed alcohol fuels Biodiesel Biofuel Biomass Butanol from Clostridium acetobutylicum Cellulosic ethanol Corn Ethanol Comparison of automobile fuel technologies DMF (potential ethanol competitor) Energy crop Energy development 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 Well-to-wheel

External links

• Fuel Sheet - Ethanol, Biofuels, Oil, and Natural Gas
• Fermentative production of lactic acid from biomass: an overview on process developments and future perspectives
• How E85 Ethanol Flex Fuel Works.
• 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 in USA.
• National Pollutant Inventory - Ethanol fact sheet
• Clean Fuels Development Coalition [28]
• Food and Fuel America.com
• Henry Ford, Charles Kettering and the Fuel of the Future (history of ethanol) [29]
• Renewable and Appropriate Energy Laboratory's survey article *Ethanol Can Contribute to Energy and Environmental Goals (.pdf format). Published in Science, January 27, 2006
• DrivingEthanol.org
• E85 Ethanol Fuel
• Thermodynamics of the Corn-Ethanol Biofuel Cycle Tad W. Patzek, Department of Civil and Environmental Engineering, University of California, Berkeley
• How far can you drive on a bushel of corn? Crunching the numbers on alternative fuels. Popular Mechanics May, 2006 issue
• Digging into the Ethanol Debate Wall Street Journal Online, June 9, 2006. Summary of the production efficiency debate, with references.
• American Coalition for Ethanol
• Ethanol: Myths and Realities