It’s light, cheap, almost infinitely customizable, and just about everything: For all its benefits, plastic—and plastic waste—is a big problem. Unