Ethanol is a monohydric primary alcohol. It melts at -117.3°C; and boils at 78.5°C;. It is miscible (i.e., mixes without separation) with water in all proportions and is separated from water only with difficulty; ethanol that is completely free of water is called absolute ethanol. Ethanol forms a constant-boiling mixture, or azeotrope, with water that contains 95% ethanol and 5% water and that boils at 78.15°C;; since the boiling point of this binary azeotrope is below that of pure ethanol, absolute ethanol cannot be obtained by simple distillation. However, if benzene is added to 95% ethanol, a ternary azeotrope of benzene, ethanol, and water, with boiling point 64.9°C;, can form; since the proportion of water to ethanol in this azeotrope is greater than that in 95% ethanol, the water can be removed from 95% ethanol by adding benzene and distilling off this azeotrope. Because small amounts of benzene may remain, absolute ethanol prepared by this process is poisonous.
Ethanol burns in air with a blue flame, forming carbon dioxide and water. It reacts with active metals to form the metal ethoxide and hydrogen, e.g., with sodium it forms sodium ethoxide. It reacts with certain acids to form esters, e.g., with acetic acid it forms ethyl acetate. It can be oxidized to form acetic acid and acetaldehyde. It can be dehydrated to form diethyl ether or, at higher temperatures, ethylene.
Ethanol is the alcohol of beer, wines, and liquors. It can be prepared by the fermentation of sugar (e.g., from molasses), which requires an enzyme catalyst that is present in yeast; or it can be prepared by the fermentation of starch (e.g., from corn, rice, rye, or potatoes), which requires, in addition to the yeast enzyme, an enzyme present in an extract of malt. The concentration of ethanol obtained by fermentation is limited to about 10% (20 proof) since at higher concentrations ethanol inhibits the catalytic effect of the yeast enzyme. (The proof concentration of an alcoholic beverage is numerically double the percentage concentration.) For nonbeverage uses ethanol is more commonly prepared by passing ethylene gas at high pressure into concentrated sulfuric or phosphoric acid to form the corresponding ester; the acid-ester mixture is diluted with water and heated, forming ethanol by hydrolysis, and the alcohol is then removed from the mixture by distillation, usually with steam.
Ethanol is used extensively as a solvent in the manufacture of varnishes and perfumes; as a preservative for biological specimens; in the preparation of essences and flavorings; in many medicines and drugs; as a disinfectant and in tinctures (e.g., tincture of iodine); and as a fuel and gasoline additive (see gasohol). Many U.S. automobiles manufactured since 1998 have been equipped to enable them to run on either gasoline or E85, a mixture of 85% ethanol and 15% gasoline. E85, however, is not yet widely available. Denatured, or industrial, alcohol is ethanol to which poisonous or nauseating substances have been added to prevent its use as a beverage; a beverage tax is not charged on such alcohol, so its cost is quite low. Medically, ethanol is a soporific, i.e., sleep-producing; although it is less toxic than the other alcohols, death usually occurs if the concentration of ethanol in the bloodstream exceeds about 5%. Behavioral changes, impairment of vision, or unconsciousness occur at lower concentrations. See alcoholism.
Organic compound, most important of the alcohols, chemical formula CH3CH2OH. Produced by fermentation, it is the intoxicating ingredient in alcoholic beverages. Ethanol for industrial purposes is made by either fermentation or chemical synthesis, then purified by distillation and, to avoid the tax levied on ethyl alcohol for drinking, made unfit to drink (see denaturation) by mixing it with compounds such as methanol, benzene, or kerosene. Ethanol has many uses as a solvent, a raw material, an extraction medium, an antifreeze, an antiseptic, and a gasoline additive and substitute. It is toxic, depressing the central nervous system, and addictive to some persons (see alcoholism). Moderate amounts depress the inhibitory activities of the brain and so appear to stimulate the mind, but larger amounts seriously impair coordination and judgment; excessive consumption can cause coma and death. Taking ethanol in combination with barbiturates or related drugs is especially dangerous.
