Methane guide
Methane is a chemical compound of carbon and hydrogen. It is a colourless, odourless and flammable gas with the molecular formula CH4 and is the simplest member of the hydrocarbon group in terms of its structure. Other names for the substance are natural gas, methyl hydrogen, carban and swamp gas.
Methane is the main component of natural gas and biogas, and is also a significant part of wood gas. Industrial and demographic developments in modern times have led to methane gas taking second place after carbon dioxide (CO2) among the greenhouse gases for whose emissions humans are responsible.
It is present in the atmosphere in smaller quantities than CO2, but its effects are around 20 to 30 times greater. As a component of natural gas, methane is not only extracted from finite underground reservoirs, but is also produced again and again as a result of biological and geological processes. Humans use it to generate heat and energy, but also as a basic product for numerous organic compounds.
The following article is intended as a guide to methane, in which the most important properties and facts about this chemical compound are described.
- Historical facts about methane gas
- Physical and chemical properties of methane gas
- Earthly deposits of methane
- Formation of methane through decomposition processes
- Extraterrestrial deposits
- Extraction and production
- Intended use
- Biology and environmental impact of methane gas
- Safety aspects
- Detection of methane
Historical facts about methane gas
The phenomenon of methane has been known for around 4,000 years. As part of escaping natural gas, it feeds flames that are known as “eternal fires”. Such fires are reflected in reports and records written over long periods of time. They often occur in areas under which oil is stored and which are exposed to tectonic faults.
An “eternal fire” in the Iraqi Baba Gurgur could, for example, be the fiery furnace described in the book of Daniel in the Bible. The then ruler Nebuchadnezzar threw some of Daniel’s companions into it as punishment for refusing to worship a golden statue.
The Temple of Apollo in Delphi, Greece, where the famous oracle of the same name was located, was built over such an eternal flame around 1000 BC. There are speculations that the divinations of the priestesses who officiated there were influenced by the inhalation of methane, ethane and ethene, all of which are slightly narcotic gases.
In China, natural gas was already being used to evaporate brine in the 4th century BC. Brine and methane sometimes escaped from the corresponding boreholes at the same time. The gas was channelled from “dry” boreholes to the brine processing sites using pipelines made of bamboo tubes.
The structure of methane was unknown until the 17th century. However, it was known in the Middle Ages as part of putrefactive gases and the danger of firedamp, which occurred when a gas mixture of methane, carbon monoxide and air ignited, was also recognised early on in the mining industry.
The first detailed research into methane was carried out in the 1660s by the Englishman Thomas Shirley, followed a little over a century later by the Italian Alessandro Volta. Around 1800, attempts were made to use a mixture of methane gas, hydrogen, nitrogen and carbon monoxide for street lighting in cities.
In 1812, after a serious mining accident in the Felling Mine in England, the English chemist Humphry Davy realised that the mine gas feared in underground mining consisted largely of methane. The disaster, which claimed 92 lives, led to the development of the so-called Davy lamp with a special screen that acted as a kind of flame arrester, preventing the gas from igniting.
The first source of natural gas was discovered in the USA in 1821 by the American William Hart. The gas was used locally for lighting. Hart later founded the first US natural gas company. In 1856, the French chemist Marcelin Berthelot succeeded in producing methane artificially from the two substances hydrogen sulphide and carbon disulphide.
In the early days of oil production, the natural gas that came to light at the same time, with its main component methane, was still uselessly flared at the heads of the wells. One of the first major pipelines with a length of 193 kilometres was built in 1891 and transported natural gas from drilling sites in Indiana to Chicago. However, at the time of the expansion of pipeline networks in the 1930s, there were still problems with methane hydrate, which formed in the pipes from methane and water and led to blockages.
The use of natural gas or methane, as we know it today in industry and private households, was only made possible after the Second World War thanks to technical developments and advances in pipeline construction. Due to the steep rise in global energy demand, methane became increasingly important for the global supply of primary energy.
Physical and chemical properties of methane gas
The colourless, odourless, flammable methane has a lower density than air, so that it rises in released form into the upper layers of the atmosphere. Its melting point is
-182.6 °C, the boiling point is -161.7 °C. When ignited, it burns with a bluish flame and without soot formation.
Under normal circumstances, methane decomposes in the air, i.e. under the influence of oxygen, into CO2 and water. This chemical reaction between one methane molecule and two oxygen molecules produces one CO2 molecule and two water molecules. However, the half-life of this process is relatively long at an estimated 14 years.
Methane is almost insoluble in water due to its non-polar characteristics. The same applies to acetone. However, it is highly soluble in ethyl alcohol, benzene and diethyl ether. If methane gas is ignited in an environment sufficiently enriched with oxygen, it burns to form carbon dioxide and water.
