methane
   HOME

TheInfoList



OR:

Methane ( , ) is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A homonuclear molecule, molecule co ...
with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
(one
carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to gro ...

carbon
atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, l ...

atom
bonded to four
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the chemical ...

hydrogen
atoms). It is a group-14 hydride, the simplest
alkane In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...
, and the main constituent of
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...

natural gas
. The relative abundance of methane on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large list of largest lakes and seas in the Solar System, volumes of water can be found throughout the Solar System, only water distributi ...

Earth
makes it an economically attractive
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

fuel
, although capturing and storing it poses technical challenges due to its
gaseous Gas is one of the four fundamental state of matter, states of matter (the others being solid, liquid, and plasma (physics), plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), chemical element, elemental molec ...
state under normal conditions for temperature and pressure. Naturally occurring methane is found both below ground and under the seafloor and is formed by both geological and biological processes. The largest
reservoir A reservoir (; from French language, French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to water storage, store fresh water or it may be a natural formation. Reservoirs can be created in a num ...

reservoir
of methane is under the seafloor in the form of
methane clathrate
methane clathrate
s. When methane reaches the surface and the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, it is known as
atmospheric methane Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising. The 20-year global ...
. The Earth's atmospheric methane concentration has increased by about 150% since 1750, and it accounts for 20% of the total
radiative forcing Radiative forcing (or climate forcing) is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change as measured by watt The watt (symbol: W) is the unit of power or radiant flux in the In ...
from all of the long-lived and globally mixed
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
es. It has also been detected on other planets, including
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosph ...

Mars
, which has implications for
astrobiology Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the abiogenesis, origins, Protocell, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplin ...
research.


Properties and bonding

Methane is a
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular Pyramid (geometry), pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex ( ...
molecule with four equivalent C–H bonds. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on
C
C
and
H
H
. The lowest-energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements. Methane is an odorless gas and appears to be colorless. It does absorb visible light especially at the red end of the spectrum due to
overtone band In vibrational spectroscopy, an overtone band is the spectral band that occurs in a vibrational spectrum of a molecule when the molecule makes a transition from the ground state (v=0) to the second excited state (v=2), where v is the vibrationa ...
s, but the effect is only noticeable if the light path is very long. This is what gives
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

Uranus
and
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

Neptune
their blue or bluish-green colors, as light passes through their atmospheres containing methane and is then scattered back out. The familiar smell of natural gas as used in homes is achieved by the addition of an
odorant An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently Vola ...
, usually blends containing tert-butylthiol, as a safety measure. Methane has a boiling point of −161.5  °C at a pressure of one
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
. As a gas, it is
flammable A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
over a range of concentrations (5.4–17%) in air at
standard pressure Standard temperature and pressure (STP) are Technical standard, standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the I ...
. Solid methane exists in several modifications. Presently nine are known. Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system (
space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...
Fmm). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it is a plastic crystal.


Chemical reactions

The primary chemical reactions of methane are
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
,
steam reforming Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen product ...
to
syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used as ...
, and
halogenation In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a chemical compound, compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the prod ...

halogenation
. In general, methane reactions are difficult to control.


Selective oxidation

Partial
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...

oxidation
of methane to
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula CH3OH (a methyl group In organic chemistry, a methyl group is an alkyl derived from m ...

methanol
, a more convenient, liquid fuel, is challenging because the reaction typically progresses all the way to
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetraval ...

carbon dioxide
and
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

water
even with an insufficient supply of
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
. The
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

enzyme
methane monooxygenase Methane monooxygenase (MMO) is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes (). There are two forms of MMO: the well-studied soluble form (s ...
produces methanol from methane, but cannot be used for industrial-scale reactions. Some homogeneously
catalyzed Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to an ...

catalyzed
systems and heterogeneous systems have been developed, but all have significant drawbacks. These generally operate by generating protected products which are shielded from overoxidation. Examples include the Catalytica system, copper
zeolite Zeolites are Microporous material, microporous, crystalline aluminosilicate materials commonly used as commercial adsorption, adsorbents and Catalysis, catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y ...

zeolite
s, and iron zeolites stabilizing the alpha-oxygen active site. One group of
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometre The micrometre (Amer ...

bacteria
catalyze methane oxidation with
nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

nitrite
as the
oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...

oxidant
in the absence of
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
, giving rise to the so-called anaerobic oxidation of methane.


