Progress in Commercialization of Biojet /Sustainable Aviation Fuels (SAF): Technologies, Potential and Challenges

December 31, 2021

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by Susan van Dyk and Jack Saddler (IEA Bioenergy Task 39) Biojet/ Sustainable Aviation Fuels (SAF) must play a major role if the aviation sector is to significantly reduce its carbon footprint. To meet its carbon reduction targets, large volumes of biojet fuel will be required (likely more than 100 billion litres per year). However, to date, commercialization has been slow and current policies preferentially incentivize the production of other fuels, such as renewable diesel, from the limited available volumes of oleochemical feedstocks.

Although alternative lower-carbon intensive propulsion systems based on electric, hybridelectric and hydrogen will likely be used in the future, in the short-to-mid-term, biojet fuels will predominate. Ongoing challenges with these other alternatives include issues such as “green” electric aircraft being limited in their range and the number of passengers carried while longer term options, such as “green” hydrogen, will require novel supply chains and new aircraft. Thus, it will be some time before low-carbon-intensity options other than biojet fuels will be commercially available, particularly for long-haul flights.

Although annual volumes of biojet fuel have increased from <10 million litres in 2018, to possibly more than 1 billion litres by 2023 (and potentially ~8 billion litres by 2030), the vast majority of this volume will be derived from oleochemicals/lipids. The upgrading of fats, oils and greases (FOGs) to HEFA-SPK (hydrotreated esters and fatty acids synthesized paraffinic kerosene) is fully commercialized and biojet production is relatively simple. It is anticipated that increased volumes of biojet will be derived via this “conventional” pathway based on expansion of current facilities and the building of new facilities. However, as demonstrated by Neste, these facilities will be primarily used for renewable diesel production with the potential to add biojet production after additional infrastructure investment, and modification of final processing, e.g. adding a distillation step, likely driven by incentivizing policies.

Other technologies which could be producing commercial volumes of biojet fuel by 2025 are Fischer-Tropsch synthesized paraffinic kerosene (FT-SPK) (based on gasification), alcohol-tojet synthesized paraffinic kerosene (ATJ-SPK) and catalytic hydrothermolysis jet (CHJ).

However, all of these processes produce multiple fuel products which typically include a biojet fuel fraction. Therefore, even though “stand-alone” biorefineries could produce more of the biojet fraction, this will be influenced by market demand, economics and policy drivers as currently, in many cases, the biojet-range molecules are diverted to the renewable diesel fraction due to policy drivers. For each of the technologies, although the percentage of the jet fraction within the total liquid fuels varies, processing conditions can be modified to increase the amount of the biojet fraction. Thus, if HEFA refiners were encouraged to produce biojet, in addition to renewable diesel, at least 15% of the current low-carbon, dropin fuels produced could be biojet. This would immediately increase the amount of biojet that could be available, at a moderate investment cost.

As will be mentioned several times, although there are several ways to make biojet fuels, the vast majority of the biojet fuel used today are produced via the HEFA pathway. It is anticipated that this pathway will predominate for at least the next ten-to-fifteen years.

Hydrotreated esters and fatty acids (HEFA) technology

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Gasification and Fischer-Tropsch synthesis

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Pyrolysis and hydrothermal liquefaction (HTL)-based technologies

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Alcohol-to-jet technologies

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Power-to-Liquids (PtL) technologies

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Coprocessing technologies

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Key take-home messages
Meeting the climate targets of the aviation sector will require significant volumes of biojet fuels. However, current production volumes are less than 150 million litres per year which is considerably less than 0.5% of total jet fuel demand, even during these times of restricted air travel. Although recent investments will see production grow to more than 1 billion litres over the next few years, the vast majority of these biojet fuels will come from HEFA IEA Bioenergy: Task 39 Progress in commercialization of biojet /Sustainable Aviation Fuels (SAF) feedstocks and technology. Other, alternative, technologies are only at the “pioneering” scale of development. Currently seven direct pathways and two coprocessing pathways have received ASTM certification with the introduction of a fast-track certification process
hopefully reducing the time required for certification. The time taken to obtain certification has been a significant barrier to more rapid biojet expansion.

