Sustainable Aviation Fuel: Challenges of Scale

By Tony Cartolano, Lee Enterprises Consulting
In 2021, the US Department of Energy announced its Sustainable Aviation Fuel Grand Challenge.[1] The intent was to supply at least three billion gallons of SAF per year by 2030 and to produce sufficient SAF to meet 100% of aviation fuel demand by 2050 (currently projected to be around 35 billion gallons per year). The goal was ultimately to achieve at least a 50% reduction in CO₂ emissions. Since then, several industry participants have weighed in on this “SAF v. petroleum-based jet fuel” conversation.

Corporate Resistance

In January 2022, Valero Energy Corp said that tax incentives for sustainable aviation fuel (SAF) in U.S. President Biden’s stalled Build Back Better legislation were not enough for the oil refiner to consider producing it instead of renewable diesel. “The incentive level proposed in that bill was not sufficient to attract additional investment to make SAF versus the base case of producing renewable diesel with an existing unit,” said Martin Parrish, senior vice president of alternative fuels at Valero, on the company’s fourth-quarter earnings call.

In November 2022, Paul Abbott, CEO of American Express Global Business Travel, said that 300 SAF plants would need to be built if the industry wanted to get to (as a practical example) 10 percent sustainable fuel by 2030. He argued there weren’t enough financial incentives to scale up the production of that fuel fast enough. In June 2023, the group noted that SAF makes up less than 0.1% of available aviation fuel today and is two- to eight times more expensive than conventional fossil-based jet fuel, as reported by IATA.

In May 2023, Boeing CEO, Dave Calhoun, told the Financial Times that SAF would “never achieve the price of jet fuel”. Opining on the aviation industry’s solutions for reaching net zero by 2050, Calhoun noted that while SAF was a more environmentally positive fuel, its cost would never be competitive with petroleum-based jet fuels.

Can SAF Compete With Petroleum-Based Jet Fuels?

Can SAF compete? Possibly. Certainly, SAF can have environmental benefits. Produced from renewable sources such as plant biomass, waste oils, or algae, it can significantly lower the carbon footprint (leading to reduced greenhouse gas emissions) compared to fossil-based jet fuel. As aviation continues to face increasing pressure to reduce its environmental impact, SAF becomes an attractive alternative.

Many airlines and aviation companies are currently making voluntary commitments to reduce their carbon emissions and achieve carbon-neutral growth. Most are increasing their investment in SAF and collaborating with producers to scale up its production. Governments and international bodies are implementing policies and regulations to support the use of SAF. This demand from the aviation industry will drive competition and work to reduce the cost of SAF, while industry and government support will continue to create a favorable market for SAF and incentives for its adoption.

SAF Technologies

To transform biomass into hydrocarbon fuels, oxygen must be removed and the long-chain molecules like cellulose and hemicellulose, need to be reduced to smaller molecules for ease of handling and combustion. Geologic activity has performed this action on buried biomass over hundreds of millions of years.  We are now seeking to perform this conversion on human time scales, which means we will need to make large investments in equipment to perform this transformation.

On average, biomass contains about 44% oxygen by weight.  Typically, this oxygen is removed by either combining with the contained carbon to create CO₂ or by combining with hydrogen to create water.  As Forsberg and Dale discussed in a recent article, to reduce the carbon footprint of biomass conversion processes, it would be beneficial to use hydrogen to remove oxygen from biomass to produce hydrocarbon fuels.

The industry started producing SAF through a low “cost of entry” process – hydrogenation of fats and oils, or hydro-processed esters and fatty acids (HEFA). This involves a relatively easy conversion of refinery assets to start producing SAF. The feedstock is a liquid, like crude oil, and refiners have experience and knowledge around hydrotreating. In the long term, however, serious questions remain about the supply of fats and oils to meet aviation needs.

Other promising technologies appear to be scalable to the required volumes. These include Fischer-Tropsch (FT) and alcohol-to-jet (ATJ). FT requires the gasification of municipal solid waste (MSW) or agricultural material (including forestry materials) to produce syngas, which is then converted to SAF. ATJ can use syngas as well to produce alcohols, or the alcohols can be produced by fermentation of various sources of biomass. To reduce the CO₂ footprint of these technologies, large quantities of sustainable hydrogen will be needed, which presents another issue: how to get sustainable or green hydrogen cost-effectively.  Forsberg and Dale suggest using nuclear energy, which presents additional development and capital investment hurdles.[2]

Most of the technologies in development have the potential to produce SAF that meets the current ASTM standards.[3] However, they are currently approved only as blendstocks up to 50% in concentration. One of the reasons for this is that they produce “linear” or paraffinic hydrocarbons. While acceptable as fuels, they do not provide the protection of jet engine seals. The aviation fuel requirements call for a certain percentage of “aromatic” compounds to prevent fuel leaks in the engines. Therefore, additional technology will be needed to produce renewable aromatic compounds suitable for use in jet fuel, if SAF is to move beyond the 50% blend limits.

Continuous research and development efforts are constantly improving the production processes and cost-efficiency of SAF. As these large investments in technologies are made, our knowledge of how to reduce the production costs of SAF should increase, as it has done for petroleum refining.  It will take this large investment in development and production capabilities to determine whether SAF will present a viable alternative to fossil-based jet fuel.

Conclusion

SAF has the potential to provide price stability for airlines as they become less reliant on severely fluctuating fossil fuel prices. While the initial production costs of SAF today look to be higher, the potential for long-term price stability and reduced exposure to price volatility are attractive options for airlines.

There are still challenges to overcome for SAF to present an alternative to fossil-based jet fuel. The industry must scale up production to meet aviation industry demand, ensuring a sustainable and diversified feedstock supply, and reducing the production costs to be somewhat comparable with fossil fuels, while providing the desired reduction in CO₂ emissions. Continued research, technological advancements, and supportive policies are crucial initially to overcome these challenges and make SAF a viable alternative to fossil-based jet fuel.

As new technologies continue to be developed, there will always be a need for technical and techno-economic evaluations as these technologies move toward commercialization. Investors need to know the costs of producing SAF, and how each technology can be scaled up to produce the volumes needed. As more incentives for SAF appear through capital support or fuel credits, there will be an increasing need for expertise to help navigate these regulations and obtain these incentives. In all this process, expertise continues to be needed to shepherd the SAF pathways through the approval process so that 100% SAF can be used. This will likely include the development of a process or processes to incorporate renewable aromatic components into the blend and the cost-effective production of green hydrogen.

About the Author.  Tony Cartolano, EngScD, has over 35 years of experience in chemical process research, process development, and process engineering and serves as a Project Director at Lee Enterprises Consulting, overseeing matters involving Pyrolysis, Hydrogenation, Intellectual Property, Chemical Processes, Process Engineering, Technology Assessments, Scale-Up, and Pilot Plants. 

[1] https://www.whitehouse.gov/briefing-room/statements-releases/2021/09/09/fact-sheet-biden-administration-advances-the-future-of-sustainable-fuels-in-american-aviation/

[2] W. Forsberg and B. Dale, “Can large integrated refineries replace all crude oil with cellulosic feedstocks for drop-in hydrocarbon biofuels?”, Hydrocarbon Processing, January 2023.

[3] As a bit of background, ASTM D7566 is the “Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons.” The process to be approved as SAF under this standard is covered in ASTM D4054, “Standard Practice for Evaluation of New Aviation Turbine Fuels and Fuel Additives.”  SAF certified under D7566 is blended with conventional jet fuel up to its maximum allowed blend ratio. As of April 2023, nine conversion processes for SAF production have been approved and eight other conversion processes are currently under evaluation (ICAO).