Acid–base reactions

Like other
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic, and their odors are usuall ...
s, methane is an extremely
weak acid Acid strength is the tendency of an acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis a ...

weak acid
. Its pKa in is estimated to be 56. It cannot be in solution, but the
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid protonation, donates a proton () to a base (chemistry), base—in other words, it is a base with a hydrogen ion added to it, as in the ...
is known in forms such as
methyllithium Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in so ...
. A variety of
positive ions An ion () is an atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has n ...
derived from methane have been observed, mostly as unstable species in low-pressure gas mixtures. These include methenium or methyl cation , methane cation , and methanium or protonated methane . Some of these have been detected in outer space. Methanium can also be produced as diluted solutions from methane with
superacid In chemistry, a superacid (according to the classical definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid ...
s.
Cation An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be po ...
s with higher charge, such as and , have been studied theoretically and conjectured to be stable. Despite the strength of its C–H bonds, there is intense interest in
catalysts Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...

catalysts
that facilitate C–H bond activation in methane (and other lower numbered
alkanes In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...

alkanes
).


Combustion

Methane's
heat of combustion The heating value (or energy value or calorific value) of a Chemical substance, substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the ...
is 55.5 MJ/kg.
Combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
of methane is a multiple step reaction summarized as follows: :CH4 + 2 O2 → CO2 + 2 H2O (, at standard conditions) Peters four-step chemistry is a systematically reduced four-step chemistry that explains the burning of methane.


Methane radical reactions

Given appropriate conditions, methane reacts with
halogen The halogens () are a group in the periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and ...

halogen
radicals as follows: :X• + CH4 → HX + CH3• :CH3• + X2 → CH3X + X• where X is a
halogen The halogens () are a group in the periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and ...

halogen
:
fluorine Fluorine is a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical c ...

fluorine
(F),
chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

chlorine
(Cl),
bromine Bromine is a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical ...

bromine
(Br), or
iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

iodine
(I). This mechanism for this process is called
free radical halogenation In organic chemistry, free-radical halogenation is a type of halogenation. This chemical reaction is typical of alkanes and alkyl-substituted aromatics under application of UV light. The reaction is used for the industrial synthesis of chloroform ( ...
. It is initiated when
UV light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
or some other
radical initiator In chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structu ...
(like peroxides) produces a halogen
atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, l ...

atom
. A two-step
chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that syst ...
ensues in which the halogen atom abstracts a hydrogen atom from a methane molecule, resulting in the formation of a hydrogen halide molecule and a methyl radical (CH3•). The methyl radical then reacts with a molecule of the halogen to form a molecule of the halomethane, with a new halogen atom as byproduct. Similar reactions can occur on the halogenated product, leading to replacement of additional hydrogen atoms by halogen atoms with dihalomethane, trihalomethane, and ultimately, tetrahalomethane structures, depending upon reaction conditions and the halogen-to-methane ratio.


Uses

Methane is used in industrial chemical processes and may be transported as a refrigerated liquid (liquefied natural gas, or
LNG Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volu ...

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. distribute large amounts of natural gas, of which methane is the principal component.


Fuel

Methane is used as a
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

fuel
for ovens, homes, water heaters, kilns, automobiles, turbines, etc.
Activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area availa ...

