Ethanol fuel
From Wikipedia, the free encyclopedia
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. Because it is easy to manufacture and process and can be made from very common crops such as sugar cane and corn, it is an increasingly common alternative to gasoline in some parts of the world.
Anhydrous ethanol (ethanol with less than 1% water) 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).[1] Most cars on the road today in the U.S. can run on blends of up to 10% ethanol,[2] and the use of 10% ethanol gasoline is mandated in some cities where harmful levels of auto emissions are possible.[3]
Ethanol can be mass-produced by fermentation of sugar or by hydration of ethylene (ethene CH2=CH2) 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,[4] as well as the energy and pollution balance of the whole cycle of ethanol production.[5][6] Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns.[7]
According to the International Energy Agency, cellulosic ethanol could allow ethanol fuels to play a much bigger role in the future than previously thought.[8] Cellulosic ethanol offers promise as resistant cellulose fibers, a major component in plant cells walls, can be used to generate ethanol. Dedicated energy crops such as switchgrass are also promising cellulose sources that can be produced in many regions of the United States.[9]
Contents
[edit] Chemistry
Glucose is created in the plant by photosynthesis.
- 6CO2 + 6H2O + light → C6H12O6 + 6O2
During ethanol fermentation, glucose is decomposed into ethanol and carbon dioxide.
- C6H12O6 → 2C2H6O + 2CO2 + heat
During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat:
- C2H6O + 3O2 → 2CO2 + 3H2O + heat
After doubling the ethanol combustion reaction because two molecules of ethanol are produced for each glucose molecule, there are equal numbers of each type of molecule on each side of the equation, and the net reaction for the overall production and consumption of ethanol is just:
- light → heat
The heat of the combustion of ethanol is used to drive the piston in the engine by expanding heated gases. It can be said that sunlight is used to run the engine.
Air pollutants are also produced when ethanol is burned in the atmosphere rather than in pure oxygen. Harmful nitrous oxide gases are produced. Nitrogen dioxide is one of the harmful gases as is a major contributor to the formation of "brown smog".[citation needed]
[edit] Sources
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.
About 5% of the ethanol produced in the world in 2003 was actually a petroleum product.[10] 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.[11] Petroleum derived ethanol (synthetic ethanol) is chemically identical to bio-ethanol and can be differentiated only by radiocarbon dating.[12]
Bio-ethanol 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 assessment.
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 and yeast 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.
[edit] Production process
The basic steps for large scale production of ethanol are: microbial (yeast) fermentation of sugars, distillation, dehydration (requirements vary, see Ethanol fuel mixtures, below), and denaturing (optional). Prior to fermentation, some crops require saccharification or hydrolysis of carbohydrates such as cellulose and starch into sugars. Saccharification of cellulose is called cellulolysis (see cellulosic ethanol). Enzymes are used to convert starch into sugar.[13]
[edit] Fermentation
Ethanol is produced by microbial fermentation of the sugar. Microbial fermentation will currently only work directly with sugars. Two major components of plants, starch and cellulose, are both made up of sugars, and can in principle be converted to sugars for fermentation. Currently, only the sugar (e.g. sugar cane) and starch (e.g. corn) portions can be economically converted. However, there is much activity in the area of cellulosic ethanol, where the cellulose part of a plant is broken down to sugars and subsequently converted to ethanol.
[edit] Distillation
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 95.6% m/m (96.5% v/v) ethanol, 4.4% m/m (3.5% v/v) water mixture may be used as a fuel alone, but unlike anhydrous ethanol, is immiscible in gasoline, so the water fraction is typically removed in further treatment in order to burn with in combination with gasoline in gasoline engines.
[edit] Dehydration
There are basically three dehydration processes to remove the water from an azeotropic ethanol/water mixture. The first process, used in many early fuel ethanol plants, is called azeotropic distillation and consists of adding benzene or cyclohexane to the mixture. When these components are added to the mixture, it forms an heterogeneous azeotropic mixture in vapor-liquid-liquid equilibrium, which when distillated produces anhydrous ethanol in the column bottom, and a vapor mixture of water and cyclohexane/benzene. When condensed, this becomes a two-phase liquid mixture. Another early method, called extractive distillation, consists of adding a ternary component which will increase ethanol relative volatility. When the ternary mixture is distillated, it will produce anhydrous ethanol on the top stream of the column.
