New continuous reaction process can help turn plant waste into sustainable aviation fuel

Published in the journal Fuel Processing Technology, the team's research demonstrated a continuous process that directly converts lignin polymers, one of the chief components of plant cells, into a form of jet fuel that could help improve performance of sustainably produced aviation fuels.

"Our 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 lead scientist Bin Yang, professor in WSU's Department of Biological Systems Engineering.

A class of structural molecules that make plants tough and woody, lignin is derived from corn stover -- the stalks, cobs and leaves left after harvest -- and other agricultural byproducts.

The team developed a process called "simultaneous depolymerization and hydrodeoxygenation," which breaks down the lignin polymer and at the same time removes oxygen to create lignin-based jet fuel. At their Richland facility, the scientists introduced dissolved lignin polymer into a continuous hydrotreating reactor to produce the fuel.

Global consumption of aviation fuel reached an all-time high of nearly 100 billion gallons in 2019, and demand is expected to increase in the coming decades. Sustainable aviation fuels derived from plant-based biomass could help minimize aviation's carbon footprint, reduce contrails and meet international carbon neutrality goals.

Lignin-based jet fuel could make sustainable fuels cleaner and more easily usable in jet engines. Thanks to their density, efficiency, and seal-swelling characteristics, hydrocarbons catalyzed from lignin could effectively replace fossil fuel-derived compounds called aromatics. Associated with contrails and climate impacts, aromatics remain in use because they enhance fuel density and help swell O-rings in metal-to-metal joints.

This research marked the team's first successful test of a continuous process, which is more feasible for commercial production. The project also used a less processed, less expensive form of lignin derived from corn stover, dubbed "technical lignin," contrasting similar research using extracted lignin bio-oil.

The team's findings suggest lignin is a promising source of aromatic-replacing cycloalkanes and other useful fuel compounds.

"The aviation enterprise is looking to generate 100% renewable aviation fuel," said Josh Heyne, research team member and co-director of the WSU-PNNL Bioproducts Institute. "Lignin-based jet fuel complements existing technologies by, for example, increasing the density of fuel blends."

Offering reduced emissions, lignin-based fuel could ultimately make sustainable aviation fuels fully "drop-in" capable, meaning they can be used with all existing engines, infrastructure and aircraft like existing fossil-derived aviation fuel.

"We're working to create an effective, commercially relevant technology for a complementary blend component that can achieve the 100% drop-in goal," Heyne said.

The research was supported by the U.S. Department of Energy's Bioenergy Technologies Office, the Pacific Northwest National Laboratory, the National Renewable Energy Laboratory and Advanced Refining Technologies LLC.

The team is now working to refine their process for better efficiency and reduced costs.