Sustainable aviation fuels: a cloudy future

The International Air Transport Association (IATA) has announced that by 2050, airlines are committed to being carbon neutral. An ambitious goal, given that their previous target was to reduce CO₂ emissions by a factor of 2 by 2050.

For several months, airlines and manufacturers have been working on SAF (Sustainable Aviation Fuel), which could reduce CO₂ emissions by 65% by 2050. Combined with more efficient engines, better traffic management and other advances that have yet to be evaluated, the results could be good. In theory…

If we take a closer look at these different fuels, the goal still seems to be out of reach for an early arrival of SAF in the aviation industry.

To illustrate, let’s take the case of Roissy Charles De Gaule airport and review the different types of SAF.

Let’s start with frying oils, as their use as fuel has become widespread among both individuals and institutions. To produce a fuel suitable for aircraft, a hydrogenation process is required. This process, although mature, is still confidential with negligible quantities produced in France. Even if slight adaptations are necessary at the engine or tank level, the main challenge lies in the value chain.

According to our calculations, it would be necessary to be able to recover all the French used frying oils (i.e. 1.5Mt) to meet the needs of Roissy. The oils of the companies thus, but also the oil of all the French households

Utopian and economically questionable given that the sector, already well structured, would have to increase its prices due to this new demand.

Next comes biofuel from cereal residues. France, the largest agricultural nation in Europe, produces 51Mt of these residues per year. Hardly recoverable, they are mostly used as fertilizer or low quality animal feed.

However, recent breakthroughs related to the fermentation of these wastes could change this situation, as these processes could produce a fairly good quality fuel for aircraft. But here again, the challenge lies in the supply chain, since by recovering 98% of the cereal residues, 100% of the fuel needs of Roissy would be met.

Promising, but here again, structuring a channel to use 100% of a resource for a single airport seems unrealistic.

Then comes a source that would, in theory, be unlimited: the manufacture of synthetic fuel by capturing CO₂ from the atmosphere. Everyone has in mind the announcement with great fanfare of the commissioning of the first CO₂ capture plant in Iceland (and its questionable energy footprint). The idea here is to produce fuel from carbon dioxide and hydrogen by a Fischer-Tropsch process (a process that is now mastered and requires little energy). Unfortunately, from a technical point of view, this solution also seems utopian.

Mathematically, it would be necessary to be able to suck in 600,000 m3 of air per second, to produce the quantity of fuel needed in Roissy. In more graphic terms, to suck in that much air, you would have to build a wall of fans equivalent to the surface of the Berlin Wall… Not impossible, provided you have the clean energy to power all those fans, a lot of space and a questionable sense of aesthetics.

Not impossible, provided you have the clean energy to power all those fans, a lot of space and a questionable sense of aesthetics.

Thus, SAF certainly offers non-negligible advantages by (re)using elements that were previously little used and available in large quantities on our territory.

Nevertheless, as in everything related to energy, the strategy of the sector must be based on a mixed approach, mixing SAF, technological breakthroughs and prospective work… on hydrogen for example…

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