With increasing attention being paid to saving energy, many methods have been proposed that avoid distillation all together for dehydration. Of these methods, a third method has emerged and has been adopted by the majority of modern ethanol plants. This new process uses molecular sieves to remove water from fuel ethanol. In this process, ethanol vapor under pressure passes through a bed of molecular sieve beads. The bead's pores are sized to allow absorption of water while excluding ethanol. After a period of time, the bed is regenerated under vacuum to remove the absorbed water. Two beds are used so that one is available to absorb water while the other is being regenerated. This dehydration technology can account for energy saving of 3,000 btus/gallon compared to earlier azeotropic distillation. Modern Corn Ethanol plant description
[edit] Technology
[edit] 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).[14][15] However, higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than could be obtained with the lower compression ratio.[16][17] 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,[18] which would render that engine unsuitable for gasoline use. When ethanol fuel availability allows high-compression ethanol-only vehicles to be practical, the fuel efficiency of such engines should be equal or greater than current gasoline engines. However, since the energy content (by volume) of ethanol fuel is less than gasoline, a larger volume of ethanol fuel (151%) would still be required to produce the same amount of energy.[19] In spite of that, as the ethanol-only vehicle wastes less energy, yielding the same or higher mileage.
A 2004 MIT study[20] and an earlier paper published by the Society of Automotive Engineers[21] identify a method to exploit the characteristics of fuel ethanol substantially better than mixing it with gasoline. The method presents the possibility of leveraging the use of alcohol to even achieve definite improvement over the cost-effectiveness of hybrid electric. The improvement consists of using dual-fuel direct-injection of pure alcohol (or the azeotrope or E85) and gasoline, in any ratio up to 100% of either, in a turbocharged, high compression-ratio, small-displacement engine having performance similar to an engine having twice the displacement. Each fuel is carried separately, with a much smaller tank for alcohol. The high-compression (which increases efficiency) engine will run on ordinary gasoline under low-power cruise conditions. Alcohol is directly injected into the cylinders (and the gasoline injection simultaneously reduced) only when necessary to suppress ‘knock’ such as when significantly accelerating. Direct cylinder injection raises the already high octane rating of ethanol up to an effective 130. The calculated over-all reduction of gasoline use and CO2 emission is 30%. The consumer cost payback time shows a 4:1 improvement over turbo-diesel and a 5:1 improvement over hybrid. In addition, the problems of water absorption into pre-mixed gasoline (causing phase separation), supply issues of multiple mix ratios and cold-weather starting are avoided.
Ethanol's higher octane rating allows an increase of an engine's compression ratio for increased thermal efficiency.[16] 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.[22] This would result in the MPG (miles per gallon) of a dedicated ethanol vehicle to be about the same as one burning gasoline.
Engines using fuel with 30% to 100% ethanol also need a cold-starting system in some countries. For E85 fuel at temperatures below 11 °C (52 °F) a cold-starting system is required for reliable starting and to meet EPA emissions standards.[23] However, the EPA does not require cold start systems on E85 vehicles. No current production E85 vehicles in the USA are equipped with these cold start systems, and they meet EPA emission guidelines. Instead, to avoid problems starting the engine during cold weather, the ethanol blend in the US has a seasonal reduction to E70 in very cold regions, where temperatures fall below -12 °C (10 °F) during the winter.[24] Sweden does a similar seasonal reduction to the blend, but ethanol is reduced to E75. Because of its warmer climate, Brazilian flex fuel vehicles do not have any provision for cold-starting.
[edit] Ethanol fuel mixtures
-
For more details on this topic, see Common ethanol fuel mixtures.
To avoid engine stall due to "slugs" of water in the fuel lines interrupting fuel flow, 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 percentage of ethanol.[25]. 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 with increased 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.[26]
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, since of July 2007 25% 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). In older model years, their engine systems contained 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. In newer models, the alcohol sensors have been removed, with the computer using only oxygen and airflow sensor feedback to estimate alcohol content. The engine control computer can also adjust (advance) the ignition timing to achieve a higher output without pre-ignition when it predicts that higher alcohol percentages are present in the fuel being burned. This method is backed up by advanced knock sensors - used in most high performance gasoline engines regardless of whether they're designed to use ethanol or not - that detect pre-ignition and detonation.
