Coal Liquefaction
Coal liquefaction is a process that transforms coal into synthetic petroleum, primarily by reacting coal with hydrogen gas under high temperatures and pressures. This method has gained attention as an alternative to traditional fossil fuels like oil and natural gas, especially in coal-rich countries seeking to enhance their energy independence. The most widely used technique in modern coal liquefaction is the Fischer-Tropsch method, which involves gasifying coal to produce synthesis gas (a mixture of hydrogen and carbon monoxide) and then converting it into synthetic crude oil using a catalyst.
Historically, the concept of converting coal to oil dates back to the early 19th century, with significant developments occurring throughout the 20th century, particularly during times of oil shortages, such as World War II and the oil crises of the 1970s. Despite its potential, coal liquefaction has faced challenges, including high production costs and environmental concerns associated with coal extraction and processing. The industry's prospects vary by region; while countries like China have made notable investments and advancements, others continue to weigh the economic and ecological implications of adopting coal liquefaction technologies. As global energy demands evolve, the future of coal liquefaction remains uncertain, with ongoing debates about its viability compared to cleaner, renewable energy sources.
Coal Liquefaction
Summary
Coal liquefaction is a catalytic process that converts different varieties of coal into synthetic petroleum by reacting coal with hydrogen gas at high temperatures and under high pressure. The resultant synthetic oil (SynOil) product has the potential to be used in place of other fossil fuels such as oil and natural gas. Coal-producing countries such as the United States have investigated the process as a way to contribute to their petroleum supplies and reduce the need to rely on imported oil.
Definition and Basic Principles
Coal liquefaction involves converting bituminous or (more rarely) anthracite coal into a liquid that can be refined into the end product. The focus is on transportation fuels to lower the direct and indirect costs that oil-importing states incur in purchasing large volumes of petroleum from abroad.
The chemical processes being used in the twenty-first century favor the indirect Fischer-Tropsch method of coal liquefaction. In this process, coal is initially subjected to very high heat to create a charred substance that can be combined with carbon dioxide and steam to produce a synthesis gas composed of hydrogen and carbon monoxide. The gas is then chemically subjected to a metallic catalyst, which transforms it into a synthetic crude oil. The resultant synthetic oil can then be refined into the desired fuel.
Whatever the method, the amount of coal necessary to produce oil is about the same. Nearly three-quarters of a ton of coal is required to produce slightly over one barrel of oil. Therefore, large-scale production of oil from coal would be a massive undertaking.
Background and History
Neither the idea nor the practice of producing oil from coal is new. As early as 1819, Charles Macintosh distilled naphtha from coal for the purpose of waterproofing textiles. However, the major breakthroughs in coal liquefaction did not occur until the period between the early 1900s, when the two processes long used as the starting points for producing oil from coal—the Bergius and Fischer-Tropsch methods—were developed.
Since then, political considerations have trumped economics in pushing countries into developing oil from coal on two notable occasions. Germany experienced an oil shortage during World War II, and South Africa feared the imposition of an oil embargo against its White minority government during apartheid. However, the high cost of imported oil or concern with its inadequate or insecure supply sparked interest in coal liquefaction on several other occasions. In 1928, Standard Oil of New Jersey and I. G. Farben joined forces to pursue a significant liquefaction project based on the Bergius process, but their venture was short-lived. No sooner was the Standard Oil-Farben deal made than the market conditions that had brought it about disappeared. The Great Depression dampened the Western demand for oil, and the discovery of rich oil fields in Texas in 1930 meant an increase in the supply of cheap crude oil in the United States.
During World War II and shortly after, concerns over the security of the oil supply and fears that the supply would not be adequate to meet the rapid postwar expansion drove a short period of government-sponsored research into creating oil from coal in the United States. However, soon after two pilot plants were established to test the Bergius and Fischer-Tropsch processes in the postwar period, imported oil from the vast, newly developed fields of the Middle East began to arrive in such abundance that an oil glut appeared likely. In 1949, the National Petroleum Council began questioning the commercial feasibility of coal-based oil, and four years later, citing the changed economic climate, the administration of President Dwight D. Eisenhower ordered the government-owned research facilities closed.
During the next twenty years, private industry continued to conduct coal liquefaction experiments, and major petroleum corporations acquired ownership of several coal companies with coal liquefaction pilot plants. Nevertheless, with the cost of oil remaining low throughout this period, research projects tended to remain very small in scale. It was not until the oil crises of the 1970s, which drove the price of imported oil from under $3 per barrel in mid-1973 to over $35 per barrel in 1979, that a third round of interest in the commercial synthetic fuels industry began. This time, major research and development programs emerged across five continents, and both public agencies and private companies initiated multibillion-dollar projects. The outcome, nonetheless, was again the same. Within a decade of the 1973 oil crisis, the rising price of oil had generated a massive recession in the oil-importing world. Demand for oil dropped precipitously, and when the price of oil began to drop, Organization of the Petroleum Exporting Countries (OPEC) members began trying to undersell one another to gain a wider share of the shrinking market, further accelerating the downward spiral in the price of oil. By then, President Ronald Reagan had drained the Synthetic Fuel Corporation created by the US Congress in 1980 of the $88 billion allocated to it for the development of an American coal liquefaction and gasification industry, and around the world, others were following his lead.
