Sustainable Aviation Fuel (SAF) is crucial for reducing the environmental impact of air travel. Currently, several technology pathways are certified for SAF production, each with unique processes and feedstocks. Among these, Hydrotreated Esters and Fatty Acids (HEFA) and Alcohol to Jet (AtJ) are prominent routes. This article delves into a comparison of HEFA and AtJ, two significant technologies in the evolving landscape of sustainable aviation fuel production.
Hydrotreated Esters and Fatty Acids (HEFA) Explained
The HEFA pathway is a well-established technology for producing SAF. It utilizes vegetable oils, waste oils, or fats as feedstocks. The process involves hydrogenation, where hydrogen is used to remove oxygen from the feedstock molecules through hydrodeoxygenation. Following this, the resulting straight paraffinic molecules undergo cracking and isomerization to achieve the desired jet fuel chain length.
The HEFA process bears similarities to the production of Hydrotreated Renewable Diesel, but it incorporates more intense cracking of longer chain carbon molecules to meet the specific requirements of SAF. Notably, HEFA-based SAF is currently the most commercially successful and widely used SAF, powering a significant majority of SAF flights to date. The maximum blend ratio for HEFA SAF is 50%, and it adheres to ASTM specification D7566 – Annex 2.
Oskar Meijerink
Alcohol to Jet (AtJ) Technology Breakdown
The Alcohol to Jet (AtJ) pathway offers another promising route to SAF production. AtJ technology converts alcohols, specifically ethanol and iso-butanol, into SAF. The process involves removing oxygen from the alcohol molecules and then linking them together through oligomerization to achieve the required carbon chain length for jet fuel.
The source of the alcohol feedstock for AtJ is not strictly defined, allowing for flexibility in sourcing from various sustainable resources. While currently less commercially mature than HEFA, AtJ holds significant potential due to the availability of alcohol feedstocks and ongoing advancements in alcohol production technologies. Similar to HEFA, AtJ SAF has a maximum blend ratio of 50% and conforms to ASTM specification D7566-4 – Annex 5.
HEFA Compared to AtJ: Key Differences and Considerations
While both HEFA and AtJ are certified and viable pathways for SAF production, they differ in several key aspects:
- Feedstock: HEFA relies on oils and fats, whereas AtJ utilizes alcohols like ethanol and iso-butanol. This difference in feedstock translates to different supply chains and feedstock availability considerations.
- Process: HEFA is based on hydrogenation and cracking of fatty acids, while AtJ involves dehydration and oligomerization of alcohols. These are distinct chemical processes with varying energy requirements and technological complexities.
- Commercial Maturity: HEFA is currently more commercially mature and widely deployed compared to AtJ. HEFA technology has a longer history of development and has achieved greater scale in SAF production. AtJ technology is still in a phase of scaling up and commercialization.
- Feedstock Sustainability: The sustainability of both pathways depends heavily on the feedstock source. Sustainable sourcing of oils and fats for HEFA and alcohols for AtJ is crucial to ensure the overall environmental benefits of SAF.
Conclusion
Both HEFA and AtJ pathways are important contributors to the growing SAF industry. HEFA has established itself as the leading commercially available SAF technology, leveraging existing refining infrastructure and readily available feedstocks. AtJ represents a promising alternative with the potential to utilize diverse alcohol sources and contribute significantly to future SAF production as technology and commercialization advance. The choice between HEFA and AtJ, and potentially other SAF pathways, will depend on factors like regional feedstock availability, technological advancements, and the evolving demands of the aviation industry in its pursuit of decarbonization.
