WSU Scientists Transform Agricultural Waste into Sustainable Jet Fuel

Lignin: An Untapped Resource for Sustainable Aviation Fuel

Lignin is a class of complex structural molecules that give plants their woody characteristics, making them rigid and resistant to degradation. It is derived from agricultural byproducts such as corn stover—the stalks, cobs, and leaves left after harvest—and is considered a waste product in many agricultural processes.

According to Professor Bin Yang, the lead researcher and a professor in WSU’s Department of Biological Systems Engineering, this development represents a critical step forward in utilizing agricultural waste to create renewable aviation fuel.

The aviation industry has significantly contributed to greenhouse gas emissions, consuming nearly 100 billion gallons of fuel in 2019. As global fuel demand is expected to increase by 32% by 2030 and potentially more than double by 2050, the need for alternative fuels is more pressing than ever.

In response, the aviation sector has focused on sustainable aviation fuels (SAFs) derived from renewable resources like plant-based biomass. However, despite the progress made in biofuels, current technologies still face challenges in meeting the aviation industry’s strict performance and volume requirements.

Lignin, often discarded or underutilized in biorefining processes, presents a promising new pathway for sustainable fuel production. It is produced in large quantities—about 300 million tons annually—and its aromatic structure makes it a viable candidate for jet fuel. However, converting lignin into fuel continuously has been a challenge until now. The WSU team’s research builds on this potential by demonstrating a novel process that could overcome many technical hurdles.

Innovative Technology: Simultaneous Depolymerization and Hydrodeoxygenation

The WSU researchers developed "simultaneous depolymerization and hydrodeoxygenation" (SDHDO), which breaks down the lignin polymer into smaller molecules while simultaneously removing oxygen. This process converts lignin into hydrocarbons, which can be used to produce lignin-based jet fuel.

The key innovation in this research is the ability to perform this conversion continuously, making it more feasible for commercial-scale production. The industry prefers Continuous processes because they can operate without interruptions, increasing efficiency and reducing costs.

The research was conducted at WSU’s facility in Richland, Washington, where the scientists introduced dissolved lignin polymers into a hydrotreating reactor to produce jet fuel. This continuous process contrasts with previous research that used batch processing, which is less efficient for large-scale production. The WSU team’s success in creating a continuous process marks a significant milestone toward commercializing lignin-based aviation fuel.

“This achievement takes this technology one step closer to real-world use by providing data that lets us better gauge its feasibility for commercial aviation,” said Professor Yang. “We now have a clearer understanding of how this process can be scaled up, making it a strong candidate for sustainable aviation fuel production.”

The Potential of Lignin-Based Jet Fuel in Aviation

Aviation is a notoriously difficult sector to decarbonize due to its heavy reliance on energy-dense liquid fuels and the challenges of electrifying aircraft. Sustainable aviation fuels are a key solution to reducing the industry’s environmental impact, and lignin-based fuels offer several advantages.

One of the primary benefits is that lignin-derived hydrocarbons can replace aromatics. These fossil fuel-derived compounds enhance fuel density and contribute to contrail formation and other environmental impacts. Aromatics are still widely used in jet fuel because they help swell O-rings in metal-to-metal joints, making them critical to fuel system performance. However, they are also a significant soot source, which has environmental and health consequences.

Lignin-based fuels could offer a cleaner alternative to fossil fuel-derived aromatics, helping to reduce the formation of contrails and improve fuel performance. In addition, the hydrocarbons produced from lignin are dense, efficient, and compatible with existing aviation infrastructure. These characteristics make lignin-based jet fuel a strong contender for use in commercial aviation, as it can be blended with conventional jet fuels to increase the renewable content while maintaining the performance characteristics required by airlines.

Overcoming Challenges for Commercialization

One of the most significant challenges facing the aviation industry is the need for “drop-in” fuels—fuels that can be used without modifying existing aircraft engines or fueling infrastructure. Lignin-based jet fuels have the potential to meet this requirement, as they offer sealing properties, energy density, and emissions profiles similar to conventional jet fuel. The WSU team’s research demonstrated that lignin-based jet fuel could be blended with conventional fuels to create a drop-in solution, moving the industry closer to producing 100% renewable aviation fuels.

The research also addressed another critical challenge: the cost and complexity of producing sustainable fuels. Using a less processed form of lignin, known as “technical lignin,” the team could reduce the cost and energy input required to produce the fuel. This contrasts with other studies that used highly processed lignin bio-oils, which are more expensive and energy-intensive.

The continuous process developed by WSU also used engineered catalysts, including a ruthenium-based catalyst (Ru-HY-60-MI), which proved effective in converting lignin into jet fuel range hydrocarbons. The researchers were able to achieve a carbon yield of 17.9%, producing a fuel rich in mono cycloalkanes and poly cycloalkanes, which are critical components for aviation fuel performance.

A Sustainable Path Forward for Aviation

The WSU team’s research represents a critical step toward making sustainable aviation fuels commercially viable. The successful demonstration of a continuous process for producing lignin-based jet fuel shows that agricultural waste can be transformed into a valuable resource for the aviation industry. By utilizing lignin, which is often discarded or burned, this technology not only provides a renewable alternative to fossil fuels but also contributes to waste reduction and more efficient resource use.

In the broader context of global sustainability goals, the aviation industry has set ambitious targets to reduce its carbon footprint. The International Air Transport Association (IATA) has committed to achieving net-zero carbon emissions by 2050, and sustainable aviation fuels will play a crucial role in meeting this goal. Lignin-based jet fuel offers a promising pathway to achieving these targets by reducing emissions, improving fuel efficiency, and providing a renewable alternative to fossil fuels.

The research was supported by several prominent organizations, including the U.S. Department of Energy’s Bioenergy Technologies Office, the Pacific Northwest National Laboratory (PNNL), the National Renewable Energy Laboratory (NREL), and Advanced Refining Technologies LLC.

With continued support and further refinement of the technology, lignin-based jet fuel could become a vital component of the aviation industry’s efforts to reduce its environmental impact and transition to a more sustainable future.