Airplanes zoom overhead with wispy-white contrails that stream behind them. The Federal Aviation Administration (FAA) controlled 43,684 flights, on average, daily in 2016, and U.S. commercial and military flights together used more than 20 billion gallons of jet fuel.
All those emissions add up. Global air travel contributed 815 million tons of CO2 emissions in 2016 — 2% of the global manmade total, according to the International Air Transport Association. Global air traffic is currently slowing down. IATA forecasts that 7.2 billion passengers will take up air travel by 2035, almost doubling the 3.8 billion that flew in 2016.
So how can air travel be made easier on the environment? University of Delaware researchers are currently working on developing an alternative jet fuel. Instead of petroleum, these researchers aim at powering planes with wood chips and corncobs — stuff that is not usually considered of much importance unless an individual is a groundhog or a beaver looking for leftovers.
Researchers in UD’s Harker Interdisciplinary Science and Engineering Laboratory are transforming this plant material, scientifically known as lignocellulosic biomass, into green products, including new chemicals and fuels. The scientists are working with with the Catalysis Center for Energy Innovation (CCEI), an Energy Frontier Research Center supported by the U.S. Department of Energy. Located at UD, the center brings together scientists from nine institutions in order to work on clean energy challenges.
According to CCEI Associate Director Basudeb Saha, one of the biggest difficulties to developing renewable jet fuel is creating a way to increase the efficiency and speed of the two critical chemical processes — deoxygenation and coupling. Since the plant material that the center works with comprises of a low carbon content, once it is broken down from a solid into a liquid, it is essential for the carbon molecules to be chemically stitched together or “coupled” in order to develop high-carbon molecules in the jet fuel range. This should be followed by removing the oxygen from these molecules to produce branched hydrocarbons. This branching is vital in order to improve the flow of fuel at the freezing temperatures of commercial flight.
International planes may fly at an altitude of 35,000 feet, where the outside temperature could be as low as -14° Centigrade, that’s the temperature at which a plane has to run, and the fuel can’t be frozen.
Basudeb Saha, CCEI Associate Director
Accelerating renewable jet fuel production
The demand continues for non-petroleum-based fuel for aviation. The FAA, more than a decade ago, had fixed a target of employing 1 billion gallons of renewable jet fuel by 2018. According to IATA, sustainable aviation fuels are essential to its pursuit of carbon neutral growth from the year 2020 on, and to a 50% reduction in net carbon emissions by the year 2050 (relative to 2005 levels). However, insufficient quantities of this alternative fuel are being generated, nor at a competitive cost.
Several U.S. companies are producing renewable jet fuel from materials such as triglycerides extracted from used grease and oil, or from a blend of carbon monoxide and hydrogen known as syngas. One company makes use of algae as its source material and also has an underground pipeline to the Los Angeles Airport (LAX), where a specific percentage gets incorporated with standard jet fuel, Saha says.
However, processing this non-conventional material needs high temperatures—350 °C (662 °F)—and also high pressure.
This is not the case for the method of using corn cobs or wood chips at UD, where Saha and his colleagues have produced new catalysts — so called “chemical goats” — capable of kickstarting the chemical reactions that can convert this plant material into fuel. One of these catalysts, developed from inexpensive graphene, resembles a honeycomb of carbon molecules. Its unique surface properties help in increasing the speed of the coupling reaction. It also runs at low temperature (60 °C). Another catalyst is capable of removing oxygen in an energy-efficient manner and creates high yields of branched molecules, up to 99%, ideal for jet fuel. Both catalysts can be recycled, and the processes are scalable.
“The low temperature and high selectivity of our process can enable cost-competitive and sustainable production of bio-based aviation fuels from lignocellulosic biomass,” Saha says.
The research has been detailed in three latest scientific articles: “Solventless C–C Coupling of Low Carbon Furanics to High Carbon Fuel Precursors Using an Improved Graphene Oxide Carbocatalyst” and “Hydrodeoxygenation of Furylmethane Oxygenates to Jet and Diesel Range Fuels: Probing the Reaction Network with Supported Palladium Catalyst and Hafnium Triflate Promoter” both featured in ACS Catalysis, which is published by the American Chemical Society, and “Catalytic Hydrodeoxygenation of High Carbon Furylmethanes to Renewable Jet-Fuel Ranged Alkanes Over a Rhenium-Modified Iridium Catalyst” was featured in ChemSusChem, an interdisciplinary journal for research at the interface of sustainability and chemistry published by ChemPubSoc Europe, an organization of 16 European chemical societies.
The UD team’s work has been published on the cover of ChemSusChem. The artwork was developed Sibao Liu, the first author of the article and a postdoctoral researcher at the center. Liu, a native of China, stated that the world-class research happening at CCEI was his catalyst for coming to UD.