Methanol
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:\n H\n |\n H-C-OH\n |\n H
Methanol burns in air forming
carbon dioxide and
water:
- 2 CH3OH + 3 O2 → 2 CO2 + 4 H2O
A methanol flame is almost colorless. Care should be exercised around burning methanol to avoid burning oneself on the almost invisible fire.
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.
History
\nIn 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 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.
References
\n*Robert Boyle, The Sceptical Chemist (1661) - contains account of distillation of wood alcohol.
Production
\nToday, 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 syngas according to the chemical equation
- CH4 + H2O → CO + 3 H2
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 50-100 atm and 250°C, it can catylize the production of methanol from carbon monoxide and hydrogen with high selectivity
- CO + 2 H2 → CH3OH
It is worth noting that the production of synthesis gas from methane produces 3
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
- CO2 + 3 H2 → CH3OH + H2O
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.
Uses
\nMethanol is used on a limited basis to fuel internal combustion engines, mainly by virtue of the fact that it is not nearly as flammable as
gasoline. Methanol blends are the fuel of choice in
open wheel racing circuits like
Champcars, as well as in
RC model airplaness.
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 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.
Other chemical derivatives of methanol include
dimethyl ether, which has replaced
chlorofluorocarbons as the propellant in
aerosol sprays, and
acetic acid.
Health and safety
\nMethanol 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. The usual fatal dose: 100-125 mL (4 oz.). 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 (adulterated) 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.)
Pure methanol has been used in open wheel racing since the mid-1960's. Unlike petroleum fires, methanol fires can be extinguished with plain water. The decision was made shortly after the death of two drivers.
Physical Properties
See also
Related sites
- The Methanol Institute Industry trade group, lots of information on methanol's use in fuel cells and as an alternative fuel.
Category:Alcohols
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