Flying to a Greener Future: Recent Developments in Sustainable aviation fuel ( SAF ) pathways

1. Introduction

As climate change intensifies, governments across the globe have become more conscious of greenhouse gas (GHG) emissions. The aviation industry accounts for 2-3% of worldwide emissions. As such, airline governing organizations, such as the International Air Transport Association, are urging the switch from fossil fuels to sustainable aviation fuels (SAFs). SAFs are fuels which release 50-100% less CO2 on a lifecycle basis, and about 400,000 commercial flights have already utilized SAFs as a part of their jet fuel blends [1][2]. Moreover, the US has also announced the SAF Grand Challenge in 2021, pledging to reduce aviation-related GHGs by 50% and to domestically produce 3 billion gallons of SAFs by 2030 [3].  
This paper briefly reviews recent literature and developments on the four most developed SAF synthetic pathways — hydrogenated esters and fatty acids (HEFA), alcohol-to-jet (AtJ), Fischer-Tropsch (FT), and power-to-liquid (PtL), listed in order of technological maturity. Figure 1 illustrates a timeline on the rollout of their research development, scalability, and eventual commercialization.

2. Hydrogenated Esters and Fatty Acids (HEFA)

The pathway with the most established literature and industrial application is HEFA. HEFA synthesis involves two major steps: pretreatment and catalytic hydrogenation of feedstocks, creating triglycerides and propane, followed by the conversion of fats into long-chain paraffinic alkanes. Because of several factors — including technological maturity, availability of agricultural feedstocks, and high scalability — HEFA is the only pathway that can produce SAFs on a commercial scale. Figure 2 shows a detailed comparison of the four major pathways, including the expected production contribution by 2030. As shown, the US Department of Energy (DOE) estimates that 66% of all SAFs will be produced via HEFA by the year 2030 [4][5].
Due to its relative technological maturity, HEFA pathways offer a diverse portfolio of feedstocks, ranging from raw oil to commercial-scale crops to lignocellulosic biomass. However, major stakeholders in the aviation industry agree that limited feedstock supply is the greatest barrier to HEFA-generated SAFs — moreover, this supply will not increase in the near-future, forcing the US to rely on imports [4]. The following section illustrates the current options for HEFA feedstocks, as well as their benefits, drawbacks, and viability.

2.1 Three Generations of HEFA Feedstocks: Prospects and Challenges
First Generation
First generation biofuels are made from crop oils, most notably from corn and soybeans. Though they offer lower GHG emissions compared to standard aviation fuels, they are subject to the “food vs fuel” dilemma. Utilization of high-value agricultural products faces economic competition from the food industry. Furthermore, allotting resources towards specialized corn and soybean fuel farms would require land, water, pesticides, and fertilizers — posing the risk of land-use GHG emissions and ecotoxicity [5][6].
The advantage of first-generation fuels lies in their established economic output. The US strongly subsidizes corn and soybean, and an estimated 14.9 and 4.3 billion bushels of corn and soybean, respectively, were harvested in 2024 [7]. However, agricultural crops may not be ideal for energy production, not only because of their pesticide usage and land-use GHG emissions, but also because of their lower energy density.
Table 1 lists the energy densities for various crops from both first- and second-generation. Soybean oil, for example, accounts for 57% of all domestic HEFA feedstock, but only has an estimated energy density of 0.47 MJ/kg [4][8]. In contrast, higher energy crops, such as carmelina and rapeseed, can achieve yields of 0.98 and 0.95 MJ/kg, respectively — all while requiring less than a quarter of soybean’s energy input. Moreover, lifecycle impact analysis (LCA) by D’Ascenzo et al. suggests soybean oil may have one of the worst global warming potentials (GWP) of all agricultural feedstock. The first row of Table 2 shows the GWP of various crops over their lifetimes of harvesting, conversion, and use as a biofuel. Soybean releases 43.6 – 390 equivalent grams of CO2/MJ [8][9]. On the other hand, palm oil is cited to have the lowest GWP of all commercial crops analyzed (18.2 g CO2 eq/MJ, reducing its GWP by up to 5.8 times compared to fossil fuels). Though soybean is the most popular domestic HEFA feedstock, its carbon footprint and energy limitations underscore the need to explore other options.

Second Generation

Second-generation biofuels use nonfood biomass. These include energy crops and waste — such as agricultural and forestry residues; inedible fats, oils, and greases (FOGs); and miscellaneous household waste (food scraps, paper, plastic) [10].
Energy crops
As the name suggests, energy crops specially grown for energy generation, though they can also serve as rotational cover crops to reduce soil depletion. These crops include species like Jatropha, Brassica carinata, and the genus Miscanthus. Of the crops D’Ascenzo et al analyzed, Jatropha is cited to have one of the least harmful GWFs, though they admit other papers report minor discrepancies. The authors contend that HEFA from Jatropha-derived oil creates 24g of equivalent CO2/MJ, whereas Kurzawska-Pietrowicz posits less than half as much (10.4 gCO2 eq) [11]. Meanwhile, Brassica carinata has been cultivated for energy in Southern Europe since at least 2007, with LCA values of 12.7 gCO2 eq/MJ [12]. A recent 2022 paper exploring B. carinata’s potential agriculture in the Southeastern US estimates its carbon footprint would be only 18-24% of conventional fossil fuels [13]. Additionally, Miscanthus is reported to have an agricultural output potential rivalling that of sugar cane, but with far fewer GHG emissions: Shu & Allrogen (2024) determined its LCA value to be -2.2 gCO2 eq/MJ [14]. LCA values are bound to differ based on production parameters and authors’ analysis methods. Regardless, these crops are energy dense with smaller GWF than even first-generation crops, making them promising candidates for future HEFA production.

