Millions of tons of plastic end up in landfills every year. It is a big societal problem and an even greater environmental threat.
In the United States, less than 9% of plastic waste is recycled. Instead, over 75% of plastic waste ends up in landfills and up to 16% is burned, a process that releases toxic gases into the atmosphere.
Researchers at the Center for Plastics Innovation (CPI) at the University of Delaware have developed a direct method to convert single-use plastic waste – plastic bags, yogurt containers, plastic bottles and bottle caps, packaging and more – in ready-to-use. molecules for jet fuels, diesel and lubricants.
The work, reported in an article in Scientific progress on Wednesday April 21, focuses on using a new catalyst and a unique process to quickly break down these most difficult to recycle plastics, called polyolefins. Polyolefins make up 60-70% of all plastics manufactured today.
The process developed by UD requires about 50% less energy than other technologies, and it does not involve the addition of carbon dioxide to the atmosphere, a reduction in emissions compared to other commonly used techniques. This can be done in a few hours at a low temperature, around 250 degrees Celsius. This is slightly higher than the oven temperature at 450 degrees Fahrenheit that you could use for roasting vegetables or making puff pastry at home.
Importantly, the UD team’s method can handle a variety of plastics, even when mixed together, a plus considering how recyclables are handled.
“Chemical conversion is the most versatile and robust approach to tackling plastic waste,” said Dion Vlachos, principal investigator of the project and Unidel Dan Rich Chair in Energy in Chemical and Biomolecular Engineering at the UD.
The co-authors of the article include Sibao Liu, a former postdoctoral researcher at UD, now associate professor of chemical engineering and technology at Tianjin University; and IPC researchers Pavel Kots, UD postdoctoral fellow; Brandon Vance, a graduate student from UD; and Andrew Danielson, a senior majoring in chemical engineering.
Create ready-to-use molecules
The UD research team used a chemical process called hydrocracking to break down plastic solids into smaller carbon molecules, then added hydrogen molecules to each end to stabilize the material to be used.
Catalytic cracking is nothing new. Refineries have used it to convert heavy crude oil into gasoline for years.
The research team’s method, however, does more than just break down the plastic. It also converts the material into branched molecules which allow them to be more directly translated into a final product.
“This makes them ready-to-use molecules for high-value lubricant or fuel applications,” said Vlachos, who also heads the Delaware Energy Institute and the Catalysis Center for Energy Innovation at UD.
The catalyst itself is actually a hybrid material, a combination of zeolites and mixed metal oxides.
Zeolites are known to have properties which make them good at creating branched molecules. Zeolites are found in things like water purification or home softening systems and detergents, where they neutralize minerals like calcium and magnesium, making hard water softer and improving the process. of laundry.
Mixed metal oxides, on the other hand, are known for their ability to break down large molecules just the right amount without overdoing it. The antacid in your medicine cabinet, for example, is a metal oxide used to break down or neutralize the acid causing an upset stomach.
“Only these two catalysts malfunction. Together, the combination works magic, melting the plastics and leaving no plastic behind,” Vlachos said.
This gives the method developed by the IPC an advantage over current techniques used today, although Vlachos stressed that more work is needed to translate these scientific methods to industry. Another plus: the team’s catalyst materials are widely used and, therefore, quite cheap and plentiful.
“These are not exotic materials, so we can quickly start thinking about how to use the technology,” he said. He and Liu have filed a provisional patent on the new bi-catalyst and unique method through UD’s Office of Economic Innovation and Partnerships.
Sustainable solutions, circular economy
Reducing plastic waste by chemically converting it into fuels can play an important role in driving a circular economy, where materials are recycled into something new at the end of their useful life, instead of being thrown away. . The recycled components can be used to make the same thing again or, in the case of fuels, be recycled into higher value products – creating both economic and environmental gains.
“This innovative catalytic approach is a significant advance in our quest for depolymerization processes that involve less energy-consuming pathways and generate very specific degradation targets,” said LaShanda Korley, Director of CPI, Emeritus Professor of Materials Science and Engineering and chemical and biomolecular engineering. understanding opens a new path towards the recovery of plastic waste. “
For Andrew Danielson, a chemical engineering major at UD involved in the project, the potential environmental benefits of converting plastic are exciting.
“Plastic waste is a serious environmental problem. I believe this research can help lead to better methods of reusing plastic, ”said Danielson, whose contributions to the work included verifying the data collected during the project by replicating the experiments.
After graduating in May, Danielson will put this research experience to work for the chemical industry. He previously landed a job in process controls, a part of the manufacturing process that involves controlling variables, such as temperature, pressure, and conductivity, among others.
The next steps in IPC research include exploring what other plastics the team’s method can process and what products it can make. For starters, Vlachos said the team hoped to expand collaborations with colleagues on campus and at the Center for Plastics Innovation to explore other avenues to make valuable products by eliminating waste.
“As this circular economy kicks in, the world will need to make less original plastics because we will reuse materials made today in the future,” he said.
Another goal is to develop methods to improve the recycling process itself.
“We want to use green electricity to boost the chemical processing involved in making new things. We’re a long way from seeing that right now, but that’s where we’re headed for the next 10-20. years, ”Vlachos said.