Fischer Tropsch synthesis
Fischer-Tropsch synthesis is the catalytic chemical reaction that converts synthesis gas (hydrogen and carbon monoxide) into liquid hydrocarbons.
It is the central step in Fischer-Tropsch technology and is used to produce synthetic crude that can be upgraded into sustainable aviation fuel, renewable diesel, and other synthetic fuels.
What is Fischer-Tropsch synthesis?
Fischer-Tropsch synthesis is a catalytic process in which carbon monoxide and hydrogen react on a catalyst surface to form hydrocarbon chains.
The simplified reaction is:
(2n + 1)H₂ + nCO → CnH(2n+2) + nH₂O
This reaction produces paraffinic hydrocarbons ranging from light gases to heavy waxes, depending on catalyst properties and operating conditions.
How does Fischer-Tropsch synthesis work?
Fischer-Tropsch synthesis begins when carbon monoxide and hydrogen adsorb onto the surface of a catalyst inside a reactor.
The process includes:
- Carbon monoxide adsorption
- Hydrogen dissociation
- Surface reaction and chain initiation
- Carbon chain growth
- Hydrocarbon desorption
Hydrocarbon molecules grow one carbon atom at a time, producing a distribution of chain lengths.
For catalyst fundamentals, see Fischer-Tropsch catalyst.
Why is Fischer-Tropsch synthesis important?
Fischer-Tropsch synthesis enables the production of liquid hydrocarbons from non-petroleum carbon sources.
This enables fuels to be made from:
- Biomass
- Municipal solid waste
- Biogas
- Natural gas
- Renewable hydrogen and captured CO₂
Because the output is hydrocarbon-based, the final fuels are compatible with existing engines and fuel infrastructure.
What products are formed during Fischer-Tropsch synthesis?
Fischer-Tropsch synthesis produces a range of hydrocarbons, not a single fuel product.
Typical products include:
- Light gases
- Naphtha-range hydrocarbons
- Middle distillates (jet and diesel range)
- Heavy waxes
These products are later upgraded into finished fuels.
Middle distillates are especially important for sustainable aviation fuel and renewable diesel.
See Fischer-Tropsch synthetic paraffinic kerosene for aviation fuel specifications.
What determines product distribution in Fischer-Tropsch synthesis?
Product distribution follows the Anderson–Schulz–Flory model, which predicts hydrocarbon chain lengths statistically.
This means:
- Shorter hydrocarbons form more frequently at lower chain-growth probability
- Longer hydrocarbons increase as chain growth probability rises
Catalyst design and operating conditions influence where the product slate falls.
What temperatures are used in Fischer-Tropsch synthesis?
Fischer-Tropsch synthesis typically operates in either low-temperature or high-temperature regimes.
Low-temperature Fischer-Tropsch (LTFT)
- ~200–240°C
- Favours heavier hydrocarbons and waxes
High-temperature Fischer-Tropsch (HTFT)
- ~300–350°C
- Favours lighter hydrocarbons
The temperature range affects selectivity, conversion, and reactor design.
Why is heat control critical during Fischer-Tropsch synthesis?
Fischer-Tropsch synthesis is highly exothermic, meaning large amounts of heat are released during the reaction.
If heat is not removed efficiently:
- Catalyst degradation increases
- Product distribution shifts
- Catalyst (and potentially reactor) stability declines
Heat management is central to reactor design.
See Fischer-Tropsch reactor for reactor engineering details.
How does Fischer-Tropsch synthesis support sustainable aviation fuel production?
Fischer-Tropsch synthesis produces synthetic hydrocarbons that can be upgraded into jet-range fuels approved for aviation use.
This is an ASTM approved pathway to produce SPK.
Fischer-Tropsch synthetic paraffinic kerosene (FT-SPK)
FT-SPK is one of the ASTM-approved pathways for sustainable aviation fuel.
For pathway context, see Sustainable aviation fuel.
Is Fischer-Tropsch synthesis commercially proven?
Yes. Fischer-Tropsch synthesis has been used commercially for decades in coal-to-liquids and gas-to-liquids applications.
Modern applications increasingly focus on:
- Biomass-to-liquids
- Biogas-to-liquids
- Waste-to-fuels
- Power-to-liquids
These pathways support lower-carbon fuel production for aviation and heavy transport.
Frequently asked questions
Is Fischer-Tropsch synthesis the same as Fischer-Tropsch technology?
No. Fischer-Tropsch synthesis is the core reaction step within the broader Fischer-Tropsch technology system.
Why does Fischer-Tropsch synthesis produce different hydrocarbon lengths?
Because chain growth occurs probabilistically on the catalyst surface according to the Anderson–Schulz–Flory distribution.
Does Fischer-Tropsch synthesis produce jet fuel directly?
No. It produces synthetic hydrocarbons that are upgraded into finished fuels such as SAF and renewable diesel.
What gases are required for Fischer-Tropsch synthesis?
Hydrogen and carbon monoxide, commonly referred to as synthesis gas or syngas. Syngas can be produced from a wide range of feedstocks.