Kerosene... Which alternatives are possible?
At a time when civil aviation emissions, which alone account for 2% of global emissions, are increasingly being criticized by the general public, the taxation of kerosene has entered the public debate in most European countries. Given the growing demand in the air transport sector, alternative jet fuels (AJFs) are among the few approaches available in the sector to reduce aviation sector emissions. Indeed, as aircraft electrification is only starting, the aviation sector is likely to continue to rely heavily on liquid fuels until 2050, particularly for long-haul flights (Hall et al., 2018). It therefore seems interesting to review the various possible alternatives to kerosene and the potential cost of developing these solutions as assessed by the International Council on Clean Transportation (ICCT) in the report "The Cost of Supporting Alternative Fuels for Jet Fuels in the European Union".
Comparison of levelized costs of production for alternative jet fuel across fuel conversion pathways.
Source : ICCT
The ICCT evaluates five AJFs production lines already certified by the standards organization ASTM International, that can be used in commercial aviation if they meet the criteria specified for blending with conventional jet fuel. The 5 categories of AJFs are as follows:
- HEFA (Maximum allowable blending rates - MABR = 50%): The HEFA route uses fatty raw materials such as vegetable oils or used fats that can then be refined into a mixture of various liquid fuels.
- Gasification-FT (MABR = 50%): This fuel conversion path includes the gasification of raw materials into synthesis gas, a mixture of CO and H2.
- Power-to-liquid (MABR = 50%): From biological raw materials, synthesis gas can be produced by electrolysis of water (using renewable electricity) and combined with captured carbon to generate a raw material suitable for FT synthesis.
- ATJ (MABR = 50%): This fuel conversion pathway uses fermentation to convert sugars, starches or hydrolyzed cellulose into an intermediate alcohol, either isobutanol or ethanol, which is then transformed and upgraded to a hydrocarbon mixture.
- SIP (MABR = 10%): This fuel conversion pathway converts sweetened feedstocks by fermentation into a molecule with a carbon chain close to that of distilled hydrocarbons that can then be used as fuel without additives.
On the graph, we can see that the production costs of the different AJF technologies vary considerably. They range from around €0.9 per litre for hydrotreated fuels made from waste fats and oils (HEFA) to €3.44 per litre for the direct conversion of sugar into jet fuel (SIP). Overall, these prices represent two to eight times the current (untaxed) price of kerosene fuels. In the study, the ICCT considers that the most cost-effective fuel for reducing carbon emissions in the short term is HEFA derived from used cooking oils. However, used fats and oils are already widely used in the road transport sector and their supply may therefore be limited. The other most effective options would be the gasification of municipal solid waste and lignocellulosic feedstocks according to the ICCT. All these costs can be put in perspective with a very likely future tax on kerosene in European countries. Debates are ongoing as to what would then be the right level for this tax so that investments can support the alternatives solutions and feedstock supply chains necessary to facilitate longer-term aviation decarbonization.
Félix Fouret, Carbon/Climate Analyst
Source : Beyond Ratings, ICCT
 Hydroprocessed esters and fatty acids
 Fischer–Tropsch process
 (Isobutanol) Alcohol To Jet
 Synthesized Iso-Paraffinic