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{| class="toccolours" border="1" style="float: right clear: right margin: 0 0 1em 1em border-collapse: collapse" width="333px"

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Methane

|-

| align="center" colspan="2" bgcolor="#ffffff" |

|-

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | General

|-

| Other names || Marsh gas

|-tes

| There was an error working with the wiki: Code[14] || CH4

|-

| There was an error working with the wiki: Code[15] || C

|-

| There was an error working with the wiki: Code[68] || 16.04 g/mol

|-

| Appearance || colorless gas

|-

| There was an error working with the wiki: Code[16] || [74-82-8]

|-

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Properties

|-

| There was an error working with the wiki: Code[17] || 0.717 kg/m3, gas

|-

| There was an error working with the wiki: Code[18] in There was an error working with the wiki: Code[19] || 3.5 mg/100 ml (17 °C)

|-

| There was an error working with the wiki: Code[69] || &minus182.5 °C (90.6 K)

|-

| There was an error working with the wiki: Code[70] || &minus161.6 °C (111.55 K)

|-

| There was an error working with the wiki: Code[71] || 90.7 K, 0.117 bar

|-

| There was an error working with the wiki: Code[72] || 190.5 K (&minus82.6 °C)at 4.6 MPa (45 atm)

|-

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Structure

|-

| There was an error working with the wiki: Code[20]

| There was an error working with the wiki: Code[21]

|-

| There was an error working with the wiki: Code[73] || Td

|-

| There was an error working with the wiki: Code[22]

| Zero

|-

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Hazards

|-

| There was an error working with the wiki: Code[23] || There was an error working with the wiki: Code[24]

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| There was an error working with the wiki: Code[25] || Highly flammable (F+)

|-

| There was an error working with the wiki: Code[74] || There was an error working with the wiki: Code[1]

|-

| There was an error working with the wiki: Code[26] || There was an error working with the wiki: Code[2]

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| There was an error working with the wiki: Code[27] || There was an error working with the wiki: Code[3], There was an error working with the wiki: Code[4], There was an error working with the wiki: Code[5], There was an error working with the wiki: Code[6]

|-

| There was an error working with the wiki: Code[75] || &minus188 °C

|-

| There was an error working with the wiki: Code[76] || 537 °C

|-

| Maximum burning temperature: || 2148 °C

|-

| There was an error working with the wiki: Code[77]s || 5&ndash15%

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! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | There was an error working with the wiki: Code[28]

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| There was an error working with the wiki: Code[29] ||

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| There was an error working with the wiki: Code[30] ||

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| There was an error working with the wiki: Code[31] || There was an error working with the wiki: Code[32], There was an error working with the wiki: Code[33], There was an error working with the wiki: Code[34], There was an error working with the wiki: Code[35]

|-

! align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Related compounds

|-

| Related There was an error working with the wiki: Code[36]There was an error working with the wiki: Code[78]

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| Related compounds || There was an error working with the wiki: Code[79]There was an error working with the wiki: Code[80]There was an error working with the wiki: Code[81]There was an error working with the wiki: Code[82]

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| Related hydrides || There was an error working with the wiki: Code[83]

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| align="center" cellspacing="3" style="border: 1px solid #C0C090 background-color: #F8EABA margin-bottom: 3px" colspan="2" | Except where noted otherwise, data are given for materials in their There was an error working with the wiki: Code[37]

|-

|}

The simplest There was an error working with the wiki: Code[38]Hydrogen4. Pure methane is There was an error working with the wiki: Code[39], but when used commercially is usually mixed with small quantities of odorants, strongly-smelling There was an error working with the wiki: Code[84] compounds such as There was an error working with the wiki: Code[85] (also called ethyl mercaptan), to enable the detection of leaks.

The principal component of Natural gas, methane is a significant and plentiful There was an error working with the wiki: Code[86]. Burning one molecule of methane in the presence of Oxygen releases one molecule of CO2 (There was an error working with the wiki: Code[87]) and two molecules of H2O (Water):

: CH4 + 2O2 ? CO2 + 2H2O

Methane's relative abundance and clean burning process makes it a very attractive fuel. However, because it is a gas and not a liquid or solid, methane is difficult to transport from the areas that produce it to the areas that consume it. Converting methane to forms that are more easily transported, such as There was an error working with the wiki: Code[88] (Liquified Natural Gas) and There was an error working with the wiki: Code[89], is an active area of research.

