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Methane
Other names Methyl hydride, Marsh gas, firedamp
Identifiers
CAS number [74-82-8]
PubChem 297
SMILES
InChI
ChemSpider ID 291
Properties
Molecular formula CH4
Molar mass 16.042 g/mol
Appearance Colorless gas
Density 0.717 kg/m3, gas
415 kg/m3 liquid
Melting point

-182.5 °C, 91 K, -297 °F

Boiling point

-161.6 °C, 112 K, -259 °F

Solubility in water 3.5 mg/100 mL (17 °C)
Hazards
MSDS External MSDS
R-phrases R12
S-phrases (S2), S9, S16, S33
NFPA 704
4
1
0
 
Flash point -188 °C
Related compounds
Related alkanes Ethane, propane
Related compounds Methanol, chloromethane, formic acid, formaldehyde, silane
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox references

Methane is a chemical compound with the molecular formula CH4. It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean burning process makes it a very attractive fuel. However, because it is a gas at normal temperature and pressure, methane is difficult to transport from its source. In its natural gas form, it is generally transported in bulk by pipeline or LNG carriers; few countries still transport it by truck.

Methane was discovered and isolated by Alessandro Volta between 1776 and 1778 when studying marsh gas from Lake Maggiore.

Methane is a relatively potent greenhouse gas with a high global warming potential of 72 (averaged over 20 years) or 25 (averaged over 100 years).[1] Methane in the atmosphere is eventually oxidized, producing carbon dioxide and water. As a result, methane in the atmosphere has a half life of seven years.

The abundance of methane in the Earth's atmosphere in 1998 was 1745 parts per billion, up from 700 ppb in 1750. Methane can trap about 20 times the heat of CO2. In the same time period, CO2 increased from 278 to 365 parts per million. The radiative forcing effect due to this increase in methane abundance is about one-third of that of the CO2 increase.[2] In addition, there is a large, but unknown, amount of methane in methane clathrates in the ocean floors. The Earth's crust contains huge amounts of methane. Large amounts of methane are produced anaerobically by methanogenesis. Other sources include mud volcanoes, which are connected with deep geological faults, and livestock (primarily cows) from enteric fermentation.

Contents

Properties

Methane is the major component of natural gas, about 87% by volume. At room temperature and standard pressure, methane is a colorless, odorless gas; the smell characteristic of natural gas as used in homes is an artificial safety measure caused by the addition of an odorant, often methanethiol or ethanethiol. Methane has a boiling point of −161 °C at a pressure of one atmosphere. As a gas it is flammable only over a narrow range of concentrations (5–15%) in air. Liquid methane does not burn unless subjected to high pressure (normally 4–5 atmospheres).

Potential health effects

Methane is not toxic; however, it is highly flammable and may form explosive mixtures with air. Methane is violently reactive with oxidizers, halogens, and some halogen-containing compounds. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia may result if the oxygen concentration is reduced to below 19.5% by displacement Template:Fact. The concentrations at which flammable or explosive mixtures form are much lower than the concentration at which asphyxiation risk is significant. When structures are built on or near landfills, methane off-gas can penetrate the buildings' interiors and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture such fugitive off-gas and vent it away from the building. An example of this type of system is in the Dakin Building, Brisbane, California.

Reactions of methane

Main reactions with methane are: combustion, steam reforming to syngas, and halogenation. In general, methane reactions are hard to control. Partial oxidation to methanol, for example, is difficult to achieve; the reaction typically progresses all the way to carbon dioxide and water.

Combustion

In the combustion of methane, several steps are involved:

Methane is believed to form a formaldehyde (HCHO or H2CO). The formaldehyde gives a formyl radical (HCO), which then forms carbon monoxide (CO). The process is called oxidative pyrolysis:

CH4 + O2 → CO + H2 + H2O

Following oxidative pyrolysis, the H2 oxidizes, forming H2O, replenishing the active species,Template:Clarify me and releasing heat. This occurs very quickly, usually in significantly less than a millisecond.

2H2 + O2 →2H2O

Finally, the CO oxidizes, forming CO2 and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur.

2CO + O2 →2CO2

The result of the above is the following total equation:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + 890 kJ/mol[3]

where bracketed "g" stands for gaseous form and bracketed "l" stands for liquid form.

Hydrogen activation

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. Despite the high activation barrier for breaking the C–H bond, CH4 is still the principal starting material for manufacture of hydrogen in steam reforming. 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.

