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Chemical process of converting coal into liquid hydrocarbons

Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon based products. However, the most common process chain is "Coal to Liquid Fuels" (CTL).

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. In total, CTL provided 92% of Germany's air fuel and over 50% of its petroleum supply in the 1940s. 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. CTL technologies have steadily improved since the Second World War. Technical development has resulted in a variety of systems capable of handling a wide array of coal types. However, only a few enterprises based on generating liquid fuels from coal have been undertaken, most of them based on ICL technology; the most successful one has been Sasol in South Africa. CTL also received new interest in the early 2000s as a possible mitigation option for reducing oil dependence, at a time when rising oil prices and concerns over peak oil made planners rethink existing supply chains for liquid fuels.

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.

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 300 bar (30 MPa) 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 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.

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. As of late October 2013, an accumulated amount of 154,000 tonnes of CO2 had been injected since 2010, which reached or exceeded the design value. In the United States, the Renewable Fuel Standard and low carbon fuel standard, such as enacted in the State of California, reflect an increasing demand for low carbon footprint fuels. Also, legislation in the United States has restricted the military's use of alternative liquid fuels to only those demonstrated to have life cycle GHG emissions less than or equal to those of their conventional petroleum based equivalent, as required by Section 526 of the Energy Independence and Security Act (EISA) of 2007.

+World (Non U. S.) Coal to Liquid Fuels Projects Project Developer Locations Type Products Start of OperationsSasol Synfuels II (West) & Sasol Synfuels III (East)Sasol (Pty) Ltd. Secunda, South AfricaCTL160,000 BPD; primary products gasoline and light olefins (alkenes)1977(II)/1983(III)Shenhua Direct Coal Liquefaction PlantShenhua GroupErdos, Inner Mongolia, ChinaCTL (direct liquefaction)20,000 BPD; primary products diesel fuel, liquefied petroleum gas, naphtha2008Yitai CTL PlantYitai Coal Oil Manufacturing Co., Ltd. Ordos, Zhungeer, ChinaCTL160,000 mt/a Fischer–Tropsch liquids2009Jincheng MTG PlantJincheng Anthracite Mining Co., Ltd. Jincheng, ChinaCTL300,000 t/a methanol from MTG process2009Sasol SynfuelsSasol (Pty) Ltd. Secunda, South AfricaCTL3,960,000 (Nm3/d) syngas capacity; Fischer–Tropsch liquids2011Shanxi Lu'an CTL PlantShanxi Lu'an Co. Ltd. Lu'an, ChinaCTL160,000 mt/a Fischer–Tropsch liquids2014ICM Coal to Liquids PlantIndustrial Corporation of Mongolia LLC (ICM)Tugrug Nuur, MongoliaCTL13,200,000 (Nm3/d) syngas capacity; gasoline2015Yitai Yili CTL PlantYitai Yili Energy Co. Yili, ChinaCTL30,000 BPD Fischer–Tropsch liquids2015Yitai Ordos CTL Plant Phase IIYitaiOrdos, Zhungeer Dalu, ChinaCTL46,000 BPD Fischer–Tropsch liquids2016Yitai Ürümqi CTL PlantYitaiGuanquanbao, Urunqi, ChinaCTL46,000 BPD Fischer–Tropsch liquids2016Shenhua Ningxia CTL ProjectShenhua Group Corporation LtdChina, Yinchuan, NingxiaCTL4 million tonnes/year of diesel & naphtha2016Clean Carbon IndustriesClean Carbon IndustriesMozambique, Tete provinceCoal waste to liquids65,000 BPD fuel2020Arckaringa ProjectAltona EnergyAustralia, SouthCTL30,000 BPD Phase I 45,000 BPD + 840 MW Phase IITBD

