Olefins, including ethylene, propylene and butenes, are major building blocks in the chemical process industries. These materials are either recovered from refinery streams or produced by cracking naphtha or LPG. Not with standing the success of these processes, there is an incentive to use methane as a raw material because of the large reserves of natural gas throughout the world.
From the prior art (Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., Vol. 5, p. 1031), methyl chloride, when heated to very high temperatures, is known to couple giving ethylene and hydrogen chloride. At somewhat lower temperatures, catalytic reactions involving methyl chloride also produce ethylene and other olefins.
The literature (U.S. Pat. No. 5,099,084) further discloses a process for the chlorination of methane using hydrogen chloride as the source of chlorine. This process, however, is attended by several drawbacks. Not only is methyl chloride produced, but the higher chlorinated methanes, including methylene chloride, chloroform and carbon tetrachloride, are also generated. In addition, when air is employed in the catalytic reaction, a substantial quantity of gases must be vented, thereby complicating emission control problems and related environmental concerns. On the other hand, the use of pure oxygen hinders the reaction due to the formation of hot spots in the catalyst bed.
There consequently exists a need for a process that starts with methane as a raw material and converts it through the formation of methyl chloride into olefins. Such an integrated process must at once be economical to operate and reduce the inefficiencies characterizing conventional processes.