Casino ethyl alcohol
Ethanol
Organic compound (CH₃CH₂OH)
For ethanol as a drug or medicine, see Alcohol (drug) and Alcohols (medicine).
Not to be confused with Ethenol or Ethynol.
| Names | |||
|---|---|---|---|
| Pronunciation | |||
| Preferred IUPAC name Ethanol[1] | |||
Other names
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| Identifiers | |||
CAS Number | |||
3D model (JSmol) | |||
| 3DMet | |||
Beilstein Reference | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| DrugBank | |||
| ECHA InfoCard | |||
Gmelin Reference | |||
IUPHAR/BPS | |||
| KEGG | |||
PubChemCID | |||
| UNII | |||
| UN number | UN | ||
CompTox Dashboard(EPA) | |||
InChI
| |||
| Properties | |||
Chemical formula | C2H6O | ||
| Molar mass | &#;g·mol−1 | ||
| Appearance | Colourless liquid | ||
| Odor | wine-like, pungent[2] | ||
| Density | g/cm3 (at 20 °C)[3] | ||
| Melting point | −&#;±&#;[3]&#;°C (−&#;±&#;&#;°F; &#;±&#;&#;K) | ||
| Boiling point | &#;±&#;[3]&#;°C (&#;±&#;&#;°F; &#;±&#;&#;K) | ||
Solubility in water | Miscible | ||
| log P | − | ||
| Vapor pressure | kPa (at 20&#;°C) | ||
| Acidity (pKa) | (H2O), (DMSO)[4][5] | ||
Magnetic susceptibility (&#;) | −·10−6 cm3/mol | ||
Refractive index (nD) | [3] | ||
| Viscosity | mPa·s (at 20&#;°C), mPa·s (at 25&#;°C)[6] | ||
Dipole moment | D[7] | ||
| Hazards | |||
| GHS labelling: | |||
Pictograms | |||
Signal word | Danger | ||
Hazard statements | H, H, HD | ||
Precautionary statements | P, P, P, P, P, P+P+P | ||
| NFPA (fire&#;diamond) | |||
| Flash point | 14 °C (Absolute)[9] | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) |
| ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA ppm (&#;mg/m3)[10] | ||
REL (Recommended) | TWA ppm (&#;mg/m3)[10] | ||
IDLH (Immediate danger) | ppm [11] | ||
| Safety data sheet (SDS) | [8] | ||
| Related compounds | |||
Related compounds | |||
| Supplementary data page | |||
| Ethanol (data page) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25&#;°C [77&#;°F], &#;kPa). Infobox references | |||
Chemical compound
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formulaCH3CH2OH. It is an alcohol, with its formula also written as C2H5OH, C2H6O or EtOH, where Et stands for ethyl. Ethanol is a volatile, flammable, colorless liquid with a characteristic wine-like odor and pungent taste.[13][14] As a psychoactivedepressant, it is the active ingredient in alcoholic drinks, and the second most consumed drug globally behind caffeine.[15]
Ethanol is naturally produced by the fermentation process of sugars by yeasts or via petrochemical processes such as ethylene hydration. Historically it was used as a general anesthetic, and has modern medical applications as an antiseptic, disinfectant, solvent for some medications, and antidote for methanol poisoning and ethylene glycol poisoning.[16][17] It is used as a chemical solvent and in the synthesis of organic compounds, and as a fuel source. Ethanol also can be dehydrated to make ethylene, an important chemical feedstock. As of , world production of ethanol was 51 gigalitres (×1010 US gallons), coming mostly from Brazil and the U.S.[18]
Etymology[edit]
Ethanol is the systematic namedefined by the International Union of Pure and Applied Chemistry for a compound consisting of an alkyl group with two carbon atoms (prefix "eth-"), having a single bond between them (infix "-an-") and an attached −OH functional group (suffix "-ol").[19]
The "eth-" prefix and the qualifier "ethyl" in "ethyl alcohol" originally came from the name "ethyl" assigned in to the group C
2H
5− by Justus Liebig. He coined the word from the German name Aether of the compound C
2H
5−O−C
2H
5 (commonly called "ether" in English, more specifically called "diethyl ether").[20] According to the Oxford English Dictionary, Ethyl is a contraction of the Ancient Greek αἰθήρ (aithḗr, "upper air") and the Greek word ὕλη (hýlē, "wood, raw material", hence "matter, substance").[21]
The name ethanol was coined as a result of a resolution on naming alcohols and phenols that was adopted at the International Conference on Chemical Nomenclature that was held in April in Geneva, Switzerland.[22]
The term alcohol now refers to a wider class of substances in chemistry nomenclature, but in common parlance it remains the name of ethanol. It is a medieval loan from Arabical-kuḥl, a powdered ore of antimony used since antiquity as a cosmetic, and retained that meaning in Middle Latin.[23] The use of 'alcohol' for ethanol (in full, "alcohol of wine") is modern and was first recorded in Before the late 18th century the term "alcohol" generally referred to any sublimated substance.[24]
