The Fischer-Tropsch process creates cleaner liquid fuels and other compounds like wax and lubricants. The diesel fuel, especially, is practically clean of contaminants such as sulfur and aromatics. It is much cleaner than typical diesel.
Briefly, how the Fischer-Tropsch synthesis works is that the syngas made from oxidizing the coal is heated to a temperature of up to 300 degrees Celsius. A metal catalyst is introduced to the gas. This creates a water-gas shift reaction, leading to the end product.
At this time, the Fischer-Tropsch process is being used in few countries; mainly South Africa and Malaysia. It’s becoming more used in Germany, the United States, and Finland. In these countries, it's mostly being looked at as an alternative if oil gets too expensive.