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Did you know that natural gas can be turned into diesel? How is it done?
With the increasing demand for energy today, the development of new sustainable energy sources has become a global focus. We all know that diesel is an important fuel for today's cars and heavy machinery, but you may not know that natural gas can be converted into diesel through a process called the Fischer–Tropsch process. This process will not only reduce dependence on oil resources, but may also become an important solution for future energy transformation.
The Fischer–Tropsch process is a set of chemical reactions that converts a mixture of gases - carbon monoxide and hydrogen - called syngas into liquid hydrocarbons.
The Fischer–Tropsch process was first developed in 1925 by German scientists Franz Fischer and Hans Tropsch. The basic principle of the process is to convert synthesis gas into liquid hydrocarbons using metal catalysts under high temperature and pressure. The specific chemical reaction can be expressed by the formula:
(2n + 1) H2 + n CO → CnH2n+2 + n H2O
In this reaction, the value of n is usually between 10 and 20, indicating the carbon chain length of the hydrocarbon compound produced. A small amount of olefins and alcohol compounds are also produced during the reaction. However, the formation of methane (n=1) is undesirable because its production means that chain growth is restricted.
The entire process is very exothermic, so the heat must be removed efficiently in the reactor. The operating conditions of the Fischer–Tropsch process are usually between 150 and 300 degrees Celsius. Such conditions can not only accelerate the reaction rate but also increase the conversion rate, but they need to be controlled to avoid the production of large amounts of methane.
To obtain the desired syngas, Fischer-Tropsch facilities first need to carry out a gasification process, which converts solid fuels such as coal or biomass into gas.
The production of syngas usually relies on gasification technology, which converts solid substances into gases for subsequent Fischer–Tropsch reactions. Depending on the starting materials, the ratio of hydrogen to carbon monoxide in the synthesis gas needs to be adjusted through the water gas shift reaction. This adjustment is particularly critical for the Fischer-Tropsch process using iron catalysts, since these catalysts are inherently reactive toward water gas shift.
Typically, the metal catalysts of choice include iron, cobalt, nickel and platinum, but nickel is not used because it produces too much methane. Iron and cobalt are the most common choices, with cobalt catalysts performing best when natural gas is used as the feedstock, while iron catalysts are better suited to using coal or biomass.
Many projects related to the Fischer–Tropsch process are gradually being implemented around the world. For example, Sasol in South Africa has the world's largest application of Fischer-Tropsch technology.
As technology has evolved, the world's largest Fischer–Tropsch facility is now located in Sasol, South Africa, producing 130,000 tonnes of synthetic fuels per year. These facilities use coal and natural gas as feedstocks and successfully convert them into diesel and other types of synthetic fuels, making a significant contribution to South Africa's energy security.
Another important example is the Pearl GTL facility in Qatar, which uses a cobalt catalyst to convert natural gas into petroleum liquids at a rate of 140,000 barrels per day at 230 degrees Celsius.
The development of the Fischer–Tropsch process not only helps to improve the efficiency of land use of energy, but also is an effective way to cope with current environmental challenges. As the demand for clean energy continues to increase, the commercialization and expansion of this process will have a profound impact on the future development of renewable energy.
Do you think the Fischer–Tropsch process can become one of the key technologies for the future energy transition?
