University of Kentucky CAER Home

Coal to Liquids - Questions and Answers


What does "Coal-to-Liquids" mean?

The term "coal-to-liquid" refers to a range of technologies and products that involve or are created by the process of liquefying coal. "Fischer-Tropsch" is another name for Coal-to-Liquid processes.


What is "coal liquefaction?"

Liquefaction is the process of converting coal into liquid substances. Direct liquefaction dissolves pulverized coal with a process liquid. Indirect liquefaction gasifies coal and then uses Fischer-Tropsch synthesis to convert the coal into liquid products.


How is coal liquefied?

The process of indirect liquefaction, the preferred method of producing CTL products, first requires coal to be gasified The gasification process exposes the coal to heat, pressure and oxygen, causing the chemical reaction that creates a gas called synthesis gas. The synthesis gas then passes over a catalyst that transforms the gas into liquid and wax CTL products. This reaction is called Fischer-Tropsch Synthesis.


What is a "catalyst?"

A catalyst is a material that accelerates a reaction without being used up in the process. In Fischer-Tropsch Synthesis, the catalyst is typically iron or cobalt.


What kind of equipment is used to liquefy coal?

Once the coal is gasified to create synthesis gas, the gas is fed into a device called an F-T reactor ("F-T" stands for "Fischer-Tropsch"). The reactor exposes the synthesis gas to the catalyst, which converts the gas into liquids and waxes.


What are some uses of CTL products?

CTL products can be refined into synthetic diesel fuel and waxes. CTL diesel is clean-burning and can be used to run jet engines as well as other vehicle engines. CTL waxes can be stored long term and used at any time.


What does "clean-burning" mean?

When a fuel is referred to as "clean-burning" it means that it emits little or no pollutants when it is used. CTL diesel is considered clean-burning because pollutants are removed before the fuel is burned. After the coal is gasified into synthesis gas, emissions can be stripped from the gas stream before the catalytic conversion. This process removes sulfur, mercury and carbon dioxide from the product.


Coal to Liquids - An Explanation

Questions? Contact Dr. Burt Davis, CAER Associate Director and Clean Fuels Scientist - Email

Information compliled by Brittany Bailey, CAER Publications