Methane is a There was an error working with the wiki: Code[90] with a There was an error working with the wiki: Code[91] over 100 years of 23.IPCC Third Assessment Report When averaged over 100 years each kg of CH4 warms the earth 23 times as much as the same mass of CO2.

The Earth's crust contains huge amounts of methane. Large amounts of methane are emitted to the atmosphere through There was an error working with the wiki: Code[92]es which are connected with deep geological faults or as the main constituent of There was an error working with the wiki: Code[93] formed naturally by Anaerobic digestion.

Properties

At There was an error working with the wiki: Code[40] at 1 There was an error working with the wiki: Code[41] pressure and is extremely There was an error working with the wiki: Code[94].

Potential health effects

Methane is not There was an error working with the wiki: Code[42]s if it ignites. It is highly flammable and may form There was an error working with the wiki: Code[95] mixtures with air. Methane is violently reactive with There was an error working with the wiki: Code[96]s, There was an error working with the wiki: Code[97]s, and some halogen-containing compounds. Methane is also an There was an error working with the wiki: Code[98] and may displace Oxygen in an enclosed space. There was an error working with the wiki: Code[99] may result if the oxygen concentration is reduced to below 18% 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 There was an error working with the wiki: Code[100]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. An example of this type of system is in the There was an error working with the wiki: Code[101], There was an error working with the wiki: Code[102].

Reactions of methane

Main reactions with methane are: combustion, hydrogen activation, and halogen reaction. In general, methane reactions are hard to control partial oxidation to There was an error working with the wiki: Code[103], for example, is difficult to achieve the reaction typically progresses all the way to There was an error working with the wiki: Code[104] and Water.

Combustion

In the Combustion of methane, several steps are involved:

Methane is belived to form a There was an error working with the wiki: Code[43] (CH3·) on heating which There was an error working with the wiki: Code[44] (HCO), which then forms There was an error working with the wiki: Code[105] (CO). The process is called oxidative There was an error working with the wiki: Code[106]:

: CH4 + O2 ? CO + H2 + H2O

Following oxidative pyrolysis, the H2 oxidizes, forming H2O, replenishing the active species, and releasing Heat. This occurs very quickly, usually in significantly less than a There was an error working with the wiki: Code[107].

: H2 + ½O2 ? H2O

Finally, the CO There was an error working with the wiki: Code[108]s, 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.

: CO + ½O2 ? CO2

Hydrogen activation

The strength of the There was an error working with the wiki: Code[109]-Hydrogen There was an error working with the wiki: Code[110] in methane is among the strongest in all hydrocarbons, and thus its use as a chemical There was an error working with the wiki: Code[111] is limited. Despite the high activation barrier for breaking the C-H bond, CH4 is still the principal starting material for manufacture of Hydrogen. The search for There was an error working with the wiki: Code[112]s which can facilitate C-H bond activation in methane and other low There was an error working with the wiki: Code[113]s is an area of research with considerable industrial significance.

Reactions with halogens

Methane undergoes reactions with all the halogens given appropriate conditions. The reactions occur as follows:

: CH4 + X2 ? CH3X + HX

Where X is a There was an error working with the wiki: Code[114]: There was an error working with the wiki: Code[115] (F), There was an error working with the wiki: Code[116] (Cl), There was an error working with the wiki: Code[117] (Br) or sometimes There was an error working with the wiki: Code[118] (I).

This mechanism for this process is called There was an error working with the wiki: Code[119] and it occurs as follows:

Initiation:

: X2 ? 2X&middot

Propagation:

: CH4 + X&middot ? &middotCH3 + HX

: &middotCH3 + X2 ? CH3X + X&middot

Termination:

: 2X&middot ? X2

: &middotCH3 + X&middot ? CH3X

: &middotCH3 + &middotCH3 ? CH3CH3

This reaction can occur as far as CX4 where the halide ions will have completely displaced the hydrogens.

Uses

Fuel

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

Methane is important for There was an error working with the wiki: Code[120] by burning it as a fuel in a Gas turbine or steam There was an error working with the wiki: Code[121]. Compared to other There was an error working with the wiki: Code[122]s, burning methane produces less There was an error working with the wiki: Code[123] for each unit of heat released. Also, methane's heat of combustion is about 902 kJ/mol, which is lower than any other hydrocarbon, but if a ratio is made with the atomic weight (16.0 g/mol) divided by the heat of combustion (902 kJ/mol) it is found that methane, being the simplest hydrocarbon, actually produces the most heat per unit mass than other complex hydrocarbons. In many cities, methane is piped into homes for domestic There was an error working with the wiki: Code[124] and cooking purposes. In this context it is usually known as natural gas. One standard cubic foot of methane will produce roughly 1,000 BTU (1.06 MJ = 293 W-hr) of energy.