Uses[edit]
Medical[edit]
Main article: Alcohol (medicine)
Anesthetic[edit]
Ethanol is the oldest known sedative, used as an oral general anesthetic during surgery in ancient Mesopotamia and in medieval times.[16][17] Mild intoxication starts at a blood alcohol concentration of &#;% and induces anesthetic coma at %.[25] However, this use carried the high risk of deadly alcohol intoxication and pulmonary aspiration on vomit, which led to use of alternatives in antiquity, such as opium and cannabis, and later diethyl ether starting in the s.[26]
Antiseptic[edit]
Ethanol is used in medical wipes and most commonly in antibacterial hand sanitizer gels as an antiseptic for its bactericidal and anti-fungal effects.[27] Ethanol kills microorganisms by dissolving their membrane lipid bilayer and denaturing their proteins, and is effective against most bacteria, fungi and viruses. However, it is ineffective against bacterial spores, but that can be alleviated by using hydrogen peroxide.[28]
A solution of 70% ethanol is more effective than pure ethanol because ethanol relies on water molecules for optimal antimicrobial activity. Absolute ethanol may inactivate microbes without destroying them because the alcohol is unable to fully permeate the microbe's membrane.[29][30] Ethanol can also be used as a disinfectant and antiseptic because it causes cell dehydration by disrupting the osmotic balance across the cell membrane, so water leaves the cell leading to cell death.[31]
Antidote[edit]
Ethanol may be administered as an antidote to ethylene glycol poisoning[32] and methanol poisoning.[33] Ethanol serves this process by acting as a competitive inhibitor against methanol and ethylene glycol for alcohol dehydrogenase.[34] Though it has more side effects, ethanol is less expensive and more readily available than fomepizole, which is also used as an antidote for methanol and ethylene glycol poisoning.[35]
Medicinal solvent[edit]
Ethanol, often in high concentrations, is used to dissolve many water-insoluble medications and related compounds. Liquid preparations of pain medications, cough and cold medicines, and mouth washes, for example, may contain up to 25% ethanol[36] and may need to be avoided in individuals with adverse reactions to ethanol such as alcohol-induced respiratory reactions.[37] Ethanol is present mainly as an antimicrobial preservative in over liquid preparations of medicine including acetaminophen, iron supplements, ranitidine, furosemide, mannitol, phenobarbital, trimethoprim/sulfamethoxazole and over-the-countercough medicine.[38]
Pharmacology[edit]
In mammals, ethanol is primarily metabolized in the liver and stomach by alcohol dehydrogenase (ADH) enzymes.[39] These enzymes catalyze the oxidation of ethanol into acetaldehyde (ethanal):[40]
- CH3CH2OH + NAD+ → CH3CHO + NADH + H+
When present in significant concentrations, this metabolism of ethanol is additionally aided by the cytochrome P enzyme CYP2E1 in humans, while trace amounts are also metabolized by catalase.[41]
The resulting intermediate, acetaldehyde, is a known carcinogen, and poses significantly greater toxicity in humans than ethanol itself. Many of the symptoms typically associated with alcohol intoxication—as well as many of the health hazards typically associated with the long-term consumption of ethanol—can be attributed to acetaldehyde toxicity in humans.[42]
The subsequent oxidation of acetaldehyde into acetate is performed by aldehyde dehydrogenase (ALDH) enzymes. A mutation in the ALDH2 gene that encodes for an inactive or dysfunctional form of this enzyme affects roughly 50&#;% of east Asian populations, contributing to the characteristic alcohol flush reaction that can cause temporary reddening of the skin as well as a number of related, and often unpleasant, symptoms of acetaldehyde toxicity.[43] This mutation is typically accompanied by another mutation in the alcohol dehydrogenase enzyme ADH1B in roughly 80&#;% of east Asians, which improves the catalytic efficiency of converting ethanol into acetaldehyde.[43]
Recreational[edit]
Main articles: Alcohol (drug) and Alcoholic drink
As a central nervous systemdepressant, ethanol is one of the most commonly consumed psychoactive drugs.[44]
Despite alcohol's psychoactive, addictive, and carcinogenic properties, it is readily available and legal for sale in most countries. There are laws regulating the sale, exportation/importation, taxation, manufacturing, consumption, and possession of alcoholic beverages. The most common regulation is prohibition for minors.
