[SMM Science Popularization] Sustainable Aviation Fuel

I. Introduction

With the growing global awareness of environmental protection, the aviation industry, as a major source of carbon emissions, is facing significant pressure to reduce emissions. To achieve sustainable development, the aviation industry is actively exploring new-type fuels, among which Sustainable Aviation Fuel (SAF) has garnered significant attention due to its environmental protection characteristics and emission reduction effects. The Hydroprocessed Esters and Fatty Acids (HEFA) pathway, as one of the main production methods for SAF, offers advantages such as technological maturity and broad commercial application prospects. This article provides a detailed introduction to the hydrogenation of sustainable aviation fuel, including the basic concept of SAF, the principles of the HEFA pathway, production processes, industry status, challenges, and future development trends.

II. Overview of Sustainable Aviation Fuel

Sustainable Aviation Fuel (SAF) refers to aviation fuel produced from biomass raw materials such as animal and plant oils and agricultural and forestry waste through specific processes. This type of fuel has combustion performance similar to traditional fossil jet fuel, but its most significant difference lies in its environmental protection characteristics. SAF can significantly reduce carbon dioxide emissions and is one of the key technologies for achieving the green transformation of the aviation industry.

The raw material sources for SAF are diverse, primarily including animal and plant oils, agricultural and forestry waste, urban waste, and other biomass resources. These raw materials can be processed through pretreatment, conversion, and refining steps to produce SAF that meets jet fuel standards. Compared to traditional fossil jet fuel, SAF significantly reduces carbon dioxide emissions during combustion, helping to mitigate global climate change.

SAF can be used in various ways, either independently or blended with fossil jet fuel. When blended, the mixing ratio of SAF can be adjusted as needed to meet the requirements of different airlines. Additionally, the storage, transportation, and usage methods of SAF are similar to those of traditional jet fuel, requiring no large-scale modifications to existing aviation infrastructure.

III. Hydroprocessed Esters and Fatty Acids (HEFA) Pathway

The Hydroprocessed Esters and Fatty Acids (HEFA) pathway is currently one of the main commercial methods for producing SAF. This pathway converts ester- and fatty acid-based raw materials into hydrocarbon compounds through hydrogenation, producing SAF that meets jet fuel standards.

1. Raw Material Sources

The raw material sources for the HEFA pathway are diverse, primarily including vegetable oils, animal fats, algal oils, and waste oils. These materials are rich in ester and fatty acid compounds, making them ideal raw materials for SAF production.

• Vegetable Oils: Such as soybean oil, rapeseed oil, and palm oil, which are rich in fatty acids and are among the key raw materials for SAF production.
• Animal Fats: Such as lard and tallow, which also contain abundant fatty acids and can be used for SAF production.
• Algal Oils: Algae are fast-growing and highly reproductive organisms with high oil content, making them a potential raw material for SAF production.
• Waste Oils: Such as used cooking oil and gutter oil, which can be processed and utilized for SAF production, achieving resource reuse.

2. Production Process

The production process of the HEFA pathway mainly includes three steps: raw material pretreatment, hydrogenation, and product fractionation.

• Raw Material Pretreatment: This involves purifying, crushing, and transesterifying the raw materials to enhance the efficiency of subsequent hydrogenation. During pretreatment, impurities and moisture in the raw materials must be removed to meet the requirements for hydrogenation.
• Hydrogenation: Under the action of catalysts, the pretreated raw materials react with hydrogen to convert them into hydrocarbon compounds. During hydrogenation, parameters such as reaction temperature, pressure, and catalyst type need to be controlled to ensure smooth reactions and product quality.
• Product Fractionation: The hydrogenated products are fractionated to obtain aviation fuel components with different boiling points. During fractionation, the products are separated and purified based on their boiling points and properties to produce SAF that meets jet fuel standards.

3. Technical Characteristics

The HEFA pathway is characterized by technological maturity, diverse raw material sources, and high product quality.

• Technological Maturity: The HEFA pathway has undergone years of research and development, making the technology relatively mature, reliable, and stable.
• Diverse Raw Material Sources: The HEFA pathway utilizes a wide range of raw materials, including vegetable oils, animal fats, algal oils, and waste oils, which are widely available in nature and easy to obtain.
• High Product Quality: Through hydrogenation and product fractionation, the HEFA pathway produces SAF that meets jet fuel standards, with quality and performance comparable to traditional jet fuel, meeting the needs of airlines.

