Researchers have come up with a method to convert food waste into jet fuel. (Image Credit: Tango Tsuttie/Unsplash)
Researchers from the National Renewable Energy Laboratory (NREL), the University of Dayton, Yale University, and Oak Ridge National Laboratory have created a method that converts food waste into sustainable aviation fuel (SAF). The process involves transforming volatile fatty acids (VAF) from fermenting food waste into paraffin molecules, which can be used in jet fuel. Their fuel already meets aviation standards, and they have collaborated with Southwest Airlines to scale up the process. Flight trials are expected to begin by 2023.
“If our refining pathway is scaled up, it could take as little as a year or two for airlines like Southwest to get the fuel regulatory approvals they need to start using wet waste SAF in commercial flights,” said NREL scientist Derek Vardon, the corresponding author of the paper. “That means net-zero-carbon flights are on the horizon earlier than some might have thought.”
A life-cycle analysis revealed that bio-paraffin could reduce greenhouse gas emissions by up to 165% compared to standard jet fuel. Most of the reduction occurs if the food waste is diverted from landfills, where it’s broken down into methane, which is 20 times more potent than CO2. These greenhouse gas reductions are achieved by targeting food waste’s huge greenhouse gas footprint. Landfill emissions are also reduced by sending less food waste to landfills.
Food waste is also effective at producing fuel. Research conducted in the past revealed that fermenters interrupt methane formation to convert the carbon energy of food waste and wet waste (food scraps, animal manure, and wastewater sludge) into VFAs. However, those studies did not explain how the fuel could meet ASTM International fuel property requirements.
The researchers increased the proportion of eco-friendly fuel combined with traditional fossil fuel to 70%. This was achieved after converting the paraffin, ensuring that it can be used in a jet engine. Soot particles were also reduced by 34%, which lowers ice crystal usage and limits the contrails effect on the climate.
This new conversion process has the potential to replace over 20% of existing jet fuel consumption in the US. More than 21 billion gallons of jet fuel are used per year, which could double by 2050. Using inexpensive and widely-available food waste lessens biofuels’ impact on the environment.
An overview scheme showing the major oxygenate and hydrocarbon molecules produced when wet waste is converted into Fast Track VFA-SAF. It also displays Aldol Condensation VFA-SAF comprised of isoparaffin-rich hydrocarbons. (Image Credit: Huq et al.)
During the conversion process, anaerobic digestion of wet waste is arrested before methanogenesis occurs, which produces VFAs (C3-C8). Afterward, Ketonization extends the VFAs carbon backbone (C5-C15). Ketonization reacts two VFAs to produce an individual ketone, which is a carbon shorter than both acids. Oxygen is then removed in the form of water and carbon dioxide.
After ketonization, ketones >C8 undergo hydrodeoxygenation to create paraffin-rich hydrocarbons. Meanwhile, ketones <C7 need an additional carbon coupling step (aldol condensation) before hydrodeoxygenation. This allows it to have a range of C8 to C18 for jet fuel.
The researchers used a catalyst to supplement the VFA molecules with more carbon. They also demonstrated how to develop long strings of energy-rich paraffin hydrocarbons that are chemically similar to those in conventional jet fuel.
This project is expected to grant £15m for various companies to research technologies that can convert household waste wood, garbage, and extra electricity into SAF.
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