Industrial uses

Methane is used in industrial chemical processes and may be transported as a refrigerated liquid (liquefied natural gas, or There was an error working with the wiki: Code[45]s distribute large amounts of Natural gas, of which methane is a significant component.

In the chemical industry, methane is the feedstock of choice for the production of Hydrogen, There was an error working with the wiki: Code[125], There was an error working with the wiki: Code[126], and There was an error working with the wiki: Code[127]. When used to produce any of these chemicals, methane is first converted to There was an error working with the wiki: Code[128], a mixture of There was an error working with the wiki: Code[129] and Hydrogen, by There was an error working with the wiki: Code[130]. In this process, methane and There was an error working with the wiki: Code[131] react on a There was an error working with the wiki: Code[132] catalyst at high temperatures (700&ndash1100 °C).

: CH4 + H2O ? CO + 3H2

The ratio of carbon monoxide to hydrogen in synthesis gas can then be adjusted via the There was an error working with the wiki: Code[133] to the appropriate value for the intended purpose.

: CO + H2O There was an error working with the wiki: Code[7] CO2 + H2

Less significant methane-derived chemicals include There was an error working with the wiki: Code[134], prepared by passing methane through an There was an error working with the wiki: Code[135], and the chloromethanes (There was an error working with the wiki: Code[136], There was an error working with the wiki: Code[137], There was an error working with the wiki: Code[138], and There was an error working with the wiki: Code[139]), produced by reacting methane with There was an error working with the wiki: Code[140] gas. However, the use of these chemicals is declining, acetylene as it is replaced by less costly substitutes, and the chloromethanes due to health and environmental concerns.

Sources of methane

Natural gas fields

The major source of methane is extraction from geological deposits known as There was an error working with the wiki: Code[46] There was an error working with the wiki: Code[47] generate natural gas.

Alternative sources

Apart from gas fields an alternative method of obtaining methane is via There was an error working with the wiki: Code[48] of organic matter including There was an error working with the wiki: Code[49].

Methane in Earth's atmosphere

Methane in the earth's atmosphere is an important greenhouse gas with a Global warming potential of 23 over a 100 year period. Its concentation has increased by about 150% since 1750 and it accounts for 20% of the total There was an error working with the wiki: Code[141] from all of the long-lived and globally mixed greenhouse gases.There was an error working with the wiki: Code[8]

The average concentration of methane at the Earth's surface in 1998 was 1,745 There was an error working with the wiki: Code[142].There was an error working with the wiki: Code[9] Its concentration is higher in the northern hemisphere as most sources (both natural and human) are larger. The concentrations vary seasonally with a minimum in the late summer.

Methane is created near the surface, and it is carried into the There was an error working with the wiki: Code[143] by rising air in the There was an error working with the wiki: Code[144]. 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 a molecule known as the There was an error working with the wiki: Code[145], a hydrogen-oxygen molecule formed when single oxygen atoms react with water vapor.

Early in the Earth's history—about 3.5 billion years ago—there was 1,000 times as much methane in the atmosphere as there is now. The earliest methane was released into the atmosphere by volcanic activity. During this time, Earth's earliest life appeared. These first, ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water. Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth's history. With no oxygen, methane stayed in the atmosphere longer and at higher concentrations than it does today.

Emissions of methane

Houweling et al. (1999) give the following values for methane emissions:

{| border="1" cellpadding="5" cellspacing="0" class="wikitable"

| Origin

| CH4 emission (Teragram/yr)

|-

!colspan=2| Natural emissions

|-

| There was an error working with the wiki: Code[146]s (incl rice production)

| 225

|-

| There was an error working with the wiki: Code[147]

| 20

|-

| There was an error working with the wiki: Code[148]s

| 15

|-

| There was an error working with the wiki: Code[149]s

| 10

|-

| Natural total

| 290

|-

!colspan=2| Anthropogenic emissions

|-

| Energy

| 110

|-

| There was an error working with the wiki: Code[150]s

| 40

|-

| There was an error working with the wiki: Code[151]s (Livestock)

| 115

|-

| Waste treatment

| 25

|-

| Biomass burning

| 40

|-

| Anthropogenic total

| 330

|}

Slightly over half of the total emission is due to human activity.

