Synthetic fuel, often called electrofuel or e-fuel, creates hydrocarbon liquids chemically identical to those derived from petroleum. This process relies on two primary feedstocks: captured carbon dioxide (\(text{CO}_2\)) and hydrogen generated using renewable electricity. The technology aims to create a closed-loop system where carbon is reused, offering an alternative to extracting fossil carbon from the ground.
How Carbon Dioxide Becomes Fuel
The conversion of atmospheric or industrial carbon dioxide into a usable liquid fuel is an energy-intensive process known as Power-to-Liquids (PtL). This process occurs in two distinct stages. The first stage involves securing the necessary inputs: carbon atoms from \(text{CO}_2\) and hydrogen atoms from water. Carbon dioxide is either captured from concentrated industrial sources, such as cement or power plants, or directly filtered from the ambient air using Direct Air Capture (DAC) technology.
Hydrogen is produced by splitting water molecules through electrolysis, powered exclusively by renewable electricity, yielding “green hydrogen.” Once \(text{CO}_2\) and green hydrogen are secured, the conversion stage begins with a high-temperature reaction to produce synthesis gas, or syngas. This is accomplished through the reverse water-gas shift reaction, which combines \(text{CO}_2\) and hydrogen to form carbon monoxide (CO) and water.
The resulting syngas, a mixture of carbon monoxide and hydrogen, is then fed into a reactor for the final conversion step: the well-established Fischer-Tropsch synthesis. This catalytic process uses metal catalysts to facilitate the reaction of the syngas molecules, building them up into longer hydrocarbon chains. The chain length of these hydrocarbons determines the type of fuel produced, such as gasoline, diesel, or jet fuel.
Diverse Fuels Created from \(text{CO}_2\)
The PtL process produces a range of fuels that serve as direct replacements for conventional fuels. A primary focus is on producing Sustainable Aviation Fuel (SAF), also called e-kerosene, which is chemically suited for the demanding requirements of jet engines. The synthesis process can also be tuned to yield e-diesel and e-gasoline, which are structurally identical to the diesel and petrol used in road transport.
A significant advantage of these synthetic fuels is their “drop-in” nature, meaning they can be blended with or completely replace conventional fuels without requiring modifications to existing engines, pipelines, or refueling infrastructure. This compatibility allows for a seamless introduction into the current global energy supply chain. Other products like e-methanol and dimethyl ether (DME) can also be synthesized, offering low-carbon options for the maritime shipping industry and other specialized applications.
The Climate Rationale for Synthetic Fuels
The motivation for developing synthetic fuels is establishing a circular carbon economy to mitigate the net release of greenhouse gases. The carbon atoms contained in the fuel are sourced from existing atmospheric \(text{CO}_2\) or waste industrial emissions, not from newly extracted fossil reserves. When the resulting synthetic fuel is burned in an engine, it releases \(text{CO}_2\) back into the atmosphere, which is the same quantity of carbon that was initially captured to produce the fuel.
This closed-loop system means the fuel’s combustion results in no net addition of new, geologically sequestered carbon to the atmosphere, defining them as carbon-neutral over their life cycle. This contrasts sharply with traditional fossil fuels, which extract ancient carbon from the earth and permanently introduce it into the atmosphere upon combustion.
Synthetic fuels are important for decarbonizing sectors that are difficult to electrify, such as long-haul aviation and maritime shipping. In these areas, the high energy density of liquid hydrocarbons is necessary for long range and heavy payload transport.
Scalability and Commercial Challenges
Despite the environmental benefits, the widespread adoption of \(text{CO}_2\)-based synthetic fuels faces hurdles related to cost and scale. Currently, e-fuels are substantially more expensive to produce than traditional fossil fuels, with estimates for e-diesel equivalents being several times higher per liter. This high cost is driven by the energy-intensive nature of the PtL process, which requires vast amounts of renewable electricity to produce green hydrogen and drive the conversion reactions.
The process is inherently inefficient in its use of electricity, as multiple conversion steps result in significant energy losses. To produce synthetic fuels on a scale comparable to current fossil fuel consumption, a massive build-out of new renewable energy infrastructure would be required, potentially competing with the direct electrification of other sectors.
Infrastructure requirements extend to the need for large-scale \(text{CO}_2\) capture facilities, whether through DAC or industrial capture, and the subsequent transport and storage of the captured carbon and hydrogen. However, government mandates and pilot projects are supporting the technology’s commercialization, with some experts predicting wider scale use between 2025 and 2030 as the cost of green hydrogen production decreases.