Bio-based aviation fuels

Production pathways

The American Society for Testing and Materials (ASTM) International has developed standards [40], [41] to approve new biobased aviation fuels, and currently six production pathways have been certified for blending with conventional aviation fuel. These include:

  • FT-SPK (Fischer-Tropsch Synthetic Paraffinic Kerosene). Biomass is converted to synthetic gas and then into bio-based aviation fuel. Maximum blending ratio is 50%.
  • FT-SPK/A is a variation of FT-SPK, where alkylation of light aromatics creates a hydrocarbon blend that includes aromatic compounds. Maximum blending ratio is 50%.
  • HEFA (Hydroprocessed Fatty Acid Esters and Free Fatty Acid). Lipid feedstocks, such as vegetable oils, used cooking oils, tallow, etc. are converted using hydrogen into green diesel, and this can be further separated to obtain bio-based aviation fuel. Maximum blending ratio is 50%.
  • HFS-SIP (Hydroprocessing of Fermented Sugars - Synthetic Iso-Paraffinic kerosene). Using modified yeasts, sugars are converted to hydrocarbons. Maximum blending ratio is 10%.
  • ATJ-SPK (Alcohol-to-Jet Synthetic Paraffinic Kerosene). Dehydration, oligomerization and hydroprocessing are used to convert alcohols, such as iso-butanol, into hydrocarbon. Maximum blending ratio is 50%.
  • Co-processing8. Biocrude up to 5% by volume of lipidic feedstock in petroleum refinery processes.

Additional pathways are currently in the ASTM certification process.

Defining the maturity level of the available bio-based aviation fuel production pathways, either from a technological or from a commercial point of view, is challenging. Despite the dynamism of the sector, only a few of the ASTM certified pathways are supplying fuel on a commercial scale. The technological maturity of each production pathway can be defined through a Technology Readiness Level - TRL [42], which ranges from 1 for basic ideas, to 9 for an actual system proven in an operational environment. Alongside the technology readiness, the commercial development of a certain fuel could be different due to various other drivers (e.g. certification issues, costs issues). To better clarify the progress of a specific fuel production pathway towards full commercialisation, the US Commercial Aviation Alternative Fuels Initiative has developed the Fuel Readiness Level (FRL) system, which has been endorsed by ICAO [43]. FRL also ranges from 1 for basic ideas to 9 for production capability established, but is tailored for approval of aviation fuel international standards.

Table 3.1 [44][45][46]

8 This pathway has been approved in April 2018 and added to Annex A1 of ASTM D1655, Standard Specification for Aviation Turbine Fuels.

Production capacity

Europe is today a key player in the wider biofuel production technology sector, with several commercial-size plants currently in operation. The production capacity of bio-based aviation fuel in the EU relies on a small number of plants, accounting for a maximum potential output of approximately 2.3 million tonnes per year (Max-EU scenario9), which potentially corresponds to about 4% of the total EU conventional fossil aviation fuel demand. It is important to note the distinction between potential bio-based aviation fuel production capacity that is discussed in this section, and the consumption of such fuels discussed in the next section, as several barriers are currently limiting market uptake.

The largest potential share of EU bio-based aviation fuel relies on the processes able to convert various feedstocks and residues into a fuel suitable for commercial flights. The most developed process to date produces Hydroprocessed Fatty Acid Esters and Free Fatty Acid (HEFA). In this process, vegetable oils and/or animal lipid feedstocks can be used to produce a fully certified bio-based alternative to fossil-based aviation fuel. The certified HEFA is a portion of the Hydrotreated Vegetable Oil (HVO) product, which is currently used within the road sector. A pathway that would allow the use of a greater share of the HVO production, thereby increasing the EU production potential, is currently being certified (HEFA expansion or HEFA+).

Refineries producing biomass derived SAF can tune their process in order to increase the output for aviation, if demand increases (Max-EU scenario). However, in view of the relatively low profitability of producing aviation fuel and road fuels, it is reasonable to assume that the actual bio-based aviation portion from the HEFA process would account for a lower share of the processing plant output than the theoretical maximum. A share of 15% has been assumed in defining a moderate bio-based aviation fuel scenario (Mod-J scenario), which results in an estimate of the current EU potential bio-based aviation fuel output equal to 0.355 million tonnes per year (Table 3.2).

The current potential production capacity is substantially based on HEFA plants, but may increase by 2020 with the announcement of new facilities and the scaling-up of existing facilities within the EU. Moreover, the recently certified coprocessing pathway may unlock a larger potential production capacity. However, significant investments into the other ASTM-certified pathways (e.g. ATJ and SIP) do not seem to be a priority at the moment for major industrial players in Europe, even if new actors are expected to become active in the market after 2020 and contribute to the growth in the moderate bio-based aviation fuel scenario.

9 The information provided in this section is based on the European Commission Directorate General Joint Research Centre (DG JRC) database on the European biofuels production plants [Prussi et al., 2019 – In press].

Price and consumption

The price of bio-based aviation fuel relative to fossil-based kerosene is one of the major barriers to its greater market penetration. Today the feedstock price represents the major component of the final bio-based aviation fuel price, and its price volatility on the EU market can also create supply problems for fuel producers. While a typical price for fossil-based aviation fuel would be €600/tonne, the price of bio-based aviation fuel produced from used cooking oil can be in the range of €950-€1,015/tonne. In addition, feedstocks that comply with sustainability requirements, such as used cooking oil and tallow used in the HEFA process, are in demand by the road fuel sector for biodiesel and green diesel production. It is expected that this competition between road and aviation will further increase in the coming years.

There are various on-going initiatives at the European level aimed at increasing the market penetration of bio-based aviation fuels. However, despite the presence of these initiatives, the current consumption in Europe is very low when compared to the potential production capacity. Only Germany reported the use of bio-based aviation fuels as part of the official 2016 figures under the framework of the Emissions Trading Directive.