What role does coal play in synthetic fuel production?

Role of Coal in Synthetic Fuel Production

Coal plays a key role in making synthetic fuels because it is a rich, carbon-based resource.
Through coal-to-liquids (CTL) processes, solid coal can be turned into liquid fuels such as gasoline, diesel, and other petroleum-like products.

Countries with large coal reserves but limited oil, like Germany (World War II) and South Africa (apartheid era), have used this technology extensively.
There are two main methods to produce synthetic fuels from coal:

1. Indirect Coal Liquefaction
2. Direct Coal Liquefaction

1. Indirect Coal Liquefaction (Fischer-Tropsch Process)

This is a two-step process where coal is first converted into gas and then into liquid fuel.

a. Gasification: Coal reacts with steam and oxygen at high temperature and pressure to form syngas, a mix of carbon monoxide (CO) and hydrogen (H₂).

b. Conversion: The syngas is cleaned and passed through a Fischer-Tropsch (FT) reactor, where catalysts like cobalt or iron turn it into liquid hydrocarbons.

c. Products: This process produces ultra-clean diesel, kerosene, and waxes with almost no sulfur. Sasol (South Africa) is the world’s largest producer using this method.

2. Direct Coal Liquefaction (Hydrogenation)

In this method, coal is turned directly into liquid fuel — no gasification step is needed.

a. Hydrogenation: Finely ground coal is mixed with a catalyst and recycled solvent or heavy oil, then heated under high pressure in a hydrogen-rich environment. This breaks down the coal and adds hydrogen to form liquid fuels.

b. Catalysts: Usually, iron-based catalysts are used to speed up the reaction.

c. Efficiency: This process can be more efficient than indirect liquefaction but needs a separate hydrogen source. The resulting fuel often requires extra refining to meet quality standards.

Environmental and Economic Considerations

1. High Carbon Emissions: Coal-to-fuel processes release a lot of CO₂. Without carbon capture and storage (CCS), emissions are higher than those from oil refining.

2. High Water Use: CTL plants consume large amounts of water, which is a problem in coal-rich but water-scarce regions.

3. Economic Challenges: Building CTL plants is expensive, and profitability depends on oil prices. When oil prices are low, synthetic fuels are less viable.

4. Clean Fuel Advantage: Fuels made via the Fischer-Tropsch process are low in sulfur and aromatics, making them cleaner-burning and better for reducing local air pollution.

In short, coal-based synthetic fuels offer an alternative to petroleum, but they come with high costs, environmental concerns, and energy demands.
They are most practical for countries aiming for energy security or oil independence with large coal reserves.