Learn more about ethanol with a free trial on Britannica.com.
| Section8 = }}
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in thermometers. In common usage, it is often referred to simply as alcohol.
Ethanol is abbreviated as EtOH, using the common organic chemistry notation of representing the ethyl group (C2H5) with Et. This designation is used both by EMS and Hospital ER staff when describing alcohol intoxication, and is found in most chemistry textbooks as well.
Ethanol is a straight-chain alcohol, and its molecular formula is C2H5OH. An alternative notation is CH3-CH2-OH, which indicates that the carbon of a methyl group (CH3-) is attached to the carbon of a methylene group (-CH2-), which is attached to the oxygen of a hydroxyl group (-OH).
Except for use of fire, the fermentation of sugar into ethanol is the earliest organic reaction known to humanity. The intoxicating effects of ethanol consumption have been known since ancient times. In modern times, ethanol intended for industrial use is also produced from by-products of petroleum refining.
Ethanol has widespread use as a solvent of substances intended for human contact or consumption, including scents, flavorings, colorings, and medicines. In chemistry, it is both an essential solvent and a feedstock for the synthesis of other products. It has a long history as a fuel for heat and light and also as a fuel for internal combustion engines.
Ethanol has been used by humans since prehistory as the intoxicating ingredient of alcoholic beverages. Dried residues on 9000-year-old pottery found in China imply that alcoholic beverages were used even among Neolithic people. Its isolation as a relatively pure compound was first achieved by Persian alchemist, Zakarīya Rāzi (Rhazes), who was renowned for his perfected methods of distillation and extraction. Other chemists who contributed to the development of distillation techniques during the Abbasid caliphate, other than Razi, include Jabir ibn Hayyan (Geber) and Al-Kindi (Alkindus).
Writings attributed to Jabir ibn Hayyan (721–815) mention the flammable vapors of boiled wine. Al-Kindi (801–873) unambiguously described the distillation of wine.
In 1796, Johann Tobias Lowitz obtained pure ethanol by filtering distilled ethanol through activated charcoal.
Antoine Lavoisier described ethanol as a compound of carbon, hydrogen, and oxygen, and in 1808 Nicolas-Théodore de Saussure determined ethanol's chemical formula. Fifty years later, Archibald Scott Couper published the structural formula of ethanol, which placed ethanol among the first chemical compounds to have their chemical structure determined.
Ethanol was first prepared synthetically in 1826 through the independent efforts of Henry Hennel in Great Britain and S.G. Sérullas in France. In 1828, Michael Faraday prepared ethanol by acid-catalyzed hydration of ethylene, a process similar to that which is used today for industrial ethanol synthesis.
Ethanol was used as lamp fuel in the United States as early as 1840, but a tax levied on industrial alcohol during the Civil War made this use uneconomical. This tax was repealed in 1906, and from 1908 onward Ford Model T automobiles could be adapted to run on ethanol. With the advent of Prohibition in 1920 though, sellers of ethanol fuel were accused of being allied with moonshiners, and ethanol fuel again fell into disuse until late in the 20th century.
Ethanol is a volatile, flammable, colorless liquid that has a strong characteristic odor. It burns with a smokeless blue flame that is not always visible in normal light.
The physical properties of ethanol stem primarily from the presence of its hydroxyl group and the shortness of its carbon chain. Ethanol’s hydroxyl group is able to participate in hydrogen bonding, rendering it more viscous and less volatile than less polar organic compounds of similar molecular weight.
Ethanol is a versatile solvent, miscible with water and with many organic solvents, including acetic acid, acetone, benzene, carbon tetrachloride, chloroform, diethyl ether, ethylene glycol, glycerol, nitromethane, pyridine, and toluene. It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides such as trichloroethane and tetrachloroethylene.
Ethanol’s miscibility with water contrasts with that of longer-chain alcohols (five or more carbon atoms), whose water miscibility decreases sharply as the number of carbons increases.
