Sustainable Aviation Fuels

In recent years, biofuels have gained prominence due to their crucial role in reducing carbon emissions and promoting a more sustainable aviation industry. This study investigates these alternative fuels’ production processes, benefits, and challenges. Bibliometric analysis has revealed a significant increase in cited articles on biofuels between 2004 and 2024. Countries such as the United States, England, and Australia play an essential role in this research landscape by investing in sustainable fuel production. The keyword analysis indicates growing interest in this field, with terms like “biofuel,” “biomass,” and “bioenergy” being most sought after by researchers. It is worth noting that sustainable aviation fuels (SAFs) utilize biomass from agricultural and forest residues, animal fats, and vegetable oils (including microalgae, sunflower, and palm oil), making them promising new technologies. However, technological challenges and market issues must still be overcome for these biofuels to reach their full potential in aviation. Future research should focus on innovative technologies to address production costs and other challenges. Ultimately, the global commitment to sustainability in aviation is not only an environmental necessity but also an opportunity for innovation and leadership in the sector. As green fuel technologies evolve, they will pave the way for cleaner, more efficient, and responsible aviation.

To achieve high-volume, cost-effective, and easily integrated SAF production, several key challenges must be addressed, including low carbon yields from SAF production, reliable feedstock sources, and competition from renewable diesel. This chapter explores the gaps and opportunities to facilitate the production of SAF as an alternative to fossil-based jet fuels. This chapter details SAF’s chemical composition, ASTM approval process, current approved SAF production technologies, and the challenges and renewable feedstocks involved in SAF production. Thermochemical and biochemical routes to SAF from renewable carbon are discussed, including R&D priorities, and techno-economic analysis (TEA) and life cycle assessment (LCA) for evaluating economic and sustainability potential.

Petroleum jet fuel, recognized for its remarkable efficiency as an energy carrier, is predominantly utilized in the aviation industry. The aviation sector is responsible for around 2.5% of worldwide CO₂ emissions and has contributed roughly 4% to global warming to date. The quest for sustainable aviation fuels (SAFs) is accelerating due to their economic viability and ecological benefits. Biomass-derived sustainable aviation fuel exhibits properties akin to traditional jet fuel while significantly diminishing its carbon footprint, hence reducing greenhouse gas emissions associated with flight. Microalgal biomass has been exploited as an excellent feedstock for sustainable aviation fuel generation and is attracting considerable interest because of its exceptional biomass output, high lipid and carbohydrate content, and cost-effective culture methods. This chapter focuses on the processing of microalgal biomass for bio-oil synthesis and its subsequent enhancement to sustainable aviation fuels (SAFs). A succinct analysis of the fuel characteristics related to SAFs is provided.

The aviation industry plays a vital role in global commerce and transportation, but its heavy reliance on fossil fuels has significant environmental impacts. To address this, there is a growing interest in green fuels, which substantially reduce carbon emissions compared to traditional fossil fuels. Producing these renewable fuels on a large scale faces several challenges, such as the availability and sustainability of raw materials. Sources like agricultural and forestry waste, algae, and urban waste align with circular economy principles, but their consistent supply and high production costs are significant hurdles. Technological advancements, such as biocatalysts, and collaborations between public and private sectors are helping overcome these challenges. Political measures, including subsidies and carbon pricing, also support the development of biofuels. This study provides a comprehensive analysis of biofuels in the aviation industry by reviewing research from the past decade. Using data from the Web of Science (WoS) database, we conducted a bibliometric analysis with tools like CiteSpace and Microsoft Excel. From 2014 to June 2024, 719 scientific publications and 15,956 citations were analyzed. The United States emerged as the leading contributor, with 202 publications and 5100 citations. However, journals from the Netherlands had the highest impact factors, exceeding 11.0, and produced the most cited articles, highlighting the quality of their research. Our analysis also shows a growing research trend, with a notable increase in publications from 2014 to 2023, peaking at 125 publications and 3465 citations in 2023. This represents a 594% increase in publications and a 38,400% increase in citations. Although 2024 data only covers the year’s first half, it includes 46 articles and 1562 citations. These findings underscore the increasing momentum in biofuel research and the critical role of technological and policy support in advancing sustainable aviation fuels.