IV. Industry Status and Challenges

1. Industry Status

Currently, many countries and companies worldwide are investing in the SAF industry, with the HEFA pathway playing a significant role. The current status of the SAF industry includes:

• Capacity Growth: In recent years, global SAF capacity has been steadily increasing and is expected to reach tens of millions of mt per year by 2030, with the HEFA pathway accounting for a significant share.
• Policy Support: Governments worldwide have introduced policies to encourage the production and use of SAF. For example, the US government has set a goal of achieving carbon neutrality in the aviation industry by 2050 and is expected to significantly increase SAF usage in the coming years.
• Corporate Participation: Many airlines, energy companies, and chemical enterprises are entering the SAF industry, actively investing in R&D and production. These companies are driving the development of the SAF industry through technological innovation and collaboration.

2. Challenges

Despite significant progress, the SAF industry faces several challenges:

• Raw Material Supply: The supply of raw materials for the HEFA pathway is constrained by factors such as production, price, and transportation. Additionally, the sustainability and environmental impact of raw materials must be considered.
• Technical Challenges: Although the HEFA pathway is relatively mature, scaling up production presents technical difficulties, such as reducing production costs, improving raw material utilization rates, and enhancing product quality.
• Market Acceptance: Currently, market acceptance of SAF remains low. Some airlines are cautious about SAF's quality and performance, while consumers have concerns about its environmental benefits and cost-effectiveness.
• Policy Support: Although governments have introduced policies to encourage SAF production and use, the strength and effectiveness of these policies need improvement. Furthermore, policy differences between countries create uncertainties for the SAF industry's development.

V. Future Development Trends

1. Technological Innovation

With continuous technological advancements, the SAF industry is expected to see more innovations. For example, improving catalysts, optimizing reaction conditions, and enhancing raw material utilization rates can further increase SAF production and quality. Additionally, new raw material sources and conversion technologies will continue to emerge, providing more possibilities for the SAF industry's development.

2. Diversification of Raw Materials

To overcome raw material supply constraints, the SAF industry will actively explore a wider variety of raw materials. Beyond traditional sources like vegetable oils, animal fats, and algal oils, urban waste and agricultural residues can also be used to produce SAF. These materials are not only widely available but also renewable and environmentally friendly, promoting the sustainable development of the SAF industry.

3. Policy Support and International Cooperation

To promote the SAF industry's development, governments will continue to introduce policies such as financial subsidies, tax incentives, and R&D support. International cooperation will also play a crucial role in advancing the SAF industry. By strengthening international collaboration, technological achievements can be shared, resource allocation optimized, and market expansion facilitated, injecting new momentum into the SAF industry's growth.

4. Growing Market Demand

With increasing global environmental awareness and the rapid development of the aviation industry, the market demand for SAF will continue to grow. In the coming years, SAF usage is expected to rise significantly, becoming a key fuel for the global aviation industry. This will provide ample market space and development opportunities for the SAF industry.

VI. Case Studies

1. Research by the US National Renewable Energy Laboratory (NREL)

The US National Renewable Energy Laboratory (NREL) has conducted a comprehensive analysis of the SAF industry via the HEFA pathway, covering raw material supply, production processes, economics, and sustainability. NREL's research indicates that the HEFA pathway is currently the only commercial method for producing large volumes of SAF. By 2030, the total SAF capacity in the US is expected to reach approximately 960 million gallons per year. Additionally, NREL highlights that future facilities will increasingly be designed to produce both SAF and renewable diesel (RD) to enhance resource utilization and economic efficiency.

2. Development of China's SAF Industry

In recent years, China has also been actively investing in the SAF industry. Energy companies such as Sinopec and PetroChina have been engaging in R&D and production to drive the industry's growth. For instance, SAF produced by Sinopec's Zhenhai Refining & Chemical has been successfully used in the first SAF demonstration flights of China's COMAC ARJ21 and C919 aircraft. Furthermore, China has introduced a series of policies to encourage SAF production and use, creating a favorable policy environment for the industry's development.

VII. Conclusion

The Hydroprocessed Esters and Fatty Acids (HEFA) pathway, as one of the main production methods for Sustainable Aviation Fuel (SAF), is characterized by technological maturity, diverse raw material sources, and high product quality. With the growing global awareness of environmental protection and the rapid development of the aviation industry, the SAF industry will face both opportunities and challenges. Through technological innovation, diversification of raw materials, policy support, and international cooperation, the sustainable development of the SAF industry can be promoted, providing strong support for the green transformation of the global aviation industry.

However, challenges such as raw material supply constraints, technical difficulties, low market acceptance, and policy uncertainties remain in the SAF industry's development. To overcome these challenges, international cooperation and exchange must be strengthened to share technological achievements and optimize resource allocation. Simultaneously, joint efforts from governments, enterprises, and research institutions are needed to drive the continuous development and improvement of the SAF industry.

In the future, with the continuous enhancement of global environmental awareness and technological progress, the SAF industry will embrace broader development prospects. We believe that with concerted efforts, SAF will become a key fuel for the global aviation industry, making significant contributions to the green transformation and sustainable development of the aviation sector.