Together with air, it forms an explosive mixture at a volume concentration of 5 % to 15 %. Such mixtures of methane and air in combination with coal dust are very much feared by miners in coal mines. Mixtures of methane, pure oxygen and chlorine can also lead to violent detonations. During oxidation, i.e. the reaction with oxygen, the individual molecules are completely torn apart. During chlorination, on the other hand, methyl chloride, chloroform, dichloromethane and tetrachloromethane are formed. Other methyl compounds are also derived from methane, including methanol, methyl halides and longer-chain alkanes.
Earthly deposits of methane
There are many different deposits of methane on earth. For example, it is constantly being produced by plant decomposition processes, including in bogs and swamps. It is also the main component of natural gas (85 % to 98 %) and is also predominant in the mine gases trapped in coal mines. Methane can form in deeper layers of the earth under high temperatures and high pressure. These sources are usually released during volcanic activity around the globe.
There are deposits of solid methane hydrate on the floors of the seas and oceans. They are formed when the gas escapes from the seabed and is compressed by the immense water pressure and low temperatures. Although initial attempts at extraction have already been made, they are not without danger. Some experts fear that large-scale extraction could cause the continental slopes, which largely consist of methane ice, to become unstable and slide away. Global marine reserves are currently estimated at 500 to 3,000 Gt (Gt = gigatonne = 1,000,000,000 tonnes). In comparison, the known coal reserves amount to 900 Gt.
The extraction and utilisation of methane hydrate could solve some energy problems. But firstly, there is still no technology for extracting it from the sea. And secondly, so much methane would be released into the atmosphere during recovery that it would contribute to even greater warming and further release of methane as a greenhouse gas. There are also fears that climate change and the associated warming of the oceans will cause the methane hydrate to melt, vaporise and thus enter the atmosphere.
Formation of methane through decomposition processes
Microorganisms make a significant contribution to the formation of methane gas. This happens when organic matter decomposes in the absence of air. In swamps, bogs and at the bottom of heavily polluted bodies of water, so-called swamp gas is formed, a mixture of methane and CO2. Biogas also consists mainly of methane (around 60 %) and CO2 (around 35 %). The remaining 5 % is hydrogen, nitrogen and hydrogen sulphide.
The microorganisms responsible for the biological formation of methane are methanogens, special types of achaea. These reduce simple organic compounds such as methanol or CO2 to methane in order to generate energy for themselves. The process is known as methanogenesis.
Around 70 % of all microbially produced methane emissions on Earth – estimated at around 500 million tonnes annually – are now attributable to human activities, for example through cultivation and animal husbandry in agriculture. Cattle farming alone is responsible for 39% of these emissions and wet rice cultivation for 17%.
Extraterrestrial deposits
Methane is not only found on Earth, but has also been detected on other planets and moons within our solar system. These include Mars, Saturn, Jupiter, Neptune, Uranus and the dwarf planet Pluto, as well as Saturn’s moons Titan and Enceladus. Methane is also found outside the solar system.
The atmosphere of Mars contains about 10.5 ppb of methane. Methane eruptions have also been reported on the red planet. As a rule, the gas cannot remain in the atmosphere. There is no evidence for the origin of meteorites. It is therefore assumed that it was newly formed on Mars, which could be a sign of life there. Another possible cause is a volcanic origin, although there is no evidence for this as yet.
One special feature is Saturn’s moon Titan. It has a temperature of -180 °C and an atmospheric pressure of around 1.6 bar, which roughly corresponds to the so-called triple point of methane. For this reason, it can occur on Titan in all three aggregate states. There are methane clouds that let methane rain down, methane rivers and lakes from which it evaporates again and thus forms a closed cycle, similar to the water cycle here on Earth. It is also assumed that there are icebergs on Titan that consist of methane and ethane.
Here is an overview of the respective methane content in the atmosphere of some planets in parts per million:
Erde: ~ 1.8 ppm
Mars: ~ 0.0105 ppm
Jupiter: 3.000 ± 1.000 ppm
Saturn: 4.500 ± 2.000 ppm
Uranus: 20.000 – 40.000 ppm
Neptune: 15.000 ± 5.000 ppm
Extraction and production
There are various methods of producing methane artificially under laboratory conditions. These mainly involve the use of aluminium carbide, sodium acetate, carbon monoxide (CO) and carbon dioxide.
- Aluminium carbide reacts with water under heat to form aluminium hydroxide and methane.
- Aluminium carbide and hydrochloric acid become aluminium chloride and methane.
- Sodium acetate and sodium hydroxide produce sodium carbonate and methane when exposed to heat.
