Fuels, Synthetic, Liquid Fuels

Abstract

Abstract The creation of liquids to be used as fuels from sources other than natural crude petroleum broadly defines synthetic liquid fuels. Synthetic liquid fuels have characteristics approaching those of the liquid fuels in commerce, specifically gasoline, kerosene, jet fuel, and fuel oil. For much of the twentieth century, the synthetic fuels emphasis was on liquid products derived from coal upgrading or by extraction or hydrogenation of organic matter in coke liquids, coal tars, tar sands, or bitumen deposits. However, much of the direction involving synthetic fuels technology has changed. The potential of natural gas, which typically has 85–95% methane, has been recognized as a plentiful and clean alternative feedstock to crude oil. The proven technology to upgrade methane is via steam reforming to produce synthesis gas, CO + H 2 . Such a gas mixture is clean and when converted to liquids produces fuels substantially free of heteroatoms such as sulfur and nitrogen. Two commercial units utilizing the synthesis gas from natural gas technology in combination with novel downstream conversion processes have been commercialized. The direct methane conversion technology has received the most research attention and involves the oxidative coupling of methane to produce higher hydrocarbons such as ethylene. A second trend in synthetic fuels is increased attention to oxygenates as alternative fuels as a result of the growing environmental concern about burning fossil‐based fuels. The environmental impact of the oxygenates is still under debate, but these alternative liquid fuels are gaining new prominence. Despite reduced prominence, coal technology is well positioned to provide synthetic fuels for the future. World petroleum and natural gas production are expected ultimately to level off and then decline. Coal gasification to synthesis gas is utilized to synthesize liquid fuels in much the same manner as natural gas steam reforming technology. Although world activity in coal liquefaction technology is minimal, the extensive development and detailed demonstration of processes for converting coal to liquid fuels should serve as solid foundation for the synthetic fuel needs of the future. Coal, tar, and heavy oil fuel reserves are widely distributed. The importance of coal gasification as a means of producing fuel gas(es) for industrial use cannot be underplayed. But coal gasification systems also have undesirable features. A range of undesirable products are also produced which must be removed before the products are used to provide fuel and/or to generate electric power. Natural gas is a plentiful resource, and there has been a marked tendency not to use other fossil fuels as SNG sources. However, petroleum oil shale, and biomass have been the subject of extensive research efforts.