Decarbonisation Technology - May 2024 Issue

Technology pathways for sustainable aviation fuel (SAF) To meet CO 2 emissions reduction targets by 2050, accelerating the development and deployment of SAF is the best option to decarbonise the aviation industry

Svetlana van Bavel and Chippla Vandu Shell Catalysts & Technologies

R efiners have successfully utilised easier- to-process used cooking oils (UCO) and animal fats to produce bio-SAF for some time. Given concerns about the limited availability of these feedstocks, fuel suppliers will need to process more challenging feedstocks, such as biomass residues and renewable (green) hydrogen and carbon dioxide (CO₂). In particular, synthetic aviation fuels (eSAF) made using power-to-liquids (PTL) technology have high potential owing to the virtually limitless supply of feedstocks, namely solar and wind energy or nuclear power, water, and CO₂. Combining the production of eSAF using PTL and bio-SAF made using biomass- to-liquids (BTL) technology can be an enabler for early projects. Crucially, the technologies for eSAF and bio-SAF have high technology readiness levels. Aviation is one of the fastest-growing sources of greenhouse gas (GHG) emissions and one of the most challenging sectors to decarbonise. At present, aviation is responsible for a relatively small proportion of global GHG emissions, viz. 3% in 2019, though the environmental impact of air traffic goes beyond CO₂ emissions, as the formation of contrails and clouds amplifies its overall climate effects. Although air travel fell significantly during the COVID‐19 pandemic, it rebounded strongly in 2023, coming very close to the pre-COVID peak level, and is expected to continue to grow. While advances in aircraft design have enhanced operational efficiency, with newer models consuming up to 20% less fuel, the surge in air traffic can be expected to negate these gains. As a result, international aviation

could contribute up to 22% of global carbon emissions by 2050. Difficulties in decarbonising aviation can be attributed to several factors. Aircraft have long lifespans so it would take decades to replace the existing fleet. Safety requirements mean high scrutiny and long lead times for the adoption of new technologies, such as battery-electric or hydrogen-powered aircraft, especially for long-haul flights. Consequently, the industry will continue to rely on high-energy-density fuels such as kerosene for decades. In addition, there are significant costs associated with many decarbonisation solutions, especially solutions that require modifications to aircraft and fuel supply infrastructure. The aviation industry will, therefore, need to use all available solutions and measures to decarbonise – no single solution will be enough on its own – and SAF is the only scalable in-sector option to help materially reduce emissions in the period to 2050. Specifications for SAF ensure it can be used as a drop-in fuel, allowing it to be blended with conventional kerosene-based jet fuel and used in the world’s existing aircraft fleet without the need for redesign or upgrade. When used unblended, currently available SAF, made from hydroprocessed esters and fatty acids (HEFA), has the potential to cut “ SAF is the only scalable in-sector option to help materially reduce emissions in the period to 2050 ”