Activated carbon
is used to store methane. Refined liquid methane is used as a
rocket fuel Rocket propellant is the reaction mass Working mass, also referred to as reaction mass, is a mass against which a system operates in order to produce acceleration. In the case of a chemical rocket, for example, the reaction mass is the Product ...
, when combined with
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military appli ...
, as in the
BE-4 The Blue Engine 4 or BE-4 is an oxygen-rich liquefied-methane-fueled staged-combustion rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive Jet (fluid), jet of fluid, usuall ...
and Raptor engines. As the major constituent of
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...

natural gas
, methane is important for electricity generation by burning it as a fuel in a gas turbine or Boiler (power generation), steam generator. Compared to other fossil fuel, hydrocarbon fuels, methane produces less
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetraval ...

carbon dioxide
for each unit of heat released. At about 891 kJ/mol, methane's
heat of combustion The heating value (or energy value or calorific value) of a Chemical substance, substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the ...
is lower than that of any other hydrocarbon, but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) 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. In this context it is usually known as
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...

natural gas
, which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 British thermal unit, BTU per standard cubic foot. Liquefied natural gas (LNG) is predominantly methane (CH4) converted into liquid form for ease of storage or transport. As a Liquid-propellant rocket, liquid rocket fuel, methane offers the advantage over kerosene of producing small exhaust molecules. This deposits less soot on the internal parts of rocket motors, reducing the difficulty of booster re-use. The lower molecular weight of the exhaust also increases the fraction of the heat energy which is in the form of kinetic energy available for propulsion, increasing the specific impulse of the rocket. Liquid methane also has a temperature range (91–112 K) nearly compatible with
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military appli ...
(54–90 K).


Chemical feedstock

Natural gas, which is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. Steam reforming, Steam methane reforming (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50 million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas. Much of this hydrogen is used in petroleum Refinery, refineries, in the production of chemicals and in food processing. Very large quantities of hydrogen are used in the Ammonia production, industrial synthesis of ammonia. At high temperatures (700–1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield a mixture of Carbon monoxide, CO and Dihydrogen, H2, known as "water gas" or "
syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used as ...
": : CH4 + water, H2O ⇌ carbon monoxide, CO + 3 hydrogen, H2 This reaction is strongly endothermic (consumes heat, Δ''H''r = 206 kJ/mol). Additional hydrogen is obtained by the reaction of carbon monoxide, CO with water via the water-gas shift reaction: : CO + H2O ⇌ carbon dioxide, CO2 + H2 This reaction is mildly exothermic (produces heat, Δ''H''r = −41 kJ/mol). Methane is also subjected to free-radical chlorination reaction, chlorination in the production of chloromethanes, although
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula CH3OH (a methyl group In organic chemistry, a methyl group is an alkyl derived from m ...

methanol
is a more typical precursor.Rossberg, M. ''et al.'' (2006) "Chlorinated Hydrocarbons" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. . Hydrogen can also be produced via the direct decomposition of methane, also known as methane Pyrolysis. Methane decomposition is a promising route for low-emission hydrogen production since no direct carbon emissions are produced unlike steam methane reforming. Temperatures in excess of 1200 °C are required to break the bonds of methane to produce Hydrogen gas and solid carbon. However, through the use of a suitable catalyst the reaction temperature can be reduced to between 600 °C - 1000 °C depending on the chosen catalyst. The reaction is moderately endothermic as shown in the reaction equation below. : (g) → C(s) + 2 (g) Delta (letter), ΔH° = 74.8 Joule per mole, kJ/mol


Generation


Geological routes

The two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic (Abiotic component, abiotic). Thermogenic methane occurs due to the breakup of organic matter at elevated temperatures and pressures in deep sedimentary Stratum, strata. Most methane in sedimentary basins is thermogenic; therefore, thermogenic methane is the most important source of natural gas. Thermogenic methane components are typically considered to be relic (from an earlier time). Generally, formation of thermogenic methane (at depth) can occur through organic matter breakup, or organic synthesis. Both ways can involve microorganisms (methanogenesis), but may also occur inorganically. The processes involved can also consume methane, with and without microorganisms. The more important source of methane at depth (crystalline bedrock) is abiotic. Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes or via water-rock reactions that occur at low temperatures and pressures, like Serpentinite, serpentinization.