Fuel[edit]
See also: Food vs. fuel
Engine fuel[edit]
Main article: Ethanol 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 one of the world's leading producers of ethanol.[48][49]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.
The US and many other countries primarily use E10 (10% ethanol, sometimes known as gasohol) and E85 (85% ethanol) ethanol/gasoline mixtures. Over time, it is believed that a material portion of the ≈billion-US-gallon (,,&#;m3) per year market for gasoline will begin to be replaced with fuel ethanol.[50]
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.[51]
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.[52]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% and cellulosic ethanol 64%, compared with pure gasoline.[53] Ethanol has a much greater research octane number (RON) than gasoline, meaning it is less prone to pre-ignition, allowing for better ignition advance which means more torque, and efficiency in addition to the lower carbon emissions.[54]
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.[55] This leads to a significantly larger photochemical reactivity and more ground level ozone.[56] This data has been assembled into The Clean Fuels Report comparison of fuel emissions[57] and show that ethanol exhaust generates &#;times as much ozone as gasoline exhaust.[58] When this is added into the custom Localized Pollution Index of The Clean Fuels Report, the local pollution of ethanol (pollution that contributes to smog) is rated , where gasoline is and higher numbers signify greater pollution.[59] The California Air Resources Board formalized this issue in by recognizing control standards for formaldehydes as an emissions control group, much like the conventional NOx and reactive organic gases (ROGs).[60]
More than 20% of Brazilian cars are able to use % ethanol as fuel, which includes ethanol-only engines and flex-fuel engines.[61] Flex-fuel engines in Brazil are able to work with all ethanol, all gasoline or any mixture of both. In the United States, 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 fleet of ethanol-burning automobiles with large national infrastructure that produces ethanol from domestically grown sugarcane.
Ethanol's high miscibility with water makes it unsuitable for shipping through modern pipelines like liquid hydrocarbons.[62] 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.[63]
Rocket fuel[edit]
Ethanol was commonly used as fuel in early bipropellantrocket (liquid-propelled) vehicles, in conjunction with an oxidizer such as liquid oxygen. The German A-4 ballistic rocket of World War&#;II (better known by its propaganda name V-2),[64] which is credited as having begun the space age, used ethanol as the main constituent of B-Stoff. Under such nomenclature, the ethanol was mixed with 25% water to reduce the combustion chamber temperature.[65][66] 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.[67] Alcohols fell into general disuse as more energy-dense rocket fuels were developed,[66] although ethanol is currently used in lightweightrocket-powered racing aircraft.[68]
Fuel cells[edit]
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 is a wide range of fuel cell concepts that have entered trials 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 the commercialization of ethanol fuel cells.[69]
Household heating and cooking[edit]
Ethanol fireplaces can be used for home heating or for decoration. Ethanol can also be used as stove fuel for cooking.[70][71]
Feedstock[edit]
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[edit]
Ethanol is considered a universal solvent, as its molecular structure allows for the dissolving of both polar, hydrophilic and nonpolar, hydrophobic compounds. As ethanol also has a low boiling point, it is easy to remove from a solution that has been used to dissolve other compounds, making it a popular extracting agent for botanical oils. Cannabis oil extraction methods often use ethanol as an extraction solvent,[72] and also as a post-processing solvent to remove oils, waxes, and chlorophyll from solution in a process known as winterization.
Ethanol is found in paints, tinctures, markers, and personal care products such as mouthwashes, perfumes and deodorants. Polysaccharidesprecipitate from aqueous solution in the presence of alcohol, and ethanol precipitation is used for this reason in the purification of DNA and RNA.
Low-temperature liquid[edit]
Because of its low freezing point of −&#;°C (−&#;°F) and low toxicity, ethanol is sometimes used in laboratories (with dry ice or other coolants) as a cooling bath to keep vessels at temperatures below the freezing point of water. For the same reason, it is also used as the active fluid in alcohol thermometers.
Chemistry[edit]
Further information: Ethanol (data page)
Chemical formula[edit]
Ethanol is a 2-carbon alcohol. Its molecular formula is CH3CH2OH. The structure of the molecule of ethanol is CH3−CH2−OH (an ethyl group linked to a hydroxyl group), 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). It is a constitutional isomer of dimethyl ether. Ethanol is sometimes abbreviated as EtOH, using the common organic chemistry notation of representing the ethyl group (C2H5−) with Et.
Physical properties[edit]
Ethanol is a volatile, colorless liquid that has a slight 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, such as propane.