As well as the various biojet processes encountering high capital and high feedstock costs, for many of the “advanced” pathways, significant technology challenges still need to be resolved, for example, upgrading challenges (HTL and pyrolysis), achieving higher biojet yields and dealing with variable bio-feedstocks with different chemistry and contaminants. It should be noted that, for all of the biojet processes, the minimum selling price of the biojet fuel is significantly higher than that of fossil derived jet fuel. Thus, policy will play a very important role in trying to bridge this price gap. In parallel, there will be an increasing focus on cost reductions such as accessing low-cost feedstocks, optimizing supply chains, increasing product yield and diversifying the product slate to include higher value commodities. It is also anticipated that, as the various technologies mature, learning rates should result in significant cost reductions. Despite these process improvements, the cost of biojet fuels will be closely linked to policies that incentivize their production and use. These policies will likely provide an opportunity for companies to improve their overall sustainability, lower the carbon intensity of fuels and become more economically competitive. As the driving force behind biojet fuel production and use is emission reduction and climate mitigation, the overall sustainability and the reduced carbon intensity of the finished fuel will be a priority.

Finally, all of the technologies described in this report will need to be pursued, if we are to deliver the significant biojet volumes that will be required. Although it is likely that ongoing improvements and optimization of processes will continue to reduce costs and facilitate biojet fuel production and use, meeting the sector’s decarbonisation targets will be challenging. READ MORE

Table of Contents
Executive Summary ........................................................................................ 1
Table of Contents .......................................................................................... 5
List of Figures............................................................................................... 7
List of Tables ............................................................................................... 8
1. Introduction.............................................................................................. 8
2. Definition and characteristics of jet fuel...........................................................10
3. ASTM certified biojet fuels and specifications .....................................................13
3.1 ASTM certification process ........................................................................13
3.2 Current ASTM certified pathways ................................................................15
3.3 Blending limits for biojet fuels and implications ..............................................17
3.4 Downstream logistics and use of biojet fuels at airports .....................................17
3.5 Comparing batch fueling and airport hydrant systems........................................18
4. Status of biojet fuel commercialization ............................................................20
5. Technology pathways used to produce biojet fuels ...............................................22
5.1 The Oleochemical Conversion Pathway .........................................................24
5.1.1 The basic process for HEFA production.....................................................24
5.1.2 Feedstocks and Pretreatment................................................................27
5.1.3 Production of biojet fuel via the HEFA process ...........................................27
5.1.4 High freezepoint HEFA as a biojet fuel.....................................................29
5.1.5 Other technologies based on lipid feedstocks .............................................29
5.1.6 Economics and sustainability of HEFA-SPK production ...................................30
5.1.7 Opportunities and challenges for the oleochemical pathway ...........................31
5.2 Thermochemical routes for biomass-to-biojet.................................................33
5.2.1 Gasification and Fischer-Tropsch synthesis for the production of biojet fuel ........33
5.2.2 Direct thermochemical liquefaction ........................................................46
5.3 Catalytic hydrothermolysis (CH) .................................................................63
5.4 Biochemical methods used to produce liquid hydrocarbon drop-in biofuels...............64
5.4.1 Biochemical production of farnesane from sugars ........................................66
5.4.2 Alcohol-to-jet technology for biojet fuel production.....................................67
5.4.3 Alcohol to jet conversion .....................................................................73
5.4.4 Economics and sustainability of the alcohol-to-jet pathways ...........................76
5.4.5 Opportunities and challenges of the ATJ technology.....................................77
5.5 Electrofuels (Power to Liquids – PtL) ............................................................78
5.5.1 Potential and challenges of the Power to Liquid technology pathway.................79
5.6 Co-processing of biobased intermediates in existing refineries for the production of low
IEA Bioenergy: Task 39 Progress in commercialization of biojet /Sustainable Aviation Fuels (SAF)CI jet fuel ................................................................................................80
5.6.1 Potential and challenges of coprocessing strategies for biojet fuel production......81
6. Conclusions ........................................................................................82
7. References ........................................................................................83