Biological routes

Most of Earth's methane is Biogenic substance, biogenic and is produced by methanogenesis,Lessner, Daniel J. (Dec 2009) Methanogenesis Biochemistry. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net a form of anaerobic respiration only known to be conducted by some members of the domain Archaea. Methanogens occupy landfills and other Soil gas, soils, ruminants (for example, cattle), the guts of termites, and the Anoxic waters, anoxic sediments below the seafloor and the bottom of lakes. Rice fields also generate large amounts of methane during plant growth. This multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is: :CO2 + 4 H2→ CH4 + 2 H2O The final step in the process is catalyzed by the enzyme Coenzyme-B sulfoethylthiotransferase, methyl coenzyme M reductase (MCR).


Ruminants

Ruminants, such as cattle, belch methane, accounting for about 22% of the U.S. annual methane emissions to the atmosphere. One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane. A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions. Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments, and to trap the gas to use its combustion energy.


Seafloor sediments

Most of the subseafloor is Anoxic waters, anoxic because oxygen is removed by Aerobic respiration, aerobic microorganisms within the first few centimeters of the seafloor sediment, sediment. Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in Clathrate hydrate, gas hydrates. These other organisms that utilize methane for energy are known as methanotrophs ('methane-eating'), and are the main reason why little methane generated at depth reaches the sea surface. Consortia of Archaea and Bacteria have been found to oxidize methane via anaerobic oxidation of methane (AOM); the organisms responsible for this are anaerobic Methanotroph, methanotrophic Archaea (ANME) and Sulfate-reducing microorganism, sulfate-reducing bacteria (SRB).


Industrial routes

Given its cheap abundance in natural gas, there is little incentive to produce methane industrially. Methane can be produced by hydrogenation, hydrogenating carbon dioxide through the Sabatier process. Methane is also a side product of the hydrogenation of carbon monoxide in the Fischer–Tropsch process, which is practiced on a large scale to produce longer-chain molecules than methane. An example of large-scale coal-to-methane gasification is the Great Plains Synfuels plant, started in 1984 in Beulah, North Dakota as a way to develop abundant local resources of low-grade lignite, a resource that is otherwise difficult to transport for its weight, Coal assay#Ash, ash content, low calorific value and propensity to spontaneous combustion during storage and transport. A number of similar plants exist around the world, although mostly these plants are targeted towards the production of long chain alkanes for use as gasoline, Diesel fuel, diesel, or feedstock to other processes. Power to gas#Power to methane, Power to methane is a technology that uses electricity, electrical power to produce hydrogen from water by electrolysis and uses the Sabatier reaction to combine hydrogen with
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetraval ...

carbon dioxide
to produce methane. As of 2021, this is mostly under development and not in large-scale use. Theoretically, the process could be used as a buffer for excess and off-peak power generated by highly fluctuating wind turbines and solar arrays. However, as currently very large amounts of natural gas are used in power plants (e.g. Combined cycle, CCGT) to produce electric energy, the losses in efficiency are not acceptable.


Laboratory synthesis

Methane can be produced by protonation of methyl lithium or a methyl Grignard reagent such as methylmagnesium chloride. It can also be made from anhydrous sodium acetate and dry sodium hydroxide, mixed and heated above 300 °C (with sodium carbonate as byproduct). In practice, a requirement for pure methane can easily be fulfilled by steel gas bottle from standard gas suppliers.


Occurrence

Methane was discovered and isolated by Alessandro Volta between 1776 and 1778 when studying marsh gas from Lake Maggiore. It is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields, with coal seam gas extraction becoming a major source (see coal bed methane extraction, a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic, and their odors are usuall ...
fuels, and sometimes accompanied by helium and nitrogen. Methane is produced at shallow levels (low pressure) by anaerobic organism, anaerobic Decomposition, decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain Petroleum, oil. Methane is generally transported in bulk by Pipeline transport, pipeline in its natural gas form, or by LNG carriers in its liquefied form; few countries transport it by truck.


