Alder SAF100 – Accelerating Development for Next Generation Sustainable Fuels  

By Derek Vardon,Chief Technology Officer & Bruno Miller, Chief Project Officer, Alder Fuels
Special to The Digest

Today, we are providing a high-level technical analysis of what we are calling Alder SAF100, a new and 100% sustainable replacement for petroleum-based jet fuel. To demonstrate the viability of reaching that crucial 100% non-fossil production objective, Alder SAF100 has been created by combining hydrocarbons derived from our foundational Alder Greencrude (AGC) platform (dominant component) with smaller volumes of traditional HEFA-SAF (minority component).  

What is most important at this stage is that we have been able to produce 100% biogenic, non-fossil SAF, which demonstrates very promising fuel properties across all key metrics. This early testing and analysis phase is a major step in Alder’s strategy to commercialize our foundational AGC biocrude platform for use by refiners for transportation fuel production, including SAF, and to illustrate the potential of the wide range of renewable products it can unlock over time.  

Summary

Our intention with this post is to share key insights and high-level analysis for the benefit of the industry and to outline the technical approaches we are deploying to transition our products from bench and pilot scale to commercial scale. Although we have a lot more work to do to scale-up production of AGC for Alder SAF100 conversion by refiners, this early analysis signals an encouraging milestone, showing the technical and performance-based potential of 100% SAF production. 

As an industry, there is an acute need to develop next-generation fuels that can catalyze the renewable energy transition. Why is this important? Passenger numbers are increasing dramatically and many of the novel aviation technologies being explored – including batteries, the use of green hydrogen, and electrification – have a lengthy and challenging developmental journey ahead [1]. Therefore, low-carbon, sustainable, cleaner burning, and scalable liquid fuels are a critical foundation in the race to ‘net zero’, particularly in difficult-to-decarbonize sectors. 

For 100% SAF produced with AGC, that means meeting the necessary safety and fuel efficiency criteria for today’s aviation fleet, while enhancing the performance and cleaner burning properties compared to traditional fossil jet fuels used worldwide today. If specific fuel properties are not met early, correcting this operational plateau during SAF’s development and commercialization could be extremely expensive and time-consuming. Furthermore, in the context of new start-ups with an ambition to deploy SAF technology and enter the renewables arena, punitive costs, delays, and timeline constraints are critically important to avoid. Fortunately, new fuel property characterization tools, computational models, and low-volume testing methods provide the essential building blocks for development and continuous iteration.  

Approach 

As previously noted, our ability to blend AGC-derived hydrocarbons as the majority component with HEFA-SAF to unlock a 100% biogenic finished jet fuel holds the promise of delivering exceptional finished jet fuel properties. Fundamentally, when scaled, the AGC biocrude platform must leverage existing refinery infrastructure. This includes current commercial producers converting fats, oils, and grease into SAF, commonly referred to as HEFA-SAF. To evaluate the potential of this hybrid production approach, Alder partnered with Washington State University (WSU), Honeywell UOP, and the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) to leverage the latest fuel property screening tools to rapidly assess and inform Alder SAF100 development [2].

The minority HEFA-SAF volumes were produced by World Energy in Paramount, California. Tests were performed with minimum volume (<100 mL) and turnaround time, allowing the development team to provide iterative feedback during hydroprocessing and downstream distillation to adjust process conditions accordingly. This approach greatly reduced development costs associated with gallon-scale sample production and full testing of the fuel property suite.  

Partners

• Hydroprocessing conditions for AGC hydrocarbons were developed in Honeywell UOP’s pilot plant facility in Riverside, IL 
• Jet-range AGC hydrocarbons were combined with World Energy’s HEFA-SAF to produce Alder SAF100 for iterative testing and development with partners 
• Tier Alpha and Tier Beta fuel property screenings of Alder SAF100 were performed by the SAF characterization lab at WSU 
• Gallon-scale samples of hydroprocessed AGC were then produced with partners and distilled by Honeywell UOP  
• Fuel properties of scaled production samples of Alder SAF100 were continuously spot-checked by Honeywell UOP and NREL to ensure third-party review before final characterization at Southwest Research Institute  

Key results

Reader note: While the data snapshot shown below is specific to Alder SAF100, this technical approach can be widely applied to benefit the wider SAF ecosystem, and to accelerate development and commercial deployment of 100% SAF. 

Higher fuel density & volumetric energy gains:

• Historically, HEFA-SAF is a lower density jet fuel than petroleum-derived jet fuel since it is comprised of only branched and straight-chain paraffins [3] 
• When AGC is hydrotreated, it provides unique cycloparaffin and low-levels of aromatic components that increase the fuel volumetric energy density when combined with today’s commercial HEFA-SAF. This Alder SAF100 final product provides a similar hydrocarbon composition and distribution as fossil jet fuel 
• A high heat of combustion enables an aircraft to fly more efficiently, as the fuel and aircraft weigh less while still having enough energy to transport people and goods safely. Additionally, if a fuel has a high combination of heat of combustion and density (or energy density), the aircraft can fly with fewer gallons consumed per mile. Alder SAF100 demonstrates strong results across these key metrics  

Lower freezing point, low temperature viscosity, & synergistic blending:

• Incorporating dominant AGC-derived cycloparaffins into minority blend HEFA-SAF lowers the freezing point. Uniquely, this blending approach lowers the freezing point of Alder SAF100 relative to each blendstock alone 
• A lower freezing point is crucial for jet fuels because of the low temperatures encountered while flying at high altitudes. As such, jet fuel must have a low freezing point 
• In addition, we see similar positive impacts regarding low-temperature fuel viscosity, which is a key property to ensure consistent flows in the fuel system lines at high elevation 

