Fischer-Tropsch process

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The Fischer–Tropsch process (or Fischer–Tropsch Synthesis or F-T) is a set of chemical reactions that turn a mixture of carbon monoxide gas and hydrogen gas into liquid hydrocarbons (fossil fuels like gasoline or kerosene).[1] The F-T process has received attention for many different reasons, like a way to make diesel low in sulfur.

Process chemistry[change | change source]

The Fischer–Tropsch process involves a lot of reactions, which lead to both wanted and unwanted results. The good reactions create chemicals called alkanes. Sometimes the gas methane (natural gas) is made, but usually people do not want this gas. Sometimes different kinds of alcohol are produced in small amounts.

Other reactions relevant to F-T[change | change source]

To make the gases needed for the F-T process, it takes many steps. For example, all chemicals going into the reactor must have all sulfur removed. For factories that start out with methane and want to make a liquid hydrocarbon (like kerosene), another important reaction is "steam reforming", which turns the methane into CO (carbon monoxide) and H2 (hydrogen gas). This is the chemical equation for how steam reforming works.

H2O + CH4 → CO + 3 H2

It says, 1 molecule of H2O (steam) plus 1 molecule of CH4 (methane) turns into 1 molecule of CO(carbon monoxide) and 3 molecules of H2(hydrogen gas).

Fischer-Tropsch catalysts[change | change source]

A catalyst is a chemical you add to a process to make it go faster or speed it up. Many different catalysts can be used for the Fischer–Tropsch process. The most common catalysts are the metals cobalt, iron, and ruthenium. These metals are all transition metals. The metal nickel can also be used, but this is usually bad. If someone uses nickel, the reaction usually makes a lot of methane. Usually people do not want a lot of methane to be made.

Cobalt seems to be the most active catalyst(it has the biggest and fastest effect on the process). Cobalt catalysts are very good for the Fischer-Tropsch process when what you are putting in is natural gas. Iron catalysts are better for when the stuff you put in is lower quality (less pure) such as coal or biomass.[2]

Most metals used for this process (like Cobalt, Nickel, and Ruthenium) stay metal when you add them to the process. Iron catalysts are very different. Many times, iron catalysts change very much and form many chemical phases, like various oxides and carbides, during the reaction. It is important to control all of these reactions of the iron during the process, or else the process might not work.

Fischer-Tropsch catalysts are famous for being very, very sensitive to adding a little bit of sulfur. A tiny amount of sulfur can mess up the reactions. Cobalt is more sensitive to sulfur than iron.

HTFT and LTFT[change | change source]

High-Temperature Fischer-Tropsch (or HTFT) is operated at temperatures of 330°C-350°C. HTFT uses an iron-based catalyst. Sasol used HTFT in Coal-to-Liquid plants (CTL). Low-Temperature Fischer-Tropsch (LTFT) is operated at lower temperatures and uses a cobalt-based catalyst. Shell used LTFT in an integrated Gas-to-Liquid (GTL) plant in Bintulu, Malaysia.[3]

Gasification[change | change source]

Gasification is turning things into gas. Some F-T factories that use coal, biomass or something else solid to start. Before these factories can start the process, they must turn the solids into gases like CO, H2, and alkanes. This process is called gasification. The gas collected from coal gasification often has a CO/H2 ratio of ~0.7 instead of the best ratio of ~2. People can adjust this ratio from 0.7 to 2.0 using the water-gas-shift-reaction.Gasification is a dirty and expensive process. Coal-based Fischer–Tropsch factories are factories that start out with coal, use gasification on it, then use the gas for the Fischer-Tropsch process. These factories can produce lots and lots of CO2. A big reason for this is because it takes very much energy to do the gasification process on the coal.[4]

History[change | change source]

The original process was invented by Franz Fischer and Hans Tropsch. They were working at the Kaiser Wilhelm Institute in the 1920s, when they invented it. Since then many changes have been made to make it better. The term "Fischer-Tropsch" now is used for many processes that are like the original one. Fischer and Tropsch wrote lots of patents, like US patent no. 1,746,464, applied 1926, published 1930.[5] It was given to the factories in Germany in 1936. Germany had lots of coal but very little petroleum. The F-T process lets people change coal into gasoline, which is important to run cars and airplanes. Because of this, the F-T process was used by Nazi Germany and Japan during World War II to produce substitute fuels for tanks and cars. F-T production of fuel was about 9% of German war production of fuels and 25% of the automobile fuel.[6]

The United States Bureau of Mines ran a program started by the Synthetic Liquid Fuels Act. The Bureau hired seven fuel scientists from Operation Paperclip in a Fischer-Tropsch plant in Louisiana, Missouri in 1946.[7][6] Operation Paperclip was a plan to get German scientists to work for the US during World War II.

