Methane

• Methyl hydrogen
• Carban
• R50

Colorless and odorless gas

Gaseous

• 0.72 kg · m -3 (gaseous, 0 ° C, 1013 hPa)
• 0.42 g · cm -3 (liquid, the boiling point )

-182 ° C

-162 ° C

• Slightly soluble in water (26 ml x l -1)
• Readily soluble in ethanol and diethyl ether

0

1.000444 (0 ° C, 101.325 kPa)

Risk

28 (relative to 100 years)

-74.87 KJ · mol -1

Template: Infobox chemical / molecular formula search available

Methane is a chemical compound selected from the group of the hydrocarbons and the simplest alkane. This colorless, odorless, flammable gas is present in nature and has been a main component of natural gas and in the chemical industry as a raw material for fuel gas and industrial syntheses of great importance.

• 2.1 Terrestrial 2.1.1 Near-surface 2.1.1.1 Biotic

• 2.2.1 Outside the earthly solar system
• 2.2.2 Mars
• 2.2.3 titanium

• 5.1 greenhouse Gas

• 7.1 Reactions with oxygen
• 7.2 Further reactions
• 7.3 biology, geology, climatology

• 9.1 Books
• 9.2 journal articles

Properties

Physical Properties

Methane melts at -182.6 ° C and boils at -161.7 ° C. Because of the non-polar property, it is hardly soluble in water, ethanol and diethyl ether, however, it dissolves well. Heat of fusion and heat of evaporation be 1.1 kJ / mole and 8.17 kJ / mol, as compared to metals, but these are very low values ​​. The calorific value Hi is 35.89 MJ · m -3 and 50,013 MJ kg -1. The Standardentropie is 188 J · mol -1 · K -1, the heat capacity of 35.69 J · mol -1 · K -1. The triple point of methane is bar at 90.67 K and 0.117, the critical point is at 190.56 K and 45.96 bar.

This colorless and odorless gas has a lower density than air, so it rises into the higher layers of the atmosphere on. There it acts as a greenhouse gas, wherein 20 - to 30 - times more effective than carbon dioxide, however, it takes much lower levels than this in the atmosphere. It reacts with oxygen there to carbon dioxide and water. This process is slow, however, the half-life is estimated at 12 years.

The UN numbers of compacted and frozen methane are 1971 and 1972. Methane is in the commercial 50 liter steel tank or vehicle fuel tank (often carbon fiber / epoxy resin on aluminum liner ) compressed to 200 bar (as CNG) in gaseous form. However, the water transport in large quantities is done in almost unpressurized ball or diaphragm tanks at approximately -160 ° C cryogenic liquid form (LNG).

Chemical Properties

Methane is the simplest alkane, and the simplest hydrocarbon, the molecular formula is CH4, the C -H bonds point into the corners of a tetrahedron. It is flammable and burns in air with a bluish, non- sooty flame. It can react explosively with oxygen or chlorine, for which an initial ignition ( supply of activation energy ) or catalysis is, however, necessary. Result in the chlorination of chloromethane, dichloromethane, chloroform and carbon tetrachloride. In the oxidation, however, the molecule is completely torn apart. From the reaction of methane molecule having two oxygen molecules creates two water and Kohlenstoffdioxidmolekül. From methane to methyl compounds are derived from such as methanol and methyl halides and also the longer alkanes.

Occurrence and formation

Earthly

It is believed that in addition to ammonia and water vapor, methane was a major component of the terrestrial primordial atmosphere.

Methane occurs varied and is constantly re- formed on the Earth, such as in biological and geological processes ( serpentinization ). The methane concentration in the Earth's atmosphere has increased from 0.8 to 1.75 ppm ( ie more than doubled: 119% ) increase from the year 1750 to the year 2000.

Near-surface

Biotic

A large part of the terrestrial methane is formed by microorganisms: The lazy organic substances absence of air in swamps or in the sediment at the bottom of the aquatic and marsh gas, a mixture of methane and carbon dioxide is formed. Biogas consists mainly of methane ( 60% ) and carbon dioxide ( about 35 %), in addition it also contains hydrogen, nitrogen and hydrogen sulfide.

The formation occurs near the surface biotic: on the one hand anaerobically in the course of methanogenesis ( from carbon dioxide and acetate for the most part ). This is caused by specific archaea, the methanogens. They use simple organic compounds such as carbon dioxide or methanol and reduce them to methane, which they gain energy. This process is called methanogenesis. For example, to be released under standard conditions at a pH of seven about 131 kJ / mol in free energy ( Gibbs free energy, ΔG0 ') in the formation of methane from CO2 and hydrogen ( H2):

A small part of the biotic formation based on the aerobic digestion of methylphosphonates.