Waste

Second-generation waste feedstocks are readily available in consumer and industrial garbage. Consequently, they often incur negative costs and reduce the CO2 emissions associated with landfill dumping. Waste feedstock circumvents the food-fuel problem faced by their first-generation counterparts, while also reducing raw material prices. However, waste is a broad category, and its myriad origins inevitably lead to contamination by toxic impurities such as heavy metals, microplastics, and pyrolytic tar. Even though waste is an abundant feedstock, lack of processing infrastructure and the risk of pollution imply it is unlikely to see industrial-scale implementation soon. [10]

Third Generation

Third generation feedstocks use microbes to produce lipids, which are then processed via HEFA into usable SAFs. Many taxa of microbes are viable, so long as they yield a high volume of lipids. For example, past research has examined the use of bacteria and fungi, particularly cyanobacteria and yeast [15].
However, recent research discovered that algae is an attractive microbial feedstock option because it is space efficient, lipid dense, and requires little maintenance. Table 3 presents the oil production of various crops in L/Hectare. Microalgae can produce up to 95,000 L/Hectare of oil, higher than any of the first- or second-generation feedstocks. This is especially notable when compared to 446 L/Hectare produced by soybean, the most popular domestic HEFA feedstock [16].

A major challenge surrounding algae is the lack of existing facilities to grow, harvest, and convert the feedstock. Developing infrastructure is the most cost-prohibitive obstacle for algae HEFA fuels. According to a recent paper by Lutzu et al. (2024), researchers are comparing two major modes of farming algae: open ponds versus closed facilities [17]. Figure 3 depicts the various configurations for both modes of algae farming.
Over 80% of the modern microalgae jet fuel is sourced from open ponds. The prevailing system is the “raceway pond,” consisting of open channels and a paddlewheel that churns the algal soup along a racetrack. These raceways are constructed by digging shallow grooves in the ground no more than 20 cm deep and lining the bottom with concrete or plastic to prevent runoff [18][19]. The appeal of this system lies in its simplicity and cheapness — Lutzu et al. cites it as the single “most economical method for the large-scale production of microalgae” [20]. However, the drawback to open ponds is the lack of control in the farming process. The substrate is exposed to its surroundings — therefore productivity by seasonal variations of sunlight and temperature, evaporative water loss, mineral accumulation, and poor CO2 transfer [21].
The other option discussed by Lutzu et al. are photobioreactors (PBRs). PBRs are closed systems which prevent the exchange of matter with their surroundings. PBRs can be custom built to control growth factors like light, temperature, pH, nutrient gradients— exchanging cheap, simple construction for increased productivity. The most significant engineering consideration for PBRs is the illumination surface area per unit volume, which can be optimized with various tank geometries, such as tubular, column, or flat panel. Recently, the plastic bag and solid-state configurations have shown promise. The plastic bag method grows microalgae in plastic bags, which can be submerged in water for temperature control [22]. It is simple and low-cost but does not offer good circulation and is prone to breakage. The solid-state method, in contrast, grows the algae as a biofilm on a solid or semi-solid (i.e. gel or mesh) surface. They feature a high surface area to volume ratio, boosting the biomass and lipid yields while reducing the water and nutrient requirements [23]. These closed systems are highly optimizable but are still in their technological infancy.
Another constraint for microalgae farming is the biomass-lipid tradeoff. It has been long reported that nutrient stress, particularly a lack of nitrogen, alters microalgae metabolism, compelling them to produce more lipids in the form of triacylglycerols. For instance, Chlorella can achieve up to 55% lipid content by weight under nutrient stress, and other species like M. salina and O. multisporus can attain lipid compositions as high as 75% [24][25][26]. However, nutrient deficiency also hampers the maximum biomass of microalgae, which impacts lipid generation. Therefore, a sweet spot of nitrogen must be compromised, which depends on variables such as the microbial strain, temperature, and available light [27]. All these algae farming techniques offer unique economic and production yield results, but continued research efforts are necessary to maximize their potential.
Despite these challenges, international demo flights are already using algae-derived HEFA fuels. Japan, in particular, has spearheaded the use of microalgae biofuel in commercial flights using the species B. braunii and Euglena sp. [28][29]. In 2021, All Nippon Airline, Japan’s largest airline company, successfully conducted a flight between Tokyo and Osaka, using a 50:50 mix of an algae-derived oil and petroleum-based jet fuel [30]. This achievement was quickly followed by a one-hour flight from Shizuoka to Nagoya, with the Embraer’s E175 using Euglena derived biofuel. Similarly, Turkish Airlines completed flights with microalgae fuel in 2022, announcing an 87% reduction in greenhouse gas emissions compared to traditional JF [31]. These demonstration flights represent an international initiative in the implementation of algal fuels, taking it one step closer to commercial reality.