Hydrogen bonding causes pure ethanol to be hygroscopic to the extent that it readily absorbs water from the air. The polar nature of the hydroxyl group causes ethanol to dissolve many ionic compounds, notably sodium and potassium hydroxides, magnesium chloride, calcium chloride, ammonium chloride, ammonium bromide, and sodium bromide. Sodium and potassium chlorides are slightly soluble in ethanol. Because the ethanol molecule also has a nonpolar end, it will also dissolve nonpolar substances, including most essential oils and numerous flavoring, coloring, and medicinal agents.
Two unusual phenomena are associated with mixtures of ethanol and water. Ethanol-water mixtures have less volume than the sum of their individual components. Mixing equal volumes of ethanol and water results in only 1.92 volumes of mixture. The addition of even a few percent of ethanol to water sharply reduces the surface tension of water. This property partially explains the “tears of wine” phenomenon. When wine is swirled in a glass, ethanol evaporates quickly from the thin film of wine on the wall of the glass. As the wine’s ethanol content decreases, its surface tension increases and the thin film “beads up” and runs down the glass in channels rather than as a smooth sheet.
Mixtures of ethanol and water that contain more than about 50% ethanol are flammable and easily ignited. An alcohol stove has been developed in India which runs on 50% ethanol/water mixture. Alcoholic proof is a widely used measure of how much ethanol (i.e., alcohol) such a mixture contains. In the 18th century, proof was determined by adding a liquor (such as rum) to gunpowder. If the gunpowder still just exploded, that was considered to be “100 degrees proof” that it was “good” liquor — hence it was called “100 degrees proof.”
Ethanol-water solutions that contain less than 50% ethanol may also be flammable if the solution is first heated. Some cooking methods call for wine to be added to a hot pan, causing it to flash boil into a vapor, which is then ignited to burn off excess alcohol.
Ethanol is slightly more refractive than water, having a refractive index of 1.36242 (at λ=589.3 nm and 18.35 °C).
The chemistry of ethanol is largely that of its hydroxyl group.
Ethanol's hydroxyl causes the molecule to be slightly basic. It is however,so very slightly basic it is almost neutral, like pure water. The pH of 100% ethanol is 7.33, compared to 7.00 for pure water. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH3CH2O−), by reaction with an alkali metal such as sodium:
or a very strong base such as sodium hydride:
This reaction is not possible in an aqueous solution, as water is more acidic, so that hydroxide is preferred over ethoxide formation.
Ethyl halides can also be produced by reacting ethanol with more specialized halogenating agents, such as thionyl chloride for preparing ethyl chloride, or phosphorus tribromide for preparing ethyl bromide.
For this reaction to produce useful yields it is necessary to remove water from the reaction mixture as it is formed.
Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate, prepared by reacting ethanol with sulfuric and phosphoric acid respectively, are both useful ethylating agents in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely-used diuretic.
Which product, diethyl ether or ethylene, predominates depends on the precise reaction conditions.
The direct oxidation of ethanol to acetic acid using chromic acid is given below.
The oxidation product of ethanol, acetic acid, is spent as nutrient by the human body as acetyl CoA, where the acetyl group can be spent as energy or used for biosynthesis.
Ethanol is produced both as a petrochemical, through the hydration of ethylene, and biologically, by fermenting sugars with yeast. Which process is more economical is dependent upon the prevailing prices of petroleum and of grain feed stocks.
The catalyst is most commonly phosphoric acid, adsorbed onto a porous support such as diatomaceous earth or charcoal. This catalyst was first used for large-scale ethanol production by the Shell Oil Company in 1947. The reaction is carried out with an excess of high pressure steam at 300°C.
