mayan : rise and fall

The Maya Empire, centered in the tropical lowlands of what is now Guatemala, reached the peak of its power and influence around the sixth century A.D. The Maya excelled at agriculture, pottery, hieroglyph writing, calendar-making and mathematics, and left behind an astonishing amount of impressive architecture and symbolic artwork. Most of the great stone cities of the Maya were abandoned by A.D. 900, however, and since the 19th century scholars have debated what might have caused this dramatic decline.

Locating the Maya

The Maya civilization was one of the most dominant indigenous societies of Mesoamerica (a term used to describe Mexico and Central America before the 16th century Spanish conquest). Unlike other scattered indigenous populations of Mesoamerica, the Maya were centered in one geographical block covering all of the Yucatan Peninsula and modern-day Guatemala; Belize and parts of the Mexican states of Tabasco and Chiapas; and the western part of Honduras and El Salvador. This concentration showed that the Maya remained relatively secure from invasion by other Mesoamerican peoples.

Within that expanse, the Maya lived in three separate sub-areas with distinct environmental and cultural differences: the northern Maya lowlands on the Yucatan Peninsula; the southern lowlands in the Peten district of northern Guatemala and adjacent portions of Mexico, Belize and western Honduras; and the southern Maya highlands, in the mountainous region of southern Guatemala. Most famously, the Maya of the southern lowland region reached their peak during the Classic Period of Maya civilization (A.D. 250 to 900), and built the great stone cities and monuments that have fascinated explorers and scholars of the region.

Early Maya, 1800 B.C. to A.D. 250

The earliest Maya settlements date to around 1800 B.C., or the beginning of what is called the Preclassic or Formative Period. The earliest Maya were agricultural, growing crops such as corn (maize), beans, squash and cassava (manioc). During the Middle Preclassic Period, which lasted until about 300 B.C., Maya farmers began to expand their presence both in the highland and lowland regions. The Middle Preclassic Period also saw the rise of the first major Mesoamerican civilization, the Olmecs. Like other Mesamerican peoples, such as the Zapotec, Totonac, Teotihuacán and Aztec, the Maya derived a number of religious and cultural traits--as well as their number system and their famous calendar--from the Olmec.

In addition to agriculture, the Preclassic Maya also displayed more advanced cultural traits like pyramid-building, city construction and the inscribing of stone monuments.

The Late Preclassic city of Mirador, in the northern Peten, was one of the greatest cities ever built in the pre-Columbian Americas. Its size dwarfed the Classic Maya capital of Tikal, and its existence proves that the Maya flourished centuries before the Classic Period. 

Cities of Stone: The Classic Maya, A.D. 250-900

The Classic Period, which began around A.D. 250, was the golden age of the Maya Empire. Classic Maya civilization grew to some 40 cities, including Tikal, Uaxactún, Copán, Bonampak, Dos Pilas, Calakmul, Palenque and Río Bec; each city held a population of between 5,000 and 50,000 people. At its peak, the Maya population may have reached 2,000,000.  

Excavations of Maya sites have unearthed plazas, palaces, temples and pyramids, as well as courts for playing the ball games that were ritually and politically significant to Maya culture. Maya cities were surrounded and supported by a large population of farmers. Though the Maya practiced a primitive type of "slash-and-burn" agriculture, they also displayed evidence of more advanced farming methods, such as irrigation and terracing.

The Maya were deeply religious, and worshiped various gods related to nature, including the gods of the sun, the moon, rain and corn. At the top of Maya society were the kings, or "kuhul ajaw" (holy lords), who claimed to be related to gods and followed a hereditary succession. They were thought to serve as mediators between the gods and people on earth, and performed the elaborate religious ceremonies and rituals so important to the Maya culture.

The Classic Maya built many of their temples and palaces in a stepped pyramid shape, decorating them with elaborate reliefs and inscriptions. These structures have earned the Maya their reputation as the great artists of Mesoamerica. Guided by their religious ritual, the Maya also made significant advances in mathematics and astronomy, including the use of the zero and the development of a complex calendar system based on 365 days. Though early researchers concluded that the Maya were a peaceful society of priests and scribes, later evidence--including a thorough examination of the artwork and inscriptions on their temple walls--showed the less peaceful side of Maya culture, including the war between rival Mayan city-states and the importance of torture and human sacrifice to their religious ritual.

Serious exploration of Classic Maya sites began in the 1830s. By the early to mid-20th century, a small portion of their system of hieroglyph writing had been deciphered, and more about their history and culture became known. Most of what historians know about the Maya comes from what remains of their architecture and art, including stone carvings and inscriptions on their buildings and monuments. The Maya also made paper from tree bark and wrote in books made from this paper, known as codices; four of these codices are known to have survived.

