|Molar mass||32.04 g/mol|
|Density and phase||0.7918 g/cm³, liquid|
|Solubility in water||Fully miscible|
|Melting point||–97 °C (176 K)|
|Boiling point||64.7 °C (337.8 K)|
|Acidity (pKa)||~ 15.5|
|Viscosity||0.59 mPa·s at 20 °C|
|Molecular shape||Tetrahedral and Bent|
|Dipole moment||1.69 D (gas)|
|EU classification||Flammable (F)
, , ,|
|Flash point||11 °C|
in air (by volume)
|6.72% - 36.50%|
|Supplementary data page|
|Structure & properties||n, εr, etc.|
|Thermodynamic data||Phase behaviour
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha, or wood spirits, is the simplest alcohol. Its chemical formula is CH3OH. It is a colorless, volatile, flammable liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). It is poisonous and should be handled with care.
Methanol is used as a solvent, fuel, and antifreeze. Its main use, however, is in the production of other chemicals. About 40 percent of methanol is converted to formaldehyde, which in turn is used for products such as plastics, paints, explosives, and textiles. It is added to ethanol to produce what is called denatured alcohol (that is, ethanol that has been rendered toxic), which has various uses in industry.
Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria. As a result, there is a low level of methanol vapor in the atmosphere. Over the course of several days, atmospheric methanol is oxidized by oxygen with the help of sunlight, to generate carbon dioxide and water.
In their embalming process, the ancient Egyptians used a mixture of substances, including methanol, which they obtained from the pyrolysis of wood. Pure methanol, however, was first isolated in 1661 by Robert Boyle, who called it spirit of box, because he produced it via the distillation of boxwood. It later became known as pyroxylic spirit. In 1834, the French chemists Jean-Baptiste Dumas and Eugene Peligot determined its elemental composition. They also introduced the word methylene to organic chemistry, forming it from Greek methy = "wine" + hŷlē = wood (patch of trees). Its intended origin was "alcohol made from wood (substance)," but it has Greek language errors. The term "methyl" was derived in about 1840 by back-formation from methylene, and was then applied to describe "methyl alcohol." This was shortened to "methanol" in 1892 by the International Conference on Chemical Nomenclature. The suffix -yl used in organic chemistry to form names of radicals, was extracted from the word "methyl."
In 1923, the German chemist Matthias Pier, working for BASF developed a means to convert synthesis gas (a mixture of carbon oxides and hydrogen) into methanol. This process used a zinc chromate catalyst, and required extremely vigorous conditions—pressures ranging from 30–100 MPa (300–1000 atm), and temperatures of about 400°C. Modern methanol production has been made more efficient through use of catalysts (commonly copper) capable of operating at lower pressures.
The use of methanol as a motor fuel received attention during the oil crises of the 1970s due to its availability and low cost. Problems occurred early in the development of gasoline-methanol blends. As a result of its low price some gasoline marketers over blended. Others used improper blending and handling techniques. This led to consumer and media problems and the last time out of methanol blends. However, there is still a great deal of interest in using methanol as a neat (unblended) fuel. The flexible-fuel vehicles currently being manufactured by General Motors, Ford, and Chrysler can run on any combination of ethanol, methanol and/or gasoline. Neat alcohol fuels will become more widespread as more flexible-fuel automobiles are manufactured.
In 2006, astronomers using the MERLIN array of radio telescopes at Jodrell Bank Observatory discovered a large cloud of methanol in space, 300 billion miles across.
A methanol flame is almost colorless. Care should be exercised around burning methanol to avoid burning oneself on the almost invisible fire.
The aluminum methoxide produced is soluble in methanol. As a result, the aluminum surface is cleaned of its oxide coating and then is readily oxidized by some dissolved oxygen. Also, the methanol can act as an oxidizer:
This reciprocal process effectively fuels corrosion until either the metal is eaten away or the concentration of CH3OH becomes negligible.
Methanol is often called wood alcohol because it was once produced chiefly as a by-product of the destructive distillation of wood. It is now produced synthetically by a multi-step process. In brief, natural gas and steam are reformed in a furnace to produce hydrogen and carbon monoxide. This step is endothermic (it absorbs heat). Next, hydrogen and carbon monoxide gases are made to react under pressure in the presence of a catalyst, to produce methanol. This synthesis step is exothermic (it releases heat).