In an older process, first practiced on the industrial scale in 1930 by Union Carbide, but now almost entirely obsolete, ethylene was hydrated indirectly by reacting it with concentrated sulfuric acid to produce ethyl sulfate, which was then hydrolyzed to yield ethanol and regenerate the sulfuric acid:
Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel, is produced by fermentation. When certain species of yeast, most importantly, Saccharomyces cerevisiae, metabolize sugar in the absence of oxygen, they produce ethanol and carbon dioxide. The chemical equation below summarizes the conversion:
The process of culturing yeast under conditions to produce alcohol is called fermentation. Ethanol's toxicity to yeast limits the ethanol concentration obtainable by brewing. The most ethanol-tolerant strains of yeast can survive up to approximately 15% ethanol by volume.
In order to produce ethanol from starchy materials such as cereal grains, the starch must first be converted into sugars. In brewing beer, this has traditionally been accomplished by allowing the grain to germinate, or malt, which produces the enzyme, amylase. When the malted grain is mashed, the amylase converts the remaining starches into sugars. For fuel ethanol, the hydrolysis of starch into glucose can be accomplished more rapidly by treatment with dilute sulfuric acid, fungally produced amylase, or some combination of the two.
Sugars for ethanol fermentation can be obtained from cellulose. Until recently, however, the cost of the cellulase enzymes capable of hydrolyzing cellulose has been prohibitive. The Canadian firm Iogen brought the first cellulose-based ethanol plant on-stream in 2004. Its primary consumer so far has been the Canadian government, which, along with the United States Department of Energy, has invested heavily in the commercialization of cellulosic ethanol. Deployment of this technology could turn a number of cellulose-containing agricultural by-products, such as corncobs, straw, and sawdust, into renewable energy resources. Other enzyme companies are developing genetically engineered fungi that produce large volumes of cellulase, xylanase, and hemicellulase enzymes. These would convert agricultural residues such as corn stover, wheat straw, and sugar cane bagasse and energy crops such as switchgrass into fermentable sugars.
Cellulose-bearing materials typically also contain other polysaccharides, including hemicellulose. When hydrolyzed, hemicellulose decomposes into mostly five-carbon sugars such as xylose. S. cerevisiae, the yeast most commonly used for ethanol production, cannot metabolize xylose. Other yeasts and bacteria are under investigation to ferment xylose and other pentoses into ethanol.
On January 14, 2008, General Motors announced a partnership with Coskata, Inc. The goal is to produce cellulosic ethanol cheaply, with an eventual goal of US$1 per U.S. gallon ($0.30/L) for the fuel. The partnership plans to begin producing the fuel in large quantity by the end of 2008. By 2011 a full-scale plant will come on line, capable of producing 50 to 100 million gallons of ethanol a year (200–400 ML/a).
The anaerobic bacterium Clostridium ljungdahlii, recently discovered in commercial chicken wastes, can produce ethanol from single-carbon sources including synthesis gas, a mixture of carbon monoxide and hydrogen that can be generated from the partial combustion of either fossil fuels or biomass. Use of these bacteria to produce ethanol from synthesis gas has progressed to the pilot plant stage at the BRI Energy facility in Fayetteville, Arkansas.
Another prospective technology is the closed-loop ethanol plant. Ethanol produced from corn has a number of critics who suggest that it is primarily just recycled fossil fuels because of the energy required to grow the grain and convert it into ethanol. There is also the issue of competition with use of corn for food production. However, the closed-loop ethanol plant attempts to address this criticism. In a closed-loop plant, the energy for the distillation comes from fermented manure, produced from cattle that have been fed the by-products from the distillation. The leftover manure is then used to fertilize the soil used to grow the grain. Such a process is expected to lower the fossil fuel consumption used during conversion to ethanol by 75%. Although energy can be created from the collection of methane from livestock manure, this can be mutually exclusive to the production of ethanol and should not be tagged on to it to make ethanol production seem more efficient or enviromentally friendly.
Though in an early stage of research, there is some development of alternative production methods that use feed stocks such as municipal waste or recycled products, rice hulls, sugarcane bagasse, small diameter trees, wood chips, and switchgrass.