Underground

Below the surface of the Earth, methane deep underground at high temperatures and pressures and is usually free in volcanic activity. It is the main component of natural gas ( 85-98 %), which occurs primarily as a companion of petroleum. Also included in the coal camps coal mine gas contains mainly methane - the abiotic origin can thermal part of the maturation process of coal ( geochemical phase of coalification ), as well as all types of kerogens and petroleum occur.

Methane exiting the seabed, is converted to methane by the high pressure -resistant and the low temperature. This is also referred to as " methane ". The carbon content of the global methane hydrate is estimated to 500-3000 gigatonnes. By comparison, the carbon content of proven coal reserves of about 900 Gt.

A recovery of methane hydrate could contribute to the solution of earthly energy problem, but it is tricky. One particular problem is for example that in the recovery amount of methane would enter the Earth's atmosphere and would help there as a potent greenhouse gas to further heating and thus further release of methane. In addition, the promotion of methane hydrate dangerous. First promotion trials are already underway. The consequences of over-exploitation are largely unexplained, researchers fear the slipping of the continental slopes, which largely of methane (which by the aid could be unstable) exist. Because of global warming and the associated sea water warming, some researchers fear the melting and evaporation of methane hydrate. This would also make methane as a greenhouse gas in the atmosphere and amplify the anthropogenic greenhouse effect.

Emission

Approximately 600 million tons of methane are emitted annually on the earth; in Germany in 1994 about 833,000 tons. About 70 % of the microbial methane emission of the earth is due to human activities. When agricultural crops and livestock methane is secreted, 39 % of these emissions are due to the cattle, 17% on wet rice cultivation.

The increasing farming of cattle, the frequent wet rice cultivation and emissions of eg landfill gases lead to an enhancement of the greenhouse effect. The archaeal methanogens are primarily responsible for the continuous formation of methane. A domestic cattle such as encountered daily from about 150-250 l of methane because the bovine stomach methanogens are involved in the decomposition of cellulose.

New findings show that plants constantly produce methane and as always contribute to the methane content of the atmosphere. The FAO writes the livestock sector to almost one fifth of anthropogenic or human-induced greenhouse gas emissions, something more than the transport sector. To what extent garlic extracts in the diet can lead to lower output rates, is examined.

Early 2014 reported the research journal Science by a meta- study of 200 studies that the U.S. Environmental Protection Agency Environmental Protection Agency ( EPA) have indicated the methane gas emissions in the U.S. for 20 years by one to three quarters too low. 40 million tons annually in the U.S. emits more than before officially accepted into the atmosphere from natural sources as well as from livestock farming, for example, 88 million cattle in the country and from leaks in conveyors and pipelines. Remains unclear to what extent the erroneous information have an impact on the calculation models for the development of the global climate.

Extraterrestrial

The atmospheres of Titan, Jupiter, Saturn, Uranus, Neptune and Pluto contain methane. Outside our solar system, methane has been detected as the first organic molecule on the planet. In space, So methane is present in large quantities on planets, comets and moons.

Outside the earthly solar system

In March 2008, methane gas was first found on a planet outside our solar system: On the ( exoplanet HD 189733b on the type of hot Jupiters ).

Mars

2009 has been reported methane eruptions on Mars; in the atmosphere of Mars methane was detected, but only about 10.5 ppb. Since it can not normally keep in the atmosphere and there is no evidence of meteorites as a source, it must have been re- formed on Mars, which may be an indication of life. However, the methane could be also of volcanic origin, for which no evidence has been yet found on Mars; 2008 was, however, demonstrated that the methane from the Lost City hydrothermal vents geochemical origin.

Titanium

On Saturn 's moon Titan prevails at -180 ° C and 1.6 bar atmospheric pressure almost the triple point of methane. Methane can therefore occur on this moon in all three states. There are clouds of methane from which rains methane, which then flows through rivers into methane lakes, where it evaporates again, thus forming a closed methane cycle (similar to the water cycle on Earth ).

Liquid methane is transparent to radar beams, the Cassini spacecraft was able to determine the depth of the lake Ligeia Mare to 170 m.

There are probably on these lakes even icebergs from methane / ethane. However, this can only float on the methane lakes, if they contain at least 5% gaseous nitrogen. When the temperature only slightly decreases the nitrogen pulls together such an extent that the ice is sinking to the bottom. If the temperature rises again, the ground ice can then ascend to the sea surface. At certain temperatures can even surface and ground ice occur simultaneously.

For the Ontario Lacus, a lake near the south pole of Titan, but the heavier ethane was detected as a main ingredient.

Discovery and Naming

The word methane probably comes from ancient Greek. The Greeks knew well already in antiquity by the flammable gas. So it was in Asia Minor places where inflamed methane gas sources. A volcano area in which occurred such gases, got by this gas also the name Methana.

Methane was referred to the alchemists in the Middle Ages as part of putrefaction gases, also known as swamp air, known.

