Methane
The simplest
hydrocarbon,
methane is a
gas with a
chemical formula of
CH4.
\nA principal component of
natural gas, methane is a significant
fuel. Burning one molecule of methane in the presence of
oxygen releases one molecule of CO
2 (
carbon dioxide) and two molecules of H
2O (
water):\n: CH
4 + 2O
2 → CO
2 + 2H
2O
Due to the
heat and
attack by the active species, the methane reacts to a
methyl radical (CH
3), which reacts to
formaldehyde (HCHO
or H
2CO). The formaldehyde reacts to a formal
radical (HCO), which then forms
carbon monoxide (CO). The process is called oxidative
pyrolysis: \n:CH
4 + O
2 
CO + H
2 + H
2O \nFollowing oxidative pyrolysis, the H
2 oxidizes, forming H
2O, replenishing the active species, and releasing heat. This occurs very quickly, usually in less than a
millisecond. \n:H
2 + ½ O
2 H
2O \nFinally, the CO oxidizes, forming CO
2 and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur. \n:CO + ½ O
2 CO
2
The strength of the
carbon-
hydrogen covalent bond in methane is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited. The search for
catalysts which can facilitate C-H bond activation in methane and other low
alkanes is an area of research with considerable industrial significance.
Pure methane is
odorless, but when used as a fuel is usually mixed with small quantities of strongly-smelling
sulfur compounds such as
ethyl mercaptan to enable the detection of leaks.
Methane is a
greenhouse gas with a
global warming potential of 21 (meaning that it has 21 times the warming ability of
carbon dioxide).
Methane results from the
decomposition of certain organic matters in the absence of
oxygen. It is therefore also classified as a
biogas.
Principal sources are\n* decomposition of organic wastes\n* natural sources (marshes) : 23 %\n*
fossil fuel extraction : 20 % See
Coal bed methane extraction\n* the processes of
digestion of animals (cattle) : 17 %\n*
bacteria found in
rice plantations : 12 %\n*
biomass anaerobic heating or combustion
80% of the world emissions are of human source. They come primarily from agricultural and other human activities. During the past 200 years, the concentration of this gas in the atmosphere doubled, passing from 0.8 to 1.7 ppm.
See also
\n*methyl group, a functional group similar to methane\n*
methanogen\n*
methanogenesis\n*
Methane clathrate\n*
Coal bed methane extraction\n*
Alkane
Category: Alkanes\ncategory: greenhouse gases
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