Power-to-liquids is, aviation fuel business Air bp believes, one of the “most promising” longer-term pathways for the production of sustainable aviation fuels (SAF). (Air bp is a unit of UK-based global major energy giant bp.) This pathway uses Fischer-Tropsch synthesis technology as an essential step in the production of synthetic kerosene (SK).

With this pathway, green energy (from whatever source) is used to extract hydrogen from water through a process of electrolysis. This green hydrogen is used to convert carbon dioxide into carbon monoxide. (The carbon dioxide could come from biogenic or industrial sources or be extracted from the air.) Using Fischer-Tropsch synthesis technology, the carbon monoxide, plus further green hydrogen, is transformed into a wax, which is then upgraded into SK. The resulting SAF is referred to as eSAF.

(South African group Sasol is the world leader in Fischer-Tropsch technology and through its business Sasol ecoFT is involved in projects to develop power-to-liquids eSAF.)

Industrial sources for carbon dioxide could include concrete, plaster and food manufacturing companies. The cement and steel industries, which are seeking to reduce their carbon emissions, could be cost-effective sources of carbon dioxide.

Power-to-liquids will also require large-scale green hydrogen production. But, as green hydrogen will be required by many industries to achieve decarbonisation, a large-scale ramp-up in its production can be expected.

“The challenge currently with eSAF technology is cost,” cautioned Air bp. “To be commercially viable and competitive with conventional jet fuel this fuel (which is expected, in the short-term, to be three to eight times the cost of conventional jet fuel and up to four times the cost of SAF made from [hydrotreated esters and fatty acids]) needs to be produced at low cost. The availability and cost of the renewable energy and carbon dioxide, as well as the expansion and improvement of green hydrogen plants must be addressed to meet market demand.”

However, alternative technologies to enable power-to-liquids production of SAF are being researched. One promising option is a methanol-to-jet pathway, which would use the same feedstocks as the Fischer-Tropsch pathway. US-based energy giant ExxonMobil is currently developing a methanol-to-jet pathway using its own processing technology and catalysts.

Germany has already established a mandate that, from 2026, 0.5% of jet fuel used in the country must be eSAF. The European Union is proposing a mandate of 0.7% of eSAF, starting in 2030, and rising to 28% of jet fuel by 2050.