METHANE: NATURAL GAS

Methane is commonly produced in nature by the bacterial decomposition of organic matter in the absence of oxygen. These conditions are found in marshes, swamps, or the muddy sediment of lakes. The occurrence of methane in such locations is the reason for its common name, marsh gas. A similar process leads to the formation of methane in the digestive tracts of certain animals, such as cows.

Methane is often found with coal and sometimes accumulates in coal mines, where it presents two kinds of hazards. It can form in pockets from which air is excluded and unwary miners can be asphyxiated, or it can mix with air to form very explosive mixtures. Natural gas, often found associated with petroleum deposits, consists primarily of methane (about 80%). Most of the remaining 20% is of higher-molecular-weight alkanes. Purified natural gas is a nontoxic, odorless substance. It is desirable to be able to detect natural gas leaks, so a very powerful odorant is added. The odorant, a sulfur-containing compound with the formula CH₃CH₂SH, makes it quite easy to detect even very small amounts of natural gas present in the air.

Tremendous quantities of natural gas are consumed worldwide because methane is an efficient, clean-burning fuel. It is used to heat homes, cook food, and power factories. Natural gas is also making inroads as an auto fuel. In addition, methane is an important feedstock (starting material) used to manufacture many other organic compounds. In the United States alone, more than 250,000 miles of pipe-line are used exclusively to distribute this source of energy to all parts of the country.

Liquefied natural gas is distributed worldwide in huge ocean-going tankers. The gas is shipped as a liquid at -160 ^oC in order to conserve space. One cubic meter of the liquefied gas is equivalent to about 600 m³ of gas at atmospheric pressure. Some of the tankers used for this purpose can transport more than 100,000 m³ of liquefied gas in one trip. The rapid depletion of two major energy sources, natural gas and petroleum, and the challenge of finding substitutes for them are major concerns of our time. There is also evidence of rising levels of methane in the atmosphere due to the use of this compound and from global warming -- as swamps warm up and tundra regions thaw, methane is re-leased into the air.