Synthetic fuel or synfuel is a liquid fuel obtained from coal, natural gas, or biomass. It may also refer to fuels derived from other solids such as plastics or rubber waste, or from the fermentation of biomatter. It may also (less often) refer to gaseous fuels produced in a similar way. Common use of the term "synthetic fuel" is to describe fuels manufactured via Fischer Tropsch conversion, methanol to gasoline conversion, or direct coal liquefaction.
Using commercially proven industrial processes, quantities of synthetic transportation fuels can be produced from non-oil fossil and biomass resources. These fuels can be produced in a manner that reduces life cycle greenhouse gas emissions, while building forwards-compatible renewable fuels infrastructure. Synthetic fuels are one of the few economically viable and industrially scalable alternatives to petroleum capable of providing a major source of the liquid transportation fuels required to run the economy, and the only known non-petroleum source of aviation fuel.
July 2009 worldwide commercial synthetic fuels production capacity is over 240,000 barrels per day (38,000 m 3 /d), with numerous new projects in construction or development.
Classification and principles
The term 'synthetic fuel' has several different meanings and it may include different types of fuels. More traditional definitions, e.g. definition given by the International Energy Agency, define 'synthetic fuel' as any liquid fuel obtained from coal or natural gas. The Energy Information Administration defines synthetic fuels in its Annual Energy Outlook 2006, as fuels produced from coal, natural gas, or biomass feedstocks through chemical conversion into syncrude and/or synthetic liquid products. A number of synthetic fuel's definitions include also fuels produced from biomass, and industrial and municipal waste. The definition of synthetic fuel may also consist of oil sands and oil shale as synthetic fuel's sources and in addition to liquid fuels also gaseous fuels are covered. On his 'Synthetic fuels handbook' a petrochemist James G. Speight included liquid and gaseous fuels as well as clean solid fuels produced by conversion of coal, oil shale or tar sands, and various forms of biomass, although he admits that in the context of substitutes for petroleum-based fuels it has even wider meaning. Depending the context, also methanol, ethanol and hydrogen may be included.
Synthetic fuels are produced by the chemical process of conversion. Conversion methods could be direct conversion, that means that the source substance is converted directly into liquid transportation fuels, or indirect conversion, that means that the source substance is converted initially into syngas which then goes through additional conversion process to become liquid fuels. Basic conversion methods are carbonization and pyrolysis, hydrogenation, and thermal dissolution.
History
See also: Oil Campaign of World War II and Synthetic Liquid Fuels ProgramDirect conversion of coal to synthetic fuel was originally developed in Germany. The Bergius process was developed by Friedrich Bergius, yielding a patent on the Bergius process in 1913. Theodor Goldschmidt invited him to build an industrial plant at his factory the Th. Goldschmidt AG in 1914. The production began only in 1919.
Also indirect coal conversion (where coal is gasified and then converted to synthetic fuels) was developed in Germany by Franz Fischer and Hans Tropsch in 1923. During the World War II, Germany used synthetic oil manufacturing (German: Kohleveredelung ) to produce substitute ( Ersatz ) oil products by using the Bergius process (from coal), the Fischer-Tropsch process (water gas), and other methods (Zeitz used the TTH and MTH processes). The Bergius process plants were the primary source of Nazi Germany's high-grade aviation gasoline and the source of most of its synthetic oil, 99% of its synthetic rubber and nearly all of its synthetic methanol, synthetic ammonia, and nitric acid. Nearly 1/3 of the Bergius production was produced by plants in Pölitz (Polish: Police ) and Leuna, with more than 1/3 more in five other plants (Ludwigshafen had a much smaller Bergius plant which improved "gasoline quality by dehydrogenation" using the DHD process).