Today, synthesis gas is most commonly produced from the methane component in natural gas rather than from coal. Three processes are commercially practiced. At moderate pressures of 1 to 2 MPa (10–20 atm) and high temperatures (around 850 °C), methane reacts with steam on a nickel catalyst to produce syngas according to the chemical equation:
This reaction, commonly called steam-methane reforming or SMR, is endothermic and the heat transfer limitations place limits on the size of the catalytic reactors used. Methane can also undergo partial oxidation with molecular oxygen to produce syngas, as the following equation shows:
this reaction is exothermic and the heat given off can be used in-situ to drive the steam-methane reforming reaction. When the two processes are combined, it is referred to as autothermal reforming. The ratio of CO and H2 can be adjusted by using the water-gas shift reaction,
to provide the appropriate stoichiometry for methanol synthesis.
The carbon monoxide and hydrogen then react on a second catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper, zinc oxide, and alumina first used by ICI in 1966. At 5–10 MPa (50–100 atm) and 250 °C, it can catalyze the production of methanol from carbon monoxide and hydrogen with high selectivity
It is worth noting that the production of synthesis gas from methane produces 3 moles of hydrogen for every mole of carbon monoxide, while the methanol synthesis consumes only 2 moles of hydrogen for every mole of carbon monoxide. One way of dealing with the excess hydrogen is to inject carbon dioxide into the methanol synthesis reactor, where it, too, reacts to form methanol according to the chemical equation
Although natural gas is the most economical and widely used feedstock for methanol production, other feedstocks can be used. Where natural gas is unavailable, light petroleum products can be used in its place. The South African firm Sasol produces methanol using synthesis gas from coal.
Methanol can enter the body by ingestion, inhalation, or absorption through the skin. It is toxic after it is metabolized in the liver by the enzyme alcohol dehydrogenase to form formaldehyde, which in turn causes blindness by destroying the optic nerve. Methanol ingestion can also be fatal because it can depress the central nervous system in the same manner as ethanol poisoning. Fetal tissue will not tolerate methanol. Dangerous doses will build up if a person is regularly exposed to vapors or handles the liquid without skin protection.
If methanol has been ingested, a doctor should be contacted immediately. The usual fatal dose is 100–125 mL (4 fl oz). Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. This is treated using ethanol or fomepizole. Either of these drugs acts to slow down the action of alcohol dehydrogenase on methanol by means of competitive inhibition, so that it is excreted by the kidneys rather than being transformed into toxic metabolites.
The initial symptoms of methanol intoxication are those of central nervous system depression: headache, dizziness, nausea, lack of coordination, confusion, drowsiness, and, at sufficiently large doses, unconsciousness and death. The initial symptoms of methanol exposure are usually less severe than the symptoms resulting from the ingestion of a similar quantity of ethyl alcohol.
Once the initial symptoms have passed, a second set of symptoms arises 10–30 hours after the initial exposure to methanol: blurring or complete loss of vision, together with acidosis. These symptoms result from the accumulation of toxic levels of formate in the bloodstream, and may progress to death by respiratory failure. The ester derivatives of methanol do not share this toxicity.
Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of methanol. The result is known as methylated spirit or "meths" (in the UK). (The latter should not be confused with meth, a common abbreviation for methamphetamine.)
Pure methanol has been used in open wheel racing since the mid-1960s. Unlike petroleum fires, methanol fires can be extinguished with plain water (while methanol is less dense than water, they are miscible, and the addition of water will cause the fire to use its heat to boil the water). In addition, a methanol-based fire burns invisibly, unlike gasoline, which burns with thick black smoke. If a fire occurs on the track, there is no smoke to obstruct the view of fast approaching drivers. The decision to permanently switch to methanol in American IndyCar racing was a result of the devastating crash and explosion at the 1964 Indianapolis 500 which killed drivers Eddie Sachs and Dave MacDonald.
One concern with the addition of methanol to automotive fuels is highlighted by recent groundwater impacts from the fuel additive methyl tert-butyl ether (MTBE). Leaking underground gasoline storage tanks created MTBE plumes in groundwater that eventually adulterated well water. Methanol's high solubility in water raises concerns that similar well water contamination could arise from the widespread use of methanol as an automotive fuel.
All links retrieved September 19, 2018.
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