21 Analytical Instrumentation
deoxygenating these feedstocks to produce hydrocarbons like conventional jet fuel. HEFA is currently the most commercially viable SAF technology, with over 20 facilities globally that produce HEFA-based jet fuels. The chemistry behind HEFA involves the hydrotreatment of triglycerides and fatty acids, which are reacted with hydrogen under high pressure to remove oxygen, resulting in hydrocarbon chains chemically equivalent to petroleum diesel¹⁵. HEFA fuels are used by various airlines for commercial fl ights, with companies like Neste leading the production.
Recent studies have shown that HEFA fuels can reduce lifecycle greenhouse gas emissions by up to 80 percent compared to conventional jet fuels. The study by Zhang et al. aimed to evaluate the performance and emission characteristics of a Jet A-1/HEFA blend in a miniature turbojet engine. The study found that the Jet A-1/HEFA blend resulted in lower CO emissions and fuel consumption compared to conventional Jet A-1 fuel, highlighting the potential environmental benefi ts of HEFA fuels. The following table summarizes the key aspects and benefi ts of HEFA fuels. The advancements and research in HEFA technology underscore their critical role in the transition towards more sustainable aviation fuels, offering signifi cant environmental benefi ts and practical applications in the aviation industry.
Alcohol-to-Jet (ATJ)
Alcohol-to-jet (ATJ) technology utilizes biomass-derived alcohols such as ethanol and butanol. The process involves dehydrating the alcohols to form olefi ns, which are then oligomerized and hydrogenated to produce jet fuel. ATJ can utilize a wide range of biomass sources, making it a fl exible option for SAF production. The chemistry behind ATJ involves catalytic steps historically used in the petroleum refi ning industry, converting alcohols into long-chain hydrocarbons suitable for jet fuel. ATJ fuels are used by airlines and supported by companies like Lanza Jet, which has made signifi cant strides in commercializing this technology. Studies have indicated that ATJ fuels can achieve a reduction in greenhouse gas emissions of up to 70 percent compared to conventional jet fuels.
One study by Geleynse et al. was to provide an economic evaluation of the ATJ conversion pathway for producing drop-in biofuels. The study found that the utilization of isobutanol offers a 34 percent lower conversion cost for the catalytic upgrading process compared to ethanol2
. Another
study by Yao et al. aimed to conduct a stochastic techno- economic analysis of ATJ fuel production, focusing on the uncertainties in feedstock costs, conversion effi ciencies, and market prices. The study showed that sugarcane is the lowest-cost feedstock with the least risks, followed by corn grain and switchgrass, with mean breakeven jet fuel prices of $0.96/L, $1.01/L, and $1.38/L, respectively23
Figure 2. This graph compares the effi cacy of three technologies in terms of their GHG Emission Reduction
mechanisms, surface chemistry, and catalyst formulation. The study highlighted that the optimized catalyst formulation could achieve a 20 percent increase in conversion effi ciency6
Its comprehensive overview of the FT process can guide future research and development efforts to optimize catalyst performance and reactor design, ultimately supporting the large-scale production of FT fuels and their adoption in the aviation industry. The progress and research in FT synthesis highlight its potential to transform sustainable aviation fuel production, providing signifi cant environmental advantages and facilitating its wider adoption in the aviation sector.
Pyrolysis . This contributes
to understanding the economic risks and benefi ts associated with ATJ fuel production, providing valuable insights for investors and policymakers to support the development and commercialization of ATJ fuels. The advancements and research in ATJ technology highlight its potential as a versatile and economically viable solution for sustainable aviation fuel production, signifi cantly contributing to the reduction of greenhouse gas emissions in the aviation industry.
Fischer-Tropsch (FT) Synthesis
Fischer-Tropsch (FT) synthesis uses feedstocks like biomass, municipal solid waste, and other carbon-rich materials. These feedstocks are gasifi ed to produce syngas, a mixture of hydrogen and carbon monoxide, which is then converted into liquid hydrocarbons through the FT process. FT can produce high-quality jet fuel and other valuable co-products. The chemistry behind FT involves the catalytic conversion of syngas into hydrocarbons, a process that can be tailored to produce specifi c types of fuels. FT fuels are used by various industries, including aviation, with companies like Velocys optimizing the process for SAF production.