Mathematics

Maya numerals

In common with the other Mesoamerican civilizations, the Maya used a base 20 (vigesimal) and base 5 numbering system (see Maya numerals). Also, the preclassic Maya and their neighbors had independently developed the concept of zero by 36 BC. Inscriptions show them on occasion working with sums up to the hundreds of millions and dates so large it would take several lines just to represent it. They produced extremely accurate astronomical observations; their charts of the movements of the moon and planets are equal or superior to those of any other civilization working from naked eye observation.

Life in the Rainforest

One of the many intriguing things about the Maya was their ability to build a great civilization in a tropical rainforest climate. Traditionally, ancient peoples had flourished in drier climates, where the centralized management of water resources (through irrigation and other techniques) formed the basis of society. (This was the case for the Teotihuacan of highland Mexico, contemporaries of the Classic Maya.) In the southern Maya lowlands, however, there were few navigable rivers for trade and transport, as well as no obvious need for an irrigation system.

By the late 20th century, researchers had concluded that the climate of the lowlands was in fact quite environmentally diverse. Though foreign invaders were disappointed by the region's relative lack of silver and gold, the Maya took advantage of the area’s many natural resources, including limestone (for construction), the volcanic rock obsidian (for tools and weapons) and salt. The environment also held other treasures for the Maya, including jade, quetzal feathers (used to decorate the elaborate costumes of Maya nobility) and marine shells, which were used as trumpets in ceremonies and warfare.

King and court

Lady Xoc, aunt-wife of king Shield Jaguar II, drawing a barbed rope through her tongue. AD 709

A typical Classic Maya polity was a small hierarchical state (ajawil, ajawlel, or ajawlil) headed by a hereditary ruler known as an ajaw (later k’uhul ajaw).^[23] Such kingdoms were usually no more than a capital city with its neighborhood and several lesser towns, although there were greater kingdoms, which controlled larger territories and extended patronage over smaller polities.^{[citation needed]} Each kingdom had a name that did not necessarily correspond to any locality within its territory. Its identity was that of a political unit associated with a particular ruling dynasty. For instance, the archaeological site of Naranjo was the capital of the kingdom of Saal. The land (chan ch’e’n) of the kingdom and its capital were called Wakab’nal or Maxam and were part of a larger geographical entity known as Huk Tsuk. Interestingly, despite constant warfare and eventual shifts in regional power, most kingdoms never disappeared from the political landscape until the collapse of the whole system in the 9th century AD. In this respect, Classic Maya kingdoms are highly similar to late Post Classic polities encountered by the Spaniards in Yucatán and Central Mexico: some polities could be subordinated to hegemonic rulers through conquests or dynastic unions and yet even then they persisted as distinct entities.

Mayanists have been increasingly accepting a "court paradigm" of Classic Maya societies which puts the emphasis on the centrality of the royal household and especially the person of the king. This approach focuses on Maya monumental spaces as the embodiment of the diverse activities of the royal household. It considers the role of places and spaces (including dwellings of royalty and nobles, throne rooms, temples, halls and plazas for public ceremonies) in establishing power and social hierarchy, and also in projecting aesthetic and moral values to define the wider social realm.

Spanish sources invariably describe even the largest Maya settlements as dispersed collections of dwellings grouped around the temples and palaces of the ruling dynasty and lesser nobles. None of the Classic Maya cities shows evidence of economic specialization and commerce of the scale of Mexican Tenochtitlan. Instead, Maya cities could be seen as enormous royal households, the locales of the administrative and ritual activities of the royal court. They were the places where privileged nobles could approach the holy ruler, where aesthetic values of the high culture were formulated and disseminated and where aesthetic items were consumed. They were the self-proclaimed centers and the sources of social, moral, and cosmic order. The fall of a royal court as in the well-documented cases of Piedras Negras or Copan would cause the inevitable "death" of the associated settlement.

Building materials

A surprising aspect of the great Maya structures is their lack of many advanced technologies seemingly necessary for such constructions. Lacking draft animals necessary for wheel-based modes of transportation, metal tools and even pulleys, Maya architecture required abundant manpower. Yet, beyond this enormous requirement, the remaining materials seem to have been readily available. All stone for Maya structures appears to have been taken from local quarries. They most often used limestone which remained pliable enough to be worked with stone tools while being quarried and only hardened once removed from its bed. In addition to the structural use of limestone, much of their mortar consisted of crushed, burnt and mixed limestone that mimicked the properties of cement and was used as widely for stucco finishing as it was for mortar.

