Hydrogenation and Isomerization of Oligomers

Following the oligomerization of olefins into long-chain hydrocarbons, additional refining steps are necessary to produce a high-quality aviation fuel that meets the stringent specifications of Jet A-1, referred to here as Biogenic Sustainable Aviation Fuel (BioSAF). The key processes involved are hydrogenation and isomerization, which transform the oligomerized products into saturated and branched hydrocarbons suitable for use in jet engines.

a. Hydrogenation

• Purpose: Hydrogenation saturates the double bonds present in the oligomerized olefins, converting unsaturated hydrocarbons into saturated hydrocarbons (alkanes). This step enhances the chemical stability of the fuel, reducing its susceptibility to oxidation and thermal degradation.

• Process Details:

  • Catalysts: Common catalysts include supported metals such as nickel, palladium, or platinum on carriers like alumina or silica.

  • Conditions: The reaction is conducted at elevated temperatures (150–350°C) and pressures (10–100 bar) in the presence of hydrogen gas.

  • Reaction Mechanism:

    R-CH=CH-R’+H2→R-CH2-CH2-R’

• Benefits:

  • Improved Stability: Saturated hydrocarbons are less reactive and have better storage stability, essential for aviation fuels.
  • Enhanced Safety: Reduces the risk of gum formation and deposits in fuel systems, ensuring reliable engine performance.

b. Isomerization

• Purpose: Isomerization rearranges the molecular structure of hydrocarbons to increase branching. This process improves the cold flow properties of the fuel, such as lowering the freezing point, which is critical for high-altitude flight where temperatures are extremely low.

• Process Details:

  • Catalysts: Bifunctional catalysts combining metallic sites (e.g., platinum) and acidic supports (e.g., chlorided alumina, zeolites).

  • Conditions: Moderate temperatures (200–400°C) and pressures (10–50 bar) under a hydrogen atmosphere to prevent coking and maintain catalyst activity.

  • Reaction Mechanism:

    Linear Hydrocarbon→Branched Isomer

• Benefits:

  • Improved Cold Flow: Branched hydrocarbons have lower freezing points and better viscosity profiles, essential for fuel performance at low temperatures.
  • Fuel Efficiency: Enhances combustion characteristics, leading to better fuel efficiency and reduced emissions.

Classification as Biogenic Sustainable Aviation Fuel (BioSAF)

a. Biogenic Origin

• Renewable Biomass Source: The fuel is derived from Dedicated Energy Crops (DECs) grown in Dedicated Energy Farms (DEFs). These fast-growing softwood trees are cultivated specifically for energy production.
• Carbon Neutrality:
  • Carbon Cycle Balance: The CO₂ emitted during fuel combustion is offset by the CO₂ absorbed during the growth of DECs, contributing to a closed carbon loop.

b. Sustainability Credentials

• Sustainable Farming Practices:
  • Land Use: DECs are grown on marginal lands or areas not suitable for food crops, minimizing land-use conflicts.
  • Environmental Impact: DEFs implement practices that preserve soil health, conserve water, and promote biodiversity.
• Lifecycle Emissions Reduction:
  • Lower GHG Emissions: BioSAF production results in significantly lower greenhouse gas emissions over its lifecycle compared to fossil-derived Jet A-1.

c. Compliance with Sustainable Aviation Fuel Criteria

• International Standards Alignment:
  • CORSIA Eligible: Meets the sustainability criteria outlined by the International Civil Aviation Organization's Carbon Offsetting and Reduction Scheme for International Aviation.
  • Certification: Can obtain certifications from recognized bodies like the Roundtable on Sustainable Biomaterials (RSB).