Atmospheric methane

In 2010, methane levels in the Arctic were measured at 1850 nmol/mol. This level is over twice as high as at any time in the last 400,000 years. Keeling Curve, Historic methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol/mol during the warm interglacial periods. The Earth's oceans are a potential important source of Arctic methane. Methane is an important
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
with a global warming potential of 34 compared to CO2 (potential of 1) over a 100-year period, and 72 over a 20-year period.Intergovernmental Panel on Climate Change, IPCC Fifth Assessment Report
Table 8.7, Chap. 8, p. 8–58
(PDF; 8,0 MB)
The Earth's atmospheric methane concentration has increased by about 150% since 1750, and it accounts for 20% of the total
radiative forcing Radiative forcing (or climate forcing) is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change as measured by watt The watt (symbol: W) is the unit of power or radiant flux in the In ...
from all of the long-lived and globally mixed greenhouse gases. The IPCC Sixth Assessment Report, AR6 of the Intergovernmental Panel on Climate Change, IPCC states: "Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities. Since 2011 (measurements reported in AR5), concentrations have continued to increase in the atmosphere, reaching annual averages of 410 ppm for carbon dioxide (CO2), 1866 ppb for methane (CH4), and 332 ppb for nitrous oxide (N2O) in 2019. (…) In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH4 and N2O were higher than at any time in at least 800,000 years (very high confidence). Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed, and increases in N2O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence)". From 2015 to 2019 sharp rises in levels of atmospheric methane have been recorded. In February 2020, it was reported that fugitive emissions and gas venting from the fossil fuel industry may have been significantly underestimated. Climate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a Climate change feedback. Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere.


Clathrates

Methane clathrates (also known as methane hydrates) are solid cages of water molecules that trap single molecules of methane. Significant reservoirs of methane clathrates have been found in arctic permafrost and along continental margins beneath the Seabed, ocean floor within the Gas hydrate stability zone, gas clathrate stability zone, located at high pressures (1 to 100 MPa; lower end requires lower temperature) and low temperatures (< 15 °C; upper end requires higher pressure). Methane clathrates can form from biogenic methane, thermogenic methane, or a mix of the two. These deposits are both a potential source of methane fuel as well as a potential contributor to global warming.Miller, G. Tyler (2007). ''Sustaining the Earth: An Integrated Approach''. U.S.A.: Thomson Advantage Books, p. 160. The global mass of carbon stored in gas clathrates is still uncertain and has been estimated as high as 12,500 Gigaton, Gt carbon and as low as 500 Gt carbon. The estimate has declined over time with a most recent estimate of ~1800 Gt carbon. A large part of this uncertainty is due to our knowledge gap in sources and sinks of methane and the distribution of methane clathrates at the global scale. For example, a source of methane was discovered relatively recently in an Mid-ocean ridge, ultraslow spreading ridge in the Arctic. Some climate models suggest that today's methane emission regime from the ocean floor is potentially similar to that during the period of the Paleocene–Eocene Thermal Maximum (PETM) around 55.5 million years ago, although there are no data indicating that methane from clathrate dissociation currently reaches the atmosphere. Arctic methane release from permafrost and seafloor methane clathrates is a potential consequence and further cause of global warming; this is known as the clathrate gun hypothesis. Data from 2016 indicate that Arctic permafrost thaws faster than predicted.


Extraterrestrial methane


Interstellar medium

Methane is abundant in many parts of the Solar System and potentially could be harvested on the surface of another solar-system body (in particular, using In situ resource utilization, methane production from local materials found on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosph ...

Mars
or Titan (moon), Titan), providing fuel for a return journey.


Mars

Methane has been detected on all planets of the Solar System and most of the larger moons. With the possible exception of Life on Mars, Mars, it is believed to have come from Abiogenic petroleum origin, abiotic processes. The Curiosity (rover), ''Curiosity'' rover has documented seasonal fluctuations of Atmosphere of Mars, atmospheric methane levels on Mars. These fluctuations peaked at the end of the Martian summer at 0.6 parts per billion. Methane has been proposed as a possible rocket propellant on future Human mission to Mars, Mars missions due in part to the possibility of synthesizing it on the planet by In situ resource utilization#Mars, in situ resource utilization. An adaptation of the Sabatier reaction, Sabatier methanation reaction may be used with a mixed catalyst bed and a Water-gas shift reaction#Reverse water-gas shift, reverse water-gas shift in a single reactor to produce methane from the raw materials available on Mars, utilizing water from the Martian soil, Martian subsoil and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetraval ...

carbon dioxide
in the Atmosphere of Mars, Martian atmosphere. Methane could be produced by a non-biological process called serpentinite, serpentinization involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars.


