One method for addressing the planet’s mounting plastic pollution issue is chemical recycling, which transforms plastic waste into useful products. Scientists said that a new study might make pyrolysis, a method used to break down hard-to-recycle mixed plastics like multilayer food packaging and make fuel as a byproduct, work better.
Pyrolysis is the process of heating plastic in an oxygen-free environment to cause material breakdown and the production of new liquid or gas fuels. However, according to the scientists, current commercial applications either operate below the required scale or can only handle a specific type of plastic.
According to Hilal Ezgi Toraman, assistant professor of energy engineering and chemical engineering at Penn State, “We have a very limited understanding of mixed-plastic pyrolysis.” When trying to develop technologies that can recycle real plastic waste, understanding the interaction effects between different polymers during advanced recycling is very important.
Low-density polyethylene (LDPE) and polyethylene terephthalate (PET), two of the most popular types of plastic, were co-pyrolyzed with various catalysts in order to study the effects of the interactions between the plastics. They discovered one catalyst might work well to turn mixed LDPE and PET waste into useful liquid fuels. Materials added to the pyrolysis process called catalysts can speed up the reaction by, for example, causing the plastic to disintegrate selectively and at lower temperatures.
According to 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, “This type of work can allow us to provide guidelines or suggestions to industry.” Before scaling up, it’s important to figure out how these materials might work well together during advanced recycling and what kinds of uses they might be good for.
The plastics, LDPE and PET, are frequently used in food packaging, which frequently consists of layers of various plastic materials designed to keep goods safe and fresh but which is also challenging to recycle using conventional methods because the layers must be separated, which is an expensive process.
According to Toraman, “If you want to recycle them, you basically need to separate those layers and maybe do something with the single streams.” But pyrolysis can handle it, making it a crucial alternative. “Finding a method that can handle the clumsy complexity of these various plastic materials is not simple.
According to the researchers, having a better mechanistic understanding of how dynamic plastic waste mixtures decompose and interact is the first step in creating new commercial pyrolysis processes.
The researchers tested each of the three catalysts they used on LDPE and PET individually and collectively, looking for interactions between the two polymers. The research was published in the journal Reaction Chemistry & Engineering by the scientists.
According to Toraman, “We saw products that could be very good candidates for gasoline applications.”
The group also created a kinetic model that was effective in simulating the interactions that occurred when LDPE and PET were co-pyrolyzed with each of the catalysts. Kinetic models are crucial for better understanding why reactions take place because they make predictions about a system’s behavior.
Toraman’s research group focuses on doing experiments under well-defined and well-controlled conditions in order to understand the interactions that happen when mixed plastics are recycled in a more advanced way and the ways in which they react.
The first steps toward process optimization, according to Toraman, are systematic and fundamental studies on comprehending reaction pathways and creating kinetic models. The results won’t be accurate if we scale up for pilot plants or large-scale operations if our kinetic models and reaction mechanisms are incorrect.
Toraman said that she hoped the study would make it easier to take care of the Earth’s resources when they are being found, processed, and used.
According to a global analysis of all mass-produced plastics, 8.3 billion metric tons of new plastic are thought to have been produced globally to this point. As of 2015, only 9% of plastic waste—which contains many hazardous chemicals—was recycled, with the majority (79%) being allowed to build up in landfills or other natural areas.
Whatever we do, Toraman declared, is preferable to doing nothing. If we don’t have a circular economy, those plastics will just end up in landfills, contaminating the oceans or leaching potentially toxic substances into the soil and water. As a result, doing something is preferable to doing nothing. Because we treat these valuable resources as waste, plastics are currently regarded as waste.
Other Penn State researchers on this project were Sean Timothy Okonsky, a doctoral student in the Department of Chemical Engineering, and J.V. Jayarama Krishna, a postdoctoral researcher in the John and Willie Leone Family Department of Energy and Mineral Engineering.
The research was made possible thanks to a $3.4 million grant Penn State received from the REMADE Institute, a public-private partnership set up by the US Department of Energy to support studies into the ineffective processes currently employed to process and upcycle mixed plastic waste.
This work was also helped by a Green award from the Penn State Energy and Environmental Sustainability Laboratory and the DOE’s Office of Energy Efficiency and Renewable Energy.
