Top 8 Synthetic Fuels

Water, acid, sand and liquid carbon dioxide are injected under heavy pressure into a natural gas well in New Mexico.
Water, acid, sand and liquid carbon dioxide are injected under heavy pressure into a natural gas well in New Mexico.
Robert Nickelsberg/Getty Images

With oil and fossil fuel resources dwindling around the world, the race to find the next big energy solution is definitely on. There may not be a magic bullet to solve that energy crisis, or a perfect fuel that is infinitely available and doesn't pollute the environment. But one option, synthetic fuels -- or synfuels -- offers some advantages and some drawbacks when compared to conventional oil-based fossil fuels. Synthetic fuel is a category of fuels that includes any fuel "produced from coal, natural gas or biomass feedstocks through chemical conversion" [source: U.S. Energy Information Administration]. These types of fuels are often called Fischer-Tropsch liquids, after the process used to create them. The synfuels category also includes fuels derived from synthetic crude, a substance similar to crude oil that is synthesized from natural resources like bitumen or oil shale [source: U.S. Energy Information Administration]. Chemically, synfuels are similar to the gasoline and diesel fuels we use today and can be used in existing engines. But producing them requires complex chemical conversions.

National governments and energy companies have been paying more attention to synthetic fuels in recent years, as rising oil prices and political instability in oil-producing countries have created incentives to seek out alternatives. The main benefit of synfuels is that they can be produced using substances like coal, natural gas and even plant waste, which are widely available. Many synfuels also burn cleaner than conventional fuel. But there are also disadvantages. While they can burn cleaner, producing synthetic fuels often causes just as much, if not more, pollution than traditional gasoline. Synfuels still remain more expensive to produce than conventional fuels, mostly because more research, development and investment are necessary to make production economically viable.

To find out about the different types of synthetic fuels currently being manufactured, keep reading.

Extra-heavy Oil

Extra-heavy oil is one of several sources of syncrude, a type of synthetic fuel that closely resembles crude oil. Extra-heavy oil occurs naturally, and forms when oil that was once buried deep in the Earth is exposed to bacteria that breaks down the hydrocarbons and changes the oil's physical properties. The oil can be recovered through open pit mining or "in situ" (on site) collection. In situ collection involves piping hot steam or gas into a well to break up the heavy oil and collecting the fluid through a second well. Both methods have their limits. Open pit mining can only be used to collect extra-heavy oil near the surface. It also damages the environment by destroying forests and animal habitats, and the large amounts of water required has to be disposed of as waste after being used [source: Clark]. In situ methods need further research to gather large amounts of heavy oil.

The production process for many synthetic fuels creates products that are more or less ready to be used in engines and vehicles. Syncrude production, on the other hand, results in a synthesized crude oil that has to be further refined to be commercially sold, just like conventional crude oil. In its natural state, extra-heavy oil is basically a more viscous form of crude. If crude flows like water, then extra-heavy oil flows like honey. To get the extra-heavy oil into a useful form, it is typically exposed to heat and gases that break down the hydrocarbons into those that can be burned as fuel and those that can't. This is similar to the process of refining crude oil into fuels, but more expensive and complicated.

Gas-to-Liquids (GTL)

Producing gas-to-liquids fuels (or GTL) involves a process of converting natural gas into liquid, petroleum-based fuels. Unlike syncrudes, GTL products are closer to the final stage of production. They don't need to be processed by a refinery before they are used as fuel. The most widely used method for converting gas to liquid fuels is the Fischer-Tropsch process (F-T synthesis) [source: U.S. Energy Information Administration]. In this process, natural gas is combined with air and then introduced into a chamber along with a catalyst, usually a compound containing cobalt or iron. The catalyst, along with a large amount of heat and pressure, triggers a chemical reaction that forms chains of hydrocarbons. Next, the gas is condensed into liquid. Depending on which catalysts are added, different hydrocarbon structures are created. F-T synthesis can produce diesel fuels, naphtha (which can be processed to make gasoline) and industrial lubricants [source: U.S. Energy Information Administration].

