Reducing plastic waste is a critical issue for people and the planet. Emerging technologies offer a wide variety of solutions including breaking down plastics that previously could not be recycled and using chemical processes to convert post-consumer plastics into fossil fuel replacements. low-density polyethylene (LDPE) and polyethylene terephthalate (PET) plastics were specifically designed with recycling in mind. Unfortunately, early solutions did not stem the growing mounds of plastic waste. Around the globe, more tons of plastic containers, plastic pellets, and even plastic particles are still being discarded and still polluting lands, rivers, beaches, and oceans. It’s clear a new and more advanced plastic recycling technology for our plastic waste problem is needed.
Currently plastic waste is indeed a huge problem in the world. Because of its durability, plastic waste accumulated in landfills and oceans tends to be trapped for centuries, causing a global environmental crisis. Even though we produce about 300 million tons of plastic waste each year, only 9% is recycled. But why are we only recycling so little? The reason is the current inefficiency and high cost of recycling plastic waste, resulting in a lack of incentives. For example, the plastics, LDPE and PET, are commonly found in food packaging, which often consists of layers of different plastic material that are engineered to keep products fresh and safe, but are also difficult to recycle with traditional processes because the layers have to be separated, which is an expensive process. Turning plastic waste into useful products through chemical recycling is one strategy for addressing Earth’s growing plastic pollution problem. Pyrolysis, which is a method used to process hard-to-recycle mixed plastics like multilayer food packaging and generate fuel as a byproduct. Pyrolysis involves heating plastic in an oxygen-free environment, causing the materials to break down and creating new liquid or gas fuels in the process. Current commercial applications, however, either operate below the necessary scale or can only handle certain type of plastics.
In a new study led by Hilal Ezgi Toraman, assistant professor of energy engineering and chemical engineering at Penn State conducted co-pyrolysis of two of the most common types of plastic, LDPE and PET, along with different catalysts to study the interaction effects between the plastics. They found one catalyst may be a good candidate for converting mixed LDPE and PET waste into valuable liquid fuels. Catalysts are materials added to pyrolysis that can aid the process, like inducing the plastic to break down selectively and at lower temperatures. The research team conducted pyrolysis on LDPE and PET separately and together and observed interaction effects between the two polymers during tests with each of three catalysts they used. The scientists reported the findings in the journal Reaction Chemistry & Engineering.
The authors findings revealed what kind of synergies exist between these materials during advanced recycling and what types of applications they may be right for before scaling up. The first step to developing new commercial pyrolysis processes hinges on having a better mechanistic understanding of how dynamic plastic waste mixtures decompose and interact. The team also developed a kinetic model that was able to accurately model the interaction effects observed during co-pyrolysis of LDPE and PET with each of the catalysts. Kinetic models attempt to predict the behavior of a system and are important for better understanding why reactions are occurring. The authors focused on doing experiments under well-defined and well-controlled conditions to understand interaction effects during advanced recycling of mixed plastics and the corresponding reaction mechanisms. The corresponding author, professor Toraman hopes the research leads to better environmental responsibility in the recovery, processing and utilization of Earth resources.
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 & Engineering (2022). DOI: 10.1039/D2RE00144F