+U. S. Coal to Liquid Fuels Projects Project Developer Locations Type Products StatusAdams Fork Energy TransGas WV CTLTransGas Development Systems (TGDS)Mingo County, West VirginiaCTL7,500 TPD of coal to 18,000 BPD gasoline and 300 BPD LPGOperations 2016 or laterAmerican Lignite Energy (aka Coal Creek Project)American Lignite Energy LLC (North American Coal, Headwaters Energy Services)MacLean County, North DakotaCTL11.5 million TPY lignite coal to 32,000 BPD of undefined fuelDelayed/CancelledBelwood Coal to Liquids Project (Natchez)RentechNatchez, MississippiCTLPetcoke to up to 30,000 BPD ultra clean dieselDelayed/CancelledCleanTech Energy ProjectUSA Synthetic Fuel Corp. (USASF)WyomingSynthetic crude30.6 mm bbls/year of synthetic crude (or 182 billion cubic feet per year)Planning/financing not securedCook Inlet Coal to Liquids Project (aka Beluga CTL)AIDEA and Alaska Natural Resources to LiquidsCook Inlet, AlaskaCTL16 million TPY coal to 80,000 BPD of diesel and naphtha; CO2 for EOR; 380 MW electrical generationDelayed/CancelledDecatur Gasification PlantSecure EnergyDecatur, IllinoisCTL1.5 million TPY of high sulfur IL coal generating 10,200 barrels per day of high quality gasolineDelayed/CancelledEast Dubuque PlantRentech Energy Midwest Corporation (REMC)East Dubuque, IllinoisCTL, polygeneration1,000 tpd ammonia; 2,000 BPD clean fuels and chemicalsDelayed/CancelledFEDC Healy CTLFairbanks Economic Development Corp. (FEDC)Fairbanks, AlaskaCTL/GTL4.2 11.4 million TPY Healy mined coal; ~40k BPD liquid fuels; 110MWPlanningFreedom Energy Diesel CTLFreedom Energy Diesel LLCMorristown, TennesseeGTLUndeterminedDelayed/CancelledFuture Fuels Kentucky CTLFuture Fuels, Kentucky River PropertiesPerry County, KentuckyCTLNot specified. Coal to methanol and other chemicals (over 100 million tons of coal supply)ActiveHunton "Green Refinery" CTLHunton EnergyFreeport, TexasCTLBitumen crude oil to 340,000 BPD jet and diesel fuelDelayed/CancelledIllinois Clean Fuels ProjectAmerican Clean Coal FuelsColes County, IllinoisCTL4.3 million TPY coal/biomass to 400 million GPY diesel and jet fuelDelayed/CancelledLima Energy ProjectUSA Synthetic Fuel Corp. (USASF)Lima, OhioIGCC/SNG/H2, polygenerationThree Phases: 1) 2.7 million barrels of oil equivalent (BOE), 2) expand to 5.3 million BOE (3) expand to 8.0 million BOE (47 billion cf/y), 516 MWActiveMany Stars CTLAustralian American Energy Co. (Terra Nova Minerals or Great Western Energy), Crow NationBig Horn County, MontanaCTLFirst phase: 8,000 BPD liquidsActive (no new information since 2011)Medicine Bow Fuel and Power ProjectDKRW Advanced FuelsCarbon County, WyomingCTL3 million TPY coal to 11,700 BPD of gasolineDelayed/CancelledNABFG Weirton CTLNorth American Biofuels GroupWeirton, West VirginiaCTLUndeterminedDelayed/CancelledRentech Energy Midwest FacilityRentech Energy Midwest Corporation (REMC)East Dubuque, IllinoisCTL1,250 BPD dieselDelayed/CancelledRentech/Peabody Joint Development Agreement (JDA)Rentech/Peabody CoalKentuckyCTL10,000 and 30,000 BPDDelayed/CancelledRentech/Peabody MinemouthRentech/Peabody CoalMontanaCTL10,000 and 30,000 BPDDelayed/CancelledSecure Energy CTL (aka MidAmericaC2LMidAmericaC2L / SiemensMcCracken County, KentuckyCTL10,200 BPD gasolineActive (no new information since 2011)Tyonek Coal to Liquids (formerly Alaska Accelergy CTL Project)Accelergy, Tyonek Native Corporation (TNC)Cook Inlet, AlaskaCBTLUndefined amount of coal/biomass to 60,000 BPD jet fuel/gasoline/diesel and 200 400 MW electricityPlanningUS Fuel CTLUS Fuel CorporationPerry County/Muhlenberg County, KentuckyCTL300 tons of coal into 525 BPD liquid fuels including diesel and jet fuelActive