3. Alcohol-to-Jet (AtJ)

3.1 Brief Overview of the Alcohol-to-Jet Process
Alcohol-to-jet (AtJ) is the second most technologically developed pathway, estimated to produce 23% of all SAFs by 2030 [5]. Conventionally, AtJ hinged on the oligomerization of ethylene derived from dehydrated ethanol. However, this required a high cracking temperature over 300℃, which decreased sustainability due to high energy demands [32]. Moreover, ethylene, short chain hydrocarbon, mostly yielded alkanes fuels shorter than 12 carbon atoms [33].
However, in recent AtJ efforts significantly improved due to the Guerbert coupling of the initial ethanol into butanol and higher alcohols [34]. The Guerbert reaction dimerizes two ethanol molecules over a catalyst. Then, hydrogenation of the resulting dimer yields C4+ hydrocarbons. This allowed longer (C8-C16) and thus more energy-dense fuel products. New research is focused on (i) improving the production via catalysis, as well as (ii) studying the physical parameters of AtJ-derived SAFs, especially aromatized fuels, for commercial deployment.

3.2 Recent AtJ research
(i) Catalytic Synthesis: Recent research efforts in AtJ synthesis have prioritized SAF production via catalysis. Figure 4 is a flowchart that illustrates the catalytic conversion of ethanol into biofuel. As it stands, high oxygen content and short chain products in the initial fast-pyrolysis steps causes energy-robbing water generation, decreased stability, and increased viscosity. Researchers are investigating the role of catalysts in the acidic dehydration of alcohol in water solvents, a critical step in cleaving C-O bonds and creating higher order Cn hydrocarbons (n>8). Multiple papers have studied the possible role of acidic aluminosilicate zeolites in the catalysis of butanol dehydration, developing new types of zeolites and enhancing their hydrophobicity [35][36].
 In a recent study, Liu et al. announced the use of a modified zeolite catalyst to generate C8-C6 products with a high selectivity [37]. The authors chose Z25-OTS as their parent catalyst, which only had a selectivity of 51.3% for C8+ chains in a pure alcohol system. They altered the acidic sites of the zeolite by grafting chlorosilanes of different lengths onto the reaction surface. Octadecyltrichlorosilane was determined as the best, with an 80.5% yield of higher order hydrocarbons, a 29.2% increase over the parent catalyst. Further characterization of the modified zeolite was performed via XRD, FTIR, and various spectroscopies. The authors reported higher acidity, greater adsorption of hydrocarbons, and improved hydrophobicity that protected reaction sites from water-based deactivation. In a mixed-alcohol system, the selectivity of C8-C16 carbons was 57.5%, an increase of 13.6% over the unmodified catalyst. The high selectivity in both the ideal and mixed-alcohol settings represent a breakthrough in the use of zeolite as a dehydration catalyst.
In another zeolite catalyst study, Liu et al. demonstrated a novel one-pot dehydration oligomerization to create biofuels from bioethanol-upgraded higher alcohols (C4-C6) [38]. This study is unique as it condenses the dehydration, oligomerization, and hydrogenation steps into a single reaction vessel. The advantage of one-pot systems is that they do not require separation and processing of the yields at each step. However, they are not energetically favorable and consquently require catalysts to drive the reaction forward. The authors used phosphotungstic acids (HPW) to modify a β-zeolite catalyst. HPW is a well-established acidic, depolymerizing catalyst on its own [39]. However, its low surface area limits the number of reaction sites and hiners its performance. Past literature demonstrated the potential of loading HPW onto porous catalytic surfaces, such as nanoscale meshes which include zeolite blends [40][41]. By loading different amounts of HPW onto β-zeolite, Liu et al. observed that 20% HPW yielded the best performance at 240℃. Dialing the composition of n-butanol and n-hexanol, it was further noted that a 3:2 ratio of the respective alkanes could boost selectivity to 59.5% for C8-C16 hydrocarbon products. This result confirms the potential of one-pot AtJ synthesis, which could streamline SAF production on a commercial scale.
Liu et al.’s extensive work on zeolites highlights just one of many attractive catalyst options. Other papers have explored catalysts centered on Ni, Pt, or TiO2 [42]. The general trend among these catalysts is that they are porous and possess a density of tunable acidic sites on their reaction surface — aiding in both the dehydration and oligomerization steps of AtJ. The plurality of such catalyst species demonstrates exciting potential for both future research and the widespread industrial adoption of AtJ biofuels.
(ii) Performance Parameters of Aromatized AtJ Fuels: Because AtJ technology is less mature compared to established pathways like HEFA, more testing is needed to ensure the performance and safety of AtJ biofuels.
Yakolieva et al. compared the physicochemical properties of AtJ-SPK (synthesized paraffinic kerosene) and AtJ-SKA (synthesized kerosene with aromatics) pathways [43]. AtJ-SPK and -SKA biofuels both undergo the three steps of alcohol dehydration into olefins, oligomerization, and hydrogenation. However, -SKA has the added step of increasing aromatic content in the fuel’s composition [44].
Although AtJ-SPK fuels are high quality due to their lack of impurities, they do not contain aromatics. While aromatics do not contribute much energy, they are vital in regulating fuel density and preventing seal shrinkage [45]. The recommended quantity of aromatics in jet fuels (JFs) is 8% by volume [46]. The lack of aromatic hydrocarbons in AtJ-SPK occasionally lowers density below ASTM standards (>775 kg/m3), limiting its maximum fractional composition in JF-SAF blends. Therefore, companies like Byogy and Swedish Biofuels have begun commercializing AtJ-SKA production, which recently passed ASTM approval in 2023 [33][45].   
Though AtJ-SKA promises better compatibility with existing JF infrastructure and technologies compared to AtJ-SPK, not many experimental tests have been conducted to confirm that hypothesis. Yakolieva et al.’s recent paper represents one of the first practical examinations of AtJ-SKA biofuels. The authors created various blends of AtJ-SPK and -SKA with JF and investigated physicochemical parameters — namely, composition, density, kinematic viscosity, freezing point, and flash point.
The most important takeaway from Yakolieva’s study is that the density of AtJ-SKA more closely resembles that of conventional JF than AtJ-SPK, owing to a higher aromatic composition. While AtJ-SPK possessed lower density and aromatics vol% (757 kg/m3 at 15℃, >0.01 fractional aromatic composition), -SKA more closely approached JF parameters (786 kg/m3 vs 795 and 15.7% vs 13.9 composition, for density and aromatic composition, respectively. Figure 5 compares the density of AtJ-SPK (line 1) and -SKA (line 2) JF blends as a function of composition. The green baseline represents the minimum acceptable density of 775 kg/ m3. AtJ-SKA/JF blends maintain density above the ASTM threshold, even at 100% composition — whereas AtJ-SPK falters at around only 50%.  
Figure 6 details the kinematic viscosity of AtJ blends as a function of composition. Yakolieva et al. report lower viscosity for AST-SKA (line 2) than -SPK (line 1), which translates to better fuel atomization and more complete combustion.
Both types of AtJ fuels possessed lower freezing points than JF (~80 vs 49℃), which may improve performance at low-temperature, high-altitude conditions. Moreover, both AtJ-SPK and -SKA possess higher flash points than JF (~48 vs 44℃), which is associated with enhanced fire safety. All this is to say that AtJ-SKA offers benefits over traditional JF, with less sacrifice of ideal density and viscosity, unlike -SPK.
    

