ＧＴＬ（Ｇａｓ Ｔｏ Ｌｉｑｕｉｄ）技術の展望

Abstract

GTL technology is one of the most promising technologies which makes it possible to convert natural gas to clean liquid fuels. They can be utilized for gasoline engine, diesel engine or fuel cell. GTL technology is composed of two or three steps: (1) Reforming of natural gas to syngas (CO+H2), (2) Conversion of syngas to liquid hydrocarbons (Fisher-Tropsch (F. T) Synthesis), or (3) Conversion of syngas to methanol and methanol to aromatics plus iso-paraffins (Methanol to Gasoline (MTG) Process).MTG process utilizes a special zeolite catalyst to convert methanol to gasoline at high temperatures, whose research octane number is about 93, and small amount of LPG. The total energy efficiency from natural gas to products is about 55%. This technology has been commercialized since 1986 in New Zealand with the scale of 15, 000 bpd.The F.T synthesis gives mainly straight chain paraffins and olefins with wide distribution of carbon number (C1_??_C100+). Products (C10_??_C20) are quite suitable material as diesel fuel, whichexhibits high cetane number (_??_70), low sulfur content (_??_0), low aromatics content (_??_0), andlow density (780g/1). These characters lead to the low emissions from diesel engine (soot, SOx, NOx and hydrocarbons).Two GTL (F. T) commercial phants have been operated since 1992 and 1993, which are developed by SASOL in South Africa and Shell in Malaysia, respectively. Lighter products (C5_??_C10) can be used as petrochemical feed stock or can be reformed to gasoline. Heavier products can be used as wax (after purification), lubricant (after isomerization) or diesel oil (after hydrocracking). Commercial GTL process has the cost competability when its scale correspond to the annual gas consumption of about 1 million ton. This means that the process can utilize the products from the gas field with rather small scale.