This chapter delves into the imperative need for green and sustainable aviation fuels, highlighting the urgency for the aviation industry to reduce its carbon footprint. It thoroughly examines various bio-jet fuel conversion technologies, including Fischer–Tropsch synthetic paraffinic kerosene (FT-SPK), hydroprocessed esters and fatty acids (HEFA), synthesized iso-paraffins (SIP), FT-SPK with aromatics (FT-SPK/A), alcohol-to-jet (ATJ), hydroprocessed hydrocarbons SPK (HH-SPK), and catalytic hydrothermolysis jet (CHJ), which were certified in the American Society for Testing and Materials (ASTM) standard in sequence. These technologies have been evaluated for their technological routes, economic feasibility, environmental impact, and scalability, providing a comparative analysis of their strengths and limitations and discussing their potential to transform the aviation sector into a more environmentally sustainable one. The HEFA and FT-SPK routes have been identified to be the most economically viable, while ATJ is not financially viable under the current prevailing market price for crude oil. The necessity of the presence of aromatics within SPK is highlighted, with the aim of achieving satisfactory compatibility with the current infrastructure. The commercial practices and flight tests of aviation biofuels are also discussed. Overall, this chapter significantly contributes to understanding the potential of aviation biofuels in achieving environmental sustainability in the aviation sector.

This chapter explores the production of sustainable aviation fuels (SAFs) from the hydroprocessing of liquid biomass fractions. Various liquid streams are derived from biomass, including bio-oil, Fischer–Tropsch (FT) wax, triglycerides, waste cooking oil, and terpenes. The challenges in converting these fractions are analyzed, such as oxygen removal and meeting industry standards for aviation fuels. It also examines catalytic processes such as hydrodeoxygenation (HDO), hydroisomerization, and hydrogenation, along with their roles in SAF production. Additionally, the chapter emphasizes the importance of sustainable hydrogen sources and the need for further research to develop cost-effective and environmentally friendly catalytic materials and processes. By optimizing these strategies, the aviation industry can move toward decarbonization and a greener future.

Aviation is a prominent source of greenhouse gas emissions. The undeniable environmental consequences of the ongoing reliance on conventional oil-derived fuels have spurred international initiatives towards alternative solutions. Cost-effective and environmentally sustainable aviation fuels (SAFs) are acknowledged as an essential component in separating carbon emissions from market expansion. Several industrial commitments and collaborations have arisen to explore alternate methods of producing bio-aviation fuels. The current focus of this study of research lies in the conversion of biomass-derived sources into bio-jet fuels at a commercial or pre-commercial level. This study provides an overview of the production method and technologies employed in the production of the fuel, the type of raw materials used and the potential for widespread use of these alternative fuels in the future. The prospects and challenges of the technologies as well as recent research focus in the area are also incorporated as the highlights.

Nowadays, the production of renewable fuels depends not only on selecting raw materials such as biomass to develop a green industry but also on using tools in the design of future chemical processes. These add up to a decrease in environmental impact considering economic and social aspects, all of this in order to have advanced sustainable processes. The production of aviation biofuels is a good example, as different alternatives have been developed, such as the route to obtain this type of biofuel considering the characteristics requested by the aviation industry or the adaptation of hybrid equipment, which requires less space and services to obtain the desired products. The application of process intensification and integration strategies are of great use for the development of a cleaner industry. The integration of these two lines of research results in advanced processes from a sustainable perspective, which contribute to the decarbonisation of the industry.

