The aviation industry faces a formidable challenge in its journey towards decarbonisation. It currently contributes around 1bn t/y of CO₂ (2.4% of all global CO₂ emissions) to the atmosphere. However, the sheer scale of this industry, with thousands of aircraft and extensive global infrastructure, presents many unique obstacles.

While new fuels and engine technologies offer possibilities for the future, these require billions in investment in new equipment and are certainly not going to bear significant fruits for many years to come. SAF offers the most viable solution today by creating a bio-based alternative that is compatible with existing aircraft and infrastructure.

Understanding SAF 
SAF represents a new era in aviation fuel technology. Unlike conventional jet fuels derived from fossil sources, SAF is produced from sustainable resources such as plant materials and waste oils. Its significance lies in its ability to seamlessly integrate into the current aviation system. Aircraft can use SAF without any modifications, making it a ‘drop-in’ solution that aligns with existing fuelling infrastructure and engines.

However, the term ‘sustainable aviation fuel’ can be misleading. Not all SAFs are created equal. The current market offers various SAF blends, each with different properties and sustainability credentials. The term often encompasses a range of bio-based fuels, including blends with conventional jet fuel, thus only marginally reducing emissions.

The success of the recent Virgin Atlantic trans-Atlantic flight powered entirely by drop-in 100% SAF marks a significant breakthrough. Although there are still many challenges to overcome for the industry to fully transition to SAF, this milestone demonstrates the potential of SAF in meeting aviation emission reduction targets. But how was this remarkable feat achieved?

The term ‘sustainable aviation fuel' can be misleading. Not all SAFs are created equal.

The key to unlocking the full potential of SAF lies in overcoming the challenges associated with its composition. Traditional jet fuel contains aromatic compounds. These ring-shaped molecules are an important component of the fuel as, among other benefits, they enhance lubricity, lower freeze point and interact with polymer seals in the engines and fuelling systems to help prevent fuel leakage. Most bio-based fuels, including popular options like hydroprocessed esters and fatty acids (HEFA) and Fischer-Tropsch (FT) products, lack these aromatic compounds. This limitation has historically restricted SAF blends to a maximum of 50% when mixed with conventional jet fuel.

Addressing this challenge is synthesised aromatic kerosene (SAK), a bio-based, aromatic-rich component, which can be blended with other SAF pathways like HEFA or FT products to create drop-in 100% SAF. Virent, the original inventor of BioForming^® sugars-to-aromatics (S2A), and Johnson Matthey have been working in close collaboration on this technology, which uses biomass sugars as feedstock. This innovation means 100% bio-based fuels can meet current jet fuel standards, offering a sustainable, high-performance fuel alternative.

The aviation industry faces a formidable challenge in its journey towards decarbonisation

Photo: iStock

Environmental and economic implications 
The environmental benefits of drop-in 100% SAF are clear. By reducing reliance on conventional fuels, SAF significantly cuts aviation’s carbon footprint. Moreover, the cleaner-burning nature of SAK leads to lower emissions of particulates and other pollutants, contributing to improved air quality. Indeed, compared with conventional jet fuel, SAK can reduce fine particulate emissions by up to 80%.

Economically, the transition to SAF is also advantageous. It leverages existing infrastructure and technology and avoids the need for costly, logistically problematic overhauls. This compatibility with current systems makes it an appealing option for a swift reduction in the environmental impact of the aviation industry.

SAK supplies the necessary aromatics for jet fuel and can be blended with a range of other SAF, accelerating the shift from conventional fuel to sustainable alternatives compatible with existing aviation technology. The various demonstration flights using BioForm^® SAK have also shown that SAK can be a ‘normaliser’ to ensure different SAF blendstocks can be brought within specification and meet aviation performance criteria.

The journey towards decarbonising aviation is complex and multifaceted. SAF blended with BioForm SAK offers a promising path forward, but its success hinges on several factors. The production of SAF must scale up to meet the demands of the global aviation industry. This expansion requires significant investment in production facilities and the development of robust supply chains.

Flexible feedstocks are an essential element in increasing SAF production. While the initial Virgin Atlantic flight used BioForm SAK produced from dextrose from corn, the synthetic aromatics can be created using a wide range of plant sugars, including beet sugar, sugar cane and corn starch, as well as cellulosic sugars produced from bagasse, corn stover, grasses, sorghum and wood, and other soluble carbohydrates. This means it is not reliant on a limited source of feedstocks and the process can be adapted to the different resources available in different regions of the world.

Currently only 0.1% of jet fuel used by US airlines is SAF and price differentials with conventional jet fuels need to be addressed. Policy support is, therefore, another crucial factor if SAF is to become a practical and viable solution to reduce aviation emissions. Governments and international bodies need to create frameworks and incentives to level pricing and encourage the production and use of SAF. Incentives, regulations and targets can drive investment and innovation in this space, propelling the industry towards a more sustainable future.

Government legislation is already supporting adoption of the new fuel. For example, the US is aiming for the equivalent of 10% SAF by 2030 and 100% by 2050, supported by its Inflation Reduction Act (IRA), which offers tax incentives for SAF production and use.

The European Union has targeted 6% SAF by 2030 and 70% by 2050, driven by proposed non-compliance penalties to mandate offtakes and kickstart large-scale SAF production. The UK has committed to introducing a mandate requiring 10% SAF by 2030. Globally, the combined measures present the potential to level the playing field between conventional and sustainable fuels.

The cost of producing and supplying SAF also needs to be addressed. The UK government has suggested buy-out prices in the range of £2 per litre (£/l) for SAF or £2.75/l for power-to-liquid (PtL) in its consultation on the UK SAF mandate. This compares with conventional Jet-A pricing around £0.44/l. Moves such as these along with ramp-up of production capacity should reduce the pricing differential of SAF with conventional jet fuel and help facilitate the economic viability of wider SAF usage.

The advent of drop-in 100% SAF, exemplified by Virgin Atlantic’s historic flight, is a testament to the potential of bio-based fuels in transforming aviation. As the industry grapples with the urgent need to reduce its carbon footprint, SAF stands out as a viable, immediate solution. The technology developed in collaboration with Virent paves the way for a new era in aviation fuel, one that promises to significantly reduce emissions without compromising performance or necessitating extensive changes to existing infrastructure. As we look to the future, SAF emerges not just as an alternative fuel, but as a cornerstone in the aviation industry’s sustainable transformation.

The views and opinions expressed in this article are strictly those of the authors only and are not necessarily given or endorsed by or on behalf of the Energy Institute.

The views and opinions expressed in this article are strictly those of the author only and are not necessarily given or endorsed by or on behalf of the Energy Institute.