Ethanol

Ethanol /ˈɛθənɒl/, also commonly called alcohol, ethyl alcohol, and drinking alcohol, is the principal type of alcohol found inalcoholic beverages, produced by the fermentation of sugars by yeasts. It is a neurotoxic, psychoactive drug, and one of the oldest recreational drugs. It can cause alcohol intoxication when consumed in sufficient quantity.

Ethanol is a volatile, flammable, colorless liquid with a slight chemical odor. It is used as an antiseptic, a solvent, a fuel, and due to its low freezing point, the active fluid in many alcohol thermometers. The molecule is a simple one, being an ethyl group linked to ahydroxyl group. Its structural formula, CH3CH2OH, is often abbreviated as C2H5OH, C2H6O or EtOH.

The stem word “eth-” used in many related compounds originates with the German word for ethanol (äthyl).

Etymology

Ethanol is the systematic name defined by the International Union of Pure and Applied Chemistry (IUPAC) for a molecule with two carbon atoms (prefix “eth-“), having a single bond between them (suffix “-ane”), and an attached functional group-OH group (suffix “-ol”).

The prefix ethyl was coined in 1834 by the German chemist Justus Liebig.Ethyl is a contraction of the Ancient Greek αἰθήρ (aithḗr, “upper air”) and the Greek word ύλη (hyle, substance).

The name ethanol was coined as a result of a resolution that was adopted at the International Conference on Chemical Nomenclature that was held in April 1892 in Geneva, Switzerland.

The term “alcohol” now refers to a wider class of substances in chemistry nomenclature, but in common parlance it remains the name of ethanol. Ultimately a medieval loan from Arabical-kuḥl, use of alcohol in this sense is modern, introduced in the mid 18th century. Before that time, Middle Latin alcohol referred to “powdered ore of antimony; powdered cosmetic”, by the later 17th century “any sublimated substance; distilled spirit” use for “the spirit of wine” (shortened from a full expression alcohol of wine) recorded 1753. The systematic use in chemistry dates to 1850.

Uses

Medical

Antiseptic

Ethanol is used in medical wipes and in most common antibacterial hand sanitizer gels at a concentration of about 62% v/v as anantiseptic. Ethanol kills organisms by denaturing their proteins and dissolving their lipids and is effective against most bacteria andfungi, and many viruses. Ethanol is ineffective against bacterial spores.

Antitussive

Ethanol is widely used, clinically and over the counter, as an antitussive agent.

Antidote

Ethanol may be administered as an antidote to methanol and ethylene glycol poisoning.

Medicinal solvent

Ethanol, often in surprisingly high concentrations, is used to dissolve many water-insoluble medications and related compounds. Proprietary liquid preparations of cough and cold remedies, analgesics, and mouth washes may be dissolved in 1 to 25% concentrations of ethanol and may need to be avoided in individuals with adverse reactions to ethanol such as alcohol-induced respiratory reactions.

Recreational

Ethanol is a central nervous system depressant and has significant psychoactive effects in sublethal doses. Based on its abilities to alter human consciousness, ethanol is considered a psychoactive drug.

The amount of ethanol in the body is typically quantified by blood alcohol content (BAC), which is here taken as weight of ethanol per unit volume of blood. Small doses of ethanol, in general, produce euphoria and relaxation; people experiencing these symptoms tend to become talkative and less inhibited, and may exhibit poor judgment. At higher dosages (BAC > 1 g/L), ethanol acts as acentral nervous system depressant, producing at progressively higher dosages, impaired sensory and motor function, slowed cognition, stupefaction, unconsciousness, and possible death. Ethanol is commonly consumed as a recreational drug, especially while socializing, due to its psychoactive effects.

Fuel

Engine fuel

The largest single use of ethanol is as an engine fuel and fuel additive. Brazil in particular relies heavily upon the use of ethanol as an engine fuel, due in part to its role as the globe’s leading producer of ethanol.Gasoline sold in Brazil contains at least 25%anhydrous ethanol. Hydrous ethanol (about 95% ethanol and 5% water) can be used as fuel in more than 90% of new gasoline fueled cars sold in the country. Brazilian ethanol is produced from sugar caneand noted for high carbon sequestration. The US uses Gasohol (max 10% ethanol) and E85 (85% ethanol)

Ethanol has been used as rocket fuel and is currently in lightweight rocket-powered racing aircraft.

Australian law limits the use of pure ethanol from sugarcane waste to 10% in automobiles. Older cars (and vintage cars designed to use a slower burning fuel) should have the engine valves upgraded or replaced.

According to an industry advocacy group, ethanol as a fuel reduces harmful tailpipe emissions of carbon monoxide, particulate matter, oxides of nitrogen, and other ozone-forming pollutants. Argonne National Laboratory analyzed greenhouse gas emissions of many different engine and fuel combinations, and found that biodiesel/petrodiesel blend (B20) showed a reduction of 8%, conventional E85 ethanol blend a reduction of 17% andcellulosic ethanol 64%, compared with pure gasoline.