4. Fischer-Tropsch (FT)

Fischer-Tropsch reactions convert gaseous mixtures of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. Traditionally, the syngas is derived from coal or natural gas, and the reaction takes place over cobalt or iron catalysts. The product stream of FT pathways consists of paraffins, olefins, and oxygenated compounds, anywhere from 1 to 70+ carbons long. In the context of SAFs, the syngas must be sustainably sourced (i.e. from biomass). In addition, the products must be isolated and refined to bring them within kerosene boiling range (149 to 288°C) and carbon lengths between 9-18 [47].
Like with AtJ, FT pathways often create pure paraffinic kerosene products (FT-SPK) with aromatic content less than the accepted 8 wt%, reducing the density below the minimum 775 kg/m3. New research has focused on creating FT SPK-A fuels with acidic catalysis. In their comprehensive 2022 article, Klerk et al. discuss several different pathways for FT SPK-A jet fuels [48].
Current refinery practices usually synthesize FT SPK-A by aromatizing FT light products or fluid catalytic cracking (FCC) of FT heavy products. The former process uses Pt on chlorinated alumina as a catalyst to reform naphtha co-feed into aromatics, a popular practice across petroleum fuel industries [49]. Using this method, the least technologically advanced refineries may produce more than 60 wt% in usable jet fuel [50]. The latter process exploits the heavy products of FT, an alkane-rich wax making up 45-50 wt% of the product in low temperature synthesis [51]. FCC — performed over silica alumina or zeolites — then alters the wax into liquid jet fuel containing aromatics. However, these processes often require aromatic co-feeds and multiple conversion units.
A new pathway invented by Greenfield Global, a fuel ethanol company, combines the oligomerization, aromatization, and alkene aromatic alkylation steps into a single conversion unit — eliminating the need for an aromatic co-feed [52]. With this method, Klerk et al. synthesized jet fuels using only FT-derived materials. They found that the resulting SAF complies with Jet-A1 specifications for parameters such as density, boiling point, and viscosity — thus proving a FT-only pathway can be technologically practical for synthesizing SAFs.
5. Power-to-Liquid (PtL)
PtL is an electric SAF (eSAF), produced by combining hydrogen from electrolysis with carbon dioxide from the atmosphere or industrial waste. First, renewable powered electrolyzers split water into hydrogen and oxygen. Captured CO2 is then converted to a feedstock and synthesized with the green hydrogen (typically via FT pathways) into liquid hydrocarbons. PtL boasts GHG reduction potentials up to 90%, while also requiring no biomass. Furthermore, because it depends on just water and CO2, the feedstock supply is theoretically unlimited [53].
However, PtL is still in its proof-of-concept stage. The global consulting firm McKinsey & Company claims “no mature, fully integrated PtL player is yet operating at scale.” The nascency of PtL technology is reflected in consumer costs. Optimistic estimates put PtL fuel prices at 1.21 EUR per liter by 2030, still 3 times that of conventional JFs [54]. The World Economic Forum suggests three cost reduction milestones must occur to commercialize PtL — renewable electricity costs must fall by 30%, electrolyzer technology by 50%, and efficient direct air capture carbon sequestration by up to 80%. Though PtL feedstock is theoretically infinite, it is only as sustainable as the renewable electricity and carbon capture technologies that it relies on. Fortunately, there is a global initiative to make PtL aviation fuels practical. In France, a $550 million investment pledges to capture 300,000 annual tons of CO2. In Chile, multiple companies, including Exxon Mobil and Siemens Energy, are collaborating to build an industrial-scale PtL facility by 2026. Finally, in the United Arab Emirates, demonstration front-end engineering designs (FEED) began for PtL plants in 2022 [53].
Though PtL holds great potential, there is still a long road ahead to full-scale commercialization. International cooperation between governments, researchers, and corporations must be achieved to bring these ideals into reality.

