The Four Core Technical Pathways for Synthetic Sustainable Aviation Fuel (SAF)

2026-01-05

As the global aviation industry accelerates its march towards carbon neutrality, Sustainable Aviation Fuel (SAF) is widely recognized as the most feasible and scalable route for aviation decarbonization in the coming decades. Whether it is the mandatory blending requirements of the EU's ReFuelEU Aviation or the official refueling of SAF in 12 domestic flights in China in 2024, SAF has become a key grasp for the aviation industry to achieve net zero.

Currently, the industry typically adopts three pathways to advance the R&D and application of SAF: Hydroprocessed Esters and Fatty Acids (HEFA), Alcohol-to-Jet (ATJ), and Fischer-Tropsch (FT) synthesis. Each of the three has its own advantages but faces varying degrees of raw material and cost bottlenecks. However, as the industry gradually moves towards the goals of "deep emission reduction" and "zero raw material restrictions", the Power-to-Liquid (PtL) process is emerging as the ultimate development direction in global consensus.

This article will introduce the industry's pathways from the dimensions of technology, raw materials, cost, and scalability, and focus on why PtL, with its disruptive potential, has become the core direction of our company's R&D.

HEFA

A Mature but Constrained Transitional Route

Hydroprocessed Esters and Fatty Acids (HEFA) is currently one of the world's largest commercial-scale SAF processes. Its technical principle is to directly convert recycled oils (using waste cooking oil, vegetable oil, animal fats, etc. as raw materials) into aviation fuel through hydrogenation treatment, featuring high technical maturity and stable product quality. In this field, Honeywell UOP is a representative enterprise in the industry.

However, it is generally acknowledged in the industry that although the synthesis technology of HEFA is relatively mature, there is an insurmountable ceiling in its raw material supply, mainly due to the following reasons:

Limited global waste oil resources
Potential competition with the food and agricultural systems
Significant fluctuations in raw material prices

Therefore, HEFA is more of a current solution rather than a future ultimate solution.

ATJ

Diversified Raw Materials, but Still in the Early Demonstration Stage

The biggest highlight of the Alcohol-to-Jet (ATJ) technology is that ethanol can be used as a unified intermediate to access various types of raw materials and ultimately converted into SAF. Taking LanzaJet's CirculAir™ technology in the United States as an example, it can produce ethanol through multiple pathways:

Bio-fermentation of waste sugars to produce ethanol
Pyrolysis of lignocellulosic biomass to produce ethanol
Gas fermentation of municipal solid waste and industrial waste gas to produce ethanol

LanzaJet流程示意图

The core advantage of ATJ lies in its wide range of raw material sources, no competition with food for arable land, and certain sustainability. However, its commercialization process is still in the demonstration scale stage, with the main limiting factors including:

Unstable ethanol storage and quality
Still low conversion efficiency
Long production chain and high cost

Therefore, although ATJ is a technical pathway with scalable potential, there is still a long development cycle before it can truly realize large-scale commercial application.

High Engineering Complexity

Fischer-Tropsch (FT) synthesis process produces syngas from biomass/solid waste, and then obtains synthetic crude oil through FT synthesis. The technical principle is mature, but its commercialization difficulty lies in:

High cost of front-end syngas production
Complex gas purification process
High engineering integration and large investment

Therefore, although FT can theoretically be scaled up to a large size, it is still limited to demonstration projects in the short term. Currently, Johnson Matthey & BP are focusing on this route.

庄信万丰&英国石油的FT工艺示意图

PtL

The Globally Recognized Ultimate Route

The Power-to-Liquid (PtL) pathway uses green electricity as energy, obtains carbon sources through Direct Air Capture (DAC), electrolytically reduces CO₂ to CO and electrolyzes to produce green hydrogen, and then performs FT or hydrogenation reactions to obtain hydrocarbons and alcohols such as jet fuel. Among all technical pathways, PtL technology is highly anticipated globally due to its raw material independence and extremely low carbon footprint, representing the cleanest and most advanced direction of SAF production technology. Carbonology chooses air-sourced PtL as the core of its R&D based on the following advantages:

1.Unlimited Raw Materials：

Unlike other pathways, Carbonology's air-sourced PtL uses only two raw materials:

Water
Air

Regardless of changes in global population growth, agricultural structure, or solid waste policies, air-sourced PtL will not be constrained by the supply side. This means that air-sourced PtL is the most potential route that can support the comprehensive decarbonization needs of the global civil aviation industry.

2.Strongest Carbon Emission Reduction Capacity: Truly Net Zero in the Whole Life Cycle

Since the carbon source of air-sourced PtL comes from Direct Air Capture (DAC), its life cycle emissions can be reduced to nearly zero. Currently, air-sourced PtL is regarded as the highest-grade SAF by policies.

Therefore, as a medium and long-term solution, air-sourced PtL, with the advantages of low cost, stable raw material sources, and scalable deployment, is expected to become a key technical pathway for SAF synthesis. It is estimated that in the future, the demand for SAF will reach 1/2 conservatively; among them, e-SAF will account for 3/4.

Our R&D and Planning for Air-Sourced PtL

Currently, our R&D center is adopting the latest DAC technology (solution method and solid-state method) + CO₂ electrolytic reduction technology (fiber electrode reactor) to realize the conversion of air-sourced CO₂ into high-value products. The goal is to achieve a significant cost breakthrough, and through modular process layout, ensure the flexibility of operation and expansion, and build a global benchmark project in the future. Our domestic first closed-loop process 100-ton pilot platform adopts dual-line synchronous iteration to quickly screen the optimal process, and conducts technical integration through investment + independent R&D + joint development to achieve industrial chain closed-loop and 100% localization.

We will complete the construction of the 100-ton project by the end of 2025, plan to scale up simultaneously in 2026 for 1,000-ton verification, conduct 10,000-ton commercial application in 2027, and start overseas project development in 2028.

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