[edit] Fuel economy
In theory, all fuel-driven vehicles have a fuel economy (measured as miles per US gallon, or liters per 100 km) that is directly proportional to the fuel's energy content.[27]In reality, there are many other variables that come in to play that affect the performance of a particular fuel in a particular engine. Ethanol contains approx. 34% less energy per unit volume than gasoline, and therefore in theory, burning pure ethanol in a vehicle will result in a 34% reduction in miles per US gallon, given the same fuel economy, compared to burning pure gasoline. This assumes that the octane ratings of the fuels, and thus the engine's ability to extract energy from the fuels, are the same.[14][15] For E10 (10% ethanol and 90% gasoline), the effect is small (~3%) when compared to conventional gasoline,[28] and even smaller (1-2%) when compared to oxygenated and reformulated blends.[29] 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. Based on EPA tests for all 2006 E85 models, the average fuel economy for E85 vehicles resulted 25.56% lower than unleaded gasoline.[30] The EPA-rated mileage of current USA flex-fuel vehicles[31] should be considered when making price comparisons, but it must be noted that E85 is a high performance fuel, with an octane rating of about 104, and should be compared to premium. In one estimate[32] the US retail price for E85 ethanol is 2.62 US dollar per gallon or 3.71 dollar corrected for energy equivalency compared to a gallon of gasoline priced at 3.03 dollar. Brazilian cane ethanol (100%) is priced at 3.88 dollar against 4.91 dollar for E25 (as July 2007).
[edit] Experience by country
The top five ethanol producers in 2006 were the United States with 4.855 billion U.S. liquid gallons (bg), Brazil (4.49 bg), China (1.02 bg), India (0.50 bg) and France (0.25 bg).[33] Brazil and the United States accounted for 70 percent of all ethanol production, with total world production of 13.5 billion US gallons (40 million tonnes). When accounting just for fuel ethanol production in 2007, the U.S. and Brazil are responsible for 88% of the 13.1 billion gallons total world production. Strong incentives, coupled with other industry development initiatives, are giving rise to fledgling ethanol industries in countries such as Thailand, Colombia, and some Central American countries. Nevertheless, ethanol has yet to make a dent in world oil consumption of approximately 4000 million tonnes/yr (84 million barrels/day).[34]
by Country (2004-2006)[33]
Top 15 countries
(Millions of U.S. liquid gallons) Annual Fuel Ethanol Production
by Country (2007)[35]
Top 15 countries/blocks
(Millions of U.S. liquid gallons)
rank Country 2006 2005 2004 World
rank Country/Region 2007
[edit] Brazil
Brazil has the largest and most successful bio-fuel programs in the world, involving production of ethanol fuel from sugar cane, and it is considered to have the world's first sustainable biofuels economy.[36][37][38] In 2006 Brazilian ethanol provided 18% of the country's road transport sector fuel consumption needs,[39][40] and by April 2008, more than 50% of fuel consumption for the gasoline market.[41][42][37] As a result of the increasing use of ethanol, 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, in 2006 reached complete self-sufficiency in oil supply.[43][44][45]
Together, Brazil and the United States lead the industrial world in global ethanol production, accounting together for 70% of the world's production[46] and nearly 90% of ethanol used for fuel. [47] In 2006 Brazil produced 16.3 billion liters (4.3 billion U.S. liquid gallons),[33] which represents 33.3% of the world's total ethanol production and 42% of the world's ethanol used as fuel.[47] Sugar cane plantations cover 3.6 million hectares of land for ethanol production, representing just 1% of Brazil's arable land, with a productivity of 7,500 liters of ethanol per hectare, as compared with the U.S. maize ethanol productivity of 3,000 liters per hectare.[48][36]
The ethanol industry in Brazil is more than 30 year-old and even though is no longer subsidized, production and use of ethanol was stimulated through:
-
Low-interest loans for the construction of ethanol distilleries Guaranteed purchase of ethanol by the state-owned oil company at a reasonable price Retail pricing of neat ethanol so it is competitive if not slightly favorable to the gasoline-ethanol blend Tax incentives provided during the 1980s to stimulate the purchase of neat ethanol vehicles.[49]
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 São Paulo established a research and technology transfer center that has been effective in improving sugar cane and ethanol yields.[49]
