Turning Plastic Waste Into Sustainable Jet Fuel

Researchers have developed a groundbreaking method to produce ethylbenzene, a crucial additive for sustainable aviation fuels, from waste polystyrene.

This innovation could dramatically reduce the aviation industry’s carbon footprint and reliance on fossil fuels, promising a cleaner, greener future in air travel with substantial cost savings and a 50% to 60% reduction in carbon emissions.

Innovative Breakthrough in Sustainable Aviation Fuels

A new study addresses a major obstacle in transitioning U.S. commercial aircraft from heavy reliance on fossil fuels to sustainable aviation fuels. Researchers have developed a cost-effective method to produce ethylbenzene — an additive that enhances the performance of sustainable aviation fuels — using polystyrene, a durable plastic commonly found in consumer products.

The findings were published recently in the journal ACS Sustainable Chemistry and Engineering.

Enhancing Fuel Performance with Ethylbenzene

Fuels made from non-petroleum sources, such as waste fat, oil, grease, or plant biomass, often lack adequate levels of aromatic hydrocarbons. These compounds are essential for maintaining fuel system performance by lubricating mechanical components and swelling seals to prevent leaks during normal operations, explained Hong Lu, a research scientist at the Illinois Sustainable Technology Center. The ISTC is part of the Prairie Research Institute at the University of Illinois Urbana-Champaign.

While ethylbenzene is an aromatic hydrocarbon and can be derived from fossil fuels, finding a sustainable way to produce it would aid the aviation industry’s conversion to sustainable jet fuels.

Goals for Sustainable Aviation

The U.S. Department of Energy, the U.S. Department of Transportation, the U.S. Department of Agriculture, and other government agencies created a roadmap for addressing the climate-related impacts of fossil-fuel-derived aviation fuels. The Sustainable Aviation Fuel Grand Challenge sets ambitious goals for the production of domestic sustainable aviation fuels to 3 billion gallons per year by 2030, and 100% of projected aviation jet fuel use, or 35 billion gallons per year, by 2050.

Present standards require a minimum of 8.4% aromatic hydrocarbons be included in any blend of sustainable aviation fuels and fossil-derived fuels “to maintain compatibility with existing aircraft and related infrastructure,” the researchers report. While this rule increases the safety and efficacy of the overall fuel mix, it severely limits the use of sustainable fuels, which currently contain only about 0.5% aromatic hydrocarbons, Lu said.

“Currently, they use a blend of 20% to 30% sustainable aviation fuels and 70% to 80% conventional jet fuel,” he said. This lag in conversion to sustainable fuels stems from several factors, one of which is the need for enough aromatic hydrocarbons in the mix. Other important factors involve qualities like the blend’s volatility, acidity, moisture content, and freeze point.

Advancements in Ethylbenzene Production from Polystyrene

Lu and his colleagues chose to develop ethylbenzene because it has a lower tendency to form soot upon burning than other highly aromatic compounds. They chose to start with polystyrene because it is rich in hydrocarbons and is abundantly available in the waste stream.

“We produce in the U.S. about 2.5 million metric tons of polystyrene every year, and almost all of it is disposed of in landfills,” Lu said.

To convert the polystyrene to ethylbenzene, the team used thermal pyrolysis, heating it to break the polymer down into a styrene-rich liquid. A second step, hydrogenation, converted it into a crude ethylbenzene, and distillation yielded a product that was 90% pure.

When mixed with a sustainable aviation fuel, the polystyrene-derived ethylbenzene performed “almost as well as ethylbenzene derived from fossil fuels,” Lu said. Further purification would improve its performance.

“We did a preliminary cost analysis, and we found that the ethylbenzene produced from waste polystyrene is cheaper than that produced from crude oil. And a lifecycle analysis of our ethylbenzene found it reduced carbon emissions by 50% to 60% compared with the ethylbenzene made from crude oil.”

Lu and his colleagues hope to further develop this additive to help expand the use of sustainable fuels in aviation.

Reference: “Production of a Sustainable Aviation Fuel Additive from Waste Polystyrene” by Ravindra Prajapati, Eliah Owyn Zaborowski, Hong Lu, Nandakishore Rajagopalan, Brajendra K Sharma, Bryan R Moser and Nalin Kumar, 18 December 2024, ACS Sustainable Chemistry & Engineering.
DOI: 10.1021/acssuschemeng.4c06748

The U.S. Department of Energy’s Small Business Innovation Research and Office of Energy Efficiency and Renewable Energy supported this study.

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