The aviation industry accounted for 2.5% of global energy-related CO2 emissions in 2023, according to the International Energy Agency (IEA).
It means there is a significant challenge, which the industry acknowledges. That is to transition, especially in terms of fuelling aircraft, in order to meet Net Zero targets and deliver a low-carbon future.
One of the potential solutions is the development of sustainable air fuel (SAF) as a cleaner alternative, given the fact it can reduce greenhouse gas emissions by around 70-80% compared to using traditional jet fuel.
Robert Boyd, Boeing's regional director (Asia Pacific) Global Sustainability Engagements and Partnerships, recently visited UNSW as part of an 'Industry Meets Academia' event to discuss aviation decarbonisation delivered by the NSW Powerfuels including Hydrogen Network, Boeing and Virgin Australia.
He said: "If we are committed to Net Zero by 2050, the only way to get there is greatly expanding sustainable aviation fuel.
"The roadmap that the International Air Transport Association puts forward is that 65% of CO2 reduction can come from SAF, so that is a big chunk.
"There are obviously environmental benefits with SAF, but there are also economic benefits for Australia. As a nation, we import 100% of our jet fuel, we don't produce a single drop of it. So if SAF can become a domestic product, that's also good for jobs and the economy here."
SAF benefits
One major benefit of SAF is that its physical and chemical characteristics are almost identical to conventional kerosene jet fuel, which is derived from petroleum. This means SAF can be mixed in with regular jet fuel with no impact on performance, with the current regulations allowing for up to a 50% mix.
SAF can also be supplied via the existing infrastructure, and used in aircraft without needing to modify airframes - the 'skeleton' of the plane - and fuel tanks.
However, SAFs are more expensive to produce and currently limited in terms of availability compared to conventional jet fuel, which is why they currently account for less than 0.1% of all aviation fuels consumed.
Existing and planned SAF projects in advanced stages are predicted to meet just 2-4% of jet fuel demand by 2030.
Which is why the IEA has stated: "Increasing the use of these sustainable aviation fuels to get in line with the Net Zero Scenario will require supportive policies and a significant ramp-up of investments in production capacity."
UNSW Scientia Professor Rose Amal, is the network lead of the NSW Powerfuel Including Hydrogen Network, (PFHN), which is part of the part of the NSW Decarbonisation Hub, a NSW Government initiative whose aim is to reduce carbon emissions to net zero by 2050.
PFHN, in collaboration with the NSW Office of the Chief Scientist and Engineer, recently helped to produce a report, the 'NSW Synthetic Aviation Fuel (e-SAF) Value Chain Study,', which outlines the pathways and challenges for developing a local e-SAF industry and highlights its role in supporting deep emissions cuts in the aviation sector.
e-SAF is a particular type of sustainable aviation fuel which is produced by combining captured carbon dioxide with hydrogen that has been generated by renewable electricity.
Prof. Amal said: "I think it is critical that we decarbonise air travel, not just globally but especially in Australia because we are a long-haul location – that is to get to other countries we have to use planes.
"The American Society for Testing and Materials (ASTM) sets the strict quality specifications for fuels to be eligible for use in the aviation industry, and they have approved eight different pathways for the production of SAF.
"So there are a lot of ways to potentially solve the problem and that's what the PFHN and others are doing – to develop all the new technologies. But we also need feedback from the aviation industry to tell us exactly what they need."
So what exactly is SAF, what problems need to be solved to speed up its development and implementation, and how can these challenges be overcome?
Not just a single SAF
Sustainable aviation fuel is a term for any jet fuel made from renewable sources – like plant oils, waste materials, and even captured carbon – which are designed to reduce the environmental impact of air travel.
SAF cuts greenhouse gas emissions significantly and it works seamlessly with existing aircraft and fuelling infrastructure.
There are several types of SAF in development, including HEFA (made from vegetable oils and animal fats), Alcohol-to-Jet (produced from plant-based alcohols), and eFuels (created using green hydrogen and captured carbon dioxide).
Each type uses different feedstocks and processes, but all aim to make flying more sustainable for the future.
Bio-SAF
Sustainable aviation fuel can be produced from sustainable organic feedstocks, in which case it is known as bio-SAF.
Biological materials – such as used cooking oil, animal fats, or plant oils — can be refined through chemical processes to create a fuel almost identical to conventional jet fuel.
One common method, called the HEFA (Hydroprocessed Esters and Fatty Acids) process, uses hydrogen to remove unwanted elements from these oils and fats, then rearranges their molecules to match the structure needed for aviation fuel.
HEFA is the most commercially mature SAF technology and is widely available, with Virgin Australia recently announcing a deal with Viva Energy to supply it with a 30% HEFA fuel blend for some of its flights out of Queensland.
However, limited supply of the required raw materials means there may not be enough feedstock to meet the aviation industry's full demand in the next 10 to 20 years, especially as competition for these resources grows.
Modelling prepared for the Air Transport Action Group's Waypoint 2050 report, opens in a new window says that bio-SAF feedstock might only supply 50% of the SAF required to meet the net-zero by 2050 target set by the International Air Transport Association (IATA).
e-SAF
e-SAF is the name given to synthetic sustainable aviation fuel which is derived from renewable energy.
Here, the production starts by using the likes of wind or solar power to split water into hydrogen, which is then combined with carbon dioxide captured from the air (or from industrial processes) to create a liquid fuel.
This is done via the Fischer-Tropsch process, well established for almost 100 years, which uses a catalyst to transform the hydrogen and CO2 gases into synthetic crude oil, which is further refined into aviation-grade fuel.
A major benefit of e-SAF is that renewable energy, green hydrogen and carbon dioxide are vastly more abundant than organic feedstocks needed for bio-SAF.
However, Dr Emma Lovell, from UNSW's School of Chemical Engineering, who has a research focus on carbon dioxide conversion, acknowledges the cost of e-SAF is currently prohibitive.
"It is around four to 10 times more expensive than current conventional fuels," Dr Lovell says.
"But I absolutely believe that can be brought down significantly. The two main factors at the moment are the cost of producing green hydrogen and the cost of direct air capture which extracts carbon dioxide from the atmosphere.
"However, there is widespread research into making both of those processes more efficient and there is significant potential for cost reductions to get to a point where there is at least competitiveness, if not parity, with the price of sustainable aviation fuel.
"The advantage compared to bio-SAF is that there's no need to make that choice between growing feedstocks for food or for fuel. The other benefit is that the e-SAF actually makes a whole range of materials, such as sustainable diesel, useful waxes and other products that are used in pharmaceuticals and cosmetics.
"So you get all of those, but in a green way, as well as fuel."
ATJ (Alcohol-to-Jet)
Alcohol-to-Jet (ATJ) fuel is another type of sustainable aviation fuel which is made by converting alcohols like ethanol or isobutanol into jet fuel through a series of chemical processes.
The alcohol is first obtained by fermenting biomass such as plant materials or agricultural waste, before being dehydrated to remove water and then chemically manipulated to create hydrocarbons that closely resemble jet fuel.
Several airlines have entered agreements to purchase ethanol-based SAF for use in major airports starting as soon as 2027.