Reactions with halogens

Methane reacts with all halogens given appropriate conditions, as follows:

CH4 + X2 → CH3X + HX

where X is a halogen: fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). This mechanism for this process is called free radical halogenation. When X is Cl, this mechanism has the following form:

1. Radical generation:

\mbox{Cl}_2 \xrightarrow[\triangle]{UV} 2\mbox{Cl}\cdot - 239 \mbox{kJ}

  • The needed energy comes from UV radiation or heating,

2. Radical exchanges:

\mbox{CH}_4 + \mbox{Cl}\!\cdot \xrightarrow{} \mbox{CH}_3\!\cdot + \mbox{HCl} + 14 \mbox{kJ}
\mbox{CH}_3\!\cdot + \mbox{Cl}_2 \xrightarrow{} \mbox{CH}_3\mbox{Cl} + \mbox{Cl}\!\cdot + 100 \mbox{kJ}

3. Radical extermination:\!

2\mbox{Cl}\!\cdot \xrightarrow{} \mbox{Cl}_2 + 239 \mbox{kJ}
\mbox{CH}_3\!\cdot + \mbox{Cl}\!\cdot \xrightarrow{} \mbox{CH}_3\mbox{Cl} + 339 \mbox{kJ}
2\mbox{CH}_3\!\cdot \xrightarrow{} \mbox{CH}_3\mbox{CH}_3 + 347 \mbox{kJ}

  • If methane and X2 are used in equimolar quantities, CH2X2, CHX3, and even CX4 are formed. Using a large overquantitity of CH4 reduces the production of CH2X2, CHX3, CX4, and thus more CH3X is formed.

Uses

Fuel

For more on the use of methane as a fuel, see: natural gas

Methane is important for electrical generation by burning it as a fuel in a gas turbine or steam boiler. Compared to other hydrocarbon fuels, burning methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's combustion heat is lower than any other hydrocarbon; but a ratio with the molecular mass (16.0 g/mol) divided by the heat of combustion (891 kJ/mol) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit than other complex hydrocarbons. In many cities, methane is piped into homes for domestic heating and cooking purposes. In this context it is usually known as natural gas, and is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot.

Methane in the form of compressed natural gas is used as a vehicle fuel, and is claimed to be more environmentally friendly than other fossil fuels such as gasoline/petrol and diesel.[who?]

Research is being conducted by NASA on methane's potential as a rocket fuel. One advantage of methane is that it is abundant in many parts of the solar system and it could potentially be harvested in situ , providing fuel for a return journey.[4] Current methane engines in development produce a thrust of 7,500 pounds , which is far from the seven million pounds needed to launch the space shuttle. Instead, such engines will most likely propel voyages from our moon or send robotic expeditions to other planets in the solar system.[5]

Recently methane emitted from coal mines has been successfully converted to electricity.[6]

Industrial uses

Methane is used in industrial chemical processes and may be transported as a refrigerated liquid (liquefied natural gas, or LNG). While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of the cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component.

In the chemical industry, methane is the feedstock of choice for the production of hydrogen, methanol, acetic acid, and acetic anhydride. When used to produce any of these chemicals, methane is first converted to synthesis gas, a mixture of carbon monoxide and hydrogen, by steam reforming. In this process, methane and steam react on a nickel catalyst at high temperatures (700–1100 °C).

CH_4 + H_2O \xrightarrow[700-1100^oC]{Ni} CO + 3H_2

The ratio of carbon monoxide to hydrogen in synthesis gas can then be adjusted via the water gas shift reaction to the appropriate value for the intended purpose.

CO + H2O → CO2 + H2

Less significant methane-derived chemicals include acetylene, prepared by passing methane through an electric arc, and the chloromethanes (chloromethane, dichloromethane, chloroform, and carbon tetrachloride), produced by reacting methane with chlorine gas. However, the use of these chemicals is declining. Acetylene is replaced by less costly substitutes, and the use of chloromethanes is diminishing due to health and environmental concerns.

Sources of methane

Natural gas fields

The major source of methane is extraction from geological deposits known as natural gas fields. It is associated with other hydrocarbon fuels and sometimes accompanied by helium and nitrogen. The gas at shallow levels (low pressure) is formed by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, sediments buried deeper and at higher temperatures than those which give oil generate natural gas. Methane is also produced in considerable quantities from the decaying organic wastes of solid waste landfills.

Alternative sources

Apart from gas fields, an alternative method of obtaining methane is via biogas generated by the fermentation of organic matter including manure, wastewater sludge, municipal solid waste (including landfills), or any other biodegradable feedstock, under anaerobic conditions. Methane hydrates/clathrates (icelike combinations of methane and water on the sea floor, found in vast quantities) are a potential future source of methane. Cattle belch methane accounts for 16% of the world's annual methane emissions to the atmosphere.[7] The livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane".[8] However animals "that put their energies into making gas are less efficient at producing milk and meat". Early research has found a number of medical treatments and dietary adjustments that help limit the production of methane in ruminants.[9][10][11]

Industrially, methane can be created from common atmospheric gases and hydrogen (produced, for example, by electrolysis) through chemical reactions such as the Sabatier process, Fischer-Tropsch process. Coal bed methane extraction is a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from an unminable coal seam.

