Synthetic fuel is a fuel that can be substituted for crude oil and natural gas. The chief sources of synthetic fuels, also called synfuels, include coal, oil shale, bituminous sands, and biomass.
Coal can be turned into gas and liquid fuels through processes called gasification and liquefaction. In one method of gasification, mined coal is combined with steam and oxygen to produce a mixture of carbon monoxide, hydrogen, and methane. This gaseous mixture can be used in place of natural gas or can be further processed to make synthetic natural gas.
Liquefaction of coal can be carried out by any of several processes. In one process, called pyrolysis, coal is heated rapidly, causing its liquids to evaporate. The vaporized coal tars are then combined with hydrogen to produce liquid fuels. The charcoallike solid that remains can also be burned as fuel.
Oil shale is a soft, fine-grained, sedimentary rock that consists partly of an organic substance called kerogen. Kerogen breaks down and releases vapors when heated. These vapors condense into liquid oil.
Bituminous sands, also called oil sands or tar sands, are saturated with bitumen, a gluelike black substance used to produce liquid fuel. The method used to recover bitumen depends on the location of the sands. Sands mined from deposits near the surface of the ground are heated with water or an organic liquid that will separate the bitumen from the sand. Further processing turns the bitumen into oil. Sands deep underground are heated where they lie to melt the bitumen, which is then pumped through heated pipes to the surface. There, it is heated further to convert the bitumen to oil and other fuels.
Biomass is any type of organic matter. All plant and animal matter contains energy that can be recovered by heating or through gasification. Some biomass can be fermented to obtain ethanol, also known as ethyl alcohol, which is often used as a gasoline additive to improve vehicle performance and reduce emissions of dangerous pollutants. Some vehicles run on fuel that is at least 85 percent ethanol.
Some types of synthetic fuels are expensive to develop. When gas or petroleum prices are low, it may not be cost effective to produce synfuels. For example, operations to develop synfuels from oil shale deposits in Colorado’s Rocky Mountains began in the late 1980’s. But a sharp decline in oil prices, and other factors, led to a shutdown of the last of these operations in 1991.
