Coal liquefaction

Coal liquefactions originally was developed at the beginning of the 20th century. The best-known CTL process is Fischer–Tropsch synthesis (FT), named after the inventors Franz Fischer and Hans Tropsch from the Kaiser Wilhelm Institute in the 1920s. The FT synthesis is the basis for indirect coal liquefaction (ICL) technology. Friedrich Bergius, also a German chemist, invented direct coal liquefaction (DCL) as a way to convert lignite into synthetic oil in 1913. Coal liquefaction was an important part of Adolf Hitler's four-year plan of 1936, and became an integral part of German industry during World War II. During the mid-1930s, companies like IG Farben and Ruhrchemie initiated industrial production of synthetic fuels derived from coal. This led to the construction of twelve DCL plants using hydrogenation and nine ICL plants using Fischer–Tropsch synthesis by the end of World War II. CTL provided 92% of Germany's air fuel and over 50% of its petroleum supply in the 1940s, partially mitigating the lack of fuel for the Nazi military. South Africa had no known domestic oil reserves at the time, and this made the country very vulnerable to disruption of supplies coming from outside, albeit for different reasons at different times. Sasol was a successful way to protect the country's balance of payment against the increasing dependence on foreign oil. For years its principal product was synthetic fuel, and this business enjoyed significant government protection in South Africa during the apartheid years for its contribution to domestic energy security. Although it was generally much more expensive to produce oil from coal than from natural petroleum, the political as well as economic importance of achieving as much independence as possible in this sphere was sufficient to overcome any objections. Early attempts to attract private capital, foreign or domestic, were unsuccessful, and it was only with state support that the coal liquefaction could start. CTL continued to play a vital part in South Africa's national economy, providing around 30% of its domestic fuel demand. The democratization of South Africa in the 1990s made Sasol search for products that could prove more competitive in the global marketplace; as of the new millennium the company was focusing primarily on its petrochemical business, as well as on efforts to convert natural gas into crude oil (GTL) using its expertise in Fischer–Tropsch synthesis. ==Methods==

Specific liquefaction technologies generally fall into two categories: direct liquefaction (DCL) and indirect liquefaction (ICL) processes. Direct processes are based on approaches such as carbonization, pyrolysis, and hydrogenation. Indirect liquefaction processes generally involve gasification of coal to a mixture of carbon monoxide and hydrogen, often known as synthesis gas or simply syngas. Using the Fischer–Tropsch process syngas is converted into liquid hydrocarbons. In contrast, direct liquefaction processes convert coal into liquids directly without having to rely on intermediate steps by breaking down the organic structure of coal with application of hydrogen-donor solvent, often at high pressures and temperatures. Since liquid hydrocarbons generally have a higher hydrogen-carbon molar ratio than coals, either hydrogenation or carbon-rejection processes must be employed in both ICL and DCL technologies. At industrial scales (i.e. thousands of barrels/day) a coal liquefaction plant typically requires multibillion-dollar capital investments. The resulting coal tars and oils from pyrolysis generally require further treatment before they can be usable as motor fuels; they are processed by hydrotreating to remove sulfur and nitrogen species, after which they are finally processed into liquid fuels. In summary, the economic viability of this technology is questionable. Hydrogenation processes One of the main methods of direct conversion of coal to liquids by hydrogenation process is the Bergius process, developed by Friedrich Bergius in 1913. In this process, dry coal is mixed with heavy oil recycled from the process. A catalyst is typically added to the mixture. The reaction occurs at between to and 20 to 70 MPa hydrogen pressure. The reaction can be summarized as follows: The Kohleoel Process, developed in Germany by Ruhrkohle and VEBA, was used in the demonstration plant with the capacity of 200 ton of lignite per day, built in Bottrop, Germany. This plant operated from 1981 to 1987. In this process, coal is mixed with a recycle solvent and iron catalyst. After preheating and pressurizing, H2 is added. The process takes place in a tubular reactor at the pressure of and at the temperature of . The Nuclear Utility Services Corporation developed hydrogenation process which was patented by Wilburn C. Schroeder in 1976. The process involved dried, pulverized coal mixed with roughly 1wt% molybdenum catalysts. Other single-stage hydrogenation processes are the Exxon Donor Solvent Process, the Imhausen High-pressure Process, and the Conoco Zinc Chloride Process. Chevron Corporation developed a process invented by Joel W. Rosenthal called the Chevron Coal Liquefaction Process (CCLP). It is unique due to the close-coupling of the non-catalytic dissolver and the catalytic hydroprocessing unit. The oil produced had properties that were unique when compared to other coal oils; it was lighter and had far fewer heteroatom impurities. The process was scaled-up to the 6 ton per day level, but not proven commercially. Indirect conversion processes Indirect coal liquefaction (ICL) processes operate in two stages. In the first stage, coal is converted into syngas (a purified mixture of CO and H2 gas). In the second stage, the syngas is converted into light hydrocarbons using one of three main processes: Fischer–Tropsch synthesis, methanol synthesis with subsequent conversion to gasoline or petrochemicals, and methanation. Fischer–Tropsch is the oldest of the ICL processes. In methanol synthesis processes syngas is converted to methanol, which is subsequently polymerized into alkanes over a zeolite catalyst. This process, under the moniker MTG (MTG for "Methanol To Gasoline"), was developed by Mobil in the early 1970s, and is being tested at a demonstration plant by Jincheng Anthracite Mining Group (JAMG) in Shanxi, China. Based on this methanol synthesis, China has also developed a strong coal-to-chemicals industry, with outputs such as olefins, MEG, DME and aromatics. Methanation reaction converts syngas to substitute natural gas (SNG). The Great Plains Gasification Plant in Beulah, North Dakota is a coal-to-SNG facility producing 160 million cubic feet per day of SNG, and has been in operation since 1984. Several coal-to-SNG plants are in operation or in project in China, South Korea and India. In another application of gasification, hydrogen extracted from synthetic gas reacts with nitrogen to form ammonia. Ammonia then reacts with carbon dioxide to produce urea. The above instances of commercial plants based on indirect coal liquefaction processes, as well as many others not listed here including those in planning stages and under construction, are tabulated in the Gasification Technologies Council's World Gasification Database. ==Environmental considerations==

Typically coal liquefaction processes are associated with significant CO2 emissions from the gasification process or as well as from generation of necessary process heat and electricity inputs to the liquefaction reactors, There are technically feasible low-emission configurations of CTL plants. High water consumption in the water-gas shift reaction or steam methane reforming is another adverse environmental effect. ==Research and development of coal liquefaction==

The United States military has an active program to promote alternative fuels use, and utilizing vast domestic U.S. coal reserves to produce fuels through coal liquefaction would have obvious economic and security advantages. But with their higher carbon footprint, fuels from coal liquefaction face the significant challenge of reducing life-cycle GHG emissions to competitive levels, which demands continued research and development of liquefaction technology to increase efficiency and reduce emissions. A number of avenues of research & development will need to be pursued, including: • Carbon capture and storage including enhanced oil recovery and developmental CCS methods to offset emissions from both synthesis and utilization of liquid fuels from coal, • Coal/biomass/natural gas feedstock blends for coal liquefaction: Utilizing carbon-neutral biomass and hydrogen-rich natural gas as co-feeds in coal liquefaction processes has significant potential for bringing fuel products' life-cycle GHG emissions into competitive ranges, • Hydrogen from renewables: the hydrogen demand of coal liquefaction processes might be supplied through renewable energy sources including wind, solar, and biomass, significantly reducing the emissions associated with traditional methods of hydrogen synthesis (such as steam methane reforming or char gasification), and • Process improvements such as intensification of the Fischer–Tropsch process, hybrid liquefaction processes, and more efficient air separation technologies needed for production of oxygen (e.g. ceramic membrane-based oxygen separation). Since 2014, the U.S. Department of Energy and the Department of Defense have been collaborating on supporting new research and development in the area of coal liquefaction to produce military-specification liquid fuels, with an emphasis on jet fuel, which would be both cost-effective and in accordance with EISA Section 526. Projects underway in this area are described under the U.S. Department of Energy National Energy Technology Laboratory's Advanced Fuels Synthesis R&D area in the Coal and Coal-Biomass to Liquids Program. Every year, a researcher or developer in coal conversion is rewarded by the industry in receiving the World Carbon To X Award. The 2016 Award recipient is Mr. Jona Pillay, executive director for Gasification & CTL, Jindal Steel & Power Ltd (India). The 2017 Award recipient is Dr. Yao Min, Deputy General Manager of Shenhua Ningxia Coal Group (China). In terms of commercial development, coal conversion is experiencing a strong acceleration. Geographically, most active projects and recently commissioned operations are located in Asia, mainly in China, while U.S. projects have been delayed or canceled due to the development of shale gas and shale oil. ==Coal liquefaction plants and projects==

World (Non-U.S.) Coal to Liquid Fuels Projects U.S. Coal to Liquid Fuels Projects ==See also==