Breweries and biofuel plants employ two methods for measuring ethanol concentration. Infrared ethanol sensors measure the vibrational frequency of dissolved ethanol using the CH band at 2900 cm−1. This method uses a relatively inexpensive solid state sensor that compares the CH band with a reference band to calculate the ethanol content. The calculation makes use of the Beer-Lambert law. Alternatively, by measuring the density of the starting material and the density of the product, using a hydrometer, the change in specific gravity during fermentation indicates the alcohol content. This inexpensive and indirect method has a long history in the beer brewing industry.
In one common industrial method to obtain absolute alcohol, a small quantity of benzene is added to rectified spirit and the mixture is then distilled. Absolute alcohol is obtained in the third fraction, which distills over at 78.3 °C (351.4 K). Because a small amount of the benzene used remains in the solution, absolute alcohol produced by this method is not suitable for consumption, as benzene is carcinogenic.
There is also an absolute alcohol production process by desiccation using glycerol. Alcohol produced by this method is known as spectroscopic alcohol—so called because the absence of benzene makes it suitable as a solvent in spectroscopy.
Other methods for obtaining absolute ethanol include desiccation using adsorbents such as starch or zeolites, which adsorb water preferentially, as well as azeotropic distillation and extractive distillation.
Pure ethanol and alcoholic beverages are heavily taxed, but ethanol has many uses that do not involve consumption by humans. To relieve the tax burden on these uses, most jurisdictions waive the tax when an agent has been added to the ethanol to render it unfit to drink. These include bittering agents such as denatonium benzoate and toxins such as methanol, naphtha, and pyridine. Products of this kind are called denatured alcohol.
Pure ethanol is classed as 200 proof in the USA, equivalent to 175 degrees proof in the UK system.
|Energy content of some fuels compared with ethanol:|
|Fuel type||MJ/L||MJ/kg|| Research|
|Liquefied natural gas||25.3||~55|
(60% Propane + 40% Butane)
(high-octane gasoline, not jet fuel)
(90% gasoline + 10% ethanol)
|Regular Gasoline||34.8||44.4||min. 91|
|Premium Gasoline||max. 95|
The largest single use of ethanol is as a motor fuel and fuel additive. The largest national fuel ethanol industries exist in Brazil (gasoline sold in Brazil contains at least 25% ethanol and anhydrous ethanol is also used as fuel in more than 90% of new cars sold in the country). The Brazilian production of ethanol is praised for the high carbon sequestration capabilities of the sugar cane plantations, thus making it a real option to combat climate change.
Henry Ford designed the first mass-produced automobile, the famed Model T Ford, to run on pure anhydrous (ethanol) alcohol—he said it was "the fuel of the future". Today, however, 100% pure ethanol is not approved as a motor vehicle fuel in the U.S. Added to gasoline, ethanol reduces ground-level ozone formation by lowering volatile organic compound and hydrocarbon emissions, decreasing carcinogenic benzene, and butadiene, emissions, and particulate matter emissions from gasoline combustion.
Combustion of ethanol in an internal combustion engine yields many of the products of incomplete combustion that are produced by gasoline and significantly larger amounts of formaldehyde and related species such as formalin, acetaldehyde, etc.. This leads to a significantly larger photochemical reactivity that generates much more ground level ozone. This data has been assembled into The Clean Fuels Report comparison of fuel emissions and shows that ethanol exhaust generates 2.14 times as much ozone as does gasoline exhaust. When this is added into the custom "Localised Pollution Index (LPI)" of The Clean Fuels Report the local pollution, i.e. that which contributes to smog, is 1.7 on a scale where gasoline is 1.0 and higher numbers signify greater pollution. This issue has been formalised by the California Air Resouces Board in 2008 by recognising control standards for formaldehydes et al as an emissions control group much like the conventional NOx and Reactive Organic Gases (ROGs).