Later improvements in quarrying techniques reduced the necessity for this limestone-stucco as the stones began to fit quite perfectly, yet it remained a crucial element in some post and lintel roofs. In the case of the common Maya houses, wooden poles, adobe and thatch were the primary materials; however, instances of what appear to be common houses of limestone have been discovered as well. Also notable throughout Maya architecture is the corbel arch (also known as a "false arch"), which allowed for more open-aired entrances. The corbelled arch improved upon pier/post and lintel doorways by directing the weight off of the lintel and onto the supporting posts.

Mysterious Decline of the Maya

From the late eighth through the end of the ninth century, something unknown happened to shake the Maya civilization to its foundations. One by one, the Classic cities in the southern lowlands were abandoned, and by A.D. 900, Maya civilization in that region had collapsed. The reason for this mysterious decline is unknown, though scholars have developed several competing theories.

Some believe that by the ninth century the Maya had exhausted the environment around them to the point that it could no longer sustain a very large population. Other Maya scholars argue that constant warfare among competing city-states led the complicated military, family (by marriage) and trade alliances between them to break down, along with the traditional system of dynastic power. As the stature of the holy lords diminished, their complex traditions of rituals and ceremonies dissolved into chaos. Finally, some catastrophic environmental change--like an extremely long, intense period of drought--may have wiped out the Classic Maya civilization. Drought would have hit cities like Tikal--where rainwater was necessary for drinking as well as for crop irrigation--especially hard.

All three of these factors--overpopulation and overuse of the land, endemic warfare and drought--may have played a part in the downfall of the Maya in the southern lowlands. In the highlands of the Yucatan, a few Maya cities--such as Chichén Itzá, Uxmal and Mayapán--continued to flourish in the Post-Classic Period (A.D. 900-1500). By the time the Spanish invaders arrived, however, most Maya were living in agricultural villages, their great cities buried under a layer of rainforest green. 

chemistry :ethanol

Ethanol

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"Grain alcohol" redirects here. It is not to be confused with Neutral grain spirit.

Ethanol
Systematic name[hide] Ethanol ·         Other manes : Drinking alcohol ·         Ethyl alcohol ·         Ethyl hydrate ·         Ethyl hydroxide ·         Ethylic alcohol ·         Grain alcohol ·         Hydroxyethane ·         Methylcarbinol
Properties
Molecular formula	C2H6O
Molar mass	46.07 g mol−1
Appearance	Colorless liquid
Density	0.789 g/cm3 (at 20°C)
Melting point	−114 °C, 159 K, -173 °F
Boiling point	78.37 °C, 352 K, 173 °F
log P	-0.18
Vapor pressure	5.95 kPa (at 20 °C)
Acidity (pKa)	15.9[2]
Basicity (pKb)	-1.9
Refractive index (nD)	1.36
Viscosity	0.0012 Pa s (at 20 °C), 0.001074 Pa s (at 25 °C)[3]
Dipole moment	1.69 D[4]
Pharmacology
Routes of administration	Intramuscular Intravenous Oral Topical
Metabolism	Hepatic
Hazards
MSDS	External MSDS
EU Index	603-002-00-5
EU classification	F
R-phrases	R11
S-phrases	(S2), S7, S16
NFPA 704	3 2 0
Flash point	13–14 °C
Autoignition temperature	362 °C
LD50	5628 mg kg−1 (oral, rat)
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
(verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. A psychoactive drug and one of the oldest recreational drugs known, ethanol produces a state known as alcohol intoxication when consumed. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a solvent, and as a fuel. In common usage, it is often referred to simply as alcohol or spirits.

Chemical formula

Ethanol is a 2-carbon alcohol with the molecular formula CH₃CH₂OH. Its empirical formula is C₂H₆O. 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). It is a constitutional isomer of dimethyl ether. Ethanol is often abbreviated as EtOH, using the common organic chemistry notation of representing the ethyl group (C₂H₅) with Et.

Name

Ethanol is the systematic name defined by the IUPAC nomenclature of organic chemistry for a molecule with two carbon atoms (prefix "eth-"), having a single bond between them (suffix "-ane"), and an attached -OH group (suffix "-ol").

History

For more details on this topic, see Distilled beverage.

The fermentation of sugar into ethanol is one of the earliest biotechnologies employed by humanity. The intoxicating effects of ethanol consumption have been known since ancient times. Ethanol has been used by humans since prehistory as the intoxicating ingredient of alcoholic beverages. Dried residue on 9,000-year-old pottery found in China imply that Neolithic people consumed alcoholic beverages.

