The second type of synthetic fuels, commonly referred to as Fischer-Tropsch liquids, use feedstock that can be converted directly into commercially viable liquid fuels, essentially skipping the syncrude step. The most common feedstocks used to produce Fischer-Tropsch synfuels include natural gas, coal and biomass (plants and plant waste). In F-T synthesis, the feedstock is subjected to very high heat -- 1,900 degrees Fahrenheit (1,037.7 degrees Celsius) or higher -- and pressure to produce a mix of carbon monoxide and hydrogen called synthesis gas (or syngas) [source: Van Bibber]. This step of the process makes Fischer-Tropsch liquid fuels much cleaner than fuels produced from crude or syncrude. Impurities like heavy metals can be easily removed from the gasifier after the syngas is filtered out. Gases like carbon and sulfur can be filtered out so they don't become pollutants when the fuel burns.
Next, the syngas is condensed into liquid form. Again put under high heat and pressure, a catalyst is introduced into the process, usually a compound containing either iron or cobalt. The catalyst triggers a chemical reaction between the hydrogen and carbon monoxide, creating long chains of hydrocarbons. Different catalysts can produce different hydrocarbon structures. These hydrocarbons are then cooled and condensed into liquid form, and filtered. Along with synthetic forms of diesel fuel or gasoline, Fischer-Tropsch synthesis can produce industrial lubricants, kerosene and other products.
Compared to syncrude products, Fischer-Tropsch liquids burn much cleaner. These synfuels have almost no particulate emissions, contain less nitrogen oxide than traditional fuels and fewer carbon monoxide emissions [source: U.S. Environmental Protection Agency]. Of course, those synfuels that use renewable resources as feedstock (like biomass) are better for the environment in the long run than those that use fossil fuels as feedstock.
The U.S. government has a vested interest in synfuels, since it has abundant access to feedstock like coal, natural gas and plant waste. Taking only one variety of synfuel into account, there is an estimated 1.3 gigatons of unused biomass inside the United States that could be used to produce synfuels [source: Coal-to-Liquids Coalition]. So, the U.S. military and other government agencies have been pushing to research synfuels in recent years. Other countries like China and Germany have also made recent investments in exploring synfuel technology [Source: U.S. Energy Information Administration]. While synthetic fuel technology is promising, it costs much more to produce than gasoline from oil. So, it most likely will not replace oil unless oil prices increase dramatically.