The GTL process in particular has mostly been used to produce diesel fuels, although it can also produce naphtha. GTL, like other Fischer-Tropsch fuels, produces fewer emissions when burned [source: U.S. Environmental Protection Agency]. The chemical separation process creates a more pure fuel, because impurities can be filtered out easily. Another benefit is that the chemical reactions involved in converting the gas to liquids create electricity, steam and water as byproducts. Those resources can either be funneled back into the production to save costs and reduce the environmental impact or sold on the commercial market to make the process more cost effective.

Shale Oil
Shale oil is a form of syncrude produced from the rock marlstone.
Shale oil is a form of syncrude produced from the rock marlstone.
Argonne National Laboratory

Shale oil is another form of syncrude produced from marlstone, a naturally occurring rock that is commonly called oil shale. Marlstone is rich in a material called kerogen, an organic material that naturally converts into crude oil when it's exposed to extreme heat and pressure. That change usually happens over millions of years, but industrial methods can replicate the process and convert the kerogen in oil shale to syncrude [source: U.S. Department of the Interior]. Production of shale oil is largely theoretical at this point and hasn't been produced on a large scale. Oil shale can be put through pyrolysis, the introduction of heat and removal of oxygen, which separates the kerogen from the rest of the rock and converts it into a liquid that can then be refined into syncrude [source: U.S. Department of the Interior].

Oil shale is extremely abundant. In fact, deposits in the Green River Formation, a region that extends through parts of Colorado, Utah and Wyoming, could contain enough oil shale to produce 800 billion to 1.8 trillion barrels, according to estimates from various scientists [source: U.S. Department of the Interior]. To put those numbers in perspective, if the lower estimate were accurate, the formation could supply the United States' oil needs for 100 years at current usage levels [source: U.S. Department of the Interior]. However, there are serious environmental drawbacks. Shale oil production leaves large amounts of waste rock behind and uses huge amounts of water. Also, until technologies are further developed and refined, the process is extremely expensive -- much more expensive per-barrel than crude oil production [source: U.S. Energy Information Administration].

Oil Sands
Aerial views of the Syncrude Canada Ltd. and Suncor Energy Inc. tar sands in Canada.
Aerial views of the Syncrude Canada Ltd. and Suncor Energy Inc. tar sands in Canada.
Veronique de Viguerie/Getty Images

Oil sands, or tar sands, are the third source of synthetic fuels that are classified as syncrude. A mix of water, clay, sand and a substance called bitumen, oil sands occur naturally. Bitumen is a very thick oil-like substance that is the consistency of very sticky Jell-O at room temperature. It contains many more impurities than conventional crude oil, including sulfur, nitrogen and heavy metals that must be removed before the bitumen can be used for fuel [source: U.S. Energy Information Administration]. The sands are usually gathered through open pit mining. In situ recovery is also possible through injecting steam or chemicals to break up the sands. But in situ collection consumes huge quantities of water and power and is also less cost-effective.

To process oil sands to a state they can be sold as syncrude, they're washed with hot water to separate the bitumen from the clay and sand. The bitumen is then subjected to huge amounts of heat and pressure, and natural gas is introduced. This converts the hydrocarbons in the material into a form that is more easily burned as fuel [source: U.S. Department of the Interior]. The massive amounts of water and power needed to transform oil sands from deep underground deposits to usable fuels make it a controversial fuel because of its environmental impact. The toll on the environment, from strip mining and the disposal of waste water, has led to much controversy in Canada, where most of the world's oil sands are currently mined [source: Kunzig].

Coal-to-Liquids (CTL)

Like GTL, coal-to-liquids (CTL) fuels are produced by isolating the hydrocarbons in existing fossil fuels and converting them to a form of synthetic fuel that can be used in existing vehicles' engines. Manufacturers use two methods to make that conversion. The first, indirect coal liquefaction (ICL), uses the same Fischer-Tropsch process as gas-to-liquids fuels. Of course, processing requires an additional step to convert the solid coal into a gas that can feed the F-T reaction. Solid coal is crushed, and then exposed to high temperature and high pressure, along with steam and oxygen, which react with the coal to produce synthesis gas. This syngas, a mixture of carbon monoxide, hydrogen and other gases, is then used in the Fischer-Tropsch reaction to create liquid fuels. In direct coal liquefaction (DCL), coal is pulverized, and then exposed to hydrogen and high levels of heat and pressure to produce liquid syncrude that can be refined. This second method is not as widely used as ICL.

