One person’s trash is another person’s jet fuel? As strange as it may seem, researchers at the University of Illinois at Urbana-Champaign believe they have found a process to make this unlikely scenario a reality, at least on a small scale.
I write this week in Natural communicationsagricultural engineers presented a strategy for taking excess food waste, converting it into biofuel, and then “upgrading” that fuel into jet fuel that can be used directly in an aircraft without requiring additional modifications to the aircraft’s infrastructure. They compared their food waste-derived fuel to industry benchmarks and found that it met all the standards needed for conventional jet fuel.
While these results are more of a proof of concept, they open up the exciting possibility of using food waste (of which there is certainly no shortage) to help the aviation industry move closer to its ambitious goal of achieving net zero carbon emissions over the next three decades.
“In a linear economy, we simply produce something, use it, and throw it away. In this project, we take the waste and recover the energy and materials to make a usable product. This fills a missing link in the circular paradigm,” Yuanhui Zhang, a professor at the University of Illinois at Urbana-Champaign and corresponding author, said in a statement.
Planes lag behind cars in reducing emissions
The U.S. Environmental Protection Agency (EPA) estimates that transportation accounted for about 29 percent of all U.S. greenhouse gas emissions in 2022 alone. Of that amount, about seven percent came from commercial aircraft. Modern cars have reduced their emissions in recent years, thanks in part to a move toward battery electric power. And while battery-powered planes are theoretically possible for some short flights, they simply don’t provide enough energy to power an airliner traveling across the country (jet fuel carries about 50 times more energy per kilogram than conventional lithium-ion batteries. As a result, jets lag behind cars in reducing emissions.
But what about so-called biomass-based sustainable aviation fuel (SAF)? Some estimates suggest that SAF, which largely refers to fuels derived from organic materials, could reduce emissions from flights by up to 80 percent, compared to conventional jet fuel. While ethanol and other biomass derivatives have been available for cars for decades, they have remained more elusive for planes because their chemical makeup does not meet the much more stringent requirements needed for jet fuel.
Sabrina Summers of the University of Illinois demonstrates hydroprocessing of biocrude oil from food waste. Image: University of Illinois at Urbana-Champaign.
Valorization of biomass into jet fuel
Meeting these requirements is where food waste comes in. In this new experiment, the team started by collecting food waste from nearby food processing plants. They then used a chemical process called hydrothermal liquefaction (HTL), which essentially mimics the way Earth naturally creates crude oil from organic matter over millions of years, but without waiting. HTL acts as a sort of advanced “pressure cooker” to speed up nature’s timeline.
With a large amount of crude oil extracted from the food scraps, the researchers then decided to convert it into jet fuel in a two-step process. The first step was to remove salt, ash, moisture and other impurities. After that, they used a cleaning process called catalytic hydrotreating to remove other unwanted elements such as nitrogen, sulfur and oxygen. All that remained were the specific hydrocarbons needed to make jet fuel. They tested different catalysts and found that cobalt-molybdenum stood out as the most efficient and commercially available metal catalyst for triggering the chemical reactions necessary for refining petroleum into aviation fuel.
The team took their food waste-derived aviation fuels and tested them against current fuel standards set by the American Society for Testing and Materials (ASTM) and the Federal Aviation Administration. It has passed the screening test and meets industry requirements without the need to introduce special additives. This means the fuel would theoretically power a commercial aircraft.
Related: [All your burning questions about sustainable aviation fuel, answered]
The results are a first step in showing that aviation fuel derived from food waste is at least possible. However, producing enough to supply an entire airliner is a different beast entirely. Developing to this level requires time, resources and large budgets outside of academia.
“Our research helps solve scientific and technical problems, and industry can then step in,” Zhang said.
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