Although distillation was well known by the early Greeks and Arabs, the first recorded production of alcohol from distilled wine was by the School of Salerno alchemists in the 12th century.^[7] The first to mention absolute alcohol, in contrast with alcohol-water mixtures, was Raymond Lull.^[7]

In 1796, Johann Tobias Lowitz obtained pure ethanol by mixing partially purified ethanol (the alcohol-water azeotrope) with an excess of anhydrous alkali and then distilling the mixture over low heat. Antoine Lavoisier described ethanol as a compound of carbon, hydrogen, and oxygen, and in 1807 Nicolas-Théodore de Saussure determined ethanol's chemical formula. Fifty years later, Archibald Scott Couper published the structural formula of ethanol. It is one of the first structural formulas determined.

Ethanol was first prepared synthetically in 1825 by Michael Faraday. He found that sulfuric acid could absorb large volumes of coal gas He gave the resulting solution to Henry Hennell, a British chemist, who found in 1826 that it contained "sulphovinic acid" (ethyl hydrogen sulfate) In 1828, Hennell and the French chemist Georges-Simon Sérullas independently discovered that sulphovinic acid could be decomposed into ethanol. Thus, in 1825 Faraday had unwittingly discovered that ethanol could be produced from ethylene (a component of coal gas) by acid-catalyzed hydration, a process similar to current 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. The tax was repealed in 1906. Original Ford Model T automobiles ran on ethanol until 1908. With the advent of Prohibition in 1920, ethanol fuel sellers were accused of being allied with moonshiners, and ethanol fuel fell into disuse until late in the 20th century

Ethanol intended for industrial use is also produced from ethylene 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 a solvent and a feedstock for the synthesis of other products. It has a long history as a fuel for heat and light, and more recently as a fuel for internal combustion engines.

Physical properties

Ethanol burning with its spectrum depicted

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 is slightly more refractive than water, having a refractive index of 1.36242 (at λ=589.3 nm and 18.35 °C).

The triple point for ethanol is 150 K at a pressure of 4.3 * 10^-4 Pa.

Solvent properties

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.^[21][23] It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides such as trichloroethane and tetrachloroethylene.^[23]

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.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). 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 1.92 volumes of mixture. Mixing ethanol and water is exothermic, with up to 777 J/mol, being released at 298 K.

Mixtures of ethanol and water form an azeotrope at about 89 mole-% ethanol and 11 mole-% water or a mixture of about 96 volume percent ethanol and 4% water at normal pressure and T = 351 K. This azeotropic composition is strongly temperature- and pressure-dependent and vanishes at temperatures below 303 K.

Hydrogen bonding in solid ethanol at −186 °C

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.

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

An ethanol-water solution that contains 40% ABV will catch fire if heated to about 26 °C (79 °F) and if an ignition source is applied to it. This is called its flash point. The flash point of pure ethanol is 16.60 °C (61.88 °F), less than average room temperature

The flash points of ethanol concentrations from 10% ABV to 96% ABV are shown below:

• 10% — 49 °C (120 °F)
• 12.5% — about 52 °C (126 °F)
• 20% — 36 °C (97 °F)
• 30% — 29 °C (84 °F)
• 40% — 26 °C (79 °F)
• 50% — 24 °C (75 °F)
• 60% — 22 °C (72 °F)
• 70% — 21 °C (70 °F)
• 80% — 20 °C (68 °F)
• 90% — 17 °C (63 °F)
• 96% — 17 °C (63 °F)

Alcoholic beverages that have a low concentration of ethanol will burn if sufficiently heated and an ignition source (such as an electric spark or a match) is applied to them. For example, the flash point of ordinary wine containing 12.5% ethanol is about 52 °C (126 °F)

 Production :

94% denatured ethanol sold in a bottle for household use

Ethanol is produced both as a petrochemical, through the hydration of ethylene and, via biological processes, by fermenting sugars with yeast. Which process is more economical depends on prevailing prices of petroleum and grain feed stocks.

Ethylene hydration

Ethanol for use as an industrial feedstock or solvent (sometimes referred to as synthetic ethanol) is made from petrochemical feed stocks, primarily by the acid-catalyzed hydration of ethylene, represented by the chemical equation

C₂H₄ + H₂O → CH₃CH₂OH

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 1947. The reaction is carried out with an excess of high pressure steam at 300 °C. In the U.S., this process was used on an industrial scale by Union Carbide Corporation and others; but now only LyondellBasell uses it commercially.