Prior to the development of electronic fuel injection (EFI) and computerized engine management, the lower energy content of ethanol required that the engine carburetor be rejetted to permit a larger volume of fuel to mix with the intake air. EFI is able to actively compensate for varying fuel energy densities by monitoring the oxygen content of exhaust gases. However, a standard EFI gasoline engine can typically only tolerate up to 10% ethanol and 90% gasoline. Higher ethanol ratios require either larger-volume fuel injectors or an increase in fuel rail pressure to deliver the greater liquid volume needed to equal the energy content of pure gasoline.
World production of ethanol in 2006 was , with 69% of the world supply coming from Brazil and the United States. More than 20% of the Brazilian fleet of cars on the streets are able to use 100% ethanol as fuel, which includes ethanol-only engines and flex-fuel engines. Flex-fuel engines in Brazil are able to work with all ethanol, all gasoline or any mixture of both. In the US flex-fuel vehicles can run on 0% to 85% ethanol (15% gasoline) since higher ethanol blends are not yet allowed. Brazil supports this population of ethanol-burning automobiles with large national infrastructure that produces ethanol from domestically grown sugar cane. Sugar cane not only has a greater concentration of sucrose than corn (by about 30%), but is also much easier to extract. The bagasse generated by the process is not wasted, but is utilized in power plants as a surprisingly efficient fuel to produce electricity.
The United States fuel ethanol industry is based largely on corn. According to the Renewable Fuels Association, as of October 30, 2007, 131 grain ethanol bio-refineries in the United States have the capacity to produce 7.0 billion US gallons (26 GL) of ethanol per year. An additional 72 construction projects underway (in the U.S.) can add 6.4 billion gallons of new capacity in the next 18 months. Over time, it is believed that a material portion of the ~150 billion gallon per year market for gasoline will begin to be replaced with fuel ethanol.
The Energy Policy Act of 2005 requires that 4 billion gallons of "renewable fuel" be used in 2006 and this requirement will grow to a yearly production of 7.5 billion gallons by 2012. In the United States, ethanol is most commonly blended with gasoline as a 10% ethanol blend nicknamed "gasohol". This blend is widely sold throughout the U.S. Midwest, and in cities required by the 1990 Clean Air Act to oxygenate their gasoline during the winter. Ethanol and isobutene are also the feedstocks for ethyl tert-butyl ether (ETBE), an oxygenate antiknock additive. The use of ethanol makes ETBE partially a biofuel, but also more expensive than the similar additive methyl tert-butyl ether (MTBE), made from methanol and isobutene.
Michael Grunwald reports that one person could be fed 365 days "on the corn needed to fill an ethanol-fueled SUV". He further reports that though "hyped as an eco-friendly fuel, ethanol increases global warming, destroys forests and inflates food prices." Environmentalists, livestock farmers, and opponents of subsidies say that increased ethanol production won't meet energy goals and may damage the environment, while at the same time causing worldwide food prices to soar. Some of the controversial subsidies in the past have included more than $10 billion to Archer-Daniels-Midland since 1980. Critics also speculate that as ethanol is more widely used, changing irrigation practices could greatly increase pressure on water resources. In October 2007, 28 environmental groups decried the Renewable Fuels Standard (RFS), a legislative effort intended to increase ethanol production, and said that the measure will "lead to substantial environmental damage and a system of biofuels production that will not benefit family farmers...will not promote sustainable agriculture and will not mitigate global climate change."
Recent articles have also blamed subsidized ethanol production for the nearly 200% increase in milk prices since 2004, although that is disputed by some. Especially since the price of fuel has driven up the costs to cultivate, grow, harvest, ship, refine, bring to market, etc, all commodities including; but not limited to, milk. Not to mention the presence of speculators, and the recent growing interest in the commodities market by investors who have been scared away from a falling stock market.
Ethanol production uses the starch portion of corn, but the leftover protein can be used to create a high-nutrient, low-cost animal feed.
