Mar-2023

Take-off for cleaner skies starts now with SAF

Sustainable aviation fuel is the most promising pathway to decarbonisation, but which routes are the most commercially advanced?

Milica Folic
Topsoe

Article Summary

Globally, 137 countries have pledged to achieve carbon neutrality by, for the most part, 2050. Governments and states worldwide are taking measures to lower GHG emissions through subsidies and legislation, including the transportation sector, which accounts for 14% of the world’s GHG emissions.

With aviation responsible for 8% of the transport sector’s emissions, there is no way the industry can fly under the radar. Change is coming, and that means sustainable aviation fuel (SAF) will be under the spotlight, with projected demand of around 15 Mt in 2030 and 200 Mt in 2050. Eventually, and as is our collective aim, both renewable jet and e-Jet fuels are expected to overtake fossil jet fuel.

Change has been coming for some time. Indeed, since 2008, airlines have been exploring the potential of SAF. However, so far, uptake has been slow, and by 2019 SAF accounted for just 0.1% of all fuel consumed by the aviation industry. In terms of ambition and tangible action, it has only been the last year or so since we have started seeing real change.

In 2022 airlines bought every drop of SAF available worldwide, test flights are being run partially or fully powered by SAF, and regulations reducing barriers to entry are anticipated to come into effect. All of which is great news for efforts to decarbonise aviation.

Routes to SAF certification
Aircraft flying around the world will be fuelled at different airports in different countries, making international fuel specifications for SAF a necessity. According to the International Civil Aviation Organisation (ICAO), there are currently 59 airports worldwide distributing SAF. Europe and the US are the main hubs, with ongoing deliveries also occurring in Malaysia, Japan, New Zealand, and at China’s Tianjin Airport.

We already see current specifications ensuring that today’s engines and aircraft do not have to be redesigned to run on SAF, thus making the transition even more achievable. At present, the focus is on SAF as a drop-in replacement to conventional jet fuel. Moreover, with current ASTM standards excluding the use of pure SAF in aircraft, a 50% blend is most common, with a maximum 10% blend available in some cases.

There are currently seven approved technology pathways to producing drop-in SAF (see Table 1). Co-processing, as seen in Table 2, is another option for decarbonising aviation and meeting the criteria for the Standard Specification for Aviation Turbine Fuels (D1655). Co-processing, which involves the simultaneous processing of fossil and renewable feedstocks, means you can use existing refining, transport, and storage facilities. This, in turn, makes it possible to convert renewable feedstocks into drop-in, ultra-low sulphur renewable jet or e-Jet fuel at economically competitive prices.

Topsoe routes to SAF
At Topsoe, we have identified the main routes we consider to be the most commercially advanced. Firstly, we have HydroFlex, which offers full feedstock flexibility whatever raw material you choose to work with. Since no two refineries or feedstock supply chains are the same, we have tailored our approach to make HydroFlex as dynamic as possible. This means more businesses will have the opportunity to use this type of SAF.

This technology utilises Topsoe’s hydroprocessing expertise to enable the processing of virgin oils, waste oils and fats, solid biomass, and plastic waste/tyres into HEFA-based SAF with minimal Carbon Intensity (CI) compared to traditional kerosene aviation fuel. Regardless of the type or quality of renewable feedstock used, the outcome is consistently high-grade, clean fuel. HydroFlex also has a high number of operating references, offers versatile process design and hardware, and comes with a comprehensive range of proprietary catalysts for renewable fuel production.

Gasified waste could be an alternative source of choice, in which a producer takes the synthetic- and gas-based route with G2L Biofuels (Gas-to-Liquid). This commercially proven technology utilises Topsoe’s hydroprocessing technologies and Sasol’s LTFT (low temperature Fischer-Tropsch) technology to produce Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK) (see Figure 1).

Further, we have G2L e-Fuels, which allows e-Fuels to be produced from green hydrogen (stemming from renewable electricity and electrolysis) and CO₂ via carbon capture. By combining synthesis gas, Fischer-Tropsch and hydroprocessing technologies, the G2L e-Fuels solution efficiently produces FT-SPK/e-Jet and green naphtha (see Figure 2). This technology results in an overall carbon efficiency of 95%+.

Feedstock availability can cause turbulence
SAF can be produced from various renewable feedstocks, including vegetable oils, waste oils and fats, solid biogenic waste, industrial flue gases, CO₂, renewable electricity, and water. As the market for and production of SAF increases, so will the need for suitable feedstocks. There are many reasons for this, not least because other segments and industries are pursuing the same feedstocks for different purposes, like road transport, marine fuel, and petrochemicals. For example, producing SAF from waste oils is the most technically mature SAF conversion pathway. However, waste oils are highly resource-constrained and are already largely consumed by the road sector. This could become a seriously limiting factor in our journey to decarbonising aviation.

But what does this have to do with legislation? The use of feedstocks, in particular first-generation renewable feedstocks, is highly regulated in some parts of the world, like the EU, with direct implications for the biofuel production required to supply mandated volumes. The International Council on Clean Transportation (ICCT) estimates that there is a resource base to meet approximately 5.5% of the EU’s projected 2030 jet fuel demand using advanced SAF – SAF that could be made from solid biomass waste, rotational crops, or recycled carbon. However, if the EU adopts weaker incentives, they estimate a maximum advanced SAF deployment of only 1.9% of the projected 2030 EU jet fuel demand. Regardless, SAF capacity derived from first- and second-generation feedstocks will not be enough to help the whole world fly sustainably.