Home / Bioethanol / What is bioethanol

What is bioethanol

 

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

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

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

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

In 2004, around 42 billion liters of ethanol were produced in the world, most of it being for use in cars. Brazil produced around 16,4 billion liters and used 2,7 million hectares of land area for this production, or 4,5% of Brazilian land area used for crop production in 2005. Around 12,4 billion liters were produced as fuel to ethanol-powered vehicles in domestic market.

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

C_6 H_{12} O_{6(l)} + H_2 O_{(l)} \rightarrow \; 2 C_2 H_5 OH_{(l)} + 2CO_{2(g)} + H_2 O_{(l)} + heat

The reaction of burning ethanol is similar to burning hydrocarbons in gasoline. Ethanol reacts with oxygen to produce carbon dioxide, water, and heat:[4]

C_2 H_5 OH_{(l)} + 3O_{2(g)}  ===> 2CO_{2(g)} + 3H_2 O_{(l)} + heat

Both fermentation and burning of ethanol release large amounts of carbon dioxide. This CO2 is exactly balanced by the carbon fixed by the feed stock plants during photosynthesis. So to the extent that ethanol displaces a fossil fuel, such as gasoline, there can be a net reduction in their release of carbon dioxide to the atmosphere.

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 yet exist that makes it economically competitive to produce ethanol from cellulosic feedstock.

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

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.

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

Production

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

Crops with higher yields of energy, such as switchgrass and sugar cane, are more effective in producing ethanol than corn. Ethanol can also be produced from sweet sorghum, a dryland crop that uses much less water than sugarcane, does not require a tropical climate and produces food and fodder in addition to fuel. The best farm crop for ethanol production is sugar beets, in terms of gallons of fuel per acre, with the lowest water requirements to grow the crop (The beet plant drives a central taproot deep into the soil and the entire beet is underground, minimimizing evaporation).

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. Thus sugarcane nets 7/.34 or about 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. When compared to gasoline, ethanol releases less greenhouse gases.

For the ethanol to be usable as a fuel, water must be removed. Most of the water is removed by distillation, but the purity is limited to 95-96% due to the formation of a low-boiling water-ethanol azeotrope. The 96% m/m (93% v/v) ethanol, 4% m/m (7% v/v) water mixture may be used as a fuel, and it's called hydrated ethyl alcohol fuel (álcool etílico hidratado combustível, or AEHC in Portuguese). In 2006/2007, an estimated 17 billion liters (4,5 billion gallons) of hydrated ethyl alcohol fuel will be produced, to be used in ethanol powered vehicles.

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

Biotechnology may improve the energy gain of bioethanol.

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

Technology

Ethanol 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.

Ethanol engines and efficiency

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 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.

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. [20]. 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. 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.

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.

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

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. 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.

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. 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.

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.

Some of the problems experienced with ethanol include:

* Ethanol-based fuels are not compatible with some fuel system components.[citation needed] 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.[citation needed]
* The use of ethanol-based fuels can negatively affect electric fuel pumps by increasing internal wear and undesirable spark generation.[citation needed]
* E-85 is not compatible with capacitance fuel level gauging indicators and may cause erroneous fuel quantity indications in vehicles that employ that system.

Fuel Economy

For vehicles with current (2006) design flexible fuel engines, fuel economy (measured as miles per gallon (MPG), or liters per 100 km) is directly proportional to energy content. Ethanol contains approx. 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 approximately 27% lower mileage than gasoline, and will require more frequent refueling. Actual performance may vary depending on the vehicle.
Hydrated ethanol × gasoline type C price table for use in Brazil
Hydrated ethanol × gasoline type C price table for use in Brazil

For the EPA-rated mileage of current USA flex-fuel vehicles, see.

This reduced fuel economy should be considered when making price comparisons. For example, if regular gasoline costs $3.00 per gallon, and E85 costs $2.19 per gallon, the prices are essentially equivalent. If the discount for E85 is less than 27%, it actually costs more per mile to use. For USA price comparisons, see.

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.[31] 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.[32] 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

Ethanol and hydrogen

Hydrogen is being analyzed as an alternative fuel, creating a hydrogen economy. Because hydrogen in its gaseous state takes up a very large volume when compared to other fuels, logistics becomes a difficult problem. One possible solution is to use ethanol to transport the hydrogen, then liberate the hydrogen from its associated carbon in a hydrogen reformer and feed the hydrogen into a fuel cell. Alternatively, some fuel cells (DEFC Direct-ethanol fuel cell) can be directly fed by ethanol or methanol. As of 2005, fuel cells are able to process methanol more efficiently than ethanol.

In early 2004, researchers at the University of Minnesota announced the invention of a simple ethanol reactor that would feed ethanol through a stack of catalysts, and output hydrogen suitable for a fuel cell. The device uses a rhodium-cerium catalyst for the initial reaction, which occurs at a temperature of about 700 °C (1300 °F). This initial reaction mixes ethanol, water vapor, and oxygen and produces good quantities of hydrogen. Unfortunately, it also results in the formation of carbon monoxide, a substance that "chokes" most fuel cells and must be passed through another catalyst to be converted into carbon dioxide. (The odorless, colorless, and tasteless carbon monoxide is also a significant toxic hazard if it escapes through the fuel cell into the exhaust, or if the conduits between the catalytic sections leak.) The ultimate products of the simple device are roughly 50% hydrogen gas and 30% nitrogen, with the remaining 20% mostly composed of carbon dioxide. Both the nitrogen and carbon dioxide are fairly inert when the mixture is pumped into an appropriate fuel cell. The carbon dioxide is released back into the atmosphere, where it can be reabsorbed by plant life. No net carbon dioxide is released, though it could be argued that while it is in the atmosphere, it does act as a greenhouse gas.

EEI has developed a new method for producing butanol from biomass. This process involves the use of two separate micro-organisms in sequence to minimize production of acetone and ethanol byproducts. Interestingly, this process produces significant amounts of hydrogen as well as butanol.

Energy balance

Main article: Ethanol fuel energy balance

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

Some scientists argue that the energy balance is negative when all factors are considered. Professors Tad Patzek and David Pimentel are the most well-known academics to make this argument. These arguments have been challenged in a report from the U.S. Department of Energy as being based on decades-old data and not considering recent advances in production or the use of more efficient source crops for ethanol fermentation. On January 2007, 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".

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

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

Effects of ethanol on agriculture

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.

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.

However, using current farming and production methods, ethanol from corn may not be fully 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. For example, 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. It only takes 1.5 gallons of Ethanol fuel to make the same amount of energy as 1 gallon of gasoline.

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. 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.

Yields of common crops associated with ethanol production

Crop litres ethanol/ha US gal/acre
Miscanthus 14031 1500
Switchgrass 10757 1150
Sweet Potatoes 10000 1069
Poplar Wood (hybrid) 9354 1000
Sweet Sorghum 8419 900
Sugar Beet 6679 714
Sugar Cane 6192 662
Cassava 3835 410
Corn (maize) 3461 370
Wheat 2591 277

Source: Petroleum Club (with permission)

Dependence on foreign oil

Only about 5% of the fossil energy required to produce bioethanol from corn is obtained from foreign oil. Current 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 foreign oil 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.

www.wikipedia.org