Methane

Methane

Methane occurs in ‘natural gas’ and the gases from oil-wells. Methane is the principal product of organic decay in swamps and marshes, the gas being set free by the action of bacteria; this method of formation in nature has given rise to the name ‘marsh-gas’ for methane. Sewage sludge which has been fermented by bacteria yields a gas containing about 70 per cent methane, and this is used as a liquid fuel. Methane also forms about 40 per cent by volume of coal-gas.

Methane may be synthesized by striking an electric arc between carbon electrodes in an atmosphere of hydrogen, or by heating a mixture of carbon and reduced nickel at 475^oC in the presence of hydrogen.

Sabatier and Senderens (1897) synthesized methane by passing a mixture of hydrogen and carbon monoxide or dioxide over finely divided nickel heated at about 300^oC , e.g.,

CO + 3H₂  → CH₄ + H₂O

Methane may conveniently be prepared by heating a mixture of anhydrous sodium acetate and soda-lime, or by reduction of methyl iodide with dissolving methals or with lithium aluminium hydride or lithium hydride. Other methods of preparation are by the action of water on aluminium carbide or methylmagnesium iodide (a Grignard regent);

Al4C3 + 12H2O  →  3CH4 +4Al(OH)3

CH3MgI + H2O  →  CH4 +MgI(OH)

Methane is obtained in vast quantities from natural gas, gas from the oil-wells, and from cracked petroleum (q.v)

Properties of methane

Methane is a colorless, odorless, non-poisonous gas; its b.p. is -164^oC/760mm, and m.p. -184^oC. It is somewhat soluble in water, 100 ml of water dissolving about 5ml of methane at 20^oC; but is quite soluble in ethanol and ether. It burns with a non-luminous flame in air or oxygen, forming carbon dioxide and water :

CH₄ + 2O₂  → CO₂ + 2H₂O

It explodes violently when mixed with air (or oxygen) and ignited, and this is believed to be the cause of explosions in coal-mines, where methane is known as fire-damp. Methane may be catalytically oxidized to methanol and formaldehyde.

Use of Methane

Methane, be heating to 1000^oC or by incomplete combustion, produces carbon in a very finely divided state. Carbon prepared this way is known as carbon black, and is used to make paints and printer’s ink; it is also used in the rubber industry for motor tyres, etc.

C + 2H₂O   ^O2   CH₄  ^1000OC  C + 2H₂

Methane is used as a source of synthesis gas. A mixture of methane and steam is passed over heated nickel (800^oC) supported on alumina.

CH₄  +  H₂O  →  CO  +  3H₂ ;                          CH₄  +  2H₂O  → CO₂  +  4H₂

The reaction to give carbon dioxide occurs to a much less extent than that to give carbon monoxide and the carbon dioxide is removed from the mixture by washing with water under pressure.

Methane is also used as a fuel and as the starting point of many chemicals.