History

In November 1776, methane was first scientifically identified by Italian people, Italian physicist Alessandro Volta in the marshes of Lake Maggiore straddling Italy and Switzerland. Volta was inspired to search for the substance after reading a paper written by Benjamin Franklin about "flammable air".Volta, Alessandro (1777
''Lettere del Signor Don Alessandro Volta ... Sull' Aria Inflammable Nativa Delle Paludi''
[Letters of Signor Don Alessandro Volta ... on the flammable native air of the marshes], Milan, Italy: Giuseppe Marelli.
Volta collected the gas rising from the marsh, and by 1778 had isolated pure methane. He also demonstrated that the gas could be ignited with an electric spark. Following the Felling mine disasters#1812 disaster, Felling mine disaster of 1812 in which 92 men perished, Sir Humphry Davy established that the feared firedamp was in fact largely methane. The name "methane" was coined in 1866 by the German chemist August Wilhelm von Hofmann. The name was derived from Methanol#History, methanol.


Etymology

Etymologically, the word ''methane'' is coined from the chemical suffix "''-ane''", which denotes substances belonging to the alkane family; and the word ''methyl'', which is derived from the German (1840) or directly from the French , which is a back-formation from the French (corresponding to English "methylene"), the root of which was coined by Jean-Baptiste Dumas and Eugène Péligot in 1834 from the Greek (wine) (related to English "mead") and (meaning "wood"). The radical is named after this because it was first detected in
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula CH3OH (a methyl group In organic chemistry, a methyl group is an alkyl derived from m ...

methanol
, an alcohol first isolated by distillation of wood. The chemical suffix ''-ane'' is from the coordinating chemical suffix ''-ine'' which is from Latin feminine suffix ''-ina'' which is applied to represent abstracts. The coordination of "-ane", "-ene", "-one", etc. was proposed in 1866 by German chemist August Wilhelm von Hofmann (1818–1892).


Abbreviations

The abbreviation CH4-C can mean the mass of carbon contained in a mass of methane, and the mass of methane is always 1.33 times the mass of CH4-C. CH4-C can also mean the methane-carbon ratio, which is 1.33 by mass. Methane at scales of the atmosphere is commonly measured in teragrams (Tg CH4) or millions of metric tons (MMT CH4), which mean the same thing. Other standard units are also used, such as nanomole (nmol, one billionth of a mole), Mole (unit), mole (mol), kilogram, and gram.


Safety

Methane is nontoxic, yet it is extremely flammable and may form explosive mixtures with air. Methane is also an asphyxiant gas, asphyxiant if the oxygen concentration is reduced to below about 16% by displacement, as most people can Cabin pressurization#Need for cabin pressurization, tolerate a reduction from 21% to 16% without ill effects. The concentration of methane at which asphyxiation risk becomes significant is much higher than the 5–15% concentration in a flammable or explosive mixture. Methane off-gas can penetrate the interiors of buildings near landfills and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture this gas and vent it away from the building. Methane gas explosions are responsible for many deadly mining disasters. A methane gas explosion was the cause of the Upper Big Branch Mine disaster, Upper Big Branch coal mine disaster in West Virginia on April 5, 2010, killing 29. high pressure jet, Natural gas accidental release has also been a major focus in the field of safety engineering, due to past accidental releases that concluded in the formation of jet fire disasters.


See also


Explanatory notes


Citations


Cited sources

*


External links


Methane
at ''The Periodic Table of Videos'' (University of Nottingham)
International Chemical Safety Card 0291


– United States Geological Survey *
CDC – Handbook for Methane Control in Mining
{{Authority control Methane, Anaerobic digestion Fuel gas Fuels Gaseous signaling molecules Greenhouse gases Industrial gases