ਮੀਥੇਨ: ਰੀਵਿਜ਼ਨਾਂ ਵਿਚ ਫ਼ਰਕ

 

 

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 °[[Celsius|C]] at a pressure of one [[Atmosphere (unit)|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).

 

Methane is not toxic; however, it is highly flammable and may form [[explosive]] mixtures with air. Methane is violently reactive with [[oxidizer]]s, [[halogen]]s, and some halogen-containing compounds. Methane is also an [[asphyxiant gas|asphyxiant]] and may displace [[oxygen]] in an enclosed space. [[Asphyxia]] may result if the oxygen concentration is reduced to below 19.5% by displacement. 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 [[landfill]]s, 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.{{Citation needed|date=January 2010}} An example of this type of system is in the [[Dakin Building]], [[Brisbane, California]].

 

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]].

 

In the [[combustion]] of methane, several steps are involved:

 

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

 

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, {{chem|CH|4}} is still the principal starting material for manufacture of hydrogen in [[steam reforming]]. The search for [[catalyst]]s which can facilitate C–H bond activation in methane and other low [[alkane]]s is an area of research with considerable industrial significance.

 

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

 

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

 

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

 

 

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.<ref>{{cite news|quote=Compressed natural gas is touted as the 'cleanest burning' alternative fuel available, since the simplicity of the methane molecule reduces tailpipe emissions of different pollutants by 35 to 97%. Not quite as dramatic is the reduction in net greenhouse-gas emissions, which is about the same as corn-grain ethanol at about a 20% reduction over gasoline|url=http://www.gas2.org/2008/04/29/natural-gas-cars-cng-fuel-almost-free-in-some-parts-of-the-country/|title=Natural Gas Cars: CNG Fuel Almost Free in Some Parts of the Country|date=April 29, 2008|author=Clayton B. Cornell}}</ref>

Recently methane emitted from coal mines has been successfully converted to electricity.<ref>[http://www.megtec.com/news_article.php?news_id=42 A Global First: Coal Mine Turns Greenhouse Gas into Green Energy]</ref>

 

 

 

:<math>\mathrm{CH}_4 + \mathrm{H_2O} \xrightarrow[700-1100 \ \mathrm{^oC}]{\mathrm{Ni}} \mathrm{CO + 3H_2} </math>

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.

 

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 organism|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 [[Petroleum|oil]] generate natural gas. Methane is also produced in considerable quantities from the decaying organic wastes of [[solid waste]] [[landfill]]s.

 

Apart from gas fields, an alternative method of obtaining methane is via [[biogas]] generated by the [[fermentation (biochemistry)|fermentation]] of organic matter including [[manure]], wastewater sludge, municipal solid waste (including landfills), or any other biodegradable feedstock, under anaerobic conditions. Methane hydrates/clathrates (ice-like 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.<ref>Miller, G. Tyler. ''Sustaining the Earth: An Integrated Approach''. U.S.A.: Thomson Advantage Books, 2007. 160.</ref> The livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane.<ref>{{cite web |url=http://www.fao.org/docrep/010/a0701e/a0701e00.HTM

|title=Livestock’s Long Shadow–Environmental Issues and Options|accessdate=2009-10-27}}</ref> Early research has found a number of medical treatments and dietary adjustments that help slightly limit the production of methane in [[ruminants]].<ref>[http://news.nationalgeographic.com/news/2002/05/0509_020509_belch.html New Zealand Tries to Cap Gaseous Sheep Burps]</ref><ref>[http://www.alternet.org/story/72339/ Research on use of bacteria from the stomach lining of kangaroos (who don't emit methane) to reduce methane in cattle]</ref>

Scientific experiments have given variable results in determining whether plants are a source of methane emissions.<ref>{{cite journal |author=Hamilton JT, McRoberts WC, Keppler F, Kalin RM, Harper DB |title=Chloride methylation by plant pectin: an efficient environmentally significant process |journal=Science (journal) |volume=301 |issue=5630 |pages=206–9 |year=2003 |month=July |pmid=12855805 |doi=10.1126/science.1085036 |url=http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=12855805}}</ref><ref>[http://sciencenow.sciencemag.org/cgi/content/full/2009/114/1 "Methane Emissions? Don't Blame Plants"], ScienceNOW, 14 January 2009</ref><ref>[http://environment.newscientist.com/article/mg19626322.900-plants-do-emit-methane-after-all.html Plants do emit methane after all], ''[[New Scientist]]'', 2 December 2007</ref>

 

{{Main|Atmospheric methane}}

{{Unreferenced|date=January 2010}}

Methane is created near the Earth's surface, primarily in soils, rivers/seas and in animal innards. It is carried into the [[stratosphere]] by rising air in the [[tropics]]. Uncontrolled build-up of methane in the atmosphere is naturally checked&nbsp;— although human influence can upset this natural regulation&nbsp;— by methane's reaction with [[hydroxyl radical]]s formed from [[singlet oxygen]] atoms and with water vapor.

 

In prehistoric times, large methane excursions have been linked with dramatic shifts in the Earth's climate, notably during the [[Paleocene-Eocene thermal maximum]] and during the [[Permian-Triassic extinction event]], which was the worst ever [[mass extinction]].{{Dubious|February 2010|date=February 2010}}

 

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 components|abiotic]] processes, with the possible exception of [[Life on Mars|Mars]].

 

{{cite journal|title= The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe |author= H. B. Niemann, et al. |journal= [[Nature]] |volume=438 |pages=779–784 |year=2005 |doi=10.1038/nature04122|pmid= 16319830|last1= Niemann|first1= HB|last2= Atreya|first2= SK|last3= Bauer|first3= SJ|last4= Carignan|first4= GR|last5= Demick|first5= JE|last6= Frost|first6= RL|last7= Gautier|first7= D|last8= Haberman|first8= JA|last9= Harpold|first9= DN|issue= 7069}}</ref>

|title = Ultraviolet Spectrometer Observations of Neptune and Triton

|author = A L Broadfoot, S K Bertaux, J E Dessler et al.

|isbn = 0-7611-3547-2

}}</ref>

 

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{{Commons|Methane}}

{{Wiktionary|methane}}

 

{{ਅਲਕੇਨ}}

 

 

[[af:Metaan]]

[[ja:メタン]]

[[ka:მეთანი]]

[[ku:Mêtan]]

[[la:Methanum]]