Methanation is the conversion of carbon monoxide and carbon dioxide (CO_x) to methane (CH₄) through

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

. The methanation reactions of CO_x were first discovered by Sabatier and Senderens in 1902. CO_''x'' methanation has many practical applications. It is a means of carbon oxide removal from process gases and is also being discussed as an alternative to

PROX PROX is an acronym for PReferential OXidation, and refers to the preferential oxidation of a carbon monoxide in a gas mixture by a catalyst. It is intended to remove trace amounts of CO from H2/CO/CO2 mixtures produced by steam reforming and wate ...

in fuel processors for mobile

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

applications. Methanation as a means of producing

synthetic natural gas Substitute natural gas (SNG), or synthetic natural gas, is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels (when it is named bio-SNG) or using electricity with power- ...

has been considered since the 1970s. More recently it has been considered as a way to store energy produced from solar or wind power using

power-to-gas Power-to-gas (often abbreviated P2G) is a technology that uses electric power to produce a gaseous fuel. When using surplus power from wind generation, the concept is sometimes called windgas. Most P2G systems use electrolysis to produce hydrogen ...

systems in conjunction with existing

natural gas storage Natural gas is a commodity that can be stored for an indefinite period of time in natural gas storage facilities for later consumption. Usage Gas storage is principally used to meet load variations. Gas is injected into storage during periods o ...

Chemical reactions

The following reactions describe the methanation of carbon monoxide and carbon dioxide respectively: :CO + 3H2 -> CH4 + H2O -206 kJ/mol :CO2 + 4H2 -> CH4 + 2 H2O -164 kJ/mol The methanation reactions are classified as

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

and their energy of formations are listed. There is disagreement on whether the CO₂ methanation occurs by first associatively adsorbing an

adatom An adatom is an atom that lies on a crystal surface, and can be thought of as the opposite of a surface vacancy. This term is used in surface chemistry and epitaxy, when describing single atoms lying on surfaces and surface roughness. The word ...

hydrogen and forming oxygen intermediates before hydrogenation or dissociating and forming a carbonyl before being hydrogenated. CO is believed to be methanated through a dissociative mechanism where the carbon-oxygen bond is broken before hydrogenation with an associative mechanism only being observed at high H₂ concentrations. Methanation reaction over different carried metal

catalysts Catalysis () is the process of increasing the 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 catalyst recyc ...

including Ni, Ru and Rh has been widely investigated for the production of CH₄ from

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 other power to gas initiatives. Nickel is the most widely used catalyst due to its high selectivity and low cost.

Industrial applications

Creation of synthetic natural gas

Methanation is an important step in the creation of synthetic or

substitute natural gas Substitute natural gas (SNG), or synthetic natural gas, is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels (when it is named Renewable natural gas, bio-SNG) or using e ...

(SNG). Coal or wood undergo gasification which creates a producer gas that must undergo methanation in order to produce a usable gas that just needs to undergo a final purification step. The first commercial synthetic gas plant opened in 1984 and is the Great Plains Synfuel plant in Beulah, North Dakota. It is still operational and produces 1500 MW worth of SNG using coal as the carbon source. In the years since its opening, other commercial facilities have been opened using other carbon sources such as wood chips. In France, the AFUL Chantrerie, located in Nantes, started in November 2017 the demonstrator MINERVE. This methanation unit of 14 Nm3/day was carried out by Top Industrie, with the support of Leaf. This installation is used to feed a CNG station and to inject methane into the natural gas boiler.

Ammonia synthesis

In ammonia production CO and CO₂ are considered

poisons Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...

to most commonly used catalysts.{{Cite journal, last=Khorsand, first=Kayvan, year=2007, title=Modeling and simulation of methanation catalytic reactor in ammonia unit, url=https://www.researchgate.net/publication/26498529, journal=Petroleum & Coal, volume=49, pages=46–53 Methanation catalysts are added after several hydrogen producing steps to prevent

carbon oxide In chemistry, an oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen. The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (). Many other stable (practically if not thermodynamic ...

buildup in the ammonia synthesis loop as methane does not have similar adverse effects on ammonia synthesis rates.

References

Organic reactions Methane Chemical processes Hydrogenation

Chemical reactions

Industrial applications

Creation of synthetic natural gas

Ammonia synthesis

See also

References