Scientific experiments have given variable results in determining whether plants are a source of methane emissions.[12][13][14]

Atmospheric methane

Methane is created near the Earths surface, and it is carried into the stratosphere by rising air in the tropics. Uncontrolled build-up of methane in Earth's atmosphere is naturally checked—although human influence can upset this natural regulation—by methane's reaction with hydroxyl radicals formed from singlet oxygen atoms and with water vapor.

Methane in the Earth's atmosphere is an important greenhouse gas with a global warming potential of 25 kg CO2 over a 100-year period. This means that a methane emission will have 25 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years. Methane has a large effect for a brief period (a net lifetime of 8.4 years in the atmosphere), whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20 year time period is 72. The Earth's methane concentration has increased by about 150% since 1750, and it accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases.[15] Usually, excess methane from landfills and other natural producers of methane are burned so CO2 is released into the atmosphere instead of methane because methane is such a more effective greenhouse gas. Recently methane emitted from coal mines has been successfully converted to electricity.

Extraterrestrial methane

Methane has been detected or is believed to exist in several locations of the solar system. It is believed to have been created by abiotic processes, with the possible exception of Mars.

  • Moon - traces are present in the thin atmosphere[16]
  • Mars - the atmosphere contains 10 ppb methane. In January 2009, NASA scientists announced that they had discovered that the planet regularly vents methane into the atmosphere in specific areas at regular times, leading some to speculate this may be a sign of biological activity going on below the surface.[17]
  • Jupiter - the atmosphere contains about 0.3% methane
  • Saturn - the atmosphere contains about 0.4% methane
  • Uranus - the atmosphere contains 2.3% methane
    • Ariel - methane is believed to be a constituent of Ariel's surface ice
    • Miranda
    • Oberon - about 20% of Oberon's surface ice is composed of methane-related carbon/nitrogen compounds
    • Titania - about 20% of Titania's surface ice is composed of methane-related organic compounds
    • Umbriel - methane is a constituent of Umbriel's surface ice
  • Neptune - the atmosphere contains 1.6% methane
    • Triton - Triton has a tenuous nitrogen atmosphere with small amounts of methane near the surface.[20][21]
  • Pluto - spectroscopic analysis of Pluto's surface reveals it to contain traces of methane[22][23]
    • Charon - methane is believed to be present on Charon, but it is not completely confirmed[24]
  • Eris - infrared light from the object revealed the presence of methane ice
  • Comet Halley
  • Comet Hyakutake - terrestrial observations found ethane and methane in the comet[25]
  • Extrasolar planet HD 189733b - This is the first detection of an organic compound on a planet outside the solar system. Its origin is unknown, since the planet's high temperature (700°C) would normally favor the formation of carbon monoxide instead.[26]
  • Interstellar clouds[27]