Research has demonstrated that FT fuels can reduce lifecycle greenhouse gas emissions by up to 90 percent compared to conventional jet fuels21
. One study by Chai et al. provided
a detailed mechanistic understanding of FT synthesis on Fe-carbide catalysts, focusing on the kinetic and mechanistic aspects of the process. The study found that the Fe-carbide catalysts exhibited a 15 percent increase in selectivity for long-chain hydrocarbons5
. Another study by Mahmoudi et al. (2017) aimed to review the FT processes, including the
Pyrolysis involves heating biomass and waste materials in the absence of oxygen to produce bio-oil, which can be refi ned to jet fuel. Pyrolysis can handle a wide variety of feedstocks and produce multiple types of biofuels. The chemistry behind pyrolysis involves the thermal decomposition of organic materials, resulting in the production of gases, liquids, and solid residues. Pyrolysis fuels are used in various applications, including aviation, with ongoing research to improve the effi ciency and scalability of the process. Studies have shown that pyrolysis-based SAFs can achieve signifi cant reductions in greenhouse gas emissions, depending on the feedstock and process conditions.
One such study by Watanasiri et al. explored the potential of catalytic fast pyrolysis (CFP) to produce SAFs. This research focuses on the catalytic fast pyrolysis of biomass, including wood, woody residues, and agricultural waste, to generate organic liquid intermediates. The study’s primary objective was to predict the properties of SAF fuels derived from the hydroprocessing of CFP-based oxygenated organic intermediates. The impact of this study on the fi eld of sustainable aviation fuels is signifi cant. Firstly, it demonstrates the viability of using biomass and waste materials as feedstocks for SAF production, which can help reduce reliance on fossil fuels and lower greenhouse gas emissions. The use of catalytic fast pyrolysis to convert these feedstocks into organic intermediates offers a promising pathway for producing high-quality SAFs. Additionally, the study’s focus on property predictions provides a framework for evaluating the performance and suitability of CFP-derived SAFs, which is crucial for their adoption in the aviation industry. The study found that the SAF produced had a carbon yield of 28 percent during the CFP process and an overall carbon yield to SAF of 11 percent, which provides valuable insights into the production and properties of SAFs derived from catalytic fast pyrolysis of biomass. It highlights the potential of this technology to contribute to the development of sustainable aviation fuels, offering a pathway to reduce the aviation sector’s carbon footprint and enhance energy security. The progress in pyrolysis technology highlights its potential to play a crucial role in producing sustainable aviation fuels, thereby helping to reduce the aviation industry’s carbon footprint and improve energy security
Power-to-Liquid Fuels .
Power-to-liquid (PtL) technology uses renewable electricity, water, and captured carbon dioxide as feedstocks. The process involves splitting water into hydrogen and oxygen using renewable electricity (electrolysis). The hydrogen is then combined with captured CO2
. Electrofuels (E-fuels)
to produce hydrocarbons
through the Fischer-Tropsch process. PtL fuels can achieve near-zero or even negative carbon emissions, depending on the source of electricity and CO2
are produced using a similar process, combining hydrogen (from water electrolysis) with CO2
to create synthetic
hydrocarbons. E-fuels offer a sustainable alternative to fossil fuels and can be produced using excess renewable energy. E-fuels and Power-to-Liquid (PtL) fuels are synthetic fuels produced using renewable electricity and captured CO2
,
but they differ mainly in their applications and production processes. E-fuels encompass a broad category of synthetic fuels, including e-diesel, e-gasoline, and e-jet fuel, designed to be used in existing internal combustion engines and infrastructure without modifi cations. This versatility makes them suitable for various transport sectors, such as aviation, marine, and heavy-duty road transport. In contrast, PtL fuels specifi cally refer to liquid hydrocarbons produced through the Fischer-Tropsch (FT) process, primarily aimed at replacing conventional jet fuels in aviation. PtL fuels can be blended with traditional kerosene and transported using existing fossil fuel infrastructure. Thus, while both e-fuels and PtL fuels are produced using similar processes, e-fuels offer a wider range of applications, whereas PtL fuels are tailored specifi cally for aviation use.
Recent advancements in PtL technology have shown promise in reducing production costs and improving effi ciency. The main objective of the study by Schmidt et al. was to explore the potential and perspectives for the future supply of renewable aviation fuel through PtL technology²⁰. The study by Brynolf et al. aimed to review the production costs of electro fuels for the transport sector, including PtL fuels²¹. They found that while current production costs are high, ongoing technological advancements and economies of scale could make electro-fuels more competitive with conventional fuels in the future. For example, Brynolf et al. found that production costs for PtL fuels could decrease by up to 50 percent with technological advancements and increased production scale. Ultimately, the progress in PtL and electro-fuel technologies underscores their potential to transform the aviation sector by offering sustainable and cost-effective alternatives to traditional jet fuels.
Recent Technological Advancements
Recent technological advancements in the past two years have further propelled the development of SAFs. Synhelion has developed a unique process to produce carbon-neutral solar fuels using concentrated solar energy to drive thermochemical reactions. This technology has the potential to produce SAFs with a signifi cantly lower carbon footprint by utilizing solar
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