Methane was discovered in 1667 by Thomas Shirley. 1772 Joseph Priestley discovered that methane produced during putrefaction. 1856, Marcellin Berthelot methane ago for the first time from carbon disulfide and hydrogen sulfide.

In older texts methane was sometimes referred to as methyl hydrogen.

Production

For the production of aluminum carbide, there are two methods, however, they are generally only used in the laboratory. The synthesis of carbon monoxide has a special importance, since the poisonous carbon monoxide, which is actually undesirable / unusable, can be put to good use, only the source of the hydrogen is in this synthesis represents a problem

• Aluminum carbide reacts with water to form aluminum hydroxide, and methane when it is heated.
• Aluminum carbide reacts with hydrochloric acid to aluminum chloride and methane.
• Of sodium acetate is heated together with sodium hydroxide, sodium carbonate, and it is formed of methane.
• Carbon monoxide reacts with hydrogen to form methane and water.
• Carbon dioxide reacts with hydrogen to form methane and water. This reaction was discovered in the 19th century by the French and the Nobel laureate Paul Sabatier Sabatier process and is therefore called.

Today too much methane is produced as a fuel in biogas plants. Also by wood gasification methane can be recovered. The methanation after previous water electrolysis is the basic principle for the production of wind and solar gas, which in the field of renewable energies, an increasing importance is attributed.

Handling, hazards and safety

At a volume fraction from 4.4 to 16.5 per cent in the air, it forms explosive mixtures or explosive atmospheres ( pea). By undetected leakage of natural gas it always comes back to serious gas explosions. Even the dreaded mine gas explosions in coal mines ( firedamp ) are due to methane - air mixtures. Methane is highly flammable, the flash point is -188 ° C, the ignition temperature at 600 ° C. Methane containers should be kept in well-ventilated places, it should be kept away from ignition sources and measures should be taken to prevent electrostatic charging. Methane under high pressures and usually at low temperatures (to increase the density ) stored in cylinders at 200 bar, in tanker ships alternatively liquefied almost unpressurized refrigerated at about -160 ° C.

Methane is stored in liquid form at low temperatures, because the density can thereby be greatly increased. For this reason it can easily lead to frostbite when leaving this cooled methane. Methane is non-toxic, the uptake of methane, however, can lead to increased respiratory rate ( hyperventilation) and increased heart rate, it can cause short-term low blood pressure, numbness in extremities, drowsiness, mental confusion and memory loss, all caused by lack of oxygen. But methane does not lead to permanent damage. If symptoms occur, you should leave the affected area and are inhaled deeply, if not then the symptoms disappear, the person concerned should be taken to a hospital.

Greenhouse gas

Methane is a potent greenhouse gas. The global warming potential of 1 kg of methane is considered a period of 100 years, 28 times higher than that of 1 kg of carbon dioxide; according to a recent study, this factor is even 33 when interactions are taken into account with atmospheric aerosols.

Use

Methane is primarily used as a fuel gas to generate heat and operation of engines by combustion. In addition to methane biogas from other sources for this purpose is obtained with a methane content of about 50 to > 70% of manure, slurry sludge or organic waste. Previously methane was obtained by pyrolysis of wood in the wood gas is generated (wood gasification). Wood gas containing methane, among other things, was because of the oil shortage during World War II for the operation of particular civilian automobiles that had the a warming wood gasifier often grown outside.

Methane is an important starting material for industrial syntheses of hydrogen, methanol, acetylene, hydrogen cyanide, carbon disulfide and methyl halides. It serves as a starting point for many other organic compounds.

Reactions

Reactions with oxygen

With oxygen, methane is a different reactions, depending on how much oxygen is available for the reaction. Only with a certain oxygen supply complete combustion of methane with optimal energy yield is possible.

Insufficient oxygen, however, undesirable by-products such as carbon monoxide (CO ) and carbon formed ( soot). Further, in this case, the usable energy is low.

Further reactions

Methane is an except with oxygen nor variety of other reactions. Many of these are very important for the chemical industry, since the emergence of products of great industrial importance.

• Methane reacts with sulfur at 700 ° C and alumina catalyst to carbon disulfide and hydrogen sulfide.
• Methane reacts with ammonia and oxygen over a platinum catalyst to give hydrocyanic acid and water.
• Methane reacts photochemically ( light- induced) with halogens to form methyl halides and hydrogen halides, here for example with chlorine.
• Methane reacts at 1400 ° C and water vapor to acetylene and hydrogen.
• Methane reacts at 800 ° C on nickel contact with water to carbon monoxide and hydrogen.

Biology, geology, climatology

Methane is oxidized to carbon dioxide and water by certain bacteria in waters and soils with oxygen ( O2). This reaction is exergonic and the bacteria use it as an energy source, which is why they are called methanotroph.

In an atmosphere containing oxygen, methane is slow, in particular, oxidized by hydroxyl radicals.