Cleaner burning fuel for today’s fleet (cycloparaffins):

• Critically, aromatics are the primary components in jet fuel leading to soot formation. This is largely due to incomplete combustion, which then forms particulate matter contributing to aircraft contrails. Soot is problematic from both an environmental and human health perspective due to its impact on radiative forcing from contrails and air quality [4, 5] 
• Jet fuel sooting tendency is evaluated with smoke point tests. The higher the smoke point number, the cleaner burning the fuel 
• However, high-sooting aromatics in fossil jet fuel have been a barrier to 100% SAF as they are needed to provide O-ring polymer seal swell in today’s aircraft. Straight-chain and branched paraffins in HEFA-SAF provide negligible O-ring swell, although they are cleaner burning 
• To address this challenge, the cycloparaffin and aromatic content in hydrotreated AGC offer an alternative to aromatics by delivering deliver seal swell for essential O-ring polymers (e.g., nitrile rubber), while reducing sooting tendency [6, 7] 
• This means a cleaner burning Alder SAF100 while maintaining performance quality 

Data summary*

*Subject to Change. Representative fuel property data for Alder SAF100. The content of this data properties is subject to change as a result of testing, new information, changes in process requirements and the availability of resources. 

Josh Heyne, Director of the Bioproducts, Sciences, and Engineering Lab, WSU, commented, “We are delighted to support Alder’s efforts to commercialize and scale Alder SAF100 production. WSU has worked with more than a dozen Alder samples and the results are promising. In addition to de-risking the scale up process, a key goal of the prescreening phase is to highlight opportunities for producers to hit their development milestones. Producing, scaling, and qualifying new sustainable fuels requires this iterative and continuous testing approach. We look forward to continuing to partner with the Alder technical team as they accelerate their important mission.” 

Zia Abdullah, Laboratory Program Manager for Bioenergy, NREL, commented, “To meet the SAF Grand Challenge goal of 100% SAF deployed throughout the U.S. aviation sector by 2050, we will require not only high production volumes of jet fuel replacements, but also just the right mix of different molecules at scale. To reach these targets, NREL has been closely collaborating with Alder on the development of their proprietary AGC platform. It is very exciting to observe this dataset, which clearly shows the potential of synergistic blending of HEFA-SAF with majority AGC hydrocarbon streams to produce Alder SAF100. Unlocking 100% SAF is the technical foundation for decarbonizing aviation and essential for the success of the 2021 Grand Challenge. We look forward to supporting Alder as they build on this positive milestone.” 

Conclusion

All paths to a ‘net zero’ aviation industry by 2050 pass through SAF [8]. The core technical work highlighted here demonstrates our ability to produce a 100% biogenic replacement for traditional fossil-based jet fuel. By taking a majority of our AGC product and combining it with smaller volumes of HEFA-SAF, we have taken a promising step towards unlocking Alder SAF100 and the refining partners that will be core to its commercial scale.  

For Alder, private and public partnership is always an essential part of this process. It has allowed us to leverage the latest jet fuel property evaluation tools and development processes needed to accelerate the production of Alder SAF100. Specifically, this approach allows Alder and its partners to screen new jet fuel samples and develop our approach in an iterative manner; the goal of which is to reduce production costs, improve performance, and lower the overall carbon intensity of our output. Importantly, this approach can be leveraged by other companies working towards developing 100% SAF. Therefore, we hope some of these learnings are valuable and actionable for mature and newer market entrants alike.  

We wish to express our sincere gratitude to our Alder technical team, strategic partners, sponsors, vendors, and investors, who have been incredibly supportive of our work to take Alder Greencrude from the lab to the marketplace. We believe AGC can be a scalable biocrude platform, particularly when utilized by refiners for transportation fuels, including SAF. We will continue to publish ongoing analysis to benefit the sector and demonstrate our learnings and discoveries. If you have feedback, comments, or are interested in our work, please reach out ([email protected]) and tell us what you think. We would love to hear from you.  

References

1. IEAAviation. (2023). https://www.iea.org/fuels-and-technologies/aviation 
2. Heyne, J., Rauch, B., Le Clercq, P. & Colket, M. Sustainable aviation fuel prescreening tools and procedures. Fuel290, 120004 (2021).
3. U.S. Department of Energy. Sustainable Aviation Fuel: Review of Technical Pathways. (2020).
4. Hui, X., Liu, W., Xue, X. & Sung, C.-J. Sooting characteristics of hydrocarbon compounds and their blends relevant to aviation fuel applications. Fuel287, 119522 (2021).
5. Yang, J., Xin, Z., He, Q. (Sophia), Corscadden, K. & Niu, H. An overview on performance characteristics of bio-jet fuels. Fuel237, 916–936 (2019).
6. U.S. Department of Transportation, Federal Aviation Administration. Impact of Alternative Jet Fuel and Fuel Blends on Non- Metallic Materials Used in Commercial Aircraft Fuel Systems. (2014).
7. Kosir, S., Heyne, J. & Graham, J. A machine learning framework for drop-in volume swell characteristics of sustainable aviation fuel. Fuel274, 117832 (2020).
8. Prussi, M. et al.CORSIA: The first internationally adopted approach to calculate life-cycleGHG emissions for aviation fuels. Renew. Sustain. Energy Rev. 150, 111398 (2021)