See also

File:Sustainable Sustainable development portal

References

  1. IPCC Fourth Assessment Report
  2. "Radiative Forces of Climate Change". Climate Change 2001: The Scientific Basis. IPCC. http://www.grida.no/climate/ipcc_tar/wg1/221.htm. Retrieved on 2008-05-26. 
  3. SCHAUM'S OUTLINE SERIES, ORGANIC CHEMISTRY
  4. http://science.nasa.gov/headlines/y2007/04may_methaneblast.htm?list123532
  5. Green, V. (2007) Hit the Gas: NASA's methane rocket could make long distance space travel possible, on the cheap. Popular Science magazine, September. pg 16-17.
  6. A Global First: Coal Mine Turns Greenhouse Gas into Green Energy
  7. Miller, G. Tyler. Sustaining the Earth: An Integrated Approach. U.S.A.: Thomson Advantage Books, 2007. 160.
  8. "Livestock’s Long Shadow–Environmental Issues and Options". http://www.virtualcentre.org/en/library/key_pub/longshad/A0701E00.htm. Retrieved on 2007-01-04. 
  9. California Cows Fail Latest Emissions Test
  10. New Zealand Tries to Cap Gaseous Sheep Burps
  11. Research on use of bacteria from the stomach lining of kangaroos (who don't emit methane) to reduce methane in cattle
  12. Hamilton JT, McRoberts WC, Keppler F, Kalin RM, Harper DB (July 2003). "Chloride methylation by plant pectin: an efficient environmentally significant process". Science (journal) 301 (5630): 206–9. doi:10.1126/science.1085036. PMID 12855805. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=12855805. 
  13. "Methane Emissions? Don't Blame Plants", ScienceNOW, 14 January 2009
  14. Plants do emit methane after all, New Scientist, 2 December 2007
  15. "Technical summary". Climate Change 2001. United Nations Environment Programme. http://www.grida.no/climate/ipcc_tar/wg1/017.htm. 
  16. Stern, S.A. (1999). "The Lunar atmosphere: History, status, current problems, and context". Rev. Geophys. 37: 453–491. doi:10.1029/1999RG900005. 
  17. http://www.washingtonpost.com/wp-dyn/content/article/2009/01/15/AR2009011502222.html
  18. H. B. Niemann, et al. (2005). "The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe". Nature 438: 779–784. doi:10.1038/nature04122. 
  19. Waite, J. H.; et al.; (2006); Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure, Science, Vol. 311, No. 5766, pp. 1419–1422
  20. A L Broadfoot, S K Bertaux, J E Dessler et al. (December 15, 1989). "Ultraviolet Spectrometer Observations of Neptune and Triton". Science 246: 1459–1466. doi:10.1126/science.246.4936.1459. PMID 17756000. http://adsabs.harvard.edu/abs/1989Sci...246.1459B. Retrieved on 2008-01-15. 
  21. Ron Miller; William K. Hartmann (May 2005). The Grand Tour: A Traveler's Guide to the Solar System (3rd ed.). Thailand: Workman Publishing. pp. 172–73. ISBN 0-7611-3547-2. 
  22. Tobias C. Owen, Ted L. Roush et al. (6 August 1993). "Surface Ices and the Atmospheric Composition of Pluto". Science 261 (5122): 745–748. doi:10.1126/science.261.5122.745. PMID 17757212. http://www.sciencemag.org/cgi/content/abstract/261/5122/745. Retrieved on 2007-03-29. 
  23. "Pluto". SolStation. 2006. http://www.solstation.com/stars/pluto.htm. Retrieved on 2007-03-28. 
  24. B. Sicardy et al. (2006). "Charon’s size and an upper limit on its atmosphere from a stellar occultation". Nature 439: 52. doi:10.1038/nature04351+. http://www.nature.com/nature/journal/v439/n7072/abs/nature04351.html. 
  25. Mumma, M.J.; Disanti, M.A., dello Russo, N., Fomenkova, M., Magee-Sauer, K., Kaminski, C.D., and D.X. Xie (1996). "[[[:Template:ADS]] Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin]". Science 272: 1310. doi:10.1126/science.272.5266.1310+. Template:ADS. 
  26. Stephen Battersby (2008-02-11). "Organic molecules found on alien world for first time". http://space.newscientist.com/article/dn13303-organic-molecules-found-on-alien-world-for-first-time.html. Retrieved on 2008-02-12. 
  27. J. H. Lacy, J. S. Carr, N. J. Evans, II, F. Baas, J. M. Achtermann, J. F. Arens (1991). "Discovery of interstellar methane - Observations of gaseous and solid CH4 absorption toward young stars in molecular clouds". Astrophysical Journal 376: 556–560. doi:10.1086/170304+. http://adsabs.harvard.edu/abs/1991ApJ...376..556L. 

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also méthane

Contents

English

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Wikipedia

Pronunciation

Noun

Singular
methane

Plural
countable and uncountable; plural methanes

methane (countable and uncountable; plural methanes)

  1. (organic chemistry, uncountable) The simplest aliphatic hydrocarbon, CH4, being a constituent of natural gas.
    Cattle emit a large amount of methane.
  2. (organic chemistry, countable) Any of very many derivatives of methane.

Synonyms

  • methyl hydride (appears in some chemistry literature)
  • carbon tetrahydride (rare, systematic name)

Translations

Anagrams


Simple English

Hydrocarbon - Methane
Molecular Formula CH4
Series (Family) - Alkanes
Previous
Next Ethane
Physical Properties
Melting Point -182.5 °C, 91 K, -297 °F
Boiling Point -161.6 °C, 112 K, -259 °F


[[File:|thumb|Structural formula of methane. C is carbon and H is hydrogen. The lines show that the atoms are joined by chemical bonds.]] [[File:|thumb|A picture to show simply how the atoms may fill space. The grey is carbon and the white is hydrogen.]] Methane is a hydrocarbon that is a gas at room temperature (20oC). Its molecular formula is CH4, so it has one carbon atom and four hydrogen atoms in a molecule. It is often found as the main part of natural gas. Methane is a greenhouse gas 22 times more effective than carbon dioxide. It is also less stable and slowly oxidates by oxygen to carbon dioxide and water.

Uses

Methane is used in gas taps in places such as chemistry classrooms, laboratories, etc. as it burns very easily because of its simple molecular structure.

Molecular structure

Methane's molecular structure is very simple. It is a single carbon atom surrounded by four hydrogen atoms.

Production

Methane can be produced by many chemical methods, but usually is found in natural gas and is obtained by fractional distillation, after it is become liquid.


Citable sentences

Up to date as of December 17, 2010

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