Commercialization[change | change source]

Fluidized bed gasification with FT-pilot in Güssing, Burgenland, Austria

The F-T process has been used on by big companies, but it is sometimes unpopular for many reasons. One is that it takes lots of money to buy equipment to get F-T factories to work. It also take lots of money to keep it running and to fix problems with it. Also, the cost of petroleum is very hard to predict. Usually, the factories only make money when they have access to "stranded gas". "Stranded gas" is what they call sources of natural gas very far from major cities, that takes too much money or resources to pump natural gas to the city. If they could just pump it to the city and sell the natural gas, they could make much more money. the direct sale of natural gas to consumers would become much more profitable. Several companies are developing the process to enable practical exploitation of so-called stranded gas reserves.

Sasol[change | change source]

The biggest F-T factories with the biggest use of F-T technology are owned and operated by the company Sasol in South Africa. South Africa is a country with lots of coal but not enough oil, just like Germany. Sasol takes coal and natural gas and uses them for the F-T Process. They produce many different substitutes for oil products, and produce most of the country's diesel fuel.[8]

Shell Middle Distillate Synthesis[change | change source]

One of the largest uses of F-T technology is in Bintulu, Malaysia. This Shell factory turns natural gas into low-sulfur diesel fuels and food-grade wax. They make 12,000 barrels/day.

In October 2006, Finnish paper and pulp manufacturer UPM announced its plans to produce biodiesel by Fischer–Tropsch process. It said that it will do this along with the manufacturing processes at its European paper and pulp plants. It will use the waste biomass, from paper and pulp manufacturing processes, as the material to turn into biodiesel.[9]

Research developments[change | change source]

Carbon dioxide reuse[change | change source]

In 2009, chemists working for the U.S. Navy studied Fischer-Tropsch for making fuels with hydrogen and electrolyzing seawater. This study produced mostly methane gas, but the rest were short-chain hydrocarbons. Further refining of the hydrocarbons produced could lead to making kerosene-based jet fuel.[10]

The abundance of CO2 makes seawater look like a good different fuel source. Scientists at the U.S. Naval Research Laboratory said that, "although the gas forms only a small proportion of air – around 0.04 per cent – ocean water contains about 140 times that concentration".[10]

References[change | change source]

  1. US Fuel Supply Statistics Chart
  2. Andrei Y. Khodakov, Wei Chu, and Pascal Fongarland “Advances in the Development of Novel Cobalt Fischer-Tropsch Catalysts for Synthesis of Long-Chain Hydrocarbons and Clean Fuels” Chemical Review, 2007, volume 107, pp 1692–1744. doi:10.1021/cr050972v
  3. page 33-41
  4. Oliver R. Inderwildi, Stephen J. Jenkins, David A. King (2008). "Mechanistic Studies of Hydrocarbon Combustion and Synthesis on Noble Metals". Angewandte Chemie International Edition 47 (28): 5253–5. doi:10.1002/anie.200800685 . PMID 18528839 .
  6. 6.0 6.1 Leckel, D., "Diesel Production from Fischer-Tropsch: The Past, the Present, and New Concepts", Energy Fuels, 2009, volume 23, 2342-2358. doi:10.1021/ef900064c
  7. German Synthetic Fuels Scientist
  8. "technologies & processes" Sasol
  9. "UPM-Kymmene says to establish beachhead in biodiesel market", NewsRoom Finland
  10. 10.0 10.1 Kleiner, Kurt (18 August 2009). "How to turn seawater into jet fuel". New Scientist. Retrieved 2009-08-20.