In 2007 the United Nations' independent expert on the right to food, called for a five-year moratorium on biofuel production from food crops, to allow time for development of non-food sources. He called recent increases in food costs because of fuel production, such as the quadrupling of world corn price in one year, a growing "catastrophe" for the poor. In February 2007, riots occurred in Mexico because of the skyrocketing price of tortillas. Ethanol has been credited as the reason for this increase in food prices. The demand for corn has had a rippling effect on many corn-based products, like tortillas. The effects of ethanol and the increasing cost of food have also been felt in Pakistan, Indonesia, and Egypt.
Oil has historically had a much higher EROEI than corn produced ethanol, according to some. However, oil must be refined into gasoline before it can be used for automobile fuel. Refining, as well as exploration and drilling, consumes energy. The difference between the energy in the fuel (output energy) and the energy needed to produce it (input energy) is often expressed as a percent of the input energy and called net energy gain (or loss). Several studies released in 2002 estimated that the net energy gain for corn ethanol is between 21 and 34 percent. The net energy loss for MTBE is about 33 percent. When added to gasoline, ethanol can replace MTBE as an anti-knock agent without poisoning drinking water as MTBE does. In Brazil, where the broadest and longest ethanol producing experiment took place, improvements in agricultural practices and ethanol production improvements led to an increase in ethanol net energy gain from 300% to over 800% in recent years. It must be noted that Brazil produces ethanol more efficiently because its primary input is the sugar from sugar cane rather than starches from corn. Consuming known oil reserves is increasing oil exploration and drilling energy consumption which is reducing oil EROEI (and energy balance) further.
Opponents claim that corn ethanol production does not result in a net energy gain or that the consequences of large scale ethanol production to the food industry and environment offset any potential gains from ethanol. It has been estimated that "if every bushel of U.S. corn, wheat, rice and soybean were used to produce ethanol, it would only cover about 4% of U.S. energy needs on a net basis. Many of the issues raised could likely be fixed by techniques now in development that produce ethanol from agricultural waste, such as paper waste, switchgrass, and other materials, but EIA Forecasts Significant Shortfall in Cellulosic Biofuel Production Compared to Target Set by Renewable Fuel Standard.
Proponents cite the potential gains to the U.S. economy both from domestic fuel production and increased demand for corn. Optimistic calculations project that the United States is capable of producing enough ethanol to completely replace gasoline consumption. In comparison, Brazil's ethanol consumption today covers more than 50% of all energy used by vehicles in that country.
In the United States, preferential regulatory and tax treatment of ethanol automotive fuels introduces complexities beyond its energy economics alone. North American automakers have in 2006 and 2007 promoted a blend of 85% ethanol and 15% gasoline, marketed as E85, and their flex-fuel vehicles, e.g. GM's " Live Green, Go Yellow" campaign. The apparent motivation is the nature of U.S. Corporate Average Fuel Economy (CAFE) standards, which give an effective 54% fuel efficiency bonus to vehicles capable of running on 85% alcohol blends over vehicles not adapted to run on 85% alcohol blends. In addition to this auto manufacturer-driven impetus for 85% alcohol blends, the United States Environmental Protection Agency had authority to mandate that minimum proportions of oxygenates be added to automotive gasoline on regional and seasonal bases from 1992 until 2006 in an attempt to reduce air pollution, in particular ground-level ozone and smog. In the United States, incidents of methyl tert(iary)-butyl ether (MTBE) groundwater contamination have been recorded in the majority of the 50 states, and the State of California's ban on the use of MTBE as a gasoline additive has further driven the more widespread use of ethanol as the most common fuel oxygenate.
A February 7, 2008 Associated Press article stated, "The widespread use of ethanol from corn could result in nearly twice the greenhouse gas emissions as the gasoline it would replace because of expected land-use changes, researchers concluded Thursday. The study challenges the rush to biofuels as a response to global warming.
