A recent study addresses a significant hurdle in transitioning commercial aircraft in the U.S. from their heavy reliance on fossil fuels to more eco-friendly aviation fuels. This research presents a cost-effective approach to generating ethylbenzene, an important additive that enhances the properties of sustainable aviation fuels, from polystyrene, a durable plastic commonly found in various consumer products.
A recent study tackles a major hurdle pertaining to the shift of commercial jets in the United States from their dependency on fossil fuels toward more sustainable aviation fuels. The research outlines a cost-efficient method for creating ethylbenzene—an additive that boosts the performance characteristics of sustainable aviation fuels—by utilizing polystyrene, a resilient plastic prevalent in many consumer items.
The results are published in ACS Sustainable Chemistry and Engineering.
According to Hong Lu, a research scientist at the Illinois Sustainable Technology Center and the lead on this study, fuels made from waste fats, oils, greases, plant materials, and other alternative resources often do not contain enough aromatic hydrocarbons. These hydrocarbons are crucial as they lubricate engine parts and expand seals to prevent leaks during standard operations.
While ethylbenzene is an aromatic hydrocarbon that can be sourced from fossil fuels, developing a sustainable production method would support the aviation sector’s transition to greener jet fuels.
Various U.S. government organizations, including the Department of Energy, Department of Transportation, and Department of Agriculture, have established a strategy for mitigating the environmental impact of aviation fuels derived from fossil sources. The Sustainable Aviation Fuel Grand Challenge aims to achieve ambitious targets, including the production of 3 billion gallons of sustainable aviation fuels annually by 2030 and reaching 100% of projected aviation kerosene consumption, or 35 billion gallons per year, by 2050.
Current regulations require that any mix of sustainable aviation fuels and fossil-derived fuels contains at least 8.4% aromatic hydrocarbons “to ensure compatibility with existing aircraft and their infrastructure,” as noted by the researchers. While adhering to this standard enhances safety and efficiency of the fuel blend, it poses a significant barrier to utilizing sustainable fuels, which currently comprise only about 0.5% aromatic hydrocarbons, according to Lu.
“At this moment, the standard practice is to blend 20% to 30% sustainable aviation fuels with 70% to 80% conventional jet fuels,” he explained. This slow adoption of sustainable fuels can be attributed to multiple factors, notably the need for adequate aromatic hydrocarbons. Other essential considerations include parameters such as the blend’s volatility, acidity, moisture levels, and freezing point.
Lu and his team opted to create ethylbenzene because it produces less soot when burned compared to other highly aromatic substances. They selected polystyrene as the starting material for its abundant hydrocarbon content and its prevalence in waste materials.
“In the United States, we generate around 2.5 million metric tons of polystyrene annually, and nearly all of it ends up in landfills,” Lu remarked.
To convert polystyrene into ethylbenzene, the research team employed thermal pyrolysis, heating the plastic to decompose it into a styrene-rich liquid. The subsequent hydrogenation process transformed this liquid into crude ethylbenzene, and distillation produced a final product that was 90% pure.
When blended with sustainable aviation fuel, the ethylbenzene generated from polystyrene demonstrated performance “almost equivalent to that of ethylbenzene sourced from fossil fuels,” according to Lu. Further purification could enhance its effectiveness.
“Our initial cost analysis revealed that the ethylbenzene derived from waste polystyrene is more economical than that obtained from crude oil. Additionally, lifecycle assessments of our ethylbenzene showed a decrease in carbon emissions by 50% to 60% when compared to ethylbenzene made from crude oil,” he added.
Lu and his colleagues aim to further refine this additive to encourage wider adoption of sustainable fuels within the aviation industry.
This research was supported by the U.S. Department of Energy’s Small Business Innovation Research program and the Office of Energy Efficiency and Renewable Energy.
