The evolution of SAFs is marked by their source materials and technological advancements, categorized into four distinct generations:

Generation 1 SAFS:

Feedstock: Derived from food crops such as vegetable oils and animal fats.

Characteristics: Established technology but raises sustainability concerns due to competition with food resources and potential indirect land use changes.

Generation 2 SAFS:

Feedstock: Utilizes non-food biomass, including agricultural and forestry residues, and municipal solid waste (MSW).

Characteristics: Offers a more sustainable solution by avoiding food resources, with some technologies still scaling to commercial levels.

Generation 3 SAFS:

Feedstock: Produced from microorganisms like algae, which convert sunlight and CO2 into oils.

Characteristics: In the R&D phase, it promises high scalability without agricultural land use but faces cultivation and processing challenges.

Generation 4 SAFS:

Feedstock: Focuses on synthetic processes using captured carbon and green hydrogen.

Characteristics: Represents the cutting-edge of SAF technology with the potential for minimal or negative carbon emissions, though still in early development stages.

Summary:

Generation 1: Established but with sustainability issues.

Generation 2: Emerging technologies with a better sustainability profile.

Generation 3: High potential but currently in R&D.

Generation 4: Innovative with a vision for carbon-negative fuels, yet to reach commercial viability.

Categories Of SAFs

Aviation has historically relied on fossil fuels, which are high in carbon sequestered over millennia, leading to increased atmospheric CO2 when burned. Transitioning to more sustainable energy sources, two main categories of SAFs stand out: biofuels and synthetic fuels, each with unique origins and production processes. 

Biofuels

Biofuels are produced from biological sources like plants, algae, or organic waste. Their production involves biological conversion methods, such as fermentation or esterification. As biofuels come from biomass that has absorbed CO2 from the atmosphere, their combustion is considered to release this recently captured CO2, making them part of a shorter carbon cycle. Examples include fuels made from vegetable oils or waste oils.

Synthetic Fuels

Synthetic fuels, also known as synfuels, are not derived from current biological processes but are manufactured through chemical reactions. These reactions transform various feedstocks into liquid fuels. Sustainable synthetic fuels are produced using feedstocks from renewable or non-fossil carbon sources, maintaining a balanced carbon cycle. Feedstock sources for sustainable synthetic fuels may include biomass, atmospheric or industrial CO2, and other renewable carbon-rich materials. However, carbon sourced from non-renewable sources like natural gas or coal is less sustainable. Common synthetic fuel production methods include Gas-to-Liquid (GTL) and Power-to-Liquid (PtL).

E-Fuels (E-SAFS)

E-fuels, a subset of synthetic fuels specifically for aviation, are generated using electricity to perform electrolysis on water, producing hydrogen that combines with captured CO2. The carbon neutrality of e-fuels hinges on using renewable energy for production and efficient CO2 capture. E-fuels can significantly reduce an aircraft’s carbon footprint when synthesized correctly.

Production of e-fuels on a large scale depends on abundant renewable electricity and advanced CO2 capture technology, highlighting the need for ongoing research and development in these areas for their practical use in aviation.

“Production of e-fuels on a large scale depends on abundant renewable electricity.“