RESEARCH STARTER

Synthetic fuels

Synthetic fuels are energy sources that do not occur naturally and can be solid, liquid, or gaseous. They are produced from abundant natural resources like coal, tar sands, oil shale, and biomass, with the primary goal of creating environmentally cleaner fuels by reducing harmful pollutants. The production process aims to eliminate sulfur, nitrogen, and other pollutants that contribute to air quality issues, such as acid rain and smog. Different methods, including hydrogenation, pyrolysis, and fermentation, are employed to convert raw materials into synthetic fuels, focusing on achieving a high hydrogen-to-carbon ratio for cleaner combustion.

Key sources for synthetic fuel production include coal, which, despite its abundance, is one of the dirtiest energy sources due to its high carbon content. Tar sands and oil shale also serve as significant feedstocks, with advancements in extraction techniques making them increasingly viable. Biomass, derived from plant materials, offers a renewable alternative and contributed about 5% of the total energy output in the U.S. in 2022. While currently less economically competitive than natural petroleum, the finite nature of fossil fuel reserves suggests that synthetic fuels will play a crucial role in future energy strategies, leading to ongoing research and development in this field.

Full Article

  • DEFINITION: Solid, liquid, or gaseous sources of energy that do not occur naturally

Given the finite nature of the world’s stores of natural petroleum, the development of economically viable, environmentally safe, and renewable synthetic fuels is important for human survival.

Synthetic fuels are normally produced from abundantly occurring natural resources such as coal, tar sands, oil shale, and biomass. One of the main objectives in the production of a synthetic fuel is to eliminate sulfur and nitrogen from the fuel compound, thereby creating an environmentally clean energy source. Oxides of nitrogen and sulfur dioxide are among the most undesirable of common air pollutants. Sulfur dioxide is one of the major causes of acid rain, which is created when sulfur dioxide combines with water vapor in the atmosphere to form sulfuric acid. Similarly, oxides of nitrogen produce nitric acid. These acids fall back to Earth in rain and are detrimental to both aquatic and botanical life. Synthetic fuel manufacturers thus strive to eliminate these pollutants, as well as others such as carbon monoxide, hydrocarbons, particulates, and photochemical oxidants, from the fuel supply.

Principles of Synthetic Fuel Manufacture

The manufacture of liquid and gaseous synthetic fuels normally involves transforming naturally occurring carbonaceous raw material through a suitable conversion process. The techniques employed include hydrogenation, devolatilization, decomposition, and fermentation. The principal aim in the manufacture of synthetic fuel is to achieve a low carbon-to-hydrogen atomic mass ratio, or a high hydrogen-to-carbon atomic ratio, whenever possible. This results in a clean-burning fuel that releases by-products that are harmless to the environment. For example, pure methane (CH4), with a molecular weight of 16, has a high hydrogen-to-carbon ratio of 4:1. Methane gas is a common component that is absorbed into coal. The method used to release the gas involves fracturing the coal and exposing it to low pressures. Coal-bed methane is one of the cleanest-burning fossil fuels; the by-products of burning it are simply carbon dioxide and water. Synthetically generated substitute natural gas is more than 90 percent methane. Natural gas (of which methane is the chief constituent) has a hydrogen-to-carbon ratio of approximately 3.4:1, which is also quite high. The ratios for liquefied petroleum gas and for naphtha lie between 2:1 and 3:1. (In comparison, the ratios for gasoline and fuel oil are less than 2:1. Bituminous coal has one of the lowest values, with a ratio of much less than 1:1.)

Coal Gasification and Liquefaction

Although coal is among the most abundant natural energy sources, it is also among the dirtiest. The composition of this solid fossil fuel is a major disadvantage; it consists of about 70 percent carbon and about 5 percent hydrogen, translating to a highly undesirable carbon-to-hydrogen mass ratio of 14:1. Coal-burning power-generating stations thus emit large quantities of gases that are harmful to the environment. Despite the use of such emission-reducing devices as electrostatic precipitators, the levels of pollutants emitted by coal-burning plants remain high. Techniques such as coal gasification and coal liquefaction yield synthetic fuels that are safer for the environment.