Except for a momentary spike in the price of oil when Iraq invaded Kuwait in 1990, which generated fears that the supply of oil would be disrupted, low oil prices remained the norm from the mid-1980s until the US invasion of Iraq in 2003. The growing demand for oil in China and India had already pushed the price toward $30 per barrel, but that figure was too low for investors to revisit the synthetic fuels option. However, in 2003, when the United States invaded Iraq, the gap between OPEC's production capacity and global demand for oil was closing. By the end of 2003, imported petroleum reached more than $30 per barrel. Two years later, it doubled to $60 per barrel. Costs eventually peaked at more than $147 per barrel in July 2008, before the high price of oil dampened demand and oil prices began to drop sharply. By then, interest in coal liquefaction as a commercial alternative to OPEC oil had been resuscitated, and several pilot projects based on the Fischer-Tropsch process were underway around the world.
In general, US coal liquefaction projects once again stalled as the nation developed its shale gas and shale oil deposits in the late 2000s and 2010s. However, some research continued, notably a government program investigating the potential of jet fuel and other military fuels derived from coal. Coal liquefaction also continued to be researched and commercially developed in other countries, especially China, through the 2010s and early 2020s.
How It Works
Although there are variations in terms of catalytic agents, the degree of heat, and the level of pressure employed, there are three broad methods for liquefying coal into oilhydrogenation, catalytic synthesis, and pyrolysis.
Hydrogenation. The first hydrogenation process to develop was the Bergius process, which produces heavy crude oil directly from coal by adding hydrogen to unprocessed coal and recycled heavy oil. Hydrogenation is the central element in the Begrius process. However, unlike the Fischer-Tropsch approach, which also uses hydrogenation, the Bergius system employs a combination of various catalysts (typically tungsten, tin, or nickel oleate) to convert the carbon directly, under very high pressure and at much higher temperatures (from 700 to more than 925 degrees Fahrenheit), into oil liquids capable of being refined into industrial and heating oil and transportation fuels.
Developed in Germany by Friedrich Bergius in 1913 and sold to the German chemical conglomerate I. G. Farben in 1924, this process was the more popular means of coal liquefaction in Germany from 1925 until the end of World War II. It was resurrected there again during the oil crises of the 1970s with the creation of a demonstration plant in Bottrop, a coal-mining center in the Ruhr region. However, that plant closed in the early 1990s. Direct liquefaction saw very limited development after the 1980s. One notable later addition was a process for simultaneously refining coal and oil.
Catalytic Synthesis. The liquefaction method more commonly used in the twenty-first century was also developed in Germany, by Franz Fischer and Hans Tropsch in 1923. This indirect method produces oil from coal by first gasifying the hydrocarbons through a combination of complex chemical reactions involving catalytic synthesis. At the heart of the process, typically at temperatures ranging from 300 to 575 degrees Fahrenheit, carbon monoxide is mixed with hydrogen in a series of catalytic chemical reactions.
In the 2010s, virtually all confirmed liquefaction projects underway, including South Africa's synthetic fuels industry, were employing some variant of this process and for understandable reasons. In a world in which liquid fuels and gas are important sources of energy, the Fischer-Tropsch process has the advantage of producing both petroleum liquids and a high volume of natural gas liquids and ethane.
Pyrolysis. In the pyrolysis process for converting coal into oil, high heat is applied to coal in an oxygen-free environment, decomposing it into oil and coal tar. Then the oil is subjected to hydrogenation to remove sulfur and other extraneous content before it is processed into fuel sources. Substantially fewer demonstration efforts have been devoted to this process because the amount of oil produced per ton of coal is less than that yielded by the Fischer-Tropsch or Bergius methods, and no major liquefaction operation at even the pilot plant level has been based on it.
Applications and Products
Because the Earth's coal reserves are substantially greater than its oil reserves, a general consensus exists within the energy industry that a significant liquefied coal industry will eventually emerge around the globe. However, despite growth in the field—particularly in China—that day has largely yet to come. Hence, any discussion of the products that can emerge from such an industry must necessarily be divided into two partsthe likely applications of a future liquefied coal industry and what has occurred within the framework of the Fischer-Tropsch method in South Africa, where a well-established oil-from-coal industry exists.
