An underused natural resource could be just what the airline industry needs to cut carbon emissions. The United States Department of Energy’s National Renewable Energy Laboratory (NREL), the Massachusetts Institute of Technology (MIT), and Washington State University have reported success in using lignin as a pathway toward a drop-in, 100 percent sustainable aviation fuel.Lignin comprises the rigid components of plant cell walls. Other parts of plants are used as biofuels, but lignin hasn’t been used much because it’s hard to break down chemically and turn it into useful products. According to newly published research, researchers have developed a method to remove oxygen from lignin so that the resulting hydrocarbons can be used as jet fuel blendstock. This study is called “Continuous Hydrodeoxygenation of Lignin to Jet-Range Aromatic Hydrocarbons” and it is published in the journal Joule.
NREL researchers Gregg Beckham, Ana Morais, and Earl Christensen are involved.
As the airline industry has pledged to significantly reduce carbon emissions, the paper emphasizes the importance of utilizing jet fuel derived from sustainable sources. In 2019, airlines worldwide consumed 106 billion gallons of jet fuel, a number that is expected to more than double by 2050. For the industry to reach its goal of net carbon neutrality in the same time frame, it will need to use a lot of sustainable aviation fuel (SAF) that can be mixed with a lot of regular fuel.
Jet fuel is a blend of various hydrocarbon molecules, such as aromatics and cycloalkanes. Current commercialized technologies are incapable of producing the necessary components for a 100% SAF. SAF blendstocks are instead combined with conventional hydrocarbon fuels. As the largest natural source of renewable aromatics, lignin may hold the key to producing a fully bio-based jet fuel. This recently published work demonstrates the complementarity of a lignin pathway with existing and developing pathways. The lignin pathway described in this new work makes it possible for the SAF to work with a fuel system at higher blend ratios.
Lignin is typically burned for heat and power or utilized in low-value applications due to its recalcitrance. Prior research has produced lignin oils with high oxygen content ranging from 27% to 34%. However, for use as jet fuel, this percentage must be reduced to less than 0.5%.
There have been other attempts to reduce the oxygen content, but the catalysts required costly noble metals and proved to be inefficient. In a continuous process, researchers from the three institutions showed that a lot of molybdenum carbide could be used as a catalyst to make a solution with about 1% oxygen.
The research was paid for by the U.S. Department of Energy’s Bioenergy Technologies Office and Center for Bioenergy Innovation.
NREL is the primary national laboratory of the U.S. Department of Energy for renewable energy and energy efficiency research and development. The Alliance for Sustainable Energy, LLC operates NREL on behalf of the Energy Department.