The process of coal gasification involves making coal react with steam at very high temperatures (in the range of 1,000 degrees Celsius, or 1,832 degrees Fahrenheit). This process produces synthetic gas. Three types of synthetic gas are in common use. Low-calorific-value gas (also called producer gas) is used in turbines. Medium-calorific-value gas (also called power gas) is used as a fuel gas by various industries. High-calorific-value gas (also called pipeline gas) is a very good substitute for natural gas and is well suited to economical pipeline transportation. Pipeline gas contains more than 90 percent methane; as a result, it has a high hydrogen-to-carbon ratio.

The process of coal liquefaction is employed to generate a liquid fuel with a high hydrogen-to-carbon ratio; it is also used to obtain low-sulfur fuel oil. Several methods are employed to accomplish coal liquefaction, including direct catalytic hydrogenation, indirect catalytic hydrogenation, pyrolysis, and solvent extraction. While these fuels may be much safer for the environment than the original coal, the process of manufacturing them produces high amounts of carbon dioxide (CO2) and other greenhouse gases.

Tar Sands and Oil Shale

Naturally occurring tar sands contain grains of sand, water, and bitumen. Bitumen, a member of the petroleum family, is a high-viscosity crude hydrocarbon. A method known as hot water extraction is used to procure bitumen from tar sands. The bitumen is subsequently upgraded to synthetic crude oil in refineries. Synthetic crude oil (also called syncrude) is similar to petroleum and can be obtained through coal liquefaction as well as from tar sands and oil shale.

Large deposits of tar sands are found in Alberta, Canada; the United States has huge reserves of oil shale in Utah, Wyoming, and Colorado. Oil shale is probably the most abundant form of hydrocarbon on earth. Oil shale is a sedimentary rock that contains kerogen, which is not a member of the petroleum family. A popular method known as retorting is used to produce oil from shale. The process involves pyrolysis, a method that reduces the carbon content in raw hydrocarbons through distillation.

Twenty-first-century technological advancements allowed shale oil to become an economically feasible alternative to petroleum. In a process known as hydraulic fracturing, or fracking, water, sand, or chemicals are injected into the rock formation under high pressure, forcing out the trapped shale oil. Extracting oil from shale and other rock formations became the most significant oil-producing method in the United States in the 2010s. By the 2020s, about 65 percent of all oil produced in the United States came from such methods.

Biomass Fuels and Gasohol

Like oil and coal, biomass is derived from plant life. Oil and coal, however, are considered nonrenewable resources, as it takes vast periods of time for geologic processes to produce these materials naturally. Because biomass consists of any material that is derived from plant life, it is produced in far shorter spans—one hundred years or less—and is thus considered renewable. Wood is the most versatile biomass resource; farm and agricultural wastes, municipal wastes, and animal wastes are also considered to be biomass. Biomass can be processed into fuel using a variety of methods. Fermentation, for example, yields ethanol, or ethyl alcohol (sometimes called grain alcohol). Other methods include combustion, gasification, and pyrolysis. According to the US Energy Information Administration, 5 percent of the total energy output in the United States in 2023 came from biomass fuels.

Gasohol is a mixture of gasoline and small quantities of ethanol. The mixture burns cleaner than conventional gasoline; however, it can cause damage to plastic and rubber materials used in automobile engines. In the United States, therefore, the Environmental Protection Agency (EPA) permits the addition of only 10 percent ethanol by volume to gasoline to create gasohol. Methanol, or methyl alcohol (also called wood alcohol), can also be combined with conventional gasoline to produce cleaner fuel; however, the EPA limits the amount of methanol in such mixtures to 3 percent.

Other Fuels

A nonpolluting rocket fuel based on alcohol and hydrogen peroxide was developed by US Navy research engineers at China Lake, California, in the 1990s. This nontoxic homogeneous miscible fuel (NHMF) can be modified and used to drive turbines, which in turn drive alternators that produce electricity. Further developments based on what has been learned about this fuel may permit its use in automobiles. During World War II, moreover, Germany produced synthetic fuels in large quantities to meet its energy demands, employing coal gasification and also creating diesel oil and aviation kerosene using a reconstitution process; this process is still in use in many places.

Although the abundance of natural petroleum limits the economic competitiveness of most synthetic fuels, the finite nature of the world’s oil supply virtually ensures that synthetic fuels will become increasingly important energy sources. The US Department of Energy and governmental agencies in many countries provide funding to encourage research into the creation of economically viable, environmentally safe, and renewable synthetic and advanced biofuels.

While the synthetic fuel industry improved the carbon neutrality of various sectors in the late twentieth and early twenty-first centuries, the positive environmental impact of synthetic fuels is often offset by the construction of production facilities and the use of conventional fuels for transportation. The large-scale production of synthetic fuels is needed to lower costs to a point that would be competitive with traditional fuels. However, large-scale production using wind and solar parks requires a significant use of land resources, which can interfere with agricultural activities, conservation efforts, and habitats for animals such as birds and bats.


Bibliography

"Biomass—Renewable Energy from Plants and Animals." US Energy Information Administration, 30 July 2024, www.eia.gov/energyexplained/biomass. Accessed 14 Sept. 2025.

Deutch, John M., and Richard K. Lester. “Synthetic Fuels.” Making Technology Work: Applications in Energy and the Environment. Cambridge UP, 2004.

Hayes, Adam. "Shale Oil: Overview, Benefits and Examples." Investopedia, 23 Aug. 2022, www.investopedia.com/terms/s/shaleoil.asp. Accessed 14 Sept. 2025.

Janaki, Sreejaun Thothaathiri, et al. “Beyond Fossil: The Synthetic Fuel Surge for a Green-Energy Resurgence.” Clean Energy, vol. 8, no. 5, 2024, pp. 1–19, doi:10.1093/ce/zkae050. Accessed 14 Sept. 2025.

Lorenzetti, Maureen Shields. Alternative Motor Fuels: A Nontechnical Guide. PennWell, 1996.

Manahan, Stanley E. “Adequate, Sustainable Energy: Key to Sustainability.” Environmental Science and Technology: A Sustainable Approach to Green Science and Technology. 2nd ed., CRC Press, 2007.

Miller, G. Tyler, Jr., and Scott Spoolman. “Nonrenewable Energy.” Living in the Environment: Principles, Connections, and Solutions. 20th ed., Brooks/Cole, 2021.

Ram, Vishal, and Surender Reddy Salkuti. “An Overview of Major Synthetic Fuels.” Energies, vol. 16, no. 6, 2023, p. 2834, doi:10.3390/en16062834. Accessed 14 Sept. 2025.

Speight, James G. Synthetic Fuels Handbook: Properties, Process, and Performance. 2nd ed., McGraw-Hill, 2020.

Full Article

  • DEFINITION: Solid, liquid, or gaseous sources of energy that do not occur naturally

Given the finite nature of the world’s stores of natural petroleum, the development of economically viable, environmentally safe, and renewable synthetic fuels is important for human survival.

Synthetic fuels are normally produced from abundantly occurring natural resources such as coal, tar sands, oil shale, and biomass. One of the main objectives in the production of a synthetic fuel is to eliminate sulfur and nitrogen from the fuel compound, thereby creating an environmentally clean energy source. Oxides of nitrogen and sulfur dioxide are among the most undesirable of common air pollutants. Sulfur dioxide is one of the major causes of acid rain, which is created when sulfur dioxide combines with water vapor in the atmosphere to form sulfuric acid. Similarly, oxides of nitrogen produce nitric acid. These acids fall back to Earth in rain and are detrimental to both aquatic and botanical life. Synthetic fuel manufacturers thus strive to eliminate these pollutants, as well as others such as carbon monoxide, hydrocarbons, particulates, and photochemical oxidants, from the fuel supply.

