Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a light, volatile, colorless and flammable liquid with a distinctive alcoholic odor similar to that of ethanol (potable alcohol), but is more acutely toxic than the latter.[
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Methanol consists of a methyl group linked to a polar hydroxyl group. With more than 20 million tons produced annually, it is used as a precursor to other commodity chemicals, including formaldehyde, acetic acid, methyl tert-butyl ether, methyl benzoate, anisole, , as well as a host of more specialized chemicals.[
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Occurrence
Small amounts of methanol are present in normal, healthy human individuals. One study found a mean of 4.5 ppm in the exhaled breath of test subjects.
Methanol is produced by anaerobic bacteria and phytoplankton.
Interstellar medium
Methanol is also found in abundant quantities in star-forming regions of space and is used in astronomy as a marker for such regions. It is detected through its spectral emission lines.
In 2006, astronomers using the MERLIN array of radio telescopes at Jodrell Bank discovered a large cloud of methanol in space across.
History
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, when he produced it via the distillation of buxus (boxwood).[Boyle discusses the distillation of liquids from the wood of the box shrub in: Robert Boyle, The Sceptical Chymist (London, England: J. Cadwell, 1661), pp. 192–195.] It later became known as "pyroxylic spirit". In 1834, the French chemists Jean-Baptiste Dumas and Eugene Peligot determined its elemental composition.[A report on methanol to the French Academy of Sciences by J. Dumas and E. Péligot began during the Academy's meeting of 27 October 1834 and finished during the meeting of 3 November 1834. See: Procès-verbaux des séances de l'Académie, 10 : 600–601. Available on: Gallica . The complete report appears in: J. Dumas and E. Péligot (1835) (Memoir on spirit of wood and on the various ethereal compounds that derive therefrom), Annales de chimie et de physique, 58 : 5–74; from : Nous donnerons le nom de méthylène (1) à un radical ... (1) Μεθυ, vin, et υλη, bois; c'est-à-dire vin ou liqueur spiritueuse du bois. (We will give the name methylene (1) to a radical ... (1) methy, wine, and hulē, wood; that is, wine or spirit of wood.)]
They also introduced the word "methylène" to organic chemistry, forming it from Greek language = "alcoholic liquid" + = "forest, wood, timber, material". "Methylène" designated a Radical theory that was about 14% hydrogen by weight and contained one carbon atom. This would be , but at the time carbon was thought to have an atomic weight only six times that of hydrogen, so they gave the formula as CH.[ They then called wood alcohol (l'esprit de bois) "bihydrate de méthylène" (bihydrate because they thought the formula was or ). 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.][For a report on the International Conference on Chemical Nomenclature that was held in April 1892 in Geneva, Switzerland, see:
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Armstrong's report is reprinted with the resolutions in English in:
The suffix -yl, which, in organic chemistry, forms names of carbon groups, is from the word methyl.
French chemist Paul Sabatier presented the first process that could be used to produce methanol synthetically in 1905. This process suggested that carbon dioxide and hydrogen could be reacted to produce methanol.
US patent 1,569,775 was applied for on 4 September 1924 and issued on 12 January 1926 to BASF;
During World War II, methanol was used as a fuel in several German military rocket designs, under the name M-Stoff, and in a roughly 50/50 mixture with hydrazine, known as C-Stoff.
The use of methanol as a motor fuel received attention during the oil crises of the 1970s. By the mid-1990s, over 20,000 methanol flexible fuel vehicles (FFVs) capable of operating on methanol or gasoline were introduced in the US. In addition, low levels of methanol were blended in gasoline fuels sold in Europe during much of the 1980s and early-1990s. Automakers stopped building methanol FFVs by the late-1990s, switching their attention to ethanol-fueled vehicles. While the methanol FFV program was a technical success, rising methanol pricing in the mid- to late-1990s during a period of slumping gasoline pump prices diminished interest in .
