Methanol is a liquid chemical with the formula CH3OH (often abbreviated MeOH). It is colorless, volatile, flammable, and poisonous. Methanol is made from the destructive distillation of wood and is chiefly synthesized from carbon monoxide and hydrogen. Its principal uses are in organic synthesis, as a fuel, solvent, and antifreeze.
Methanol is a polar liquid at room temperature. It is used as antifreeze, solvent, fuel, and as a denaturant for ethanol. The chemical is also used to produce biodiesel via transesterification reaction.
Because methanol has toxic properties, it is frequently used as a denaturant additive for ethanol manufactured for industrial purposes. Methanol is frequently called wood alcohol because it was once produced primarily as a byproduct of the destructive distillation of wood.
Today, three methods are commonly used to produce synthesis gas from the methane component in natural gas. The methods are steam-methane or SMR, which is endothermic, partial oxidation with molecular oxygen, which is exothermic, and the combination of the two, which is referred to as autothermal reforming.
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Ancient Egyptians used a mixture of substances that included methanol in their embalming process. They obtained the methanol from pyrolysis of wood. Pyrolysis is the chemical decomposition of condensed organic substances by heating.
However, pure methanol wasn’t isolated until 1661 by Robert Boyle, who produced the chemical through the distillation of boxwood. The chemical later became known as pyroxylic spirit. The French chemists Jean-Baptiste Dumas and Eugene Peligot determined its elemental composition in 1834.
The term “methyl” was derived from the word “methylene,” which was coined by Dumas and Peligot in 1840. It was then applied to describe “methyl alcohol.” The International Conference on Chemical Nomenclature shortened this to “methanol” in 1892. When German chemists Alwin Mittasch and Mathias Pier developed a means to convert synthesis gas into methanol, a patent was filed on Jan. 12, 1926.
In 2006 astronomers at Jodrell Bank Observatory using the Merlin array of radio telescopes, discovered a large cloud of methanol in space, 300 billion miles across.
Catalysts that are capable of operating at lower temperatures such as copper are used to efficiently produce modern methanol. Low pressure methanol (LPM) was developed by ICI in the late 1960s with the technology owned by Johnson Matthey, the leading licensor of methanol technology.
Natural gas is the most economical and widely used feedstock for methanol production. However, other feedstocks can be used. Coal is increasing in popularity as a feedstock for methanol production, particularly in China. Additionally, mature technologies available for biomass gasification are being implemented for methanol production.
In humans, methanol has a high toxicity. As little as 10 mL can cause permanent blindness if ingested by destruction of the optic nerve. Only 30 ml can be fatal, although the typical fatal dose is 100-125 ml (4 fl oz). However, toxic effects take hours before they are evident and effective antidotes can often prevent permanent damage.
Methanol is toxic by two mechanisms. First, methanol, whether ingested, inhaled, or absorbed through the skin can be fatal due to its CNS depressant properties in the same manner as ethanol poisoning. Second, in a process of toxication, where it is metabolized to formic acid via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. The reaction to formate proceeds completely, with no detectable formaldehyde remaining. Formate is toxic because it inhibits mitochondrial cyochrome c oxidase, causing the symptoms of hypoxia at the cellular level, and also causing metabolic acidosis among a variety of other metabolic disturbances. Fetal tissue will not tolerate methanol.
Methanol poisoning can be treated with the antidotes ethanol or fomepizole. Both of these drugs act to reduce the action of alcohol dehydrogenase on methanol by means of competitive inhibition so it is excreted by the kidneys rather than being transformed into toxic metabolites.
The initial symptoms of methanol intoxication include central nervous system depression, headache, dizziness, nausea, lack of coordination, confusion, and with 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 ethanol.
Once the initial symptoms have passed, a second set of symptoms come into play, 10 to as many as 30 hours after the initial exposure to methanol, including blurring or complete loss of vision and acidosis. These symptoms are the result of the accumulation of toxic levels of formate in the bloodstream, and may progress to death by respiratory failure. The methanol ester derivatives do not share this toxicity.