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 hydrolysed to yield ethanol and regenerate the sulfuric acid:

C₂H₄ + H₂SO₄ → CH₃CH₂SO₄H

CH₃CH₂SO₄H + H₂O → CH₃CH₂OH + H₂SO₄

Fermentation

Main article: Ethanol fermentation

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel,^{[citation needed]} is produced by fermentation. When certain species of yeast (e.g., Saccharomyces cerevisiae) metabolize sugar in reduced-oxygen conditions they produce ethanol and carbon dioxide. The chemical equations below summarize the conversion:

C₆H₁₂O₆ → 2 CH₃CH₂OH + 2 CO₂

C₁₂H₂₂O₁₁ + H₂O → 4 CH₃CH₂OH + 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. Toxicity of ethanol to yeast limits the ethanol concentration obtainable by brewing; higher concentrations, therefore, are usually obtained by fortification or distillation. The most ethanol-tolerant strains of yeast can survive up to approximately 15% ethanol by volume.^[41]

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.

Cellulosic ethanol

Main article: Cellulosic ethanol

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 undergoing hydrolysis, 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 was to produce cellulosic ethanol cheaply, with an eventual goal of US$1 per US gallon ($0.30/L) for the fuel. The partnership planned to begin producing the fuel in large quantity by the end of 2008, and by 2011 to have a full-scale plant on line, capable of producing 50 million US gallons (190,000 m³) to 100 million US gallons (380,000 m³) of ethanol a year (200–400 ML/a. In October 2011, an article on the Coskata website stated that a "semi-commercial" pilot plant in Madison, Pennsylvania, had been running successfully for 2 years and that a full scale facility was planned for Alabama.

Hydrocarbon-based ethanol production

A process developed and marketed by Celanese Corporation under the name TCX Technology uses hydrocarbons such as natural gas or coal for ethanol production rather than using fermented crops such as corn or sugarcane.

Prospective technologies

Ethanol plant in Turner County, South Dakota

The anaerobic bacterium Clostridium ljungdahlii, 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. The BRI technology has been purchased by INEOS.

The bacterium E.coli when genetically engineered with cow rumen genes and enzymes can produce ethanol from corn stover.

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, renewable energy for distillation comes from fermented manure, produced from cattle that have been fed the DDSG by-products from grain ethanol production. The concentrated compost nutrients from manure are then used to fertilize the soil and grow the next crop of grain to start the cycle again. Such a process is expected to lower the fossil fuel consumption used during conversion to ethanol by 75%.

An alternative technology allows for the production of biodiesel from distillers grain as an additional value product. 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.

Testing

Infrared reflection spectra of liquid ethanol, showing the -OH band centered at ~3300 cm⁻¹ and C-H bands at ~2950 cm⁻¹.

Near infrared spectrum of liquid ethanol.

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.

Purification

Main article: Ethanol purification

Ethylene hydration or brewing produces an ethanol–water mixture. For most industrial and fuel uses, the ethanol must be purified. Fractional distillation can concentrate ethanol to 95.6% by volume (89.5 mole%). This mixture is an azeotrope with a boiling point of 78.1 °C, and cannot be further purified by distillation as is. 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.

Apart from distillation, ethanol may be dried by addition of a desiccant, such as molecular sieves, cellulose, and cornmeal. The desiccants can be dried and reused.

Other techniques that have been proposed include:^[

Liquid-liquid extraction of ethanol from an aqueous solution

• Extraction of ethanol from grain mash by supercritical carbon dioxide
• Pervaporation
• Reverse osmosis
• Pressure swing adsorption

Grades of ethanol

Denatured alcohol

Main article: Denatured alcohol

Pure ethanol and alcoholic beverages are heavily taxed as a psychoactive drug, 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.

Absolute alcohol

Absolute or anhydrous alcohol refers to ethanol with a low water content. There are various grades with maximum water contents ranging from 1% to ppm levels. Absolute alcohol is not intended for human consumption. If azeotropic distillation is used to remove water, it will contain trace amounts of the material separation agent (e.g. benzene). Absolute ethanol is used as a solvent for laboratory and industrial applications, where water will react with other chemicals, and as fuel alcohol. Spectroscopic ethanol is an absolute ethanol with a low absorbance in ultraviolet and visible light, fit for use as a solvent in ultraviolet-visible spectroscopy.

Pure ethanol is classed as 200 proof in the USA, equivalent to 175 degrees proof in the UK system.

Rectified spirits

Rectified spirit, an azeotropic composition containing 4% water, is used instead of anhydrous ethanol for various purposes. Wine spirits are about 188 proof. The impurities are different from those in 190 proof laboratory ethanol.

Reactions

For more details on this topic, see Alcohol.

