Natural gas is expected to be an effective energy against global warming, and therefore an interest in techniques using natural gas has grown. Typically, natural gas contains ethane (C2H6) in an amount ranging from 1 to 10%, propane (C3H8) in an amount less than 5%, butane (C4H10) in an amount less than 2%, pentane (C5H12) in an amount less than 1% and hexane (C6H14) in an amount less than 0.5%, other than methane (CH4) contained in an amount ranging from 70 to 98% as a main component.
In the use of natural gas, methane gas serving as the main component is held in high regard so that ethane contained in the natural gas is sometimes eliminated when the natural gas is put into storage in liquefied form or when the natural gas is transported through a pipeline or the like.
In Europe and the United States, ethane is generally known as a raw material for ethylene production in petrochemical industry; however, in Again nations including Japan, a raw material for ethylene is naphtha and therefore ethane is treated as a redundant gas so as not to be recognized to be important.
One of prior arts of producing benzene from lower hydrocarbons is disclosed in patent literature 1 (Japanese Patent Provisional Publication No. 2005-255605), in which a main lower hydrocarbon is methane and the other usable lower hydrocarbons are exemplified by ethane, ethylene, propylene, n-butane, isobutene, n-butene and isobutene. Patent literature 1 is to provide an art widely applicable to lower hydrocarbons, and not to focus on ethane for studying the effective use of ethane.
As discussed above, ethane is still treated as a redundant gas and is not yet effectively used, even though it exists as a reformed gas (a raw gas) which is not yet used in a gasification process for a lignitious coal or the like, the process being seen in steelmaking industry. Therefore, it is a vital object to develop an art of achieving the effective use of ethane.                Patent literature 1: Japanese Patent Provisional Publication No. 2005-255605        