Principles of Synthetic Fuel Manufacture

The manufacture of liquid and gaseous synthetic fuels normally involves transforming naturally occurring carbonaceous raw material through a suitable conversion process. The techniques employed include hydrogenation, devolatilization, decomposition, and fermentation. The principal aim in the manufacture of synthetic fuel is to achieve a low carbon-to-hydrogen atomic mass ratio, or a high hydrogen-to-carbon atomic ratio, whenever possible. This results in a clean-burning fuel that releases by-products that are harmless to the environment. For example, pure methane (CH4), with a molecular weight of 16, has a high hydrogen-to-carbon ratio of 4:1. Methane gas is a common component that is absorbed into coal. The method used to release the gas involves fracturing the coal and exposing it to low pressures. Coal-bed methane is one of the cleanest-burning fossil fuels; the by-products of burning it are simply carbon dioxide and water. Synthetically generated substitute natural gas is more than 90 percent methane. Natural gas (of which methane is the chief constituent) has a hydrogen-to-carbon ratio of approximately 3.4:1, which is also quite high. The ratios for liquefied petroleum gas and for naphtha lie between 2:1 and 3:1. (In comparison, the ratios for gasoline and fuel oil are less than 2:1. Bituminous coal has one of the lowest values, with a ratio of much less than 1:1.)

Coal Gasification and Liquefaction

Although coal is among the most abundant natural energy sources, it is also among the dirtiest. The composition of this solid fossil fuel is a major disadvantage; it consists of about 70 percent carbon and about 5 percent hydrogen, translating to a highly undesirable carbon-to-hydrogen mass ratio of 14:1. Coal-burning power-generating stations thus emit large quantities of gases that are harmful to the environment. Despite the use of such emission-reducing devices as electrostatic precipitators, the levels of pollutants emitted by coal-burning plants remain high. Techniques such as coal gasification and coal liquefaction yield synthetic fuels that are safer for the environment.

The process of coal gasification involves making coal react with steam at very high temperatures (in the range of 1,000 degrees Celsius, or 1,832 degrees Fahrenheit). This process produces synthetic gas. Three types of synthetic gas are in common use. Low-calorific-value gas (also called producer gas) is used in turbines. Medium-calorific-value gas (also called power gas) is used as a fuel gas by various industries. High-calorific-value gas (also called pipeline gas) is a very good substitute for natural gas and is well suited to economical pipeline transportation. Pipeline gas contains more than 90 percent methane; as a result, it has a high hydrogen-to-carbon ratio.

The process of coal liquefaction is employed to generate a liquid fuel with a high hydrogen-to-carbon ratio; it is also used to obtain low-sulfur fuel oil. Several methods are employed to accomplish coal liquefaction, including direct catalytic hydrogenation, indirect catalytic hydrogenation, pyrolysis, and solvent extraction. While these fuels may be much safer for the environment than the original coal, the process of manufacturing them produces high amounts of carbon dioxide (CO2) and other greenhouse gases.

Tar Sands and Oil Shale

Naturally occurring tar sands contain grains of sand, water, and bitumen. Bitumen, a member of the petroleum family, is a high-viscosity crude hydrocarbon. A method known as hot water extraction is used to procure bitumen from tar sands. The bitumen is subsequently upgraded to synthetic crude oil in refineries. Synthetic crude oil (also called syncrude) is similar to petroleum and can be obtained through coal liquefaction as well as from tar sands and oil shale.

Large deposits of tar sands are found in Alberta, Canada; the United States has huge reserves of oil shale in Utah, Wyoming, and Colorado. Oil shale is probably the most abundant form of hydrocarbon on earth. Oil shale is a sedimentary rock that contains kerogen, which is not a member of the petroleum family. A popular method known as retorting is used to produce oil from shale. The process involves pyrolysis, a method that reduces the carbon content in raw hydrocarbons through distillation.

Twenty-first-century technological advancements allowed shale oil to become an economically feasible alternative to petroleum. In a process known as hydraulic fracturing, or fracking, water, sand, or chemicals are injected into the rock formation under high pressure, forcing out the trapped shale oil. Extracting oil from shale and other rock formations became the most significant oil-producing method in the United States in the 2010s. By the 2020s, about 65 percent of all oil produced in the United States came from such methods.