Methanol is a common laboratory solvent. It is especially useful for HPLC and UV/VIS spectroscopy due to its low UV cutoff.
By far, the largest use of methanol is in manufacture of other chemicals. Approximately 40 percent of methanol is converted to formaldehyde. It is then used to make other products as diverse as plastics, plywood, paints, explosives, and permanent press textiles.
In the early 1970s, Mobil developed a methanol to gasoline process for producing vehicle ready gasoline. One of the facilities was built in New Zealand at Motunui in the 1980s. Then in the 1990s, the United States used large amounts of methanol to produce the gasoline additive methyl tert-butyl ether (MTBE). MTBE was taken off the market in the US, it is still widely used in other parts of the world. In addition to direct use as a fuel, methanol is a component in the transesterification of triglycerides to yield a form of biodeisel.
Other chemical derivatives of methanol include dimethyl ether, which has replaced chlorofluorocarbons as an aerosol spray propellant, and acetic acid. Dimethyl ether or “DME” also can be blended with liquefied petroleum gas (LPG) for home heating and cooking, and can be used as a diesel replacement transportation fuel.
Fuel for vehicles
Methanol is used to fuel internal combustion engines on a limited basis, primarily because it is not nearly as flammable as gasoline. Methanol is more difficult to ignite than gasoline and produces just one-eighth of the heat. Many racing classes including drag racers and mud racers use methanol as their primary fuel source. Methanol is required with a supercharged engine in a Top Alcohol Dragster and, until the end of 2006, all vehicles in the Indianapolis 500 had to run methanol. Mud racers have mixed methanol with gasoline and nitrous oxide to produce more power than gasoline and nitrous oxide alone.
One of the drawbacks of methanol as a fuel is its corrosivity to some metals, including aluminium. Methanol, although a weak acid, attacks the oxide coating that normally protects the aluminium from corrosion:
6 CH3OH + Al2O3 → 2 Al(OCH3)3 + 3 H2O
The resulting methoxide salts are soluble in methanol, resulting in clean aluminium surface, which is readily oxidized by some dissolved oxygen. Also the methanol can act as an oxidizer:
6 CH3OH + 2 Al → 2 Al(OCH3)3 + 3 H2
This reciprocal process effectively fuels corrosion until either the metal is eaten away or the concentration of CH3OH is negligible. Concerns with methanol’s corrosivity have been addressed by using methanol compatible materials, and fuel additives that serve as corrosion inhibitors.
When produced from wood or other organic materials, the resulting organic methanol (bioalcohol) has been suggested as renewable alternative to petroleum-based hydrocarbons. Low levels of methanol can be used in existing vehicles, with the use of proper cosolvents and corrosion inhibitors. The European Fuel Quality Directive allows up to 3 percent methanol with an equal amount of cosolvent to be blended in gasoline sold in Europe. Today, China uses more than one billion gallons of methanol per year as a transportation fuel in both low level blends in existing vehicles, and as high level blends in vehicles designed to accommodate the use of methanol fuels.
Methanol is a traditional denaturant for ethanol, thus giving the term “methylated spirit.”
Methanol is also used as a solvent, and as an antifreeze in pipelines and windshield washer fluid.
In some wastewater treatment plants, a small amount of methanol is added to wastewater to provide a food source of carbon for the denitrifying bacteria, which convert nitrates to nitrogen to reduce the denitrification of sensitive aquifers.
During World War II, methanol was used as a fuel in several German military rocket designs, under the name M-Stoff, and in a mixture as C-Stoff.
In the early 1900s, methanol was used as an automobile coolant antifreeze.
Methanol is also a denaturing agent in polyacrylamide gel electrophoresis.
Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, allowing them to be miniaturized to an unprecedented degree. Combined with the relatively easy and safe storage and handling of methanol, this may open the possibility of fuel cell-powered consumer electronics, such as laptop computers and mobile phones.
Methanol is also widely used as fuel in camping and boating stoves. Methanol burns well in unpressurized burners. Alcohol stoves often require little more than a cup to hold fuel. This lack of complexity makes them a favorite of hikers spending extended time in the wilderness.