In the early 1970s, a process was developed by Mobil for producing gasoline fuel from methanol.
Between the 1960s and 1980s methanol emerged as a precursor to the feedstock chemicals acetic acid and acetic anhydride. These processes include the Monsanto acetic acid synthesis, Cativa process, and Tennessee Eastman acetic anhydride process.
Applications
Production of formaldehyde, acetic acid, methyl tert-butyl ether
Methanol is primarily converted to formaldehyde, which is widely used in many areas, especially Polymer. The conversion entails oxidation:
Acetic acid can be produced from methanol.
Methanol and isobutene are combined to give methyl tert-butyl ether (MTBE). MTBE is a major octane booster in gasoline.
Methanol to hydrocarbons, olefins, gasoline
Condensation of methanol to produce and even aromatic systems is the basis of several technologies related to gas to liquids. These include methanol-to-hydrocarbons (MtH), methanol to gasoline (MtG), methanol to olefins (MtO), and methanol to propylene (MtP). These conversions are catalyzed by as heterogeneous catalysts. The MtG process was once commercialized at Motunui in New Zealand.
Gasoline additive
The European Fuel Quality Directive allows fuel producers to blend up to 3% methanol, with an equal amount of cosolvent, with gasoline sold in Europe. In 2019, it is estimated that China used as much as 7 million tons of methanol as transportation fuels, representing over 5% of their fuel pool.
Other chemicals
Methanol is the precursor to most simple , , and methyl ethers.
Niche and potential uses
Energy carrier
Methanol is a promising energy carrier because, as a liquid, it is easier to store than hydrogen and natural gas. Its energy density is, however, lower than methane, per kg. Its combustion energy density is 15.6 joule/liter (LHV), whereas that of ethanol is 24 and gasoline is 33 MJ/L.
Further advantages for methanol is its ready biodegradability and low environmental toxicity. It does not persist in either aerobic (oxygen-present) or anaerobic (oxygen-absent) environments. The half-life for methanol in groundwater is just one to seven days, while many common gasoline components have half-lives in the hundreds of days (such as benzene at 10–730 days). Since methanol is miscibility with water and biodegradable, it is unlikely to accumulate in groundwater, surface water, air or soil.[ Evaluation of the Fate and Transport of Methanol in the Environment , Malcolm Pirnie, Inc., January 1999.]
Fuel
Methanol is occasionally used to fuel internal combustion engines. It burns forming carbon dioxide and water:
Methanol fuel has been proposed for ground transportation. The chief advantage of a methanol economy is that it could be adapted to gasoline internal combustion engines with minimum modification to the engines and to the infrastructure that delivers and stores liquid fuel. Its energy density, however, is less than gasoline, meaning more frequent fill ups would be required. However, it is equivalent to super high-octane gasoline in horsepower, and most modern computer-controlled fuel injection systems can already use it.
Methanol is an alternative fuel for ships that helps the shipping industry meet increasingly strict emissions regulations. It significantly reduces emissions of (SO x), NOx (NO x) and particulate matter. Methanol can be used with high efficiency in marine diesel engines after minor modifications using a small amount of pilot fuel (dual fuel).
In China, methanol fuels industrial boilers, which are used extensively to generate heat and steam for various industrial applications and residential heating. Its use is displacing coal, which is under pressure from increasingly stringent environmental regulations.
Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, which lets them be greatly miniaturized.
Methanol is also a widely used fuel in camping and boating stoves. Methanol burns well in an unpressurized burner, so alcohol stoves are often very simple, sometimes little more than a cup to hold fuel. This lack of complexity makes them a favorite of hikers who spend extended time in the wilderness. Similarly, the alcohol can be gelled to reduce risk of leaking or spilling, as with the brand "Sterno".
Methanol is mixed with water and injected into high performance diesel and gasoline engines for an increase of power and a decrease in intake air temperature in a process known as water methanol injection.