Biomass Fuels and Gasohol

Like oil and coal, biomass is derived from plant life. Oil and coal, however, are considered nonrenewable resources, as it takes vast periods of time for geologic processes to produce these materials naturally. Because biomass consists of any material that is derived from plant life, it is produced in far shorter spans—one hundred years or less—and is thus considered renewable. Wood is the most versatile biomass resource; farm and agricultural wastes, municipal wastes, and animal wastes are also considered to be biomass. Biomass can be processed into fuel using a variety of methods. Fermentation, for example, yields ethanol, or ethyl alcohol (sometimes called grain alcohol). Other methods include combustion, gasification, and pyrolysis. According to the US Energy Information Administration, 5 percent of the total energy output in the United States in 2023 came from biomass fuels.

Gasohol is a mixture of gasoline and small quantities of ethanol. The mixture burns cleaner than conventional gasoline; however, it can cause damage to plastic and rubber materials used in automobile engines. In the United States, therefore, the Environmental Protection Agency (EPA) permits the addition of only 10 percent ethanol by volume to gasoline to create gasohol. Methanol, or methyl alcohol (also called wood alcohol), can also be combined with conventional gasoline to produce cleaner fuel; however, the EPA limits the amount of methanol in such mixtures to 3 percent.

Other Fuels

A nonpolluting rocket fuel based on alcohol and hydrogen peroxide was developed by US Navy research engineers at China Lake, California, in the 1990s. This nontoxic homogeneous miscible fuel (NHMF) can be modified and used to drive turbines, which in turn drive alternators that produce electricity. Further developments based on what has been learned about this fuel may permit its use in automobiles. During World War II, moreover, Germany produced synthetic fuels in large quantities to meet its energy demands, employing coal gasification and also creating diesel oil and aviation kerosene using a reconstitution process; this process is still in use in many places.

Although the abundance of natural petroleum limits the economic competitiveness of most synthetic fuels, the finite nature of the world’s oil supply virtually ensures that synthetic fuels will become increasingly important energy sources. The US Department of Energy and governmental agencies in many countries provide funding to encourage research into the creation of economically viable, environmentally safe, and renewable synthetic and advanced biofuels.

While the synthetic fuel industry improved the carbon neutrality of various sectors in the late twentieth and early twenty-first centuries, the positive environmental impact of synthetic fuels is often offset by the construction of production facilities and the use of conventional fuels for transportation. The large-scale production of synthetic fuels is needed to lower costs to a point that would be competitive with traditional fuels. However, large-scale production using wind and solar parks requires a significant use of land resources, which can interfere with agricultural activities, conservation efforts, and habitats for animals such as birds and bats.


Bibliography

"Biomass—Renewable Energy from Plants and Animals." US Energy Information Administration, 30 July 2024, www.eia.gov/energyexplained/biomass. Accessed 14 Sept. 2025.

Deutch, John M., and Richard K. Lester. “Synthetic Fuels.” Making Technology Work: Applications in Energy and the Environment. Cambridge UP, 2004.

Hayes, Adam. "Shale Oil: Overview, Benefits and Examples." Investopedia, 23 Aug. 2022, www.investopedia.com/terms/s/shaleoil.asp. Accessed 14 Sept. 2025.

Janaki, Sreejaun Thothaathiri, et al. “Beyond Fossil: The Synthetic Fuel Surge for a Green-Energy Resurgence.” Clean Energy, vol. 8, no. 5, 2024, pp. 1–19, doi:10.1093/ce/zkae050. Accessed 14 Sept. 2025.

Lorenzetti, Maureen Shields. Alternative Motor Fuels: A Nontechnical Guide. PennWell, 1996.

Manahan, Stanley E. “Adequate, Sustainable Energy: Key to Sustainability.” Environmental Science and Technology: A Sustainable Approach to Green Science and Technology. 2nd ed., CRC Press, 2007.

Miller, G. Tyler, Jr., and Scott Spoolman. “Nonrenewable Energy.” Living in the Environment: Principles, Connections, and Solutions. 20th ed., Brooks/Cole, 2021.

Ram, Vishal, and Surender Reddy Salkuti. “An Overview of Major Synthetic Fuels.” Energies, vol. 16, no. 6, 2023, p. 2834, doi:10.3390/en16062834. Accessed 14 Sept. 2025.

Speight, James G. Synthetic Fuels Handbook: Properties, Process, and Performance. 2nd ed., McGraw-Hill, 2020.

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