Straight Vegetable Oil SVO as Diesel replacement fuel
This article is about ethanol used as a fuel.
Ethanol can be used as fuel for automobiles either alone (E100) in a special engine or as an additive to gasoline for petroleum engines.
Ethanol can be blended with gasoline in varying quantities to reduce the consumption of petroleum fuels, as well as to reduce air pollution. The resulting fuel is known in the United States as gasohol, or gasoline type C in Brazil. Two common mixtures in the United States are E10 and E85 which contain 10% and 85% ethanol, respectively, while the common mixtures in Brazil are gasoline type C and its high octane variants, which contain 20% to 25% ethanol (also the only kind of gasoline legally sold in fuel stations).
Ethanol is also increasingly used as an oxygenate additive for standard gasoline, as a replacement for methyl t-butyl ether (MTBE), the latter chemical being responsible for considerable groundwater and soil contamination. Ethanol can also be used to power fuel cells.
Ethanol derived from crops (bio-ethanol) is a potentially sustainable energy resource that may offer environmental and long-term economic advantages over fossil fuel (gasoline). It is readily obtained from the sugar or starch in crops such as maize, miscanthus and sugarcane. Ethanol made from maize, however, was found to use a significant amount of energy compared to the energy value of the produced fuel. On the other hand, sugarcane has enough energy not only for completely sustained ethanol production, but also for generating surplus (currently at 108 MJ/ton), that may be sold to utilities. Sustainability of ethanol production is not a matter of energy balance, but of availability of land area and soil and biodiversity preservation.
Bioethanol is the result of conversion of feedstock. Agricultural feedstocks such as switchgrass are considered renewable because they get energy from the sun using photosynthesis. Ethanol as a substitute for gasoline is often created by harvesting a crop such as switchgrass and processing it for less money than it costs to pump oil and refine it into gasoline.
Much 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. This process is cheaper than the traditional fermentation associated with alcoholic beverages. 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 from South Africa and Saudi Arabia, but there are also large plants in the United States, Europe and Japan. Petroleum derived ethanol (synthetic ethanol) is a widely used industrial solvent and has a considerable variety of other applications, Including use as fuel additive.
Four countries have developed significant bioethanol fuel programs: Brazil, Colombia, China and the United States. Ethanol can be produced from a variety of feedstocks, such as sugar cane, miscanthus, sugar beet, sorghum, switchgrass, barley, hemp, kenaf, (sweet) potatoes, cassava, sunflower, fruit, molasses, whey or skim milk, corn, corn cobs, grain, wheat, wood, paper, straw, cotton, grain sorghum, barley, other biomass, well as many types of cellulose waste. One result of increased use of ethanol is increased demand for the feedstocks such as corn, sugarcane, or switchgrass. Large-scale production of agricultural alcohol for fuel may require substantial amounts of cultivable land with fertile soils and water. This may lead to environmental damage such as deforestation. Ethanol's energy (CH3CH2OH) comes from the carbon-based feedstocks which get their energy from sunlight, water, and photosynthesis.
Ethanol can be produced in different ways, using a variety of feedstocks. Brazil uses sugarcane as primary feedstock, but a large variety of feedstocks are possible. For information on Brazil's method of ethanol production, see ethanol fuel in Brazil.
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, which is a dryland crop which uses much less water than sugarcane and produces food, fuel and fodder from the same piece of land.
Basic steps for dry mill production of ethanol are: refining into starch, liquification and saccharification (hydrolysis of starch into glucose), fermentation, distillation, dehydration, and denaturing (optional). Carbon dioxide, a potentially harmful greenhouse gas, is emitted during fermentation.
Ethanol produced by fermentation results in a solution of ethanol in water. During ethanol fermentation, glucose is evolved into ethanol and carbon dioxide. The equation is:
C6H12O6 → 2 CH3CH2OH + 2 CO2
For the ethanol to be usable as a fuel, water must be removed. The oldest method is distillation, but the purity is limited to 95-96 % due to the formation of a low-boiling water-ethanol azeotrope. The 96% ethanol, 4% 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 2002, almost 5 billion liters (1,3 billion gallons) of hydrated ethyl alcohol fuel were produced in Brazil, to be used in ethanol powered vehicles.
It is not possible to obtain ethanol of purity > 96 % by distilling any more dilute solution. For blending with gasoline, purities of 99.5 to 99.9% are required, depending on temperature, to avoid separation. Currently, the most widely used purification method is a physical adsorption process using molecular sieves.
In the past, when farmers distilled their own ethanol, they sometimes used radiators as part of the still. The radiators often contained lead, which would get into the ethanol. Lead entered the air during the burning of contaminated fuel, possibly leading to neural damage. However this was a relatively minor source of lead since at the time tetraethyl lead was used as a mainstream gasoline additive. Today, ethanol for fuel use is produced almost exclusively from purpose-built plants, avoiding any lead presence.
