As aviation looks towards its net zero goals, sustainable aviation fuels are expected to play the largest single part in reducing emissions between today and 2050. But what are the key types of these SAFs, and when will they come on-stream?
SAFs are critical to achieving aviation’s net zero goals. “Projections estimate that SAF by 2050 will deliver around 63% of the emissions reductions necessary to achieve aviation’s net-zero emissions by 2050 goal,” explains Jorrian Dorlandt from SAF powerhouse Nexte.
Air bp’s global aviation sustainability director Andreea Moyes concurs: “kerosene is likely still to be the main source of energy for aviation, since hydrogen for example is unlikely to be able to address long-haul wide body aircraft propulsion in this time frame, and the turnover of aircraft in the fleet takes time. So SAF is critical to meeting the industry’s 2050 goals. Any additional contribution that hydrogen and renewable electricity can make as sources of propulsion in this time frame is also important.”
This will require a substantial amount of investment: the industry estimates that aviation alone will require some 450–500 million tonnes of SAF annually by 2050.
That will need to come from a variety of feedstocks and through a variety of processes. Just how many? That depends on who you ask, mostly because there are various feedstocks, treatments, and conversion processes that can either be classified as one kind of SAF or separated out into multiple kinds.
Regardless of the number, it all starts with what’s available now
“All pathways can be used for the aviation industry,” explains Neste’s Dorlandt, “but the HEFA pathway is currently the most commercially viable and the type Neste as the world’s leading SAF producer uses. Some pathways are more suited to particular locations, for example municipal solid waste is most easily accessible when closer to landfill.”
Beyond that, says Dorlandt, “it’s the feedstock type and sourcing that is really more important. In general waste and residue type feedstock should be preferred rather than feedstock that potentially competes with food. Neste has been using waste and residue raw materials for a decade which now represent more than 90% of our global renewable raw material inputs. Neste MY SAF is made from 100% waste and residues, like used cooking oil and animal fat waste.”
Neste is working on further pathways, including lignocellulosic raw materials, municipal solid waste, algae, and power-to-liquid, which uses carbon captured from the atmosphere.
Categorisations of the different types of biofuels differ slightly, based on whether some of the categories are split out into sub-categories.
Air bp currently combines some future technologies from the seven approved SAF pathways to get five categories: hydroprocessed esters and fatty acids, municipal solid waste, alcohol to jet, second-generation biomass (which combines multiple technology pathways), and eSAF.
Each can be blended with fossil jet fuel, but at different maximum percentages, mostly because of different aromatic compounds within SAF versus fossil jet fuels and their effects on engines. As an example, sulphur within fossil jet fuels causes some sealing materials to swell for a tight fit, but this is not present (or is not present to the same extent) in SAF.
Air bp says that most of the approved pathways can currently be blended at 50%, but synthesised iso-paraffins produced from fermented sugars and hydroprocessed hydrocarbons produced from algal oils max out at 10%.
The industry’s expectation is that research and development to increase these percentages will bring results faster than any situation where SAF production means that these blending percentages are a material constraint.
Hydroprocessed esters and fatty acids (HEFA): available now
HEFA, says Air bp’s Andreea Moyes, makes up “the majority of what is supplied today — this technology is currently commercial. The key opportunities or advantages of this pathway are that it uses fungible feedstock, scalable technology, is capital light and offers back integration to refineries. One constraint is that it competes with renewable diesel (HVO) for highly limited feedstock. A longer-term constraint is that feedstock is limited unless oil seed energy crops emerge post 2035.”
Overall, Moyes notes, “HEFA is a near-term option that uses fungible feedstock and back-integrates to refineries.”
Municipal solid waste (MSW): 2025–2030
MSW is relatively near-term in timescale, and is presently in commercial demonstrations. Its benefits include that its feedstock is actually negative in cost and that the Fischer-Tropsch technology also integrates to eSAF processes. However, it is an investment risk, requires high capital investment, needs to be close to major cities (not necessarily a dealbreaker for aviation use) and that its carbon reduction depends on avoiding landfill emissions.
Overall, it’s a decent near-term option in proximity to large urban areas.
Alcohol to jet (ATJ): 2025–2035
ATJ, certainly in the nearer term, largely means ethanol-to-jet, which is a mature technology. “Key opportunities,” says Air bp’s Moyes,” are that it is a capital light process and that it is attractive in areas with existing ethanol capacity (e.g. US/Brazil). One near-term constraint is the opportunity cost to sell ethanol for road transport is high. A longer-term constraint is the opportunity cost to sell as a chemical may be high. There are also concerns around sustainability. The key take away is that first generation alcohol to jet is capital light and produces SAF from existing ethanol markets.”
Second-generation biomass: 2030–2035
Slightly further away in the timeline are the multiple technologies that can be categorised as second-generation biomass. While substantial and diverse feedstocks are available, and the overall potential is relatively low cost and long-term, near-term blockers around cost and technology could delay implementation.
eSAF: 2030–2040
Most early references to eSAF are around combining green hydrogen and carbon dioxide, but methanol and other pathways at R&D stage are also likely to become available.
Long-term, it’s a strong contender, says Moyes. “It is progressing at the pace of renewables, there is a societal preference and [eSAF] has the highest sustainability credentials. Constraints in the near term include cost and technology readiness and that improvements are required in multiple areas of technology. Longer-term constraints include capital costs and build rates for eSAF and power/hydrogen.”
Across all the pathways, Moyes urges, “over the long term, investment in advanced technologies is required to process SAF feedstocks more efficiently at greater scale and investment in the development of sustainable and scalable feedstock options. Governments have a role as increasing production requires long-term policy certainty to reduce investment risks, as well as a focus on the research, development and commercialisation of improved production technologies and innovative sustainable feedstocks.”
The digital agenda will play a strong role too, especially around the operation of SAF plants and Industry 4.0, as well as the requirement for emissions transparency.
“Verification and certification of carbon emissions is important for SAF,” Neste’s Jorrian Dorlandt says, “as users would like to report on carbon emissions of air travel. We see positive developments here, for example with the Science Based Targets initiative, which has aviation guidance that supports using SAF — making it possible for companies to use SAF to meet their science-based targets and report on those.”
Author: John Walton
Published: 11th August 2022
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