The commercialization and diversification of SAF production technologies have been limited thus far. Currently, the hydroprocessed esters and fatty acids (HEFA) process dominates the production pipeline due to its proven commercial viability. While the HEFA pathway is currently the most mature and widely adopted method for SAF production, its limitations highlight the necessity for diversifying production pathways.

The HEFA pathway primarily depends on lipid-rich feedstocks such as used cooking oil (UCO), animal fats, and oilseed crops. However, the availability of these feedstocks is limited, and there is potential competition with food production and other biofuel applications. This dependency poses a risk to the scalability and sustainability of SAF production.

Diversification in production pathways is essential to address these limitations, enhance feedstock availability, and ensure a stable and resilient supply chain for SAF.

By exploring various production pathways, we can tap into a broader range of feedstocks, leverage different technological processes, and mitigate the risks associated with over-reliance on any single method. This chapter delves into the different production pathways for SAF, examining their feedstocks, processes, advantages, and limitations.

There are various SAF production pathways, each at different levels of commercialization. These pathways differ in their feedstock sources and have varying limitations when it comes to blending with conventional jet fuel. The industry is exploring multiple options to develop and scale up SAF production, reflecting the diverse approaches being pursued in this field. This chapter focuses on four key pathways which are summarised in Figure 12 : HEFA, ATJ, Gasification Fischer-Tropsch (GFT), and PtL.

HEFA currently dominate the SAF market, accounting for over 90% of production. HEFA utilizes oil-based feedstocks such as jatropha, algae, camelina, and yellow grease. It has a blending limitation of 50% and is at an advanced stage of commercialization. However, it faces significant constraints in sustainable feedstock supply, which may impact its long-term scalability.

Emerging technologies like ATJ and GFT are at earlier stages of commercialization but show promise in unlocking more abundant and lower-cost feedstocks. ATJ, for instance, utilizes cellulosic biomass and can blend up to 50%. This pathway is still developing but offers significant potential for scaling up using diverse biomass sources. GFT, which can also blend up to 50%, uses municipal solid waste and energy crops as feedstocks. GFT is poised to leverage the vast amounts of waste materials available, thus presenting a viable route for large-scale SAF production in the future.

PtL represents a cutting-edge approach by offering a fully synthetic route to carbon-neutral fuels. While PtL is still in the early stages of commercialization, it promises to produce SAF with a minimal carbon footprint by synthesizing fuels from carbon dioxide and water using renewable energy. This pathway can achieve a 50% blend with conventional jet fuel and is expected to become a critical technology for long- term sustainability in aviation.

The remainder of this chapter presents four leading SAF production pathways, focusing on their technology readiness, current production capacity, cost competitiveness, highlights notable projects and partnerships exemplifying the status and trajectory of each technology. Finally, we will share our perspective on how the SAF production mix is likely to evolve in the near, medium, and long term.

ATJ technology converts alcohols derived from various sources into jet fuel. The process, also known as alcohol oligomerization, utilizes alcohols such as methanol, ethanol, butanol, and long-chain fatty alcohols as feedstocks. ATJ offers a promising pathway for developing drop-in or fungible SAF, overcoming the blend wall limitation of ethanol in gasoline- powered vehicles, which is typically capped at 10-15%. One notable subset of ATJ is methanol-to-jet (MTJ), which specifically focuses on converting methanol into jet fuel.

Companies at the forefront of ATJ commercialization, such as Lanzajet, Gevo, and Velocys, are retrofitting existing facilities or constructing new ones to convert diverse feedstocks into SAF. Lanzajet focuses on retrofitting ethanol plants to minimize environmental impact, while Gevo utilizes corn starches, and Velocys converts municipal waste. The ability to use abundant, lower-cost waste materials as feedstocks is a significant advantage of ATJ, potentially providing a more sustainable and economical method of SAF production compared to traditional oils. MTJ, as a subset of ATJ, also benefits from these advantages, as methanol can be derived from various sources, including biomass, municipal waste, and industrial gases.

However, ATJ face several challenges in scaling up to commercial production. The capital costs associated with ATJ facilities are higher compared to traditional refineries, which can hinder investment and adoption. Additionally, the technology needs to demonstrate its viability at a commercial scale to attract further investment and support. To boost ATJ’s viability and accelerate its deployment, policy support through incentives such as tax credits, loan guarantees, and LCFS is crucial.

GFT is another promising method for converting various types of waste materials such as municipal solid waste (MSW), agricultural residues, and forestry wastes into SAF. This process involves several steps: first, biomass undergoes gasification to produce syngas, a mixture primarily composed of carbon monoxide (CO) and hydrogen (H2). This syngas is then purified and conditioned to remove impurities before being converted into liquid fuels (DoE, 2023).