Ethanol is classified as a primary alcohol, meaning that the carbon its hydroxyl group attaches to has at least two hydrogen atoms attached to it as well. Many ethanol reactions occur at its hydroxyl group

Ester formation

In the presence of acid catalysts, ethanol reacts with carboxylic acids to produce ethyl esters and water:

RCOOH + HOCH₂CH₃ → RCOOCH₂CH₃ + H₂O

This reaction, which is conducted on large scale industrially, requires the removal of the water from the reaction mixture as it is formed. Esters react in the presence of an acid or base to give back the alcohol and a salt. This reaction is known as saponification because it is used in the preparation of soap. Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate are prepared by treating ethanol with sulfur trioxide and phosphorus pentoxide respectively. Diethyl sulfate is a useful ethylating agent in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely used diuretic.

Dehydration

Strong acid desiccants cause the dehydration of ethanol to form diethyl ether and other byproducts. If the dehydration temperature exceeds around 160 °C, ethylene will be the main product. Millions of kilograms of diethyl ether are produced annually using sulfuric acid catalyst:

2 CH₃CH₂OH → CH₃CH₂OCH₂CH₃ + H₂O (on 120 °C)

Combustion

Complete combustion of ethanol forms carbon dioxide and water vapor:

C₂H₅OH (l) + 3 O₂ (g) → 2 CO₂ (g) + 3 H₂O (g); (ΔH_c = −1371 kJ/mol^[64]) specific heat = 2.44 kJ/(kg·K)

Acid-base chemistry

Ethanol is a neutral molecule and the pH of a solution of ethanol in water is nearly 7.00. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH₃CH₂O⁻), by reaction with an alkali metal such as sodium

2 CH₃CH₂OH + 2 Na → 2 CH₃CH₂ONa + H₂

or a very strong base such as sodium hydride:

CH₃CH₂OH + NaH → CH₃CH₂ONa + H₂

The acidity of water and ethanol are nearly the same, as indicated by their pKa of 15.7 and 16 respectively. Thus, sodium ethoxide and sodium hydroxide exist in an equilbrium that is closely balanced:

CH₃CH₂OH + NaOH CH₃CH₂ONa + H₂O

Halogenation

Ethanol is not used industrially as a precursor to ethyl halides, but the reactions are illustrative. Ethanol reacts with hydrogen halides to produce ethyl halides such as ethyl chloride and ethyl bromide via an S_N2 reaction:

CH₃CH₂OH + HCl → CH₃CH₂Cl + H₂O

These reactions require a catalyst such as zinc chloride.^[40] HBr requires refluxing with a sulfuric acid catalyst.^[40] Ethyl halides can, in principle, also be produced by treating ethanol with more specialized halogenating agents, such as thionyl chloride or phosphorus tribromide.

CH₃CH₂OH + SOCl₂ → CH₃CH₂Cl + SO₂ + HCl

Upon treatment with halogens in the presence of base, ethanol gives the corresponding haloform (CHX₃, where X = Cl, Br, I). This conversion is called the haloform reaction. " An intermediate in the reaction with chlorine is the aldehyde called chloral:

4 Cl₂ + CH₃CH₂OH → CCl₃CHO + 5 HCl

Oxidation

Ethanol can be oxidized to acetaldehyde and further oxidized to acetic acid, depending on the reagents and conditions. This oxidation is of no importance industrially, but in the human body, these oxidation reactions are catalyzed by the enzyme liver alcohol dehydrogenase. The oxidation product of ethanol, acetic acid, is a nutrient for humans, being a precursor to acetyl CoA, where the acetyl group can be spent as energy or used for biosynthesis.

Uses

As a fuel

Energy content of some fuels compared with ethanol:
Fuel type	MJ/L	MJ/kg	Research octane number
Dry wood (20% moisture)		~19.5
Methanol	17.9	19.9	108.7
Ethanol	21.2	26.8	108.6
E85 (85% ethanol, 15% gasoline)	25.2	33.2	105
Liquefied natural gas	25.3	~55
Autogas (LPG) (60% propane + 40% butane)	26.8	50.
Aviation gasoline (high-octane gasoline, not jet fuel)	33.5	46.8	100/130 (lean/rich)
Gasohol (90% gasoline + 10% ethanol)	33.7	47.1	93/94
Regular gasoline/petrol	34.8	44.4	min. 91
Premium gasoline/petrol			max. 104
Diesel	38.6	45.4	25
Charcoal, extruded	50	23

 Ethanol fuel

The largest single use of ethanol is as a motor fuel and fuel additive. More than any other major country, Brazil relies on ethanol as a motor fuel. 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 cars sold in the country. Brazilian ethanol is produced from sugar cane and noted for high carbon sequestration. The US uses Gasohol (max 10% ethanol) and E85 (85% ethanol) ethanol/gasoline mixtures.

USP grade ethanol for laboratory use.