The development of a liquefied coal industry in the oil-importing world is likely. The United States, for example, throughout the first decade of the twenty-first century, was persistently importing 60 percent or more of its petroleum needs, at a cost of hundreds of billions of dollars. Moreover, because more than half of the petroleum used in the United States goes into the transportation sector, it is assumed that the majority of any synthetic oil produced in the United States or elsewhere in the oil-importing world will be used in that sector to achieve the target goal of reducing the amount of oil imported as much as possible. While the development of other fossil fuels has long prevented the US coal liquefaction industry from emerging, these resources are finite. Of course, coal is also a nonrenewable energy resource, and one with serious environmental consequences, so it is possible that renewable energy sources will be developed instead of coal liquefaction, depending on economic, political, and social trends.
As for South Africa, liquefied coal has figured into its overall energy equation since 1955, when the South Africa Coal Oil and Gas Corporation (SASOL) began liquefying cheap coal mined by inexpensive local labor into state-subsidized gasoline. That first Fischer-Tropsch-based plant was subsequently devoted entirely to producing gas from coal, but in the interim, SASOL opened two additional coal-into-oil plants that together produce nearly 200,000 barrels of oil per day. SASOL has more than half a century of experience in converting coal to liquids, and in addition to transportation fuel, it produces a variety of chemical solvents and waxes using the Fischer-Tropsch method. However, even the increase in petroleum prices after 2003 did not encourage it to expand its liquefaction operations, and South Africa still imports about two-thirds of its petroleum needs.
Careers and Course Work
Careers involving the development of alternative energy sources will almost certainly expand in the twenty-first century as the demand for oil inevitably continues to rise even if Western countries are able to reduce the number of internal combustion engines on their highways. With that demand, a long-term rise in the price of oil is also probable. Consequently, scientists trained in the applied fields of chemistry, earth sciences, geology, environmental science, and physics, with specialization in alternative fuel development, can expect to be in demand. Whether those specializing in coal liquefaction technologies will be swept up in that demand and find more employment opportunities, however, is more debatable. The case for pursuing coal liquefaction has altered little in a century.
Coal remains far more abundantly available than petroleum and is found in significant deposits on every continent. Moreover, liquefaction processes based on the Fischer-Tropsch method have reportedly reduced the cost of coal liquefaction to levels that should be competitive at the likely cost of future OPEC oil imports. These arguments have not convinced investors to dive heavily into coal liquefaction projects in light of the developed world's swing toward more environmentally clean energy sources. Coal is a dirtier fossil fuel than oil or natural gas, and increased coal production and processing in large volumes in synthetic oil industries carries a risk of increased air pollution and groundwater contamination. Those inclined to pursue chemistry and thermal physics courses for future careers in alternative energy fuels may benefit from specializing in coal gasification or oil production from tar sands rather than coal liquefaction.
Social Context and Future Prospects
The economic assumptions driving early twenty-first-century interest in coal liquefaction are that coal can be converted into oil at a reasonable cost and that this coast can be competitive with that of OPEC oil or other fuels (including domestic oil and gas and renewable sources). To this may be added a third assumption, that Western societies will understand that the social costs of importing oil are greater than the environmental risks involved in increasing coal consumption. With none of these factors guaranteed, the development of the coal liquefaction remains uncertain.
Despite the obstacles posed by the existing oil industry and environmental concerns, the coal liquefaction industry has seen some areas of progress. Most notably, China significantly increased investment in liquefaction technology in the 2010s, and several plants opened in that country. Other nations, including India and South Korea, also saw a surge of interest in the process in this period and established projects. Still, as a global commercial undertaking, coal liquefaction remains a technology in search of its time.
Further Reading
Bartis, James T., Frank Camm, and David S. Ortiz. Producing Liquid Fuels from Coal: Prospects and Policy Issues. RAND Corporation, 2008.
Crow, Michael, et al. Synthetic Fuel Technology Development in the United States: A Retrospective Assessment. Westport, Conn.: Greenwood Press, 1988.
"Direct Liquefaction Processes." National Energy Technology Laboratory, US Dept. of Energy, netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/direct-liquefaction. Accessed 8 June 2024.
"Indirect Liquefaction Processes." National Energy Technology Laboratory, US Dept. of Energy, netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/indirect-liquefaction. Accessed 8 June 2024.
International Energy Agency. Coal Liquefaction: A Technology Review. Paris: Organization for Cooperation and Development, 1982.
Schobert, Harold H. Rethinking Coal: Chemicals and Carbon-Based Materials in the 21st Century. Oxford University Press, 2022.
Speight, J. G. Synthetic Fuels Handbook: Properties, Process, and Performance. McGraw-Hill, 2008.
Xiaobin Zhang, et al. “Theoretical Analysis of Hydrogen Solubility in Direct Coal Liquefaction Solvents.” International Journal of Coal Science & Technology, vol. 11, no. 1, 2024, pp. 1–11. doi.org/10.1007/s40789-024-00674-0.
Yanarella, Ernest J., and William C. Green, eds. The Unfulfilled Promise of Synthetic Fuels: Technological Failure, Policy Immobilism, or Commercial Illusion. New York: Greenwood Press, 1987.
Zhuang, Qianlin. From Coal to Hydrogen: A Long Journey of Energy Transition. Springer, 2024