Biotechnology can help to improve the energetic productions of bioethanol.
Ethanol fuel mixtures
Generally, the higher the ethanol component of a gasohol blend, the lower its suitability for gasoline-powered car engines. Pure ethanol reacts with or dissolves certain rubber and plastic materials and must not be used in unmodified engines. Additionally, pure ethanol has a much higher octane rating (116 AKI, 129 RON) than ordinary gasoline (86/87 AKI, 91/92 RON), requiring changes to the compression ratio or spark timing to obtain maximum benefit.  To change a pure-gasoline-fueled car into a pure-ethanol-fueled car, larger carburetor jets (about 30-40% larger by area) are needed. (Methanol requires an even larger increase in area, to roughly 50% larger.) Ethanol engines also need a cold-starting system to ensure sufficient vaporization for temperatures below 13 °C (55 °F) to maximize combustion and minimize uncombusted nonvaporized ethanol. On the other hand, if 10 to 30% ethanol is mixed with gasoline, no engine modification is typically needed. Many modern cars can run on these mixtures very reliably.
Beginning with the model year 1999, an increasing number of vehicles in the world are manufactured with engines which can run on any gasoline from 0% ethanol up to 85% ethanol without modification. Many light trucks (a class containing minivans, SUVs and pickup trucks) are designed to be dual fuel or flexible fuel vehicles, since they can automatically detect the type of fuel and change the engine's behavior, principally air-to-fuel ratio and ignition timing to compensate for the different octane levels of the fuel in the engine cylinders.
Local production and use of ethanol
Ethanol fuel in Brazil
As of 2004, Brazil was the largest producer and consumer of ethanol fuel in the world. Since the 1980s, Brazil has developed an extensive domestic ethanol fuel industry upon sugarcane production and refining. Brazil produces approximately 4 billion gallons of ethanol per year. Ethanol factories in Brazil maintain a positive (+34%) energy balance by burning the non-sugar waste from sugarcane. The development of ethanol in Brazil was sponsored by its government. All gasoline in Brazil must be at least 20%~25% alcohol. Brazil can make ethanol for about $1.00 per gallon. Newer cars in Brazil are flexible fuel vehicles, or they are able to burn pure ethanol instead of gasoline. Ethanol fuel in Brazil has decreased the country's dependence on oil, increased air quality, and provided useful byproducts to generate electricity.
Ethanol fuel in Colombia
Colombia’s fuel ethanol program got a start in 2002 when the government passed a law which mandates oxygen enrichment of gasoline. This was initially done to reduce carbon monoxide emissions from cars. Later regulations exempted biomass-derived ethanol from some taxes on gasoline, thus making ethanol cheaper than gasoline. This trend was reinforced when petroleum prices went up starting in 2004 and with it the interest in renewable fuels (at least for cars). In Colombia the price of both gasoline and ethanol are controlled by the government. Complementing this ethanol program is a biodiesel program to oxygenate diesel fuel and produce a renewable fuel from vegetable oil.
Initially all the interest in ethanol production has come from the existing sugar industry, as it is relatively easy to add an ethanol back end to a sugar mill and the energy usage is similar to that needed to produce sugar. The government aims to gradually convert the nation’s auto fuel supplies to a mixture of 10 percent ethanol and 90 percent gasoline. Ethanol plants are being encouraged by tax breaks. There has been interest in ethanol plants from yuca (cassava) and from new sugar cane plantations, but producing inexpensive carbohydrates has not been achieved.
The first fuel ethanol plant in Colombia began production in October 2005, with output of 300,000 liters a day in the Cauca region. By March 2006 five plants, all in the Cauca Valley, are operational with a combined capacity of 1,050,000 liters per day or 357 million liters per year. In the Cauca Valley of Colombia sugar is harvested year round and the new distilleries have very high availability. The total investment in these plants is $100 million. By , Colombia hopes to have a capacity of 2,500,000 liters per day, which is the requirement for adding 10% ethanol to the gasoline. The ethanol fuel produced is currently used in the main cities close to the Cauca Valley, such as Bogota, Cali, and Pereira. There is not enough production for the rest of the country.
Ethanol fuel in the United States
Ethanol use and production in the United States is steadily increasing. Archers Daniels Midland claims to be the largest producer of fuel ethanol in the US. As gasoline prices continue to increase, ethanol may become a more profitable alternative to gasoline. Roughly 685 gas stations, out of a total of 165,000 carry E85 pumps. Ethanol is predominantly only available in the Midwest and California, where most ethanol is refined. As of June 19, 2006 in the US, there are 4.8 billion gallons (18.17 million m³) per year capacity for ethanol production with capacity of 2.22 billion gallons (8.4 million m³) per year under construction.  For example, the U.S. company Pacific Ethanol is currently building more ethanol facilities in the western U.S.
