ISTC research could boost SAF end market

Research conducted at the Illinois Sustainable Technology Center (ISTC) in that state could help overcome what has been cited as a challenge in the adoption of sustainable aviation fuels (SAF) in commercial aircraft.

SAF derived from waste fat, oil and grease (FOG), plant biomass or other non-petroleum sources can lack sufficient levels of aromatic hydrocarbons, which help keep fuel systems operational by lubricating mechanical parts and swelling the seals that protect from leaks during normal operations, says the lead researcher.

Hong Lu, a research scientist at the ISTC, which is a division of the Prairie Research Institute at the University of Illinois Urbana-Champaign, says the finding could help commercial aircraft operators in the United States switch away from their reliance on fossil fuels to the use of more SAF.

The study, according to the ISTC, details a cost-effective method for producing ethylbenzene—an additive that improves the functional characteristics of SAF—from discarded polystyrene (PS) plastic.

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 more comprehensively sustainable jet fuels, say the project’s backers.

Currently, commercial airlines using SAF use a blend of 20 to 30 percent SAF and 70 to 80 percent conventional jet fuel, says Lu. The researchers says one of the factors is the need for jet fuel to contain enough aromatic hydrocarbons in the mix.

Lu and his colleagues chose to develop ethylbenzene because it has a lower tendency to form soot when burning compared with other highly aromatic compounds, and they chose to start with PS because it is rich in hydrocarbons and is abundantly available in the discarded materials stream, according to the ISTC.

“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,” says Lu.

To convert the discarded PS into ethylbenzene, the team used thermal pyrolysis, heating it to break the polymer down into what they call a styrene-rich liquid. A second step, hydrogenation, converted it into a crude ethylbenzene, and distillation yielded a product that was 90 percent pure, says the ISTC.

When mixed with SAF, the PS-derived ethylbenzene performed “almost as well as ethylbenzene derived from fossil fuels,” says Lu. He says 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,” continues the researcher. He says a life cycle analysis of ISTC’s ethylbenzene “found it reduced carbon emissions by 50 to 60 percent compared with the ethylbenzene made from crude oil.”

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

The research ties into the Sustainable Aviation Fuel Grand Challenge created by the U.S. Departments of Energy, Transportation and Agriculture. Those departments also have set goals for the production of domestic SAF to 3 billion gallons per year by 2030 and 100 percent of projected aviation jet fuel use, or 35 billion gallons per year, by 2050.

According to the ISTC, Lu and his colleagues hope to further refine the developed additive to help expand the use of SAF. The team’s findings have been reported in the journal ACS Sustainable Chemistry and Engineering.