Details
All A B C D E F G H I K L M N O P Q R S T U V W
Methane
Marsh or mine gas, chemical symbol CH4. Methane is the first of a homologous series of saturated hydrocarbons. It is a colourless, odourless gas with a boiling point of -164.5°С and melting point of -182.5°С. Its relative air density is 0.554 at 20°С. Methane burns with an almost colourless flame, and has a calorific value of 50.08 MJ/kg (11,954 kcal/kg). Methane is the principal component in natural gas (77-99% by volume), associated oil (31-90%) and coal-mine gas (34-40%); it also occurs in volcanic gases, and is formed by anaerobic decay of organic substances under the influence of methane-forming bacteria (swamp gas). The atmospheres of Saturn and Jupiter are largely composed of methane. Methane is formed during thermal processing of oil and oil products (10-57% by volume), and during coking and hydrogenation of black coal (24-34%). In the laboratory, methane can be obtained by smelting sodium acetate with an alkali, or by adding water to methyl magnesium iodide or aluminium carbide.
Methane forms an explosive mixture with air. Methane released during underground development of mineral deposits, as well as during coal and briquette preparation, is particularly dangerous. A concentration in air of 5-6% methane will burn around a heat source (at an ignition temperature of 650-750°C). Concentrations of 5-6% to 14-16% will explode, and concentrations of greater than 16% will burn in a supply of oxygen; reducing the concentration of methane in such cases can lead to an explosion. Moreover, a significant increase in methane concentration in the air can cause suffocation (a 43% concentration of methane, for example, is the equivalent of a 12% concentration of CO2).
A methane explosion spreads at a speed of 500-700 m/sec; the gas pressure of an explosion in an enclosed space is 1 MN/m2.
Methane ignites with a small delay following contact with a heat source. This property is used in the manufacture of safety explosives and explosion-proof electrical equipment. A special operating regime is used at facilities (mainly mines) where risks associated with methane are particularly high.
Methane is the most thermically stable saturated hydrocarbon. It is widely used as a household and industrial fuel, and as a raw material in industry. Chlorination of methane produces methyl chloride, methylene chloride, chloroform and carbon tetrachloride. Partial combustion of methane produces carbon black, catalytic oxidation produces formaldehyde, and interaction with sulphur produces carbon disulphide. Thermal-oxidative cracking and electro-cracking of methane are important industrial methods used to produce acetylene. Catalytic oxidation of a methane-ammonia mix forms the basis for industrial production of prussic acid. Methane is used as a source of hydrogen during ammonia production, and also to obtain water gas (a so-called synthesis gas). CH4 + H2O = CO + 3H2, used for industrial synthesis of hydrocarbons, alcohols, aldehydes, etc. Another important derivative of methane is nitromethane.