- Carbon monoxide and hydrogen become methane and water.
- Carbon dioxide also reacts with hydrogen to form methane and water (Sabatier process, named after the French chemist and Nobel Prize winner Paul Sabatier).
Synthesis from carbon monoxide is particularly important among these processes. In this process, CO, which is normally undesirable or unusable due to its toxicity, can be put to good use.
In addition to these classic laboratory methods, methane is now also produced as a fuel in biogas plants and in wood gasification.
Intended use
The bacterial decomposition during the putrefaction processes of organic compounds is utilised economically to produce biogas. Organic waste, slurry, manure and sewage sludge serve as the basis for this. In wood gasification, which has been used for some time, methane is obtained from wood through pyrolysis – a thermochemical decomposition of organic compounds in the absence of oxygen. Biogas and other methane gas mixtures are used to generate heat and energy. Wood gas was used to power vehicles during the Second World War, among other things.
Methane is also an important basic product for synthesising methanol, hydrogen, hydrogen cyanide, ethine, carbon disulphide and methyl halides. Its reactions with oxygen and other substances produce numerous substances that are of great importance to the chemical industry.
Methane may play an important role in future Mars missions. The Mars Society, a non-profit organisation founded in 1998 and committed to the exploration and colonisation of Mars, has developed a concept for this. According to this concept, methane is to be extracted from the CO2 in the planet’s atmosphere using the Sabatier process mentioned above and utilised as fuel for the return to Earth.
Biology and environmental impact of methane gas
Alongside water vapour and ammonia, methane was an important building block of the primeval atmosphere. It has probably played a significant role in the development of today’s Earth’s atmosphere. The American chemist and biologist Stanley Miller carried out a famous experiment on this in 1953. In his experimental apparatus, he recreated what he assumed to be the primeval atmosphere and the primeval ocean of the earliest geological period and exposed them to electrical discharges with which he simulated lightning.
After just one week, around 15 % of the methane had been converted into organic compounds. These included the amino acids contained in proteins. With this experiment, Miller succeeded in proving that biologically important building blocks of life can be created under natural but abiotic conditions.
After carbon dioxide, methane is now regarded as a significant greenhouse gas, with a warming potential 20 to 30 times greater than that of CO2. Natural methane producers are a major problem with regard to the greenhouse effect. Plants constantly produce the gas and contribute to the methane content in the atmosphere. Of particular importance are the widespread cultivation of wet rice and cattle farming. A single domestic cow produces between 150 litres and 250 litres of methane every day, as bacteria in the cow’s stomach are partly responsible for the decomposition of cellulose.
Safety aspects
Methane forms explosive mixtures with a proportion of 5 % to 15 % in the air volume. For this reason, unnoticed releases of natural gas, whose main component is methane, often lead to gas explosions with serious consequences for people and material assets. The flash point of -188 °C and the ignition temperature of 600 °C make methane highly flammable and therefore dangerous to handle.
Containers with the gas should therefore always be placed in adequately ventilated locations where there are no sources of ignition in the vicinity. Effective measures must also be taken to prevent possible electrical charging. Storage takes place under high pressure (around 150 bar in gas cylinders) or at very low temperatures, which increases the density (on tankers at around -160 °C).
Methane has no toxic effect on humans. However, ingestion for a short time can lead to increased heart rates and hyperventilation. Other effects caused by a simultaneous lack of oxygen include low blood pressure, drowsiness, slight mental confusion, memory loss and numbness in the limbs. Permanent damage is not caused by the gas. If the above symptoms occur, leave the affected area as quickly as possible and then breathe in and out deeply for a while. If the symptoms do not disappear, affected persons must be treated by a doctor in a hospital.
If liquid methane stored at very low temperatures escapes quickly from a pressurised container, people in the vicinity may suffer hypothermia and frostbite on their skin.
Detection of methane
The facts in our methane guide show that methane must be handled with care due to its high flammability and risk of explosion. Accidental leaks of methane from storage tanks and production facilities must therefore be avoided wherever possible. This requires constant measurements in the areas at risk. Modern and common methods for this are measurements with catalytic sensors or infrared technology.
As a recognised manufacturer of gas detectors and gas measuring devices, Compur Monitors provides stationary and mobile measuring technology for this purpose, which enables reliable and precise measurement of methane levels in the ambient air. These include the Statox 501 and Statox 503 models, Infratox, Micro 5 and Microclip, HRC, ARE as well as MC IR and LC IR. All devices are easy to calibrate and allow methane concentrations to be recorded and read quickly.
Dr. Josef von Stackelberg
Managing Director COMPUR MONITORS GmbH & Co. KG
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