Ethanol may also be utilized as a rocket fuel, and is currently in lightweight rocket-powered racing aircraft.

Australian law limits of the use of pure ethanol sourced from sugarcane waste to up to 10% in automobiles. It has been recommended that older cars (and vintage cars designed to use a slower burning fuel) have their valves upgraded or replaced.

According to an industry advocacy group for promoting ethanol called the American Coalition for Ethanol, 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 the greenhouse gas emissions of many different engine and fuel combinations. Comparing ethanol blends with gasoline alone, they showed reductions of 8% with the biodiesel/petrodiesel blend known as B20, 17% with the conventional E85 ethanol blend, and that using cellulosic ethanol lowers emissions 64%.

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 that generates much 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 does gasoline exhaust. When this is added into the custom Localised Pollution Index (LPI) of The Clean Fuels Report the local pollution (pollution that contributes to smog) is 1.7 on a scale 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).

Ethanol pump station in São Paulo, Brazil where the fuel is available commercially.

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

A Ford Taurus "fueled by clean burning ethanol" owned by New York City.

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 (26,000,000 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.

United States Postal Service vehicle running on E85, a "flex-fuel" blend in Saint Paul, Minnesota.

One problem with ethanol is its high miscibility with water, which means that it cannot be efficiently shipped through modern pipelines, like liquid hydrocarbons, over long distances.Mechanics also have seen increased cases of damage to small engines, in particular, the carburetor, attributable to the increased water retention by ethanol in fuel

In 2011, the Open Fuel Standard Coalition introduced a bill into Congress that would mandate most cars sold in the United States to be warranted to run on ethanol, as well as methanol and gasoline. The bill aims to provide enough financial incentive to find better ways to make ethanol fuel so it could compete economically against gasoline.

Alcoholic beverages

Ethanol is the principal psychoactive constituent in alcoholic beverages, with depressant effects on the central nervous system. It has a complex mode of action and affects multiple systems in the brain, the most notable one being its agonistic action on the GABA receptors. Similar psychoactives include those that also interact with GABA receptors, such as benzodiazepines, barbiturates, gamma-hydroxybutyric acid (GHB) Ethanol is metabolized by the body as an energy-providing nutrient, as it metabolizes into acetyl CoA, an intermediate common with glucose and fatty acid metabolism that can be used for energy in the citric acid cycle or for biosynthesis.

Alcoholic beverages vary considerably in ethanol content and in foodstuffs they are produced from. Most alcoholic beverages can be broadly classified as fermented beverages, beverages made by the action of yeast on sugary foodstuffs, or 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 they are fermented from. 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 classifications 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 and 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.

The ethanol content in alcoholic beverages can be increased 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. Ice beer (also known by the German term Eisbier or 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 a portion of the sugar in grape juice; such beverages are not only more ethanol-rich but are often sweeter than other wines.

Alcoholic beverages are used in cooking for their flavors and because alcohol dissolves hydrophobic flavor compounds.

Just as industrial ethanol is used as feedstock for the production of industrial acetic acid, alcoholic beverages are made into vinegar. Wine and cider vinegar are both named for their respective source alcohols, whereas malt vinegar is derived from beer.

Feedstock

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, ethyl amines, and, to a lesser extent, butadiene.

Antiseptic

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

Treatment for poisoning by other alcohols

Ethanol is sometimes used to treat poisoning by other, more toxic alcohols, in particular methanoland ethylene glycol. Ethanol competes with other alcohols for the alcohol dehydrogenase enzyme, lessening metabolism into toxic aldehyde and carboxylic acid derivatives, and reducing one of the more serious toxic effect of the glycols to crystallize in the kidneys.

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 perfumes and deodorants. It may also be used as a solvent or solute in cooking, such as in vodka sauce.

Historical uses

Before the development of modern medicines, ethanol was used for a variety of medical purposes. It has been known to be used as a truth drug (as hinted at by the maxim "in vino veritas"), as medicine for depression and as an anesthetic

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.

Pharmacology

Ethanol binds to acetylcholine, GABA, serotonin, and NMDA receptors. It also appears to cause an increase in dopamine through a poorly understood process that may involve inhibiting the enzyme that breaks dopamine down.^[92]

The removal of ethanol through oxidation by alcohol dehydrogenase in the liver from the human body is limited. Hence, the removal of a large concentration of alcohol from blood may follow zero-order kinetics. This means that alcohol leaves the body at a constant rate, rather than having an elimination half-life.

Also, the rate-limiting steps for one substance may be in common with other substances. For instance, the blood alcohol concentration can be used to modify the biochemistry of methanol and ethylene glycol. Methanol itself is not highly toxic, but its metabolites formaldehyde and formic acid are; therefore, to reduce the concentration of these harmful metabolites, ethanol can be ingested to reduce the rate of methanol metabolism due to shared rate-limiting steps. Ethylene glycol poisoning can be treated in the same way.

