Sustainable jet fuel could be made from corn stover and other plant waste, according to new research from Washington State University. The team used a continuous process that directly converts lignin polymers, one of the chief components of plant cells, into a type of jet fuel that has the potential to make sustainable aviation fuels (SAF) cleaner and more compatible with jet engines.
According to the researchers, hydrocarbons derived from lignin could replace fossil fuel-based aromatics, which are used to increase fuel density and maintain O-ring seals in metal joints. Aromatics interact with the polymer seals in a jet’s fueling system, causing them to swell and preventing fuel leakage and fire risk.
While aromatics make up a relatively small percentage of jet fuel, they are nonetheless a necessary component. The need for aromatics also limits the percentage of sustainable aviation fuel (SAF) that can be added. To meet the global Jet A fuel specification, synthetic fuels must contain between 8-25% aromatics. That means only a maximum of 50% SAF can be blended with traditional jet fuel.
Aromatics are a class of hydrocarbons that are conventionally derived from crude oil, as well as coal and natural gas. When burned, aromatics produce more soot than other hydrocarbons, which contribute to the formation of contrails and toxic air pollution.
Lignin is a class of structural molecules that make plants tough and woody. It can be derived from many agricultural byproducts, including corn stover, aka “technical lignin,” in the case of the WSU research.
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.
Notably, the research marked the team’s first successful test of a continuous process, which is more feasible for commercial production. “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.
Yang and his associates believe lignin-based aromatics could effectively replace fossil fuel-derived compounds. Lignin-based fuel could also 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.
The team is now working to refine their process for better efficiency and reduced costs. 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. (Sources: WSU, AviationWeek, LabManager)