6. Conclusion

In summary, there have been many developments for SAF synthetic pathways.
As the most established method, HEFA is ready to deploy commercially. The focus now is scaling up the supply of compatible feedstocks by 2030. Recent research on HEFA explored impact assessments for established first- and second-generation biofuels. Third-generation microalgal feedstocks also demonstrated new prospects in farming methods and demo flights.
On the other hand, AtJ should show successful demonstrations by 2030 and commercial deployment by 2040. Recent breakthroughs include Guerbert coupling of higher alcohols and enhanced catalytic synthesis, improving yields and efficiency. The focus going forward is to establish a reliable source of ethanol, most likely in corn.
FT and PtL pathways are still in their research and development phase, and commercial deployment is delayed until 2050 or further. Experiments on FT synthesis have improved the aromatization of the alkane fuel products, making it more technologically practical. PtL, though the greenest of all pathways, is still in its infancy. The price of PtL fuels is prohibitively high but should drop with more advances in carbon capture and water-splitting technology.
All these efforts help lead the aviation sector toward a greener future in the global fight against climate change.

About the Authors

Dr. Raj Shah is a Director at Koehler Instrument Company in New York, where he has worked for the last 25 plus years. He is an elected Fellow by his peers at IChemE, ASTM, AOCS, CMI, STLE, AIC, NLGI, INSTMC, Institute of Physics, The Energy Institute and The Royal Society of Chemistry. An ASTM Eagle award recipient, Dr. Shah recently coedited the bestseller, “Fuels and Lubricants handbook”, details of which are available at ASTM’s Long-awaited Fuels and Lubricants Handbook https://bit.ly/3u2e6GY
He earned his doctorate in Chemical Engineering from The Pennsylvania State University and is a Fellow from The Chartered Management Institute, London. Dr. Shah is also a Chartered Scientist with the Science Council, a Chartered Petroleum Engineer with the Energy Institute and a Chartered Engineer with the Engineering council, UK. Dr. Shah was recently granted the honorific of “Eminent engineer” with Tau beta Pi, the largest engineering society in the USA. He is on the Advisory board of directors at Farmingdale university (Mechanical Technology), Auburn Univ (Tribology), SUNY, Farmingdale, (Engineering Management) and State university of NY, Stony Brook (Chemical engineering/ Material Science and engineering). An Adjunct
Professor at the State University of New York, Stony Brook, in the Department of Material Science and Chemical Engineering, Raj also has over700 publications and has been active in the energy industry for over 3 decades. More information on Raj can be found at https://shorturl.at/JDPZN
Contact: rshah@koehlerinstrument.com

Dr. Vikram Mittal, PhD is an Associate Professor in the Department of Systems Engineering at the United States Military Academy.  His research interests include energy modeling, technology forecasting, and Alternative fuels. Previously, he was a senior mechanical engineer at the Charles Stark Draper Laboratory.  He holds a PhD in Mechanical Engineering from MIT, an MS in Engineering Sciences from Oxford, and a BS in Aeronautics from Caltech. Dr. Mittal is also a combat veteran and a major in the U.S. Army Reserve.

Mr. Bob Fang is part of a thriving internship program at Koehler Instrument company in Holtsville, and is a student of Chemical Engineering at Stony Brook University, Long Island, NY where Dr.’s Shah and Mittal are on the external advisory board of directors