One acre of land can yield about 7,110 pounds (3,225 kg) of corn, which can be processed into 328 gallons (1240.61 liters) of ethanol. That is about 26.1 pounds (11.84 kg) of corn per gallon.
Much overlooked in most discussions about ethanol from corn are the by-products from the production of ethanol. Depending on the way it is processed, the processing yields several beneficial products, some of which are used for food production and feedstocks.
Alcoholic beverages vary considerably in their ethanol content and in the foodstuffs from which they are produced. Most alcoholic beverages can be broadly classified as fermented beverages, beverages made by the action of yeast on sugary foodstuffs, or as distilled beverages, beverages whose preparation involves concentrating the ethanol in fermented beverages by distillation. The ethanol content of a beverage is usually measured in terms of the volume fraction of ethanol in the beverage, expressed either as a percentage or in alcoholic proof units.
Fermented beverages can be broadly classified by the foodstuff from which they are fermented. Beers are made from cereal grains or other starchy materials, wines and ciders from fruit juices, and meads from honey. Cultures around the world have made fermented beverages from numerous other foodstuffs, and local and national names for various fermented beverages abound.
Distilled beverages are made by distilling fermented beverages. Broad categories of distilled beverages include whiskeys, distilled from fermented cereal grains; brandies, distilled from fermented fruit juices, and rum, distilled from fermented molasses or sugarcane juice. Vodka and similar neutral grain spirits can be distilled from any fermented material (grain or potatoes are most common); these spirits are so thoroughly distilled that no tastes from the particular starting material remain. Numerous other spirits and liqueurs are prepared by infusing flavors from fruits, herbs, and spices into distilled spirits. A traditional example is gin, which is created by infusing juniper berries into a neutral grain alcohol.
In a few beverages, ethanol is concentrated by means other than distillation. Applejack is traditionally made by freeze distillation, by which water is frozen out of fermented apple cider, leaving a more ethanol-rich liquid behind. Eisbier (more commonly, eisbock) is also freeze-distilled, with beer as the base beverage. Fortified wines are prepared by adding brandy or some other distilled spirit to partially-fermented wine. This kills the yeast and conserves some of the sugar in grape juice; such beverages are not only more ethanol-rich, but are often sweeter than other wines.
Alcoholic beverages are sometimes used in cooking, not only for their inherent flavors, but also because the alcohol dissolves hydrophobic flavor compounds which water cannot.
Ethanol is an important industrial ingredient and has widespread use as a base chemical for other organic compounds. These include ethyl halides, ethyl esters, diethyl ether, acetic acid, butadiene, and ethyl amines.
|50||Euphoria, talkativeness, relaxation|
|100||Central nervous system depression, impaired motor and sensory function, impaired cognition|
|>140||Decreased blood flow to brain|
|300||Stupefaction, possible unconsciousness|
The amount of ethanol in the body is typically quantified by blood alcohol content (BAC), the milligrams of ethanol per 100 milliliters of blood. The table at right summarizes the symptoms of ethanol consumption. Small doses of ethanol generally produce euphoria and relaxation; people experiencing these symptoms tend to become talkative and less inhibited, and may exhibit poor judgment. At higher dosages (BAC > 100 mg/dl), ethanol acts as a central nervous system depressant, producing at progressively higher dosages, impaired sensory and motor function, slowed cognition, stupefaction, unconsciousness, and possible death.
In America, about half of the deaths in car accidents occur in alcohol-related crashes. There is no completely-safe level of alcohol for driving; the risk of a fatal car accident rises with the level of alcohol in the driver's blood. However, most drunk driving laws governing the acceptable levels in the blood while driving or operating heavy machinery set typical upper limits of blood alcohol content (BAC) between 0.05% to 0.08%.
Ethanol is not a carcinogen. However, the first metabolic product of ethanol, acetaldehyde, is toxic, mutagenic, and carcinogenic. Also, ethanol's effect on the liver can contribute to immune suppression. Consequently, consumption of alcoholic beverages can be an aggravating factor in carcinogenesis.