Ethanol combustion in an internal combustion engine yields many of the products of incomplete combustion produced by gasoline and significantly larger amounts of formaldehyde and related species such as acetaldehyde.This leads to a significantly larger photochemical reactivity and more ground level ozone.These data have been assembled into The Clean Fuels Report comparison of fuel emissions and show that ethanol exhaust generates 2.14 times as much ozone as gasoline exhaust.When this is added into the custom Localised Pollution Index (LPI) of The Clean Fuels Report, the local pollution of ethanol (pollution that contributes to smog) is rated 1.7, where gasoline is 1.0 and higher numbers signify greater pollution. The California Air Resources Board formalized this issue in 2008 by recognizing control standards for formaldehydes as an emissions control group, much like the conventional NOx and Reactive Organic Gases (ROGs).

World production of ethanol in 2006 was 51 gigalitres (1.3×1010 US gal), with 69% of the world supply coming from Brazil and the United States. More than 20% of Brazilian cars 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 or efficient. 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 used in power plants to produce electricity.

In the United States, the ethanol fuel industry is based largely on corn. According to the Renewable Fuels Association, as of 30 October 2007, 131 grain ethanol bio-refineries in the United States have the capacity to produce 7.0 billion US gallons (26,000,000 m3) of ethanol per year. An additional 72 construction projects underway (in the U.S.) can add 6.4 billion US gallons (24,000,000 m3) of new capacity in the next 18 months. Over time, it is believed that a material portion of the ≈150-billion-US-gallon (570,000,000 m3) per year market for gasoline will begin to be replaced with fuel ethanol.

Sweet sorghum is another potential source of ethanol, and is suitable for growing in dryland conditions. The International Crops Research Institute for the Semi-Arid Tropics(ICRISAT) is investigating the possibility of growing sorgham as a source of fuel, food, and animal feed in arid parts of Asia and Africa. Sweet sorghum has one-third the water requirement of sugarcane over the same time period. It also requires about 22% less water than corn (also known as maize). The world’s first sweet sorghum ethanol distillery began commercial production in 2007 in Andhra Pradesh, India.

Ethanol’s high miscibility with water makes it unsuitable for shipping through modern pipelines like liquid hydrocarbons.[45] Mechanics have seen increased cases of damage to small engines (in particular, the carburetor) and attribute the damage to the increased water retention by ethanol in fuel.

Rocket Fuel

Ethanol was commonly used as fuel in early bipropellant rocket (liquid propelled) vehicles, in conjunction with an oxidizer such as liquid oxygen. The German V-2 rocket of World War II, credited with beginning the space age, used ethanol, mixed with 25% of water to reduce the combustion chamber temperature. The V-2’s design team helped develop U.S. rockets following World War II, including the ethanol-fueled Redstone rocket which launched the first U.S. satellite.Alcohols fell into general disuse as more efficient rocket fuels were developed.

Fuel Cells

Commercial fuel cells operate on reformed natural gas, hydrogen or methanol. Ethanol is an attractive alternative due to its wide availability, low cost, high purity and low toxicity. There are a wide range of fuel cell concepts that have been trialled including direct-ethanol fuel cells, auto-thermal reforming systems and thermally integrated systems. The majority of work is being conducted at a research level although there are a number of organizations at the beginning of commercialization of ethanol fuel cells.

Household heating

An example of a bio-ethanol fire in the form of a traditional fireplace, using fire-proof ceramic simulated wood logs for effect.

Ethanol fuels flue-less, real flame fireplaces.Ethanol is kept in a burner containing a wick such as glass wool, a safety shield to reduce the chances of accidents and an extinguisher such as a plate or shutter to cut off oxygen.

It provides almost the same visual benefits of a real flame log or coal fire without the need to vent the fumes via a flue as ethanol produces very little hazardous carbon monoxide, and little or no noticeable scent. It does emit carbon dioxide and requires oxygen. Therefore, external ventilation of the room containing the fire is needed to ensure safe operation.

An additional benefit is that, unlike a flue based fireplace, 100% of the heat energy produced enters the room. This serves to offset some of the heat loss from an external air vent, as well as offset the relatively high cost of the fuel compared to other forms of heating.

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Further information: § Reactions

Ethanol is an important industrial ingredient. It has widespread use as a precursor for other organic compounds such as ethyl halides, ethyl esters, diethyl ether, acetic acid, and ethyl amines.

Solvent

Ethanol is miscible with water and is a good general purpose solvent. It is found in paints, tinctures, markers, and personal care products such as mouthwashes, perfumes and deodorants. However, polysaccharides precipitate from aqueous solution in the presence of alcohol, and ethanol precipitation is used for this reason in the purification of DNAand RNA.