References

1. World Economic Forum. (2020). Clean Skies for Tomorrow Sustainable Aviation Fuels as a Pathway to Net-Zero Aviation In Collaboration with McKinsey & Company. https://www3.weforum.org/docs/WEF_Clean_Skies_Tomorrow_SAF_Analytics_2020.pdf
2. International Air Transport Association (IATA) : Developing Sustainable Aviation Fuels https://www.iata.org/en/programs/ environment/sustainable-aviation-fuels/.
3. Sustainable Aviation Fuel Grand Challenge | Biomass Research & Development. (n.d.). Biomassboard.gov. https://biomassboard.gov/sustainable-aviation-fuel-grand-challenge
4. Oscar Rosales Calderon, Tao, L., Abdullah, Z., Talmadge, M., Milbrandt, A., Smolinski, S., Moriarty, K., Bhatt, A., Zhang, Y., Ravi, V., Skangos, C., Davis, R., & Payne, C. (2024). Sustainable Aviation Fuel State-of-Industry Report: Hydroprocessed Esters and Fatty Acids Pathway. OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information). https://doi.org/10.2172/2426563
5. Howe C., Rolfes E., O’Dell K., McMurtry B., Razdan S., Otwell A. (2024). Sustainable Aviation Fuel. Retrieved February 7, 2025, from https://liftoff.energy.gov/wp-content/uploads/2024/12/LIFTOFF_-Sustainable-Aviation-Fuel_Updated-2.6.25.pdf
6. Walls, L. E., and Rios-Solis, L. (2020). Sustainable production of microbial isoprenoid derived advanced biojet fuels using different generation feedstocks: a review. Front. Bioeng. Biotechnol. 8, 599560. doi:10.3389/fbioe.2020.599560
7. Corn and soybean production down in 2022, USDA reports Corn stocks down, soybean stocks down from year earlier Winter Wheat Seedings up for 2023. (2022). Usda.gov. https://www.nass.usda.gov/Newsroom/2025/01-10-2025.php
8. D’Ascenzo, F., Vinci, G., Savastano, M., Amici, A., & Ruggeri, M. (2024). Comparative Life Cycle Assessment of Sustainable Aviation Fuel Production from Different Biomasses. Sustainability, 16(16), 6875. https://doi.org/10.3390/su16166875
9. Zhu, X., Xiao, J., Wang, C., Zhu, L., & Wang, S. (2022). Global warming potential analysis of bio-jet fuel based on life cycle assessment. Carbon Neutrality, 1(1). https://doi.org/10.1007/s43979-022-00026-4
10. Borrill, E., Koh, L., & Yuan, R. (2024). Review of technological developments and LCA applications on biobased SAF conversion processes. Frontiers in Fuels, 2. https://doi.org/10.3389/ffuel.2024.1397962
11. Kurzawska-Pietrowicz, P. Life Cycle emission of selected Sustainable Aviation Fuels—A review. Transp. Res. Proc. 2023, 75, 77–85.
12. Gasol, C. M., Gabarrell, X., Anton, A., Rigola, M., Carrasco, J., Ciria, P., Solano, M. L., & Rieradevall, J. (2007). Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe. Biomass and Bioenergy, 31(8), 543–555. https://doi.org/10.1016/j.biombioe.2007.01.026
13. Field, J. (2022) Modeling the yield, biogenic emissions, and soil carbon sequestration outcomes of Brassica carinata grown in the southeastern US as a winter cash crop and sustainable aviation fuel feedstock. Authorea.
14. Shu, Y., & Allroggen, F. (2024). Assessment of Sustainable Aviation Fuel Production Potential Using Crop Allocation Optimization. https://dspace.mit.edu/bitstream/handle/1721.1/155409/Shu-zshu-SM-AeroAstro-2024-thesis.pdf?sequence=1&isAllowed=y
15. Eds. Shashi Kant Bhatia, Parmjit Singh Panesar, Ranjit Gurav Microbial Biofuel. (2025).Google Books. https://books.google.com/books?hl=en&lr=&id=tyJGEQAAQBAJ&oi=fnd&pg=PA173&dq=cyanobacteria+hefa&ots=9qt2V9x0vo&sig=HlmZvrv9PZWIBMH3WWzLA5xvQW4#v=onepage&q&f=false
16. Sharma, V., Abul Kalam Hossain, Ganesh Duraisamy, & Griffiths, G. (2023). Microalgal Biodiesel: A Challenging Route toward a Sustainable Aviation Fuel. Fermentation, 9(10), 907–907. https://doi.org/10.3390/fermentation9100907
17. Lutzu, G. A., Usai, L., Ciurli, A., Chiellini, C., Di Caprio, F., Pagnanelli, F., Parsaeimehr, A., Malina, I., Malins, K., Fabbricino, M., Cesaro, A., Policastro, G., Cao, G., & Concas, A. (2024). Engineering strategies of microalgal cultivation for potential jet fuel production – A critical review. Journal of Environmental Chemical Engineering, 12(5), 113886. https://doi.org/10.1016/j.jece.2024.113886
18. Sharma, K. K., Schuhmann, H., & Schenk, P. M. (2012). High Lipid Induction in Microalgae for Biodiesel Production. Energies, 5(5), 1532–1553. https://doi.org/10.3390/en5051532