Ethanol's adiabatic flame temperature for combustion in air is °C or °F.[73]
Ethanol is slightly more refractive than water, having a refractive index of (at λ=&#;nm and &#;°C or &#;°F).[74] The triple point for ethanol is ± 20 K.[75]
Solvent properties[edit]
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. Its main use as a solvent is in making tincture of iodine, cough syrups, etc.[74][76] It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides such as trichloroethane and tetrachloroethylene.[76]
Ethanol's miscibility with water contrasts with the immiscibility of longer-chain alcohols (five or more carbon atoms), whose water miscibility decreases sharply as the number of carbons increases.[77] The miscibility of ethanol with alkanes is limited to alkanes up to undecane: mixtures with dodecane and higher alkanes show a miscibility gap below a certain temperature (about 13&#;°C for dodecane[78]). The miscibility gap tends to get wider with higher alkanes, and the temperature for complete miscibility increases.
Ethanol-water mixtures have less volume than the sum of their individual components at the given fractions. Mixing equal volumes of ethanol and water results in only volumes of mixture.[74][79] Mixing ethanol and water is exothermic, with up to &#;J/mol[80] being released at &#;K.
Mixtures of ethanol and water form an azeotrope at about 89 mole-% ethanol and 11 mole-% water[81] or a mixture of % ethanol by mass (or about 97% alcohol by volume) at normal pressure, which boils at K (78&#;°C). This azeotropic composition is strongly temperature- and pressure-dependent and vanishes at temperatures below &#;K.[82]
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.[76]Sodium and potassium chlorides are slightly soluble in ethanol.[76] Because the ethanol molecule also has a nonpolar end, it will also dissolve nonpolar substances, including most essential oils[83] and numerous flavoring, coloring, and medicinal agents.
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.
Flammability[edit]
An ethanol–water solution will catch fire if heated above a temperature called its flash point and an ignition source is then applied to it.[84] For 20% alcohol by mass (about 25% by volume), this will occur at about 25&#;°C (77&#;°F). The flash point of pure ethanol is 13&#;°C (55&#;°F),[85] but may be influenced very slightly by atmospheric composition such as pressure and humidity. Ethanol mixtures can ignite below average room temperature. Ethanol is considered a flammable liquid (Class 3 Hazardous Material) in concentrations above % by mass (% by volume; 6 proof).[86][87][88]
Dishes using burning alcohol for culinary effects are called flambé.
Natural occurrence[edit]
Ethanol is a byproduct of the metabolic process of yeast. As such, ethanol will be present in any yeast habitat. Ethanol can commonly be found in overripe fruit.[91] Ethanol produced by symbiotic yeast can be found in bertam palm blossoms. Although some animal species, such as the pentailed treeshrew, exhibit ethanol-seeking behaviors, most show no interest or avoidance of food sources containing ethanol.[92] Ethanol is also produced during the germination of many plants as a result of natural anaerobiosis.[93] Ethanol has been detected in outer space, forming an icy coating around dust grains in interstellar clouds.[94] Minute quantity amounts (average ppb) of endogenous ethanol and acetaldehyde were found in the exhaled breath of healthy volunteers.[95]Auto-brewery syndrome, also known as gut fermentation syndrome, is a rare medical condition in which intoxicating quantities of ethanol are produced through endogenousfermentation within the digestive system.[96]
Production[edit]
Ethanol is produced both as a petrochemical, through the hydration of ethylene and, via biological processes, by fermenting sugars with yeast.[97] Which process is more economical depends on prevailing prices of petroleum and grain feed stocks.
Sources[edit]
World production of ethanol in was 51 gigalitres (×1010&#;US&#;gal), with 69% of the world supply coming from Brazil and the U.S.[18] Brazilian ethanol is produced from sugarcane, which has relatively high yields (% more fuel than the fossil fuels used to produce it) compared to some other energy crops.[98] Sugarcane 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 discarded, but burned by power plants to produce electricity. Bagasse burning accounts for around 9% of the electricity produced in Brazil.[99]
In the s most industrial ethanol in the U.S. was made as a petrochemical, but in the s the U.S. introduced subsidies for corn-based ethanol.[] According to the Renewable Fuels Association, as of 30 October , grain ethanol bio-refineries in the U.S. have the capacity to produce 7×109&#;US&#;gal (26,,&#;m3) of ethanol per year. An additional 72 construction projects underway (in the U.S.) can add &#;billion US gallons (24,,&#;m3) of new capacity in the next 18 months.[50]
In India ethanol is made from sugarcane.[]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 is investigating the possibility of growing sorghum 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. The world's first sweet sorghum ethanol distillery began commercial production in in Andhra Pradesh, India.[]
Hydration[edit]
Ethanol can be produced from petrochemical feed stocks, primarily by the acid-catalyzedhydration of ethylene. It is often referred to as synthetic ethanol.