Drug effects

Pure ethanol will irritate the skin and eyes.^]Nausea, vomiting and intoxication are symptoms of ingestion. Long-term use by ingestion can result in serious liver damage. Atmospheric concentrations above one in a thousand are above the European Union Occupational exposure limits.

BAC (g/L)	BAC (% v/v)	Symptoms
0.5	0.05%	Euphoria, talkativeness, relaxation
1	0.1 %	Central nervous system depression, nausea, possible vomiting, impaired motor and sensory function, impaired cognition
>1.4	>0.14%	Decreased blood flow to brain
3	0.3%	Stupefaction, possible unconsciousness
4	0.4%	Possible death
>5.5	>0.55%	Death

Effects on the central nervous system

Ethanol is a central nervous system depressant and has significant psychoactive effects in sublethal doses; for specifics, see "Effects of alcohol on the body by dose". Based on its abilities to change the human consciousness, ethanol is considered a psychoactive drug. Death from ethanol consumption is possible when blood alcohol level reaches 0.4%. A blood level of 0.5% or more is commonly fatal. Levels of even less than 0.1% can cause intoxication, with unconsciousness often occurring at 0.3–0.4%.

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. The table at right summarizes the symptoms of ethanol consumption. 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 a central nervous system depressant, producing at progressively higher dosages, impaired sensory and motor function, slowed cognition, stupefaction, unconsciousness, and possible death.

Ethanol acts in the central nervous system by binding to the GABA-A receptor, increasing the effects of the inhibitory neurotransmitter GABA (i.e., it is a positive allosteric modulator).

Prolonged heavy consumption of alcohol can cause significant permanent damage to the brain and other organs. See Alcohol consumption and health.

According to the US National Highway Traffic Safety Administration, in 2002 about "41% of people fatally injured in traffic crashes were in alcohol related crashes".The risk of a fatal car accident increases exponentially with the level of alcohol in the driver's blood. 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% and 0.08%.

Discontinuing consumption of alcohol after several years of heavy drinking can also be fatal. Alcohol withdrawal can cause anxiety, autonomic dysfunction, seizures, and hallucinations. Delirium tremens is a condition that requires people with a long history of heavy drinking to undertake an alcohol detoxification regimen.

The reinforcing effects of alcohol consumption are also mediated by acetaldehyde generated by catalase and other oxidizing enzymes such as cytochrome P-4502E1 in the brain. Although acetaldehyde has been associated with some of the adverse and toxic effects of ethanol, it appears to play a central role in the activation of the mesolimbic dopamine system.

Effects on metabolism

Ethanol within the human body is converted into acetaldehyde by alcohol dehydrogenase and then into the acetyl in acetyl CoA by acetaldehyde dehydrogenase. Acetyl CoA is the final product of both carbohydrate and fat metabolism, where the acetyl can be further used to produce energy or for biosynthesis. As such, ethanol is a nutrient. However, the product of the first step of this breakdown, acetaldehyde ,is more toxic than ethanol. Acetaldehyde is linked to most of the clinical effects of alcohol. It has been shown to increase the risk of developing cirrhosis of the liver and multiple forms of cancer.

During the metabolism of alcohol via the respective dehydrogenases, NAD is converted into reduced NAD. Normally, NAD is used to metabolise fats in the liver, and as such alcohol competes with these fats for the use of NAD. Prolonged exposure to alcohol means that fats accumulate in the liver, leading to the term 'fatty liver'. Continued consumption (such as in alcoholism) then leads to cell death in the hepatocytes as the fat stores reduce the function of the cell to the point of death. These cells are then replaced with scar tissue, leading to the condition cirrhosis.

Drug interactions

Ethanol can intensify the sedation caused by other central nervous system depressant drugs such as barbiturates, benzodiazepines, opioids, phenothiazines, and anti-depressants

Magnitude of effects

Some individuals have less effective forms of one or both of the metabolizing enzymes, and can experience more severe symptoms from ethanol consumption than others. However, those having acquired alcohol tolerance have a greater quantity of these enzymes, and metabolize ethanol more rapidly.

Other effects

Frequent drinking of alcoholic beverages has been shown to be a major contributing factor in cases of elevated blood levels of triglyceridesEthanol is not a carcinogen.^[106][107] However, the first metabolic product of ethanol in the liver, acetaldehyde, is toxic, mutagenic, and carcinogenic.Ethanol is also widely used, clinically and over the counter, as an antitussive agent.