Synthetic Fuels

"Synthetic fuel" generally refers to a liquid fuel obtained from a specific feedstock such as natural gas, coal, or a biomass.
synthetic gas

photo by Lars Sundström

Syngas to Synfuel

The creation of synthetic, liquid fuel is usually acheived through the combination of two chemical processes:

Gasification
Biomass is converted to gas through controlled combustion. This product is called "syngas".
Fischer-Tropsch Synthesis
A carbon monoxide and hydrogen mixture is converted into liquid via a catalyst (usually iron, cobalt or ruthenium).

The result these processes is a low sulfur fuel (ULSD) with renewable potential.

Basic types of synthetic fuel

Gas to liquids (GTL)
The resulting non-renewable fuel when natural gas, methane-rich gases or another gaseous hydrocarbon is refined into liquid. In the case of natural gas, remember that it is a by-product of oil refining. If you have ever driven by an oil refinery you have seen the flames burning at the tops of stacks. That is natural gas, the refinery “flares” it, meaning they burn it, releasing pollutants into the atmosphere. GTL makes good use of the gas.
Coal to liquids (CTL)
The resulting non-renewable fuel (it can be gasoline, diesel, methanol) when coal is converted to a liquid.
Biomass to liquids (BTL)
The resulting renewable fuel when biomass is converted to a liquid. BTLs are produced utilizing either conversion, via the Fischer-Tropsch process, or through anaerobic decomposition.

CO2 Emissions

Although GTL does not reduce carbon dioxide emissions by much, the reduction is significantly better than CTL fuels.

BTL carbon dioxide emissions are the lowest among synthetic fuels and substantially lower than normal diesel because combustion only releases the carbon dioxide captured within the original biomass.

Fuel Blends

Synthetic fuels can be blended with gas or diesel at any ratio, at the tank.

Infrastructure

Synthetic fuels could utilize every aspect of the existing gas/diesel infrastructure, from pipelines to fuel stations to the tanks on current cars.

Advantages

Synthetics fuels can be used by existing gas and diesel vehicles without engine modifications.

Generally speaking, they offer lower nitrogen oxide, hydrocarbon, carbon monoxide, and carbon dioxide emissions than their conventional counterparts.

Disadvantages

Although emissions are indeed lower, they’re still emissions, especially when compared with zero emission vehicles.

The goal of alternative fuels is to end reliance on fossil fuels, something which (with the exception of BTL) synthetic fuels do not accomplish.

The Future

Synthetic fuels may have value as transition fuels to help us move from gas/diesel to the likes of hydrogen and pure electrical power. It’s hard to expect anything beyond that.

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