ਮੀਥੇਨ

ਵਿਕੀਪੀਡੀਆ, ਇਕ ਅਜ਼ਾਦ ਵਿਸ਼ਵਗਿਆਨਕੋਸ਼ ਤੋਂ
(ਮਿਥੇਨ ਤੋਂ ਰੀਡਿਰੈਕਟ)
ਇਸ ’ਤੇ ਜਾਓ: ਨੇਵੀਗੇਸ਼ਨ, ਖੋਜ

ਮੀਥੇਨ ਇੱਕ ਰਸਾਇਣਕ ਯੋਗਕ ਹੈ ਜਿਹਦਾ ਫਾਰਮੂਲਾ CH4 ਹੈ। ਇਹ ਸਭ ਤੋਂ ਸੌਖਾ ਅਲਕੇਨ ਹੈ , ਅਤੇ ਕੁਦਰਤੀ ਗੈਸ ਦਾ ਭਾਗ ਹੈ। ਇਹ ਆਮ ਤਾਪਮਾਨ ਉੱਤੇ ਇੱਕ ਗੈਸ ਹੈ ਅਤੇ ਆਕਸੀਜਨ ਦੀ ਹਾਜ਼ਰੀ ਵਿੱਚ ਬਲ ਕੇ ਕਾਰਬਨ ਡਾਈਆਕਸਾਈਡ ਅਤੇ ਪਾਣੀ ਬਣਾਉਂਦੀ ਹੈ। ਇਸ ਦੀ ਖੋਜ ਵੋਲਟਾ ਨੇ ਕੀਤੀ।


ਵਿਸ਼ੇਸ਼ਤਾਵਾਂ[ਸੋਧੋ]

ਮੀਥੇਨ ਕੁਦਰਤੀ ਗੈਸ ਦਾ ਮੁੱਖ ਭਾਗ ਹੈ ਜੋ ਆਇਤਨ ਦੇ ਅਨੁਸਾਰ 87% ਹੁੰਦੀ ਹੈ। ਸਧਾਰਣ ਹਾਲਤ ਤੇ ਮੀਥੇਨ ਰੰਗਹੀਨ ਗੰਧਹੀਣ ਗੈਸ ਹੈ 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[ਸੋਧੋ]

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. 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.[citation needed] An example of this type of system is in the Dakin Building, Brisbane, California.

Reactions of methane[ਸੋਧੋ]

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[ਸੋਧੋ]

In the combustion of methane, several steps are involved:

Methane is thought to form a formaldehyde (HCHO or H{{Chem}}'s autolinking cannot cope with this many parameters.). 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 {{Chem}}'s autolinking cannot cope with this many parameters. oxidizes, forming H{{Chem}}'s autolinking cannot cope with this many parameters., releasing heat. This occurs very quickly, usually in significantly less than a millisecond.

2 H2 + O2 → 2 H2O

Finally, the CO oxidizes, forming {{Chem}}'s autolinking cannot cope with this many parameters. and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur.

2 CO + O2 → 2 CO2

The result of the above is the following total equation:

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) + 891 kJ/mol

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

Hydrogen activation[ਸੋਧੋ]

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}}'s autolinking cannot cope with this many parameters. 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[ਸੋਧੋ]

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:

\mathrm{Cl_2 \xrightarrow[\triangle]{UV} 2Cl^\bullet - 239 \; kJ}

The needed energy comes from UV radiation or heating,

2. Radical exchange:

CH4 + Cl· → CH3· + HCl + 14 kJ
CH3· + Cl2 → CH3Cl + Cl· + 100 kJ

3. Radical extermination:

2 Cl· → Cl2 + 239 kJ
CH3· + Cl· → CH3Cl + 339 kJ
2 CH3· → CH3CH3 + 347 kJ

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.

ਵਰਤੋਂ[ਸੋਧੋ]

Fuel[ਸੋਧੋ]

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 heat of combustion is lower than any other hydrocarbon but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) 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.[੧]

Research is being conducted by NASA on methane's potential as a rocket fuel.[੨] One advantage of methane is that it is abundant in many parts of the solar system and it could potentially be harvested in situ (i.e. on the surface of another solar-system body), providing fuel for a return journey.[੩]

Current methane engines in development produce a thrust of ਫਰਮਾ:Convert/LonAoffDbSoff, which is far from the ੭੦,੦੦,੦੦੦ lbf (ਫਰਮਾ:Convert/MN) 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.[੪]

Recently methane emitted from coal mines has been successfully converted to electricity.[੫]

ਮਾਇਕ ਵਰਤੋਂ[ਸੋਧੋ]

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).

\mathrm{CH}_4 + \mathrm{H_2O} \xrightarrow[700-1100 \ \mathrm{^oC}]{\mathrm{Ni}} \mathrm{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.

ਮਿਥੇਨ ਦੇ ਸੋਮੇ[ਸੋਧੋ]

ਕੁਦਰਤੀ ਗੈਸ ਦੇ ਸੋਮੇ[ਸੋਧੋ]

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.

ਹੋਰ ਸੋਮੇ[ਸੋਧੋ]

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 (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.[੬] The livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane.[੭] Early research has found a number of medical treatments and dietary adjustments that help slightly limit the production of methane in ruminants.[੮][੯]

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 non-minable coal seam.

Scientific experiments have given variable results in determining whether plants are a source of methane emissions.[੧੦][੧੧][੧੨]

ਵਾਤਾਵਰਣੀ ਮਿਥੇਨ[ਸੋਧੋ]

1rightarrow.png ਮੁੱਖ ਲੇਖ ਲਈ ਵੇਖੋ: Atmospheric methane
2006-2009 Methane concentration in the upper troposphere.

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 — 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 compared to 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.[੧੩] Usually, excess methane from landfills and other natural producers of methane is 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 utilized to generate electricity.

Arctic methane release from permafrost and clathrates is an expected consequence of global warming.[੧੪]

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 ]

ਪੁਲਾੜ ਵਿੱਚ ਮਿਥੇਨ[ਸੋਧੋ]

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 outgassed from the surface[੧੫]
  • Mars – the atmosphere contains 10 ppb methane. In January 2009, NASA scientists announced that they had discovered that the planet often vents methane into the atmosphere in specific areas, leading some to speculate this may be a sign of biological activity going on below the surface.[੧੬]
  • Jupiter – the atmosphere contains about 0.3% methane
  • Saturn – the atmosphere contains about 0.4% methane
    • Iapetus
    • Titan — the atmosphere contains 1.6% methane and thousands of methane lakes have been detected on the surface[੧੭]
    • Enceladus – the atmosphere contains 1.7% methane[੧੮]
  • 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.[੧੯][੨੦]
  • Plutospectroscopic analysis of Pluto's surface reveals it to contain traces of methane[੨੧][੨੨]
    • Charon – methane is believed to be present on Charon, but it is not completely confirmed[੨੩]
  • 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[੨੪]
  • 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.[੨੫]
  • Interstellar clouds[੨੬]

ਹੋਰ ਵੇਖੋ[ਸੋਧੋ]

References[ਸੋਧੋ]

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  2. Lunar Engines, Aviation Week & Space Technology, 171, 2 (13 July 2009), p. 16: "Aerojet has completed assembly of a 5,500-pound-thrust liquid oxygen/liquid methane rocket engine—a propulsion technology under consideration as the way off the Moon for human explorers"
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