The global shift toward environmentally friendly renewable fuels is necessary to reduce dependence on fossil fuels and meet the climate goals established by competent international organizations. The aviation sector, a major GHG emitter, must reduce emissions to mitigate environmental impacts. In this context, the use of biojet fuels (or Sustainable Aviation Fuels, SAFs) as “drop-in” fuels has received great attention since it is considered the most efficient and fastest technique towards decarbonization. However, current technologies for converting biomass into biojet fuel have a high production cost and sales prices are not competitive with those of fossil jet fuel. Thus, this study evaluated the potential of an integrated system for biojet fuel production to satisfy the demand of the Brazilian market. The system was made up of four technologies: Alcohol-to-jet (ATJ), Fischer-Tropsch (FT), Syngas fermentation (SF), and direct sugar hydrocarbons (DSHC) using sugarcane as raw material, and jatropha fruit was also considered as raw material for the HEFA route. On the other hand, a techno-economic and environmental assessment was carried out to estimate the sales price of biojet fuel, the number of hectares to be used in biomass cultivation and the environmental impact generated in the production chain. The results demonstrated that an integrated system is a promising alternative for biojet fuel production generating an attractive sales price (1.09 US$ l⁻¹) compared to individual conversion routes and a competitive sales price (0.55 US$ l⁻¹) against fossil jet fuel. In addition, the use of hectares is reduced and environmental impacts are approximately similar to those generated by the individual conversion route as long as an adequate share (%) of a given route is chosen.

The aviation sector faces big challenges in order to promote its sustainable growth, and in recent years, this sector has been pioneering leading strategies to achieve its decarbonization. Among them, the production and use of sustainable aviation fuel highlights. This biofuel can be used in existing aircraft, guaranteeing technical, safety, and environmental criteria. Nevertheless, the main challenge is the achievement of economic feasibility, with regard to its fossil counterpart. In this context, the biorefinery is a processing scheme that allows the complete use of biomasses for the production of biofuels, value-added products as well as bioenergy. In this processing scheme, the profitability relies on several products, which can help to reach the economic feasibility of this aviation biofuel. Therefore, this chapter presents a revision on the use of biorefineries for the production of sustainable aviation fuel. Moreover, future trends related to the production of this biofuel through biorefineries are discussed.

Nowadays, the production of transport fuels from renewable sources promises a positive impact due to their low carbon footprint. Studies have shown a lower impact on CO₂ emissions during the combustion of these biofuels. Despite this, and together with their production, an emission cycle is maintained which supports the decarbonization goals of the energy industry. On the other hand, the transport industry is demonstrating objectives to reduce the effects of climate change through the implementation of biofuels, and efforts to use them have been no exception. This is not an easy task for aviation systems, as there are limitations compared to ground transport due to the nature of the aviation fuels that have been deployed and the effects they have on combustion, emissions, and performance.

Air transport serves as a fundamental driver of global economic growth, playing a pivotal role in generating employment opportunities, fostering international trade, fueling the tourism industry, and underpinning sustainable development on a global scale. It serves as a conduit for global connectivity and a catalyst for both social and economic prosperity. However, amid these manifold benefits, the aviation sector faces substantial challenges, the most significant of which is the carbon dioxide (CO₂) emissions produced by fossil jet fuels.

Despite accounting for a relatively modest 2–3% of global carbon emissions, the aviation industry faces a discouraging trajectory, with emissions projected to escalate dramatically, potentially reaching as high as 22–30% by mid-century due to the industry’s growth.

This chapter examines the intricate challenges surrounding the pursuit of environmental sustainability within the aviation ecosystem, with a particular focus on the CO₂ emissions originating from flight operations. While the aviation industry often spotlights airlines and their operations, it is essential to recognize the multitude of companies and stakeholders intricately involved in aviation activities. Key stakeholders encompass airports, ground handling companies, air navigation service providers, and regulatory authorities. The interplay among these entities significantly influences each other’s success, impacting sustainability initiatives within the broader aviation ecosystem.

This chapter presents an overview of the distinctive characteristics of the aviation ecosystem, providing insights into its current market dynamics and the evolving landscape of sustainability considerations. We consider the complexities of fostering an environmentally sustainable aviation ecosystem in the context of the challenges that must be overcome. To achieve our collective environmental sustainability objectives, the aviation ecosystem must establish shared goals, aligned action plans, and comprehensive metrics. Regulatory frameworks play a pivotal role in facilitating this alignment, ultimately maximizing the environmental sustainability of the aviation sector as a whole.

Countries worldwide are actively developing and implementing updated policies related to sustainable energy transition. The need to transition to biofuels with a low-carbon footprint is growing due to global efforts to replace fossil fuels incrementally with other sources, such as biofuels, including those for aviation. Aviation fuels refer to petroleum-based fuels or blends of petroleum and synthetic fuels used to power aircraft. To decrease emissions, airlines can transition from petroleum-based fuels to sustainable aviation fuel (SAF). The International Air Transport Association (IATA) states that SAF could help airlines cut emissions by 65%, achieving net-zero carbon emissions from their operations by 2050. However, the production of aviation fuels has significant environmental and techno-economic impacts that need to be considered.