19. S.-H. Ho, X. Ye, T. Hasunuma, J.-S. Chang, A. Kondo. Perspectives on engineering strategies for improving biofuel production from microalgae--a critical review.Biotechnol. Adv., 32 (2014), pp. 1448-1459
20. A. Morillas-España, T. Lafarga, A. Sánchez-Zurano, F.G. Acién-Fernández, C. González-López Microalgae based wastewater treatment coupled to the production of high value agricultural products: current needs and challenges. Chemosphere, 291 (2022)
21. González-González, L. M., Correa, D. F., Ryan, S., Jensen, P. D., Pratt, S., & Schenk, P. M. (2018). Integrated biodiesel and biogas production from microalgae: Towards a sustainable closed loop through nutrient recycling. Renewable and Sustainable Energy Reviews, 82, 1137–1148. https://doi.org/10.1016/j.rser.2017.09.091
22. Moreno Osorio, J. H., Pollio, A., Frunzo, L., Lens, P. N. L., & Esposito, G. (2021). A Review of Microalgal Biofilm Technologies: Definition, Applications, Settings and Analysis. Frontiers in Chemical Engineering, 3. https://doi.org/10.3389/fceng.2021.737710
23. Wang, J., Liu, W., & Liu, T. (2017). Biofilm based attached cultivation technology for microalgal biorefineries—A review. Bioresource Technology, 244, 1245–1253. https://doi.org/10.1016/j.biortech.2017.05.136
24. Anandraj, A., White, S., & Bwapwa, J. K. (2021). Temperature and nutrient coupled stress on microalgal neutral lipids for low‐carbon fuels production. Biofuels, Bioproducts and Biorefining. https://doi.org/10.1002/bbb.2221
25. El-Sheekh, M. M., Mansour, H. M., Bedaiwy, M. Y., & El-shenody, R. A. (2022). Influence of nutrient supplementation and stress conditions on the biomass and lipid production of Microchloropsis salina for biodiesel production. Biomass Conversion and Biorefinery. https://doi.org/10.1007/s13399-022-03434-9
26. Kumar, M. S., Hwang, J.-H., Reda, Kabra, A. N., Ji, M.-K., & Jeon, B.-H. (2014). Influence of CO2 and light spectra on the enhancement of microalgal growth and lipid content. Journal of Renewable and Sustainable Energy, 6(6). https://doi.org/10.1063/1.4901541
27. Falfushynska, H. (2024). Advancements and Prospects in Algal Biofuel Production: A Comprehensive Review. Phycology, 4(4), 548–575. https://doi.org/10.3390/phycology4040030
28. SUSTAINABLE AVIATION FUELS ROAD-MAP Fueling the future of UK aviation. (n.d.). https://www.sustainableaviation.co.uk/wp-content/uploads/2020/02/SustainableAviation_FuelReport_20200231.pdf
29. Sustainable Aviation Fuel Review of Technical Pathways. (n.d.). https://www.energy.gov/sites/prod/files/2020/09/f78/beto-sust-aviation-fuel-sep-2020.pdf
30. Honeywell Technology Enables First Jet Flights with Sustainable Aviation Fuel Produced by Microalgae. (2016). Honeywell.com. https://uop.honeywell.com/en/news-events/2021/november/honeywell-technology-enables-first-jet-flights-with-sustainable-aviation-fuel-produced-by-microalgae
31. Aguila, V. (2022, February 3). Turkish Airlines Introduces Sustainable Aviation Fuel on its Flights - Biofuels Central. Biofuels Central. https://biofuelscentral.com/turkish-airlines-sustainable-aviation-fuel-flights/
32. Betz, M., Fuchs, C., Zevaco, T. A., Arnold, U., & Sauer, J. (2022). Production of hydrocarbon fuels by heterogeneously catalyzed oligomerization of ethylene: Tuning of the product distribution. Biomass and Bioenergy, 166, 106595. https://doi.org/10.1016/j.biombioe.2022.106595
33. Geleynse, S., Brandt, K., Garcia‐Perez, M., Wolcott, M., & Zhang, X. (2018). The Alcohol‐to‐Jet Conversion Pathway for Drop‐In Biofuels: Techno‐Economic Evaluation. ChemSusChem, 11(21), 3728–3741. https://doi.org/10.1002/cssc.201801690
34. Portillo Crespo, M. A., Vidal-Barrero, F., Azancot, L., Reina, T. R., & Campoy, M. (2022). Insights on Guerbet Reaction: Production of Biobutanol From Bioethanol Over a Mg–Al Spinel Catalyst. Frontiers in Chemistry, 10. https://doi.org/10.3389/fchem.2022.945596
35. Xu, S., Sheng, H., Ye, T., Hu, D., & Liao, S. (2016). Hydrophobic aluminosilicate zeolites as highly efficient catalysts for the dehydration of alcohols. Catalysis Communications, 78, 75–79. https://doi.org/10.1016/j.catcom.2016.02.006
36. Han, X., Wang, L., Li, J., Zhan, X., Chen, J., & Yang, J. (2011). Tuning the hydrophobicity of ZSM-5 zeolites by surface silanization using alkyltrichlorosilane. Applied Surface Science, 257(22), 9525–9531. https://doi.org/10.1016/j.apsusc.2011.06.054
