Methanol, also known as methyl alcohol or wood alcohol, is a chemical compound with chemical formula CH3OHH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid that is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. The chemical structure is:
H | H-C-OH | HMethanol burns in air forming carbon dioxide and water:
Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria. As a result, there is a small fraction of methanol vapor in the atmosphere. Over the course of several days, atmospheric methanol is oxidized by oxygen and sunlight to carbon dioxide.
|Table of contents|
4 Health and safety
5 Physical Properties
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 wood alcohol. 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 the Greek words methu, meaning "wine," and hyle, meaning "wood". 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.
In 1923, the German chemist Matthias Pier, working for BASF developed a means to convert synthesis gas (a mixture of carbon monoxide and hydrogen derived from coke and used as the source of hydrogen in synthetic ammonia production) into methanol. This process used a zinc chromate catalyst, and required extremely vigorous conditions—pressures ranging from 300-1000 atm, and temperatures of about 400°C. Modern methanol production has been made more efficient through the use of catalysts capable of operating at lower pressures.
Today, synthesis gas is usually produced from the methane in natural gas rather than from coal. At moderate pressures (10-20 atm) and high temperatures (around 850°C), methane reacts with steam on a nickel catalyst to produce carbon monoxide and hydrogen according to the chemical equation
copper, zinc oxide, and alumina first used by ICI in 1966. At 50-100 atm and 250°C, it can catylize the production of methanol from carbon monoxide and hydrogen with high selectivity
moless 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
petroleum products can be used in its place. The South African firm Sasol produces methanol using synthesis gas from coal.
Methanol is used on a limited basis as a motor fuel. When produced from wood or other organic materials, the resulting organic methanol (bioalcohol) has been suggested as renewable alternative to petroleum-based hydrocarbons. However, one cannot use BA100 (100% bioalcohol) in modern petroleum cars without modification. One can use B100 (100% biodiesel) in unmodified petrodiesel cars). Methanol blends are used as fuel in open wheel racing circuits like CART.
Methanol is also used as a solvent and as an antifreeze in pipelines. The largest use of methanol by far, however, is in making other chemicals. About 40% of methanol is converted to formaldehyde, and from there into products as diverse as plastics, plywood, paints, explosives, and permanent press textiles.
In the 1990s, large amounts of methanol were used in the United States to produce the gasoline additive methyl tert-butyl ether (MTBE). The 1990 Clean Air Act required certain major cities to use MTBE in their gasoline to reduce photochemical smog. However, by the late 1990s, it was found that MTBE had leaked out of gasoline storage tanks and into the groundwater in sufficient amounts to affect the taste of municipal drinking water in many areas. Moreover, MTBE was found to be a carcinogen in animal studies. In the resulting backlash, several states banned the use of MTBE, and its future production remains uncertain.
Health and safety
Methanol is toxic, as its metabolites formic acid and formaldehyde cause blindness and death. It enters the body by ingestion, inhalation, or absorption through the skin. Dangerous doses will build up if a person is regularly exposed to fumes or handles liquid without skin protection. If methanol has been ingested, a doctor should be contacted immediately. Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. One treatment is the injection of ethanol: this slows down the breakdown of methanol by the liver, so that the toxic metabolites can not build up.
Symptoms of methanol ingestion are similar to those of intoxication: headache, dizziness, nausea, lack of coordination, confusion, drowsiness, followed by unconsciousness and death.
The ester derivatives of methanol do not share this toxicity.
Ethanol is sometimes denatured (made undigestable) by the addition of methanol. The result is known as methylated spirits or meths. (The latter should not be confused with meth, a common abbreviation for methamphetamine.)