What is SAF?
Sustainable Aviation Fuel (SAF) is a cleaner alternative to conventional fossil jet fuel, designed to reduce greenhouse gas emissions from aviation. SAF is made from renewable sources like plant oils, waste fats, municipal waste, and agricultural residues. Unlike traditional jet fuel, which is derived from crude oil, SAF can lower carbon emissions by up to 80% over its lifecycle, depending on the feedstock and production methods used.
SAF works as a "drop-in" fuel, meaning it can be blended with conventional jet fuel without requiring changes to aircraft engines or fueling infrastructure. This flexibility makes it easier to integrate into existing aviation operations. The adoption of SAF is a key part of the aviation industry's strategy to achieve net-zero emissions by 2050.
Though SAF has a smaller environmental impact, challenges include high production costs, limited availability, and the need for scaling up production. However, as demand grows and technology advances, SAF is expected to play a crucial role in decarbonizing aviation and reducing its environmental footprint.
SAF Production Pathways
There are several SAF production pathways that have been approved by international aviation regulatory bodies like ASTM International (formerly the American Society for Testing and Materials). Each pathway converts various types of feedstocks into jet fuel that meets strict performance and safety standards. As of now, the following production pathways have been approved for SAF:
1. HEFA-SPK (Hydroprocessed Esters and Fatty Acids – Synthetic Paraffinic Kerosene)
- Feedstock: Used cooking oils, animal fats, vegetable oils, and other lipid-rich materials.
- Process: Hydroprocessing is used to convert oils and fats into hydrocarbons that resemble traditional jet fuel.
- Blend Limit: SAF produced by HEFA-SPK can be blended with conventional jet fuel up to 50%.
2. FT-SPK (Fischer-Tropsch – Synthetic Paraffinic Kerosene)
- Feedstock: Biomass, municipal solid waste, and other carbon-rich materials.
- Process: Biomass undergoes gasification to produce syngas, which is then converted into liquid hydrocarbons using the Fischer-Tropsch process.
- Blend Limit: Can be blended with conventional jet fuel up to 50%.
3. ATJ-SPK (Alcohol-to-Jet – Synthetic Paraffinic Kerosene)
- Feedstock: Sugars, starches, and lignocellulosic biomass are fermented to produce alcohols like ethanol or isobutanol.
- Process: The alcohols are chemically converted into jet fuel components via dehydration, oligomerization, and hydrogenation.
- Blend Limit: SAF produced by ATJ-SPK can be blended up to 50% with conventional jet fuel.
4. SIP (Synthetic Iso-Paraffins) / HFS-SIP (Hydroprocessed Fermented Sugars to Synthetic Iso-Paraffins)
- Feedstock: Sugar-rich materials, such as sugarcane or corn.
- Process: Sugars are fermented to produce a molecule called farnesene, which is then hydrogenated into a hydrocarbon suitable for jet fuel.
- Blend Limit: SAF produced by SIP is limited to a 10% blend with conventional jet fuel.
5. FT-SPK/A (Fischer-Tropsch with Aromatics)
- Feedstock: Biomass, municipal solid waste, and carbon-rich materials.
- Process: Similar to FT-SPK, but the process includes an additional step to produce aromatic compounds necessary for fuel density and other properties.
- Blend Limit: Can be blended with conventional jet fuel up to 50%.
6. CHJ (Catalytic Hydrothermolysis Jet)
- Feedstock: Plant oils and animal fats.
- Process: Hydrothermolysis is used to break down oils and fats into jet fuel-like hydrocarbons, which are then refined to meet fuel standards.
- Blend Limit: Can be blended with conventional jet fuel up to 50%.
7. IH2 (Integrated Hydropyrolysis and Hydroconversion)
- Feedstock: Biomass and other organic materials.
- Process: Biomass is subjected to high temperatures and hydrogen to produce hydrocarbons in a single step, followed by refining to meet jet fuel specifications.
- Blend Limit: Still in development with varying blend limits.
These pathways are in various stages of commercial deployment, with HEFA being the most mature and widely used. The blend limits imposed on SAF ensure that the fuel can be used safely without affecting aircraft performance or requiring modifications to engines. As technology advances, additional pathways may be approved, and the blend limits may increase.
What are SAF Benefits?
- Significantly reduces emissions of greenhouse gases compared with petroleum-based jet fuel
- Reduces emissions of harmful compounds around airports during take-off and landing
- Powers aircraft with similar properties as conventional jet fuel
- Domestically produced in support of U.S. energy independence