GFT offers distinct advantages, particularly the utilization of non-food feedstocks at relatively low costs. Historically, GFT technology has been employed to produce liquid fuels from coal and natural gas. However, adapting it to handle heterogeneous waste streams poses challenges, particularly in ensuring the syngas purity meets the stringent requirements for efficient Fischer-Tropsch catalysis (Worley, 2024).

In terms of commercialization, GFT is still in its early stages compared to other SAF production methods like HEFA and ATJ. Currently, a few companies are pioneering commercial-scale GFT biorefineries:

Fulcrum BioEnergy is launching a plant in Nevada designed to process 175,000 tons of household garbage annually (WEF, 2024).

Red Rock Biofuels is constructing a facility in Oregon aimed at converting 136,000 tons of wood waste into 15 million gallons of GFT jet and diesel fuel annually (WEF, 2024).

Velocys is developing a GFT plant in Mississippi with plans to process 100,000 tons of wood waste annually, yielding 20 million gallons of SAF (WEF, 2024).

One of the primary challenges facing GFT is its high capital cost. For instance, Fulcrum BioEnergy’s Nevada biorefinery required an investment exceeding $500 million to achieve an annual output of 11 million gallons. To overcome this financial hurdle, developers have relied heavily on government grants, loan guarantees, and long-term offtake agreements to secure positive final investment decisions. Additionally, policies such as low carbon fuel standards in states like California, Oregon, and Washington are crucial as they enhance project viability and attract investment by improving financial returns as projects scale up and technology designs are optimized. These standards create a market demand for SAF, thereby supporting the economic feasibility of GFT facilities.

PtL represents the future vision for creating carbon- neutral jet fuels using renewable electricity, water, and atmospheric CO2. This process, also known as electrofuels, starts with renewable power splitting water to produce green hydrogen. This hydrogen is then combined with captured CO2 to synthesize liquid hydrocarbons using established methods such as FT or MTJ.

PtL technologies offer several advantages over traditional biofuel methods by eliminating the constraints and sustainability issues associated with biomass feedstocks. Unlike biofuels, which rely on agricultural or waste biomass, PtL processes use electricity and water, avoiding concerns like land use limitations, deforestation, and soil degradation. This makes PtL a more sustainable and scalable solution for fuel production.

Geographically, PtL can be deployed wherever there is access to low-cost renewable energy sources such as solar, wind, or hydroelectric power. This capability allows for fuel production in regions unsuitable for biomass cultivation, decentralizing production and reducing transportation emissions and costs. By utilizing abundant renewable energy sources, PtL enhances energy security and market stability.

From an environmental standpoint, PtL offers near- zero lifecycle GHG emissions by capturing CO2 from the atmosphere to synthesize fuel. By using renewable energy throughout the process, PtL minimizes additional GHG emissions, aligning with global climate objectives and reducing dependence on fossil fuels. This sustainable approach to carbon recycling helps mitigate the overall carbon footprint of the fuel.

The fuels produced by PtL meet all specifications required for jet fuels and are compatible with existing jet engines without modifications (McKinsey, 2022). This compatibility facilitates a seamless transition from fossil fuels to sustainable alternatives, accelerating the adoption of cleaner aviation fuels and significantly reducing the environmental impact of the aviation industry.

However, PtL faces significant economic and scaling challenges. The cost of renewable hydrogen from water electrolysis is currently higher than hydrogen derived from fossil fuels, and carbon capture is energy- intensive. Under optimistic conditions of low-cost renewable electricity and affordable carbon capture technologies, PtL could potentially achieve cost parity with petroleum jet fuel by 2040, but this would require substantial investment in renewable power capacity dedicated to hydrogen production (WEF, 2024).

Initial commercial PtL plants are expected to be much smaller than traditional refineries, producing between 10 to 100 million litres per year. For instance, Norsk e-Fuel is developing a 10 million litre PtL pilot plant in Norway using wind power and direct air capture, while Synhelion is piloting a novel solar thermochemical approach at a smaller scale in Germany, Spain, and Chile.

In essence, PtL represents a promising pathway towards SAF, leveraging renewable resources to produce drop-in fuels that meet stringent industry standards while minimizing environmental impact. However, overcoming economic and scaling challenges will be crucial for realizing its full potential.

Leading energy companies are investing in PtL technology to gain an early-mover advantage. Sunfire and Climeworks are collaborating on PtL technology, while Lufthansa is exploring its integration into future fuel supplies.

Although PtL offers the most promising long-term solution for carbon-neutral aviation, its widespread adoption faces challenges. In the near term, HEFA will remain the dominant SAF production method, with ATJ and GFT beginning commercial-scale operations. Government support and industry commitments are crucial for improving economics and driving scale-up across all pathways through 2050.

The choice of SAF pathway depends on regional factors such as feedstock availability, costs, and carbon reduction goals. Increasing biofuel demand could strain agricultural production, highlighting the need to prioritize waste residues and synthetic PtL routes. A diversified approach across multiple pathways, guided by sustainability criteria and supportive policies, is essential to meet aviation’s decarbonization targets.