Synthetic fuel, often termed Synfuel, represents liquid hydrocarbon fuels manufactured from raw materials other than crude oil. Today, synthetic fuels are gaining renewed attention globally to bolster energy security and address the challenge of decarbonizing sectors difficult to electrify, particularly long-distance transportation like aviation. The process transforms diverse feedstocks into a clean-burning liquid compatible with existing infrastructure and engines, reducing reliance on conventional petroleum products.
Fossil-Based Raw Materials
The traditional and most commercially established feedstocks for synthetic fuel production are non-renewable resources derived from geological deposits. These fossil sources are predominantly coal and natural gas, utilized in processes known as Coal-to-Liquids (CTL) and Gas-to-Liquids (GTL). These materials provide the carbon backbone necessary to construct hydrocarbon chains.
Coal must first undergo gasification, a high-temperature conversion process that turns the solid coal into synthesis gas (syngas), composed mainly of carbon monoxide (CO) and hydrogen (H₂). This indirect liquefaction method utilizes abundant coal reserves. However, the conversion of coal often results in significant carbon dioxide emissions.
Natural gas, primarily methane (CH₄), is utilized in the Gas-to-Liquids process, which is generally more efficient than CTL due to its higher inherent hydrogen content. The gas is typically converted into syngas through steam reforming or partial oxidation. The GTL process is attractive for utilizing “stranded gas” located in remote areas, converting it into easily transportable liquid fuels.
Alternative Carbon Sources
Moving beyond fossil resources, a new generation of synthetic fuels relies on carbon sources that are renewable or recycled. One major category is Biomass-to-Liquids (BtL), which converts organic materials like agricultural residues, forestry waste, and municipal solid waste into syngas. The gasification process turns the solid organic matter into the carbon monoxide and hydrogen blend required for synthesis. Using biomass feedstocks allows for a net reduction in life-cycle carbon emissions, as the carbon released during combustion was recently captured from the atmosphere.
A distinctly modern approach involves capturing carbon dioxide (CO₂), often paired with renewable electricity in a system known as Power-to-Liquids (PtL). The CO₂ acts as the recycled carbon feedstock, closing the loop on carbon emissions. The CO₂ can be sourced from concentrated industrial emissions or directly captured from the ambient air using Direct Air Capture (DAC) technology.
The PtL pathway, which produces e-fuels, treats carbon as a resource to be reused rather than a raw material to be extracted. By combining captured CO₂ with “green” hydrogen, the resulting liquid fuel is considered climate-neutral because the carbon released upon burning was previously removed from the atmosphere or industrial waste stream. Although PtL technology is still in the pioneer phase, it offers a path toward a theoretically unlimited carbon feedstock supply.
Essential Non-Carbon Inputs
The conversion of any carbon feedstock into a synthetic liquid fuel requires two fundamental inputs that are not the primary source of carbon: water and massive amounts of energy. Water (H₂O) is a necessary reactant because it is the primary source of the hydrogen component (H₂) required for syngas production. In fossil-based processes, the hydrogen is often generated from the water component of steam in a chemical reaction with methane, known as steam methane reforming.
For the newer, more sustainable PtL processes, water is split into hydrogen and oxygen using an electrolyzer powered by electricity, a process called electrolysis. This “green hydrogen” production is the initial and energy-intensive step for carbon-neutral fuels. Across all synthetic fuel pathways, water is also consumed for cooling and steam generation in the high-temperature conversion processes.
The second non-carbon input is the immense energy required to drive the entire synthesis process. Converting feedstocks into liquid hydrocarbons is highly endothermic, meaning it absorbs substantial heat and power. For fossil-based fuels, this energy often comes from burning a portion of the raw material itself, which adds to the overall carbon footprint. Sustainable synthetic fuels must rely on large inputs of renewable electricity to power the electrolyzers and the subsequent chemical synthesis.
Final Synthetic Fuel Outputs
The final stage of the production process, typically involving the Fischer-Tropsch synthesis, converts the syngas into various long-chain hydrocarbons. By controlling the reaction conditions, such as temperature, pressure, and the choice of catalyst, manufacturers can tailor the final product slate to meet stringent performance standards.
A major focus is the production of synthetic kerosene, used as Sustainable Aviation Fuel (SAF). Since direct electrification is not yet feasible for long-haul flights, this synthetic jet fuel offers a viable path to decarbonization. Synthetic diesel and gasoline are also common outputs, designed to be drop-in replacements for their petroleum-derived counterparts.
These synthetic products frequently possess qualities superior to conventional petroleum fuels, such as being ultra-low in sulfur and having high purity. The resulting liquid fuels are essentially colorless and odorless hydrocarbons, which offer improved combustion characteristics.