37. Liu, Z., Gong, Y., Jiang, T., Xiao, C., Pang, Y., Chen, B., Song, J., & Wang, T. (2025). Enhancing carbon chain extension of higher alcohols to jet fuels by surface hydrophobicity modification of HZSM-5. Energy, 318, 134866. https://doi.org/10.1016/j.energy.2025.134866
38. Liu, Z., Liao, J., Gong, Y., Song, J., & Wang, T. (2023). Efficient production of jet-fuel precursors via one-pot dehydration-oligomerization of higher alcohols from upgrading of bioethanol. Energy Conversion and Management, 299, 117833–117833. https://doi.org/10.1016/j.enconman.2023.117833
39. Du, B., Liu, B., Yang, Y., Wang, X., & Zhou, J. (2019). A Phosphotungstic Acid Catalyst for Depolymerization in Bulrush Lignin. Catalysts, 9(5), 399–399. https://doi.org/10.3390/catal9050399
40. Yang, Y., You, Y., Wu, J., Feng, J., & Zhang, Y. (2020). Phosphotungstic acid encapsulated in USY zeolite as catalysts for the synthesis of cyclohexylbenzene. Journal of the Iranian Chemical Society, 18(3), 573–580. https://doi.org/10.1007/s13738-020-02063-1
41. Yu, Z., Chen, X., Zhang, Y., Tu, H., Pan, P., Li, S., Han, Y., Piao, M., Hu, J., Shi, F., & Yang, X. (2022). Phosphotungstic acid and propylsulfonic acid bifunctionalized ordered mesoporous silica: A highly efficient and reusable catalysts for esterification of oleic acid. Chemical Engineering Journal, 430, 133059. https://doi.org/10.1016/j.cej.2021.133059
42. Goh, B. H. H., Chong, C. T., Ong, H. C., Seljak, T., Katrašnik, T., Józsa, V., Ng, J.-H., Tian, B., Karmarkar, S., & Ashokkumar, V. (2022). Recent advancements in catalytic conversion pathways for synthetic jet fuel produced from bioresources. Energy Conversion and Management, 251, 114974. https://doi.org/10.1016/j.enconman.2021.114974
43. Yakovlieva, A., Boichenko, S., Boshkov, V., Korba, L., & Hocko, M. (2023). EXPERIMENTAL STUDY OF PHYSICAL-CHEMICAL PROPERTIES OF ADVANCED ALCOHOL-TO-JET FUELS. Aviation, 27(1), 1–13. https://doi.org/10.3846/aviation.2023.18564
44. Han, G. B., Jang, J. H., Ahn, M. H., & Jung, B. H. (2019, December 16). Recent Application of Bio-Alcohol: Bio-Jet Fuel. https://doi.org/10.5772/intechopen.89719
45. Van Dyk, S., & Saddler, J. (2021). Progress in Commercialisation of Biojet fuels/SAF: Technologies, potential and challenges. https://www.ieabioenergy.com/wp- content/uploads/2021/07/Van-Dyk-Saddler-IEA-Bioenergy-T39-Webinar-13-July-2021-SvanDyk-publish.pdf
46. Anuar, A., Undavalli, V. K., Khandelwal, B., & Blakey, S. (2021). Effect of fuels, aromatics and preparation methods on seal swell. The Aeronautical Journal, 125(1291), 1542–1565. https://doi.org/10.1017/aer.2021.25
47. De La Ree, A. (2011). Fischer-Tropsch Catalyst for Aviation Fuel Production [Review of Fischer-Tropsch Catalyst for Aviation Fuel Production]. NASA Glenn Research Center. https://ntrs.nasa.gov/api/citations/20120000727/downloads/20120000727.pdf
48. de Klerk, A., Chauhan, G., Halmenschlager, C., Link, F., Montoya Sánchez, N., Gartley, B., El‐Sayed, H. E. M., Sehdev, R., & Lehoux, R. (2023). Sustainable aviation fuel: Pathways to fully formulated synthetic jet fuel via Fischer–Tropsch synthesis. Energy Science & Engineering. https://doi.org/10.1002/ese3.1379
49. Catalytic naphtha reforming. Antos GJ, Aitani AM, eds. CRC Press; 2004 50. de Klerk A. Fischer–Tropsch jet fuel process. Patent US 10,011,789 (Sasol Technology, filing date 2 January 2014, granted 3 July 2018
51. Greener Fischer–Tropsch processes for fuels and feedstocks. Maitlis PM, De Klerk A, eds. Wiley-VCH; 2013.
52. de Klerk A, Sehdev R, Lehoux RR. A process for producing synthetic jet fuel. Patent application WO 2020/154810 (Greenfield Global, filing date 30 January 2019, published 6 August 2020)
53. McKinsey & Company. (2022). Clean Skies for Tomorrow: Delivering on the Global Power-to-Liquid Ambition [Review of Clean Skies for Tomorrow: Delivering on the Global Power-to-Liquid Ambition]. World Economic Forum. https://www.mckinsey.com/~/media/mckinsey/industries/aerospace%20and%20defense/our%20insights/clean%20skies%20for%20tomorrow%20delivering%20on%20the%20global%20power%20to%20liquid%20ambition/clean-skies-for-tomorrow-delivering-on-the-global-power-to-liquid-ambition.pdf
54. Seymour, K., Held, M., Stolz, B., Georges, G., & Boulouchos, K. (2024). Future costs of power-to-liquid sustainable aviation fuels produced from hybrid solar PV-wind plants in Europe. Sustainable Energy & Fuels, 8(4), 811–825. https://doi.org/10.1039/D3SE00978E