Coal-to-liquids fuels can be more environmentally friendly, because they burn cleaner than conventional gasoline or diesel. Byproducts of CTL manufacturing, including water, electricity and metals can be sold to offset the costs of CTL processing and make the process more sustainable. But there are serious environmental drawbacks, too. CTL production consumes huge amounts of water before it creates any. It also releases carbon dioxide emissions and large amounts of solid waste called "slag," which is what's left of the coal after all of its usable chemicals have been extracted [source: Van Bibber].

Biomass-to-Liquids (BTL)

Coal-to-liquids and gas-to-liquids fuels are produced by manipulating the hydrocarbons in non-oil fossil fuels so that they are chemically similar to the hydrocarbons in oil and gasoline. Biomass-to-liquids fuels work according to the same theory, except that the hydrocarbons come from freshly dead organic material, not organic material that has been decomposed and compressed over millions of years. BTL fuels can be made from wood, crops, straw and grain. The advantage of BTL is that it can be made from parts of those plants that are not useful for food or manufacturing.

The production process is similar to other synfuels: Syngas is used to start a Fischer-Tropsch reaction that eventually produces liquid fuels. The biomass is burned in a low oxygen environment to produce syngas, a step that requires less energy than other synfuels. But it takes comparatively large quantities of biomass feedstock (the raw material that is synthesized) to make fuel. Five tons (about 4.5 metric tons) of feedstock (or approximately 3 acres or 1.2 hectares of crops) equal 1 ton (0.9 metric tons) of manufactured BTL [source: U.S. Energy Information Administration]. BTL also costs much more money to produce than CTL or GTL. Biomass takes up much more space than other synfuel feedstocks, so it costs more to store and transport. BTL is not nearly as widespread as other forms of synfuels, which means companies would have to invest a lot of money to get BTL programs up and running. Despite the cost, BTL could be easier on the environment in the long run, since plants grown to produce the fuel could cancel out some of its CO2 emissions.

Fuel from Waste
Solid waste like old tires can be used to make feedstock for synfuel production.
Solid waste like old tires can be used to make feedstock for synfuel production.

For the same reasons plants and plant waste can be used to make feedstock for synfuel production, solid waste can also feed the process. Usable solid waste includes old tires, sewage and waste from landfills [source: Speight]. As long as it contains organic matter (and high levels of carbon), it can be used to create some form of fuel. Waste used for feedstock undergoes the same process as other synfuel feedstocks. It is burned under special conditions to produce syngas, which then goes through the Fischer-Tropsch process to be synthesized into liquid fuel. As an alternative, the gas that landfills naturally emit as waste decomposes can be used to produce synthetic fuel.

Fuel from Atmospheric Carbon

Still in the theoretical stage, the concept of deriving fuel from atmospheric CO2 was developed by scientists at Los Alamos National Laboratories. In this process, large amounts of air containing carbon dioxide pollutants would be exposed to liquid potassium carbonate. The CO2 in the air combines with the potassium carbonate, while the other components of the air do not. The CO2 can then be separated from the potassium compound by applying electricity. Once the CO2 is separated, it is converted to syngas and then into liquid fuels following methods used to create other synfuels [source: Martin]. Scientists at other laboratories and institutions have agreed that the process works, in theory. However, the main obstacle is that the process of isolating CO2 from the air and converting it into syngas requires massive amounts of power [source: Martin]. The Los Alamos scientists suggest nuclear power as the best option [source: Martin]. It will also require huge capital investments to take the concept from theory to execution. On the bright side, the entire process is theoretically carbon neutral. It would produce as much carbon as it consumes.


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