The Fischer–Tropsch synthesis is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. The process, a key component of gas to liquids technology, produces a synthetic lubrication oil and synthetic fuel, typically from coal, natural gas, or biomass. The Fischer–Tropsch process has received intermittent attention as a source of low-sulfur diesel and jet fuel and to address the supply or cost of petroleum-derived hydrocarbons.
The Fischer-Tropsch conversion system was discovered by German scientists and has been operational in various locations throughout the world since the early 1930s. Thousands of Fischer-Tropsch systems have operated during the last 80 years most notably responsible for driving energy economies of wartime Nazi Germany. There has been continued interest of varying intensity in Fischer-Tropsch technology ever since.
SASOL in South Africa has produced liquid fuels from coal for approximately 30 years. Many US oil companies have been conducting research and have built pilot plants or smaller plants. Interest in Fischer-Tropsch fuels is increasing because they will lessen dependence on foreign oil, reduce the number of different fuels required, and reduce environmental impacts because they burn cleaner than other liquid fuels.
The U.S. military is the world’s largest buyer of fuel, consuming 8 billion gallons per year. The US Department of Defense and Department of Energy have partnered with corporations to produce raw liquid Fischer-Tropsch fuels from natural gas, which are further refined to create jet and diesel fuels. These fuels have been engine tested and produce very little particulates or pollutants. Their jet fuel, mixed 50:50 with conventional petroleum-derived fuel, has been successfully been tested by the Air Force in a flight of a B-52 jet with all eight of its engines fueled by the mixture.
Several reactions are required to obtain the gaseous reactants required for Fischer–Tropsch catalysis. Reactant gases entering a Fischer–Tropsch reactor must be desulfurized. Otherwise, sulfur-containing impurities neutralize the catalysts and inhibit the Fischer–Tropsch reaction.
At this point the overall Fischer-Tropsch process consists of two steps: the first is known as Steam Methane Reformation or SMR. In the SMR process, which necessarily precedes the Fischer-Tropsch process, a molecule of CH4 is introduced to the SMR catalyzing environment at the same time as a molecule of H2O is introduced at an 800̊ C (1,365̊ F) environment.
A nickel (Ni) catalyst facilitates a reaction between the CH4 and H2O to produce a carbon monoxide (CO) and three (3) hydrogen (H2) molecules. From the SMR both the CO and H2 molecules are entrained into the Fischer-Tropsch reactor, which is maintained at a precise temperature at or very close to 250̊ C (449̊ F), a controlled pressure and a set flow-rate. In the presence of a specific catalyst, these gases again react, this time forming hydrocarbon chains, CH3-(CH2)n-CH3, (where the chain length is n+2) and (n+2) H2O molecules.
Because the Fischer-Tropsch synthesis is a complex chemical reaction whose efficiency is dependent upon temperature, pressure, flow-rate, and catalyst composition, it is important to focus intensely upon the optimization of all of these variables.