Converting plastic waste into useful products through chemical recycling is a strategy to tackle the growing problem of plastic pollution on the planet. A new study may improve the ability of one method, called pyrolysis, to process difficult-to-recycle mixed plastics, such as multilayer food packaging, and generate fuel as a by-product, the scientists said.
In pyrolysis, plastic is heated in an oxygen-free environment, causing the materials to break down and create new liquid or gaseous fuels. However, current commercial applications either operate below the necessary scale or can only handle certain types of plastics, the scientists said.
“We have a very limited understanding of mixed plastic pyrolysis,” said Hilal Ezgi Toraman, an assistant professor of energy and chemical engineering at Penn State. “Understanding the interaction effects between different polymers during advanced recycling is very important as we try to develop technologies that can recycle real waste plastic.”
The scientists performed co-pyrolysis of two of the most common types of plastic, low-density polyethylene (LDPE) and polyethylene terephthalate (PET), along with different catalysts to study the interaction effects between the plastics. They found that one catalyst could be a good candidate for converting mixed LDPE and PET waste into valuable liquid fuels. Catalysts are materials added to pyrolysis that can support the process, such as selectively breaking down the plastic at lower temperatures.
“This kind of work can allow us to provide guidance or suggestions to the industry,” said Toraman, the Virginia S. and Philip L. Walker Jr. Faculty Fellow in the John and Willie Leone Family Department of Energy and Mineral Engineering at Penn. State. “It’s important to discover what kinds of synergies there are between these materials during advanced recycling and what types of applications they might be suitable for before we scale.”
The plastics, LDPE and PET, are commonly found in food packaging, which often consists of layers of different plastic materials designed to keep products fresh and safe, but are also difficult to recycle with traditional processes because the layers must be separated. , which is an expensive process.
“If you want to recycle them, you basically have to separate those layers and maybe do something with the single streams,” Toraman said. “But pyrolysis can handle it, so it’s a very important option. It’s not easy to find such a technique that can accept the messy complexity of these different plastic materials.”
The first step to developing new commercial pyrolysis processes depends on having a better mechanistic understanding of how dynamic plastic waste mixtures decompose and interact, the scientists said.
The scientists performed pyrolysis on LDPE and PET separately and together and observed interaction effects between the two polymers during tests with each of the three catalysts they used. The scientists reported the findings in the journal Reaction Chemistry and Engineering.
“We’ve seen products that can be very good candidates for gasoline applications,” Toraman said.
The team also developed a kinetic model capable of accurately modeling the interaction effects observed during co-pyrolysis of LDPE and PET with each of the catalysts. Kinetic models try to predict the behavior of a system and are important to better understand why reactions take place.
Toraman’s research group focuses on conducting experiments under well-defined and well-controlled conditions to understand interaction effects during advanced recycling of mixed plastics and the associated reaction mechanisms.
“Systematic and fundamental studies on understanding reaction pathways and developing kinetic models are the first steps toward process optimization,” Toraman said. “If we don’t get our kinetic models right, our reaction mechanisms not accurate, and if we scale up for pilot plants or large-scale operations, the results won’t be accurate.”
Toraman said she hopes the research leads to greater environmental responsibility in the recovery, processing and use of Earth’s resources.
A global analysis of all mass-produced plastics found that an estimated total of 8.3 billion tons of new plastics are generated worldwide to date. As of 2015, 79% of plastic waste, which contains numerous hazardous chemicals, has been left to accumulate in landfills or natural environments, with about 12% being incinerated and only 9% being recycled.
“Whatever we do is better than doing nothing,” Toraman said. “We have to reintroduce those plastics back into the economy, to have a circular economy, otherwise they just end up in landfills, potentially ending up toxic substances in the soil and water or polluting the oceans. So do something, find a value , is better than nothing. Plastics are currently considered waste because we treat these valuable raw materials as waste.”
Other Penn State researchers on this project were Sean Timothy Okonsky, a doctoral student in the Department of Chemical Engineering, and JV Jayarama Krishna, a postdoctoral researcher in the John and Willie Leone Family Department of Energy and Mineral Engineering.
How we can convert plastic waste into green energy
Sean Timothy Okonsky et al, Catalytic co-pyrolysis of LDPE and PET with HZSM-5, H-beta and HY: experiments and kinetic modelling, Reaction Chemistry and Engineering (2022). DOI: 10.1039/D2RE00144F
Quote: Scientists improve process to turn hard-to-recycle plastic waste into fuel (2022, September 29) retrieved September 29, 2022 from https://phys.org/news/2022-09-scientists-hard-to-recycle- plastic-fuel.html
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