There are no longer light vehicles in Brazil running on pure gasoline. Since 1977 the government made mandatory to blend 20% of ethanol (E20) with gasoline (gasohol), requiring just a minor adjustment on regular gasoline motors. Today the mandatory blend is allowed to vary nationwide between 20% to 25% ethanol (E25) and it is used by all regular gasoline vehicles, plus three million cars running on 100% hydrated ethanol and six million of dual or flexible-fuel vehicles. The Brazilian car manufacturing industry developed full flexible-fuel vehicles that can run on any proportion of gasoline and ethanol.[50] Introduced in the market in 2003, these vehicles became a commercial success.[51] On August 2008, the fleet of "flex" cars and light commercial vehicles had reached 6 million new vehicles sold, which represents around 23% of Brazil's light motor vehicle fleet.[52] The ethanol-powered and "flex" vehicles, as they are popularly known, are manufactured to tolerate hydrated ethanol, an azeotrope comprised of 95.6% ethanol and 4.4% water.[30]
[edit] United States
United States fuel ethanolproduction and imports
(2001-2007)[33]
(Millions of U.S. liquid gallons)
and small exports in 2005
The United States produces and consumes more ethanol fuel than any other country in the world. Ethanol use as fuel dates back to Henry Ford, who in 1896 designed his first car, the "Quadricycle" to run on pure ethanol.[30] Then in 1908, he produced the famous Ford Model T capable of running on gasoline, ethanol or a combination of both.[53][30] Ford continued to advocate for ethanol as fuel even during the prohibition.[30]
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. In 2007 Portland, Oregon, became the first city in the United States to require all gasoline sold within city limits to contain at least 10% ethanol.[54][55] As of January 2008, three states — Missouri, Minnesota, and Hawaii — require ethanol to be blended with gasoline motor fuel. Many cities are also required to use an ethanol blend due to non-attainment of federal air quality goals.[56]
Several motor vehicle manufacturers, including Ford, Chrysler, and GM, sell flexible-fuel vehicles that can use gasoline and ethanol blends ranging from pure gasoline all the way up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on U.S. roads.[57]
In the USA there are currently 1,587 stations distributing ethanol, although most stations are in the corn belt area.[58][59] One of the debated methods for distribution in the US is using existing oil pipelines,[60] which raises concerns over corrosion. In any case, some companies proposed building a 1,700-mile pipeline to carry ethanol from the Midwest through Central Pennsylvania to New York. [61]
The production of fuel ethanol from corn in the United States is controversial for a few reasons. Production of ethanol from corn is 5 to 6 times less efficient than producing it from sugarcane. Ethanol production from corn is highly dependent upon subsidies and it consumes a food crop to produce fuel.[32] The subsidies paid to fuel blenders and ethanol refineries have often been cited as the reason for driving up the price of corn, and in farmers planting more corn and the conversion of considerable land to corn (maize) production which generally consumes more fertilizers and pesticides than many other land uses.[32] This is at odds with the subsidies actually paid directly to farmers that are designed to take corn land out of production and pay farmers to plant grass and idle the land, often in conjunction with soil conservation programs, in an attempt to boost corn prices. Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns. A theoretically much more efficient way of ethanol production has been suggested to use sugar beets which make about the same amount of ethanol as corn without using the corn food crop especially since sugar beets can grow in less tropical conditions than sugar cane.[62]
[edit] Europe
European Union (GWh)[63]
1 tonne bioethanol = 0,64 toe
European Union (GWh)[63]
The consumption of bioethanol is largest in Europe in Germany, Sweden, France and Spain. Europe produces equivalent to 90% of its consumption (2006). Germany produced ca 70% of its consumption, Spain 60% and Sweden 50% (2006). In Sweden there are 792 E85 filling stations and in France 131 E85 service stations with 550 more under construction.[58]
On Monday, September 17, 2007 the first ethanol fuel pump was opened in Reykjavik, Iceland. This pump is the only one of its kind in Iceland. The fuel is imported by Brimborg, a Volvo dealer, as a pilot to see how ethanol fueled cars work in Iceland.
In The Netherlands regular petrol with no bio-additives is slowly outphased, since EU-legislation has been passed that requires the fraction of nonmineral origin to become minimum 5,75% of the total fuel consumption volume in 2010. This can be realised by substitutions in diesel or in petrol of any biological source; or fuel sold in the form of pure biofuel. (2007:) There are only a few gas stations where E85 is sold, which is an 85% ethanol, 15% petrol mix.[64] Directly neighbouring country Germany is reported to have a much better biofuel infrastructure and offers both E85 and E50. Biofuel is taxed equally as regular fuel. However, fuel tanked abroad cannot be taxed and a recent payment receipt will in most cases suffice to prevent fines if customs check tank contents. (Authorities are aware of high taxation on fuels and cross-border fuel refilling is a well-known practice.)