Regulations and subsidies
In Brazil, Colombia and the United States, the use of ethanol from sugar cane and grain as car fuel has been heavily promoted by government programs. Some individual U.S. states in the corn belt began subsidizing ethanol from corn (maize) after the Arab oil embargo of 1973. The Energy Tax Act of 1978 authorized an excise tax exemption for biofuels, chiefly gasohol. The excise tax exemption alone has been estimated as worth US$1.4 billion per year. Another U.S. federal program guaranteed loans for the construction of ethanol plants, and in 1986 the U.S. even gave ethanol producers free corn. Colombia's ethanol program was started by a law which would exempt biomass-derived ethanol from some taxes on gasoline.
In August 2005, President Bush signed a comprehensive energy bill which included a requirement to increase the production of ethanol and biodiesel from 4 to 7.5 billion US gallons (15 to 28 million m³) within the next ten years. It is expected that in the short term the majority of this increase will come from ethanol produced from corn.
Directive 2003/30/EC of the European Parliament promotes the replacement of fossil fuels by biofuels: amongst them bio-ethanol to be blended into petrol. The United Kingdom has adopted a national policy of encouraging the use of biofuels including ethanol, although the taxation of alternative fuels like biodiesel is almost as onerous as that on conventional fossil fuels..
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 (1292 degrees 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.
Ethanol fuel energy balance
For ethanol to contribute significantly to transportation fuel needs, it would need to have a positive net energy balance. To evaluate the net energy of ethanol, four variables must be considered: the amount of energy contained in the final ethanol product, the amount of energy directly consumed to make the ethanol (such as the diesel used in tractors), the quality of the resulting ethanol compared to the quality of refined gasoline and the energy indirectly consumed (in order to make the ethanol processing plant, etc). Although a topic of debate, some research that ignores energy quality suggests it takes as much or more fossil fuel energy (in the forms of diesel, natural gas and coal) to create an equivalent amount of energy in the form of ethanol. In other words, the energy needed to run the tractors, produce the fertilizer, process the ethanol, and the energy associated with the wear and tear on all of the equipment used in the process (known as fixed asset depreciation to economists) may be more than the energy derived from burning ethanol. Two important flaws are cited in response to that argument. First, the energy quality is ignored, the economic effects of which are large. Principal economic effects of energy quality comparison are the cleanup costs of soil contamination stemming from gasoline releases to the environment and medical costs from air pollution resulting from refining and burning gasoline. The second point is that the inclusion of development of ethanol plants instills a bias against that product based strictly upon the pre-existence of gasoline refining capacity. The real decision should be based upon the long-term economic and social returns. The first counter-argument, however, is contested. Burning a gallon of cleaner ethanol is still pointless if it implicitly requires burning two gallons of dirty gasoline to create that ethanol in the first place. New techniques for producing ethanol from plant cellulose (cellulosic ethanol) create more ethanol per unit of energy input, and may fundamentally shift production to a positive energy balance when they reach economies of scale. Cellulosic ethanol can also be created from farm residue such as wheat straw, further defraying the energy costs of production.
Compared with conventional unleaded gasoline, ethanol is a clean burning fuel source that combusts cleanly 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. As a fuel additive, ethanol being more volatile, carries with it gasoline as it evaporates, thus releasing more Volatile organic compounds (VOCs).
Pure usage of ethanol rather than gasoline in your vehicle reduces its total carbon dioxide emissions, mile for mile, by about 13%. This is in part due to the agricultural processing needed to create the biofuel itself produces certain CO emissions.
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 at a much 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..
Ethanol is considered "renewable" because it is primarily the result of conversion of the sun's energy into usable energy. Current estimates are that the sun will be a usable source of energy for several billion years. Oil production, however, is predicted to peak between 2021 and 2112 . 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 must be considered carefully as to viability/suitability as a renewable energy source. The degree to which its energy balance is positive is a factor determining how favourable it might be as a replacement for fossil fuels. For example, one study critical of ethanol assumes massive use of pesticides and fertilizers; in fact, corn grown for fuel would not need the same pesticide usage, since consumer reaction to corn as a food (not crop productivity) is the main reason for prolific pesticide applications.
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 and other crops 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 the for every unit of energy put towards ethanol production, 1.3 units are returned. 
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.
Dependency on foreign oil
A somewhat related argument is that developed regions like the United States and Europe, and increasingly the developing nations of Asia, mainly India and China, consume much more fossil fuels than they can extract from their territory, becoming dependent upon foreign suppliers as a result. As of 2006 the energy policy of the United Kingdom recognizes it has become a net primary energy importer and is seeking increased foreign sources; near term targets are natural gas import from Norway. Even if the energy balance is negative, US production involves mostly domestic fuels such as natural gas and coal, so the impact on oil importation is still positive.