Synthetic fuel grades included "T.L. fuel ", "first quality aviation gasoline", "aviation base gasoline", and "gasoline - middle oil"; and "producer gas" and diesel were synthesized for fuel as well (e.g., converted armored tanks used producer gas). By early 1944, German synthetic fuel production had reached more than 124,000 barrels per day (19,700 m 3 /d) from 25 plants, including 10 in the Ruhr Area. In 1937, the four central Germany lignite coal plants at Böhlen, Leuna, Magdeburg/Rothensee, and Zeitz, along with the Ruhr Area bituminous coal plant at Scholven/Buer, had produced 4.8 million barrels (760 × 10
^3 m 3 ) of fuel. Four new hydrogenation plants (German: hydrierwerke ) were subsequently erected at Bottrop-Welheim (which used "Bituminous coal tar pitch"), Gelsenkirchen (Nordstern), Pölitz, and, at 200,000 tons/yr Wesseling. Nordstern and Pölitz/Stettin used bituminous coal, as did the new Blechhammer plants. Heydebreck synthesized food oil, which was tested on concentration camp prisoners. the Geilenberg Special Staff was using 350,000 mostly foreign forced laborers to reconstruct the bombed synthetic oil plants, and, in an emergency decentralization program, to build 7 underground hydrogenation plants for bombing protection (none were completed). (Planners had rejected an earlier such proposal because the war was to be won before the bunkers would be completed.) In July 1944, the 'Cuckoo' project underground synthetic oil plant (800,000 m 2 ) was being "carved out of the Himmelsburg" North of the Mittelwerk, but the plant was unfinished at the end of WWII.Indirect FT technologies were brought to the US after World War 2, and a 7,000 barrels per day (1,100 m 3 /d) plant was designed by HRI, and built in Brownsville Texas. The plant represented the first commercial use of high-temperature Fischer Tropsch conversion. It operated from 1950 to 1955, when it was shut down when the price of oil dropped due to enhanced production and huge discoveries in the Middle East.
Direct coal conversion plants were also developed in the US after WW2, including a 3 TPD plant in Lawrenceville, NJ, and a 250-600 TPD Plant in Catlettsburg, KY.
South Africa uses the Fischer-Tropsch process to produce most of that country's diesel. Another form of synthetic oil is produced at Syncrude sands plant in Alberta, Canada. This huge facility removes highly viscous bitumen from oil sands mined nearby, and uses a variety of processes of hydrogenation to turn it into high-quality synthetic crude oil. The Syncrude plant supplies about 14% of Canada's petroleum output. A similar plant is the smaller nearby facility owned by Suncor.
Processes
There are numerous processes that can be used to produce synthetic fuels.
These broadly fall into three categories: Indirect, Direct, and Biofuel processes.
Indirect conversion
Indirect conversion has the widest deployment worldwide, with global production totaling around 260,000 barrels per day (41,000 m 3 /d), and many additional projects under active development.
Indirect conversion broadly refers to a process in which biomass, coal, or natural gas is converted to a mix of hydrogen and carbon monoxide known as syngas either through gasification or steam methane reforming, and that syngas is processed into a liquid transportation fuel using one of a number of different conversion techniques depending on the desired end product.
The primary technologies that produce synthetic fuel from syngas are Fischer-Tropsch synthesis and the Mobil process (also known as Methanol To Gasoline, or MTG). There are some technologies under development to produce ethanol from syngas, though these have not yet been demonstrated at commercial scale.
The Fischer-Tropsch process reacts syngas with typically a cobalt or iron-based catalyst, and transforms the gas into liquid products (primarily diesel fuel and jet fuel) and potentially waxes (depending on the FT process employed).
The process of producing synfuels through indirect conversion is often referred to as coal-to-liquids (CTL), gas-to-liquids (GTL) or biomass-to-liquids (BTL), depending on the initial feedstock. At least three projects (Ohio River Clean Fuels, Illinois Clean Fuels, and Rentech Natchez) are combining coal and biomass feedstocks, creating hybrid-feedstock synthetic fuels known as Coal and Biomass To Liquids (CBTL).
Indirect conversion process technologies
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