The paper industry produces millions of tons of lignin as an unwanted waste product. Researchers have now used the organic plant material to make a jet fuel that they say could give its petroleum-based counterpart a run for its money.
The lignin-derived jet fuel should give higher performance and fuel efficiency with fewer emissions and lower cost than conventional fuel, the team reported in the journal Fuel. And it could be mixed with other biofuels to be a drop-in replacement for fossil fuels.
The airline industry, under pressure to reduce its carbon emissions and meeting environmental standards, is looking keenly at sustainable aviation fuels as a path forward. Delta, JetBlue, and United Airline have all recently signed big agreements to purchase millions of gallons of bio jet fuels over the next decade or two. Much of it is made from used cooking oil and waste animal fat.
The new work uses a widely available waste product as its raw material. Lignin, a major molecule that makes up plant tissue, is the second most abundant natural material on the earth. It acts as a glue that binds cellulose fibers together to make plant cell walls stiff and strong. But while trees need it, the paper and pulp industry don’t, so they typically burn the waste lignin for fuel.
Bin Yang, a biological systems engineer at Washington State University and co-author of the paper, developed a patented process to convert lignin from agricultural waste into bio-jet fuel. He and his colleagues from the University of Dayton and Pacific Northwest National Laboratory used several tests and predictions in the laboratory to analyze fuel properties that are important to jet engine operation, such as fuel energy density, seal swell, efficiency, and emissions.
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The lignin-based fuel had higher density and lower emissions, they found. Conventional jet fuels uses so-called aromatic compounds to provide the higher energy density, which give them the unique and important ability to swell the rings used to seal metal joints in engines. The downside is that aromatics can increase soot emissions and contrails, which contribute to the climate impact of aviation.
But the new biofuel seals the rings just as well as aromatics because of its high density, without the associated emissions. “The fact that these molecules show sealant volume swell comparable with aromatics opens the door to develop jet fuels with virtually no aromatics, very low emissions and very high-performance characteristics,” the authors write.
“This process creates a cleaner, more energy-dense fuel,” Yang said in a press release. “That’s exactly what sustainable aviation fuels need for the future.”