The techno-economic analysis (TEA) and life cycle assessment (LCA) of SAF production evaluate the feasibility and profitability of producing SAF from different feedstocks and process technologies, along with its environmental and social impact. Scientists and engineers are developing and optimizing conversion technologies and manufacturing strategies, while the state of the art in TEA and LCA for SAF is evolving. Currently, there are key areas of research and development. One critical area focuses on the development of advanced feedstocks and conversion technologies. This includes exploring the use of nonfood crops such as algae or cellulosic waste biomass and developing more efficient and cost-effective conversion processes, such as pyrolysis or gasification.

Another area of research involves enhancing process efficiency and economics. This includes optimizing feedstock selection, evaluating different biorefinery concepts, and reducing energy and water consumption. Additionally, there is growing interest in integrating SAF with other industries, such as power or chemical conversion, to take advantage of economies of scale and reduce costs.

Evaluating the economic and environmental sustainability of SAF is a crucial area of research, and there are ongoing efforts to improve the assessment methodologies and metrics used to evaluate these factors. The development of advanced feedstocks and conversion technologies is critical to the success of SAF, as is evaluating the environmental and social impact of the production process. The use of nonfood crops such as algae or cellulosic waste biomass can help increase the sustainability of SAF and decrease the reliance on food crops. The efficient and cost-effective conversion of these feedstocks into SAF is also an area of intense research. Pyrolysis or gasification, for example, can be used to convert feedstocks into SAF.

Optimizing feedstock selection and evaluating different biorefinery concepts can improve process efficiency and reduce costs. Reducing energy and water consumption during the production process is also critical. Integrating SAF with other industries, such as power or chemical conversion, can help reduce costs and take advantage of economies of scale. This approach can help increase the sustainability of the production process and make SAF more economically viable. To ensure the economic and environmental sustainability of SAF, ongoing research is focused on improving the assessment methodologies and metrics used to evaluate these factors. The development of advanced feedstocks and conversion technologies, as well as the evaluation of the environmental and social impact of the production process, is critical to the success of SAF.

Sustainable aviation biofuels are emerging as environmentally preferable alternatives to conventional petroleum-derived fuels due to their reduced environmental footprint through mitigating greenhouse gas emissions. This study aims to delve into the substantial strides made in the research and production of these biofuels, encompassing the development of cutting-edge technologies and highly efficient production processes. An extensive analysis conducted on the Web of Science database from 2014 to 2024 identified a substantial corpus of 541 publications pertinent to the subject matter. The United States emerged as the preeminent contributor with 166 articles, closely followed by China with 139. Within the domain of energy fuel research, there was a notable representation of 35.1% of the total scholarly output. Despite the promising potential of sustainable aviation biofuels (SAFs), significant hurdles remain, notably the constrained availability of sustainable feedstock on a commercial scale, which could impede the economic feasibility of large-scale production. Nonetheless, SAFs signify a pivotal opportunity to advance the sustainability agenda within the aviation sector and foster long-term environmental stewardship. This necessitates sustained research, innovation and infrastructural development investments to catalyse their widespread production and utilization, aligning with overarching ecological objectives.

According to the International Energy Agency, transport sector accounts for more than a third of CO₂ global total emissions. Inside this sector, road transportation contributes with almost 75% of the emissions, followed by aviation with 12%. In spite of the fact that the contribution of aviation is small, the growth forecasts indicated that it could significantly be increased. Due to this, the aviation sector established goals and strategies to achieve its decarbonization and ensure its sustainable development. These strategies include improvements in the efficiency of engines, operational measures, emissions market trade, and also sustainable aviation fuels. Among all of them, the production and use of sustainable aviation fuel is the most promising to be implemented in the short term, as no modifications or replacement of the existing aircraft is required. This biofuel can be produced from any biomass through several production processes. Therefore, in this chapter, a future outlook regarding what has been done and where the efforts need to be focused is discussed.