Climate tech explained: sustainable aviation fuels

Virtually no human activity is as difficult to decarbonise as flying. Relatively light, energy-dense aviation fuel — or Jet A-1, as the most common type is known — packs vast amounts of energy into a tiny amount of space and weight. Finding an equally efficient alternative is a daunting prospect. “Jet A-1 verges on being perfect in terms of weight for power,” explains Andrew Charlton of aviation consultancy Aviation Advocacy. Right now, the leading alternatives are “sustainable aviation fuels”. These are produced from non-fossil sources — including used cooking oil, animal fats, or even carbon from the air — and can be used as a direct replacement for Jet A-1. But there are many questions about how quickly the production of such fuels can be scaled up, their cost, and the effect of their production on other activities, such as agriculture. The main “feedstock” for SAF, at present, is used cooking oil. The oil is filtered and “hydrogenated” — a process in which the oxygen is replaced with hydrogen, to turn it into a hydrocarbon. The resulting mixture is distilled. Producers are also working on ways to turn material from municipal waste into SAF. There is considerable excitement, also, about the potential for a technology called “power-to-liquids” or “e-fuels”, which uses electrolysis to turn carbon pulled from the air into a carbon-based fuel. Lauren Riley, chief sustainability officer for the US’s United Airlines, describes that technology as particularly exciting. “You avoid that whole concern about constraints on feedstocks,” Riley says, referring to concerns about the availability of other material to turn into SAF. “Power-to-liquid, literally, is pulling carbon out of the atmosphere and you do that using sustainable power.” Story has more.<br/>