- C2H4 + H2O → C2H5OH
The catalyst is most commonly phosphoric acid,[][]adsorbed onto a porous support such as silica gel or diatomaceous earth. This catalyst was first used for large-scale ethanol production by the Shell Oil Company in [] The reaction is carried out in the presence of high pressure steam at &#;°C (&#;°F) where a ethylene to steam ratio is maintained.[][] This process was used on an industrial scale by Union Carbide Corporation and others. It is no longer practiced in the US as fermentation ethanol produced from corn is more economical.[]
In an older process, first practiced on the industrial scale in 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 hydrolyzed to yield ethanol and regenerate the sulfuric acid:[]
- C2H4 + H2SO4 → C2H5HSO4
- C2H5HSO4 + H2O → H2SO4 + C2H5OH
From carbon dioxide[edit]
Ethanol has been produced in the laboratory by converting carbon dioxide via biological and electrochemical reactions.[][]
CO2 + H
2O → CH
3CH
2OH + side products
Fermentation[edit]
Main article: Ethanol fermentation
See also: Yeast in winemaking
Ethanol in alcoholic beverages and fuel is produced by fermentation. Certain species of yeast (e.g., Saccharomyces cerevisiae) metabolize sugar (namely polysaccharides), producing ethanol and carbon dioxide. The chemical equations below summarize the conversion:
C
6H
12O
6 → 2 CH
3CH
2OH + 2 CO2
C
12H
22O
11 + H
2O → 4 CH
3CH
2OH + 4 CO2
Fermentation is the process of culturing yeast under favorable thermal conditions to produce alcohol. This process is carried out at around 35–40&#;°C (95–&#;°F). Toxicity of ethanol to yeast limits the ethanol concentration obtainable by brewing; higher concentrations, therefore, are obtained by fortification or distillation. The most ethanol-tolerant yeast strains can survive up to approximately 18% ethanol by volume.
To produce ethanol from starchy materials such as cereals, 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 enzymeamylase. When the malted grain is mashed, the amylase converts the remaining starches into sugars.
Cellulose[edit]
Main article: Cellulosic ethanol
Sugars for ethanol fermentation can be obtained from cellulose. 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 agricultural residues such as sugarcane bagasse and energy crops such as switchgrass may also be fermentable sugar sources.[]
Testing[edit]
Breweries and biofuel plants employ two methods for measuring ethanol concentration. Infrared ethanol sensors measure the vibrational frequency of dissolved ethanol using the C−H band at &#;cm−1. This method uses a relatively inexpensive solid-state sensor that compares the C−H 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.
Purification[edit]
Distillation[edit]
Ethylene hydration or brewing produces an ethanol–water mixture. For most industrial and fuel uses, the ethanol must be purified. Fractional distillation at atmospheric pressure can concentrate ethanol to % by weight ( mole%). This mixture is an azeotrope with a boiling point of &#;°C (&#;°F), and cannot be further purified by distillation. Addition of an entraining agent, such as benzene, cyclohexane, or heptane, allows a new ternary azeotrope comprising the ethanol, water, and the entraining agent to be formed. This lower-boiling ternary azeotrope is removed preferentially, leading to water-free ethanol.[]
Molecular sieves and desiccants[edit]
Apart from distillation, ethanol may be dried by addition of a desiccant, such as molecular sieves, cellulose, or cornmeal. The desiccants can be dried and reused.[]Molecular sieves can be used to selectively absorb the water from the % ethanol solution.[] Molecular sieves of pore-size 3&#;Ångstrom, a type of zeolite, effectively sequester water molecules while excluding ethanol molecules. Heating the wet sieves drives out the water, allowing regeneration of their desiccant capability.[]
Membranes and reverse osmosis[edit]
Membranes can also be used to separate ethanol and water. Membrane-based separations are not subject to the limitations of the water-ethanol azeotrope because the separations are not based on vapor-liquid equilibria. Membranes are often used in the so-called hybrid membrane distillation process. This process uses a pre-concentration distillation column as the first separating step. The further separation is then accomplished with a membrane operated either in vapor permeation or pervaporation mode. Vapor permeation uses a vapor membrane feed and pervaporation uses a liquid membrane feed.
Other techniques[edit]
A variety of other techniques have been discussed, including the following:[]
Grades of ethanol[edit]
Denatured alcohol[edit]
Main article: Denatured alcohol
Pure ethanol and alcoholic beverages are heavily taxed
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