Other applications
Methanol is used as a denaturant for ethanol, the product being known as denatured alcohol or methylated spirit. This was commonly used during the US prohibition to discourage consumption of Moonshine liquor, and ended up causing several deaths.
It is sometimes used as a fuel in alcohol lamps, portable fire pits and camping stoves.
Methanol is used as a solvent and as an antifreeze in pipelines and windshield washer fluid. Methanol was used as an automobile coolant antifreeze in the early 1900s.
In some Sewage treatment, a small amount of methanol is added to wastewater to provide a carbon food source for the denitrifying bacteria, which convert to nitrogen gas and reduce the nitrification of sensitive .
Methanol is used as a destaining agent in polyacrylamide gel electrophoresis.
Production
From synthesis gas
Carbon monoxide and hydrogen react over a catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper and , catalyst support on alumina, as first used by ICI in 1966. At 5–10 MPa (50–100 atm) and , the reaction
is characterized by high selectivity (>99.8%). The production of syngas from methane produces three moles of hydrogen for every mole of carbon monoxide, whereas the synthesis consumes only two moles of hydrogen gas per 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 equation
In terms of mechanism, the process occurs via initial conversion of CO into , which is then hydrogenation:[Deutschmann, Olaf; Knözinger, Helmut; Kochloefl, Karl and Turek, Thomas (2012) "Heterogeneous Catalysis and Solid Catalysts, 3. Industrial Applications" in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim. ]
where the byproduct is recycled via the water-gas shift reaction
This gives an overall reaction
which is the same as listed above. In a process closely related to methanol production from synthesis gas, a feed of hydrogen and can be used directly.
Biosynthesis
The catalytic conversion of methane to methanol is effected by enzymes including methane monooxygenases. These enzymes are mixed-function oxygenases, i.e. oxygenation is coupled with production of water
Both Fe- and Cu-dependent enzymes have been characterized.
Global emissions of methanol by plants are estimated at between 180 and 250 million tons per year.
Green methanol
As of 2023, 0.2% of global methanol production is produced in ways that have relatively low greenhouse gas emissions; this is known as "green" methanol.
Another method of producing green methanol involves combining hydrogen, carbon dioxide, and a catalyst under high heat and pressure.
Quality specifications and analysis
Methanol is available commercially in various purity grades. Commercial methanol is generally classified according to ASTM purity grades A and AA. Both grade A and grade AA purity are 99.85% methanol by weight. Grade "AA" methanol contains trace amounts of ethanol as well.
Methanol for chemical use normally corresponds to Grade AA. In addition to water, typical impurities include acetone and ethanol (which are very difficult to separate by distillation). UV-vis spectroscopy is a convenient method for detecting aromatic impurities. Water content can be determined by the Karl-Fischer titration.
Safety
Methanol is highly flammable. Its vapours are slightly heavier than air and can travel to a distant ignition source and ignite. Methanol fires should be extinguished with dry chemical, carbon dioxide, water spray or alcohol-resistant foam.[ Methanol flames are invisible in daylight.
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Toxicity
Ingesting as little as of pure methanol can cause permanent blindness by destruction of the optic nerve. is potentially fatal.
Methanol is Toxicity by two mechanisms. First, methanol can be fatal due to effects on the central nervous system, acting as a central nervous system depressant in the same manner as ethanol poisoning. Second, in a process of toxication, it is metabolism to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver.
Outbreaks of methanol poisoning have occurred primarily due to contamination of Ethanol. It is also worth noting that ethanol is a natural antidote to methanol poisoning.
Because of its toxic properties, methanol is frequently used as a denaturant additive for ethanol manufactured for industrial uses. This addition of methanol exempts industrial ethanol (commonly known as "denatured alcohol" or "methylated spirit") from liquor excise taxation in the US and other countries.
See also
Further reading
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Robert Boyle, The Sceptical Chymist (1661) – contains account of distillation of wood alcohol.
External links