Living plants (e.g. forests) have recently been identified as a potentially important source of methane. The recent paper calculated emissions of 62–236 Tg yr-1, and "this newly identified source may have important implications".There was an error working with the wiki: Code[10]There was an error working with the wiki: Code[11] However the authors stress "our findings are preliminary with regard to the methane emission strength".There was an error working with the wiki: Code[12]

Removal processes

The major removal mechanism of methane from the atmosphere is by reaction with the There was an error working with the wiki: Code[152] (·OH), which may be produced when a There was an error working with the wiki: Code[153] strikes a molecule of water vapor:

: CH4 + &middotOH &rarr &middotCH3 + H2 O

This reaction in the There was an error working with the wiki: Code[154] gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with &middotOH, &middotCl and &middotO1D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.

Sudden release from methane clathrates

At high pressures, such as are found on the bottom of the ocean, methane forms a solid There was an error working with the wiki: Code[50]. An unknown, but possibly very large quantity of methane is trapped in this form in ocean sediments. The sudden release of large volumes of methane from such sediments into the atmosphere has been suggested as a possible cause for rapid There was an error working with the wiki: Code[155] events in the earth's distant past, such as the There was an error working with the wiki: Code[156] of 55 million years ago.

One source estimates the size of the methane hydrate deposits of the oceans at ten million million tons (10 exagrams). Theories suggest that should global warming cause them to heat up sufficiently, all of this methane could again be suddenly released into the atmosphere. Since methane is twenty-three times stronger (for a given weight, averaged over 100 years) than CO2 as a greenhouse gas this would immensely magnify the greenhouse effect, heating Earth to unprecedented levels.

Release of methane from bogs

Although less dramatic than release from clathrates, but already happening, is an increase in the release of methane from bogs as There was an error working with the wiki: Code[157] melts. Although records of permafrost are limited, recent years (1998 and 2001) have seen record thawing of permafrost in There was an error working with the wiki: Code[158] and There was an error working with the wiki: Code[159].

Recent measurements in Siberia show that the methane released is five times greater than perviously estimated There was an error working with the wiki: Code[13].

Extraterrestrial methane

Methane has been detected or is believed to exist in several locations of the There was an error working with the wiki: Code[51] processes, with the possible exception of There was an error working with the wiki: Code[52].

There was an error working with the wiki: Code[160]

There was an error working with the wiki: Code[53]

There was an error working with the wiki: Code[54]

There was an error working with the wiki: Code[55]

There was an error working with the wiki: Code[56] - (There seems to be hydrocarbon lakes around the polar regions)

There was an error working with the wiki: Code[57]

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There was an error working with the wiki: Code[161]

There was an error working with the wiki: Code[66]

There was an error working with the wiki: Code[67]

There was an error working with the wiki: Code[162]

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Traces of methane gas are present in the thin atmosphere of the Earth's There was an error working with the wiki: Code[164].

Methane has also been detected in There was an error working with the wiki: Code[165]s.

Methane is believed to be present on Charon, but it is not 100% confrimed.

Related concepts

There was an error working with the wiki: Code[166], a type of Hydrocarbon of which methane is simplest member.

Anaerobic digestion

There was an error working with the wiki: Code[167]

There was an error working with the wiki: Code[168]

There was an error working with the wiki: Code[169]

There was an error working with the wiki: Code[170], form of water ice which contains methane.

There was an error working with the wiki: Code[171], There was an error working with the wiki: Code[172] that produce methane as a metabolic by-product.

There was an error working with the wiki: Code[173], the formation of methane by There was an error working with the wiki: Code[174].

There was an error working with the wiki: Code[175], There was an error working with the wiki: Code[176] that are able to grow using methane as their only source of carbon and energy.

There was an error working with the wiki: Code[177], a functional group similar to methane.

There was an error working with the wiki: Code[178]

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External links and references

Methane thermodynamics gas resources

Inorganic Methane cms.llnl.gov

International Chemical Safety Card 0291 ilo.org

Methane Hydrates marine.usgs.gov, fact sheets.

edsanvil, Computational Chemistry Wiki

Molview from bluerhinos.co.uk

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

Safety data for methane

See also

- PowerPedia

- Main Page

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