Sustainable
Aviation Fuel

1. Biomass Feedstock Preparation 

• Feedstock Types: Common biomass feedstocks include agricultural residues (like corn stover, straw), forestry residues (wood chips, sawdust), and dedicated energy crops (switchgrass, miscanthus). 

• Pre-treatment: The biomass is pre-treated to ensure uniformity and reduce moisture content. This may involve drying, grinding, and sometimes pelletizing the biomass to facilitate efficient gasification. 

​

2. Gasification 

• Process: The prepared biomass is fed into a gasifier, where it is subjected to high temperatures (700-1500°C) in a controlled environment with limited oxygen. 

• Reaction: Under these conditions, the biomass undergoes thermochemical conversion into a synthesis gas (syngas), a mixture primarily composed of carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂), and small amounts of methane (CH₄) and other gases. 

• Syngas Composition: The syngas composition can be adjusted by varying the gasification conditions, such as temperature, pressure, and the amount of oxygen or steam. 

​

3. Syngas Cleanup and Conditioning 

• Process: The raw syngas produced from gasification contains impurities such as particulates, tar, sulfur compounds, and other contaminants that must be removed. 

• Cleaning Steps: The syngas is passed through several cleaning processes, including filtration, scrubbing, and chemical absorption, to remove particulates, sulfur compounds, and other impurities. 

• Conditioning: The hydrogen-to-carbon monoxide (H₂/CO) ratio in the syngas is then adjusted through a water-gas shift reaction to optimize it for Fischer-Tropsch synthesis. The adjusted syngas typically has an H₂/CO ratio of around 2:1. 

​

4. Fischer-Tropsch (FT) Synthesis 

• Process: The conditioned syngas is fed into a Fischer-Tropsch reactor, where it is catalytically converted into long-chain hydrocarbons. 

• Catalysis: The FT process uses a catalyst, typically iron or cobalt-based, to facilitate the chemical reactions. The syngas reacts over the catalyst at temperatures of 200-350°C and pressures of 20-40 bar. 

• Products: The FT synthesis produces a mixture of hydrocarbons, ranging from light gases to waxes, which can be further processed into different fuels. The primary products are synthetic crude oil (syncrude) and water. 

​

5. Hydrocracking and Upgrading 

• Process: The heavy hydrocarbon chains (waxes) produced in the FT process are then subjected to hydrocracking, where they are broken down into shorter, more useful molecules. 

• Reaction: In the hydrocracking unit, the FT waxes are mixed with hydrogen and passed over a catalyst at high temperatures and pressures. This process converts the heavy hydrocarbons into lighter fractions, including kerosene-range hydrocarbons suitable for SAF. 

• Fractionation: The resulting mixture is then separated into different fuel fractions through distillation or fractionation. The kerosene fraction, which meets the specifications for jet fuel, is separated as SAF. 

​

6. Blending 

• Process: Like other SAF processes, the synthetic kerosene produced from biomass via the FT process must be blended with conventional jet fuel to meet current aviation fuel standards (ASTM D7566). 

• Quality Assurance: The blended fuel undergoes rigorous testing to ensure it meets all necessary specifications, including energy content, flash point, and freezing point. 

​

7. Distribution and Use 

• Process: The blended SAF is then distributed to airports, where it can be used in existing aircraft engines without any modifications. 

• Environmental Impact: SAF produced from biomass via the gasification and Fischer-Tropsch process can significantly reduce greenhouse gas emissions compared to conventional jet fuel, potentially achieving reductions of up to 80%, depending on the feedstock and process efficiency.