Recent Advances in Direct Conversion of Natural Gas to Liquid Fuels
Natural gas is an abundant resource in the world as well as petroleum.There have been many research activities on the conversion of natural gas to liquid fuels. In New Zealand, the famous GTG (Gas To Gasoline) plant has been operated commercially since 1986, producing gasoline of over 570, 000t/y which is about one third of the domestic demand of liquid fuels in the nation. Another plant converting natural gas to liquid fuels by Fischer-Tropsch process is now being constructed in Malaysia by Shell. However, these indirect processes include syngas production from methane, which needs very high operation cost.
On the other hand, direct conversion of methane to liquid fuels without syngas production is a developing technology. It is expected that the fuels are produced in lower cost.
The followings are considered as possible processes.
1) Oxidative coupling of methane (OCM)-Oligomerization process, in which methane is converted to C2 compounds with oxygen, followed by polymerization of C2 to liquid fuels.
2) Oxyhydrochlorination (OHC)-Oligomerization process, in which methane is converted to chloromethane with hydrogen chloride and oxygen, followed by polymerization of chloromethane to the liquid.
3) Direct Methanol Synthesis (DMS)-Methanol To Gasoline (MTG) process, in which methane is partially oxidized to methanol, then converted to gasoline by Mobil's MTG process.
Among these, the OCM process seems to be the most feasible one at present technology level. A few OCM processes for production of liquid fuels have been developed independently by ARCO (USA), IFP (France) and CSIRO (Australia). Recently, Japan National Oil Corporation has started the joint study project titled “Natural Gas Conversion Process” which is cooperative work with Japan Petroleum Exploration Co., Ltd. and Cosmo Research Institute.
In this review, recent advances in direct conversion of methane in the world and the outline of the Japanese new project are described.