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Winter 2018

Corncobs Take Flight: Producing Jet Fuel from Agricultural Waste

Discovering a catalyst to convert renewable resources into jet fuel

Angela Norton

A branched alkane chain jet-fuel molecule, called 6-butylundecane, is made from trifuran (made from corncobs or other agricultural waste) with an iridium-rhenium oxide catalyst. Image courtesy of Angela Norton, CCEI

In 2016, worldwide air travel resulted in approximately 815 million tons of carbon dioxide emissions, equating to 2 percent of the global human-made total. The International Air Transport Association recognizes the impact of these emissions on the environment and, as a result, aims to cut carbon emissions in half by the year 2050 (relative to 2005 levels).

How does the association plan to achieve this goal? One approach is through the development of sustainable aviation fuels (SAFs).

Putting corncobs to good use. Sustainable jet fuels are made from renewable, bio-based feedstocks, such as corncobs, woodchips, and other agricultural waste, and deliver up to an 80 percent reduction in carbon emissions compared to traditional fossil fuels.

Although SAFs have the benefit of reducing carbon emissions, there are challenges that prevent them from replacing fossil fuels.

“Branching” out. The biorenewable feedstocks to make SAFs have two primary limitations. First, biomass molecules contain a low number of carbon atoms. These molecules must be coupled to create high-carbon molecules necessary for aviation fuels. Second, high-carbon coupled molecules with branched backbones contain oxygen, which must be removed to keep fuels from freezing at high altitudes.

As a result, biorenewable feedstocks must undergo chemical transformations, usually at temperatures as high as 350 degrees Celsius (about 660 degrees Fahrenheit) and pressures reaching 6 MPa—that’s 60 times greater than atmospheric pressure—before being used as aviation fuels. These transformations are expensive and lead to the formation of undesirable side products, such as low-carbon alkanes.

The good news is that researchers at the Catalysis Center for Energy Innovation (CCEI), an Energy Frontier Research Center, have discovered a catalyst to overcome energy-intensive processes and produce branched-chain jet-fuel molecules.

Iridium-rhenium oxide catalyst. Catalysts are key players in chemical reactions—they speed up reactions but do not permanently change as a result of the reaction. The researchers in CCEI found an effective catalyst to convert trifuran, a chemical derived from corncobs or other agricultural waste, into branched-chain jet-fuel molecules that do not contain oxygen, such as 6-butylundecane (see figure).

The researchers studied several catalysts. They found a catalyst containing iridium and rhenium oxide is the most effective to deoxygenate trifuran. The researchers tested this catalyst because it had demonstrated effectiveness in similar reactions to the one shown. In addition, previous work showed the catalyst results in nearly no carbon-carbon cracking, thereby enabling the formation of high-carbon molecules necessary for jet fuels. The two metal sites act synergistically to enhance the catalytic performance. Through this work, the CCEI team developed a reaction condition at which the catalyst enables up to 99 percent jet-fuel yield at low temperatures (170 degrees Celsius or about 340 degrees Fahrenheit). Importantly, the catalyst remains active after three consecutive uses. The low-temperature, high-product yield and reusable nature of the catalyst may enable cost-competitive and sustainable production of bio-based aviation fuels.

Making jet fuels from agricultural waste materials is challenging but nonetheless possible. Through design of efficient catalysts such as those at CCEI, we move one step closer to the ultimate goal: a sustainable future with less carbon emissions.

More Information

Liu S, S Dutta, W Zheng, NS Gould, Z Cheng, B Xu, B Saha, and DG Vlachos. 2017. “Catalytic Hydrodeoxygenation of High Carbon Furylmethanes to Renewable Jet-Fuel Ranged Alkanes over a Rhenium-Modified Iridium Catalyst.” ChemSusChem 10(16):3225-3234. DOI: 10.1002/cssc.201700863

Acknowledgments

This work was supported as part of the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Basic Energy Sciences. Resources were used at the Advanced Materials Characterization Laboratory at the University of Delaware. The team also acknowledges instrumentation support from the National Science Foundation.

About the author(s):

  • Angela Norton is a Ph.D. candidate in chemical and biomolecular engineering at the University of Delaware. She is a member of the Catalysis Center for Energy Innovation (CCEI) Energy Frontier Research Center working under the advisement of Dionisios Vlachos, director of CCEI. Her research focuses on studying how catalysts play a role in converting biomass to fuels and chemicals.

Turning Corncobs into Jet Fuel

New material overcomes limits to convert agricultural waste into freeze-free fuel

At the Catalysis Center for Energy Innovation, scientists discovered catalysts to convert renewable resources into jet fuel. Image courtesy of Nathan Johnson, PNNL

If you need to get across the country quickly, you book a flight. There isn’t another option. Air travel releases hundreds of millions of tons of carbon dioxide into the air each year. Efforts to reduce that amount include finding renewable ways to make jet fuel. The challenges include finding an energy-efficient process that produces the long, branched hydrocarbon molecules needed. At the Catalysis Center for Energy Innovation (CCEI), scientists designed a catalyst that ticks off nearly every box: It requires far less heat and pressure than traditional approaches, it’s reusable, and it produces little waste. With this new route to making aviation fuel, scientists are a step closer to reducing carbon emissions from air travel. The University of Delaware leads the CCEI.

More Information

Liu S, S Dutta, W Zheng, NS Gould, Z Cheng, B Xu, B Saha, and DG Vlachos. 2017. “Catalytic Hydrodeoxygenation of High Carbon Furylmethanes to Renewable Jet-Fuel Ranged Alkanes over a Rhenium-Modified Iridium Catalyst.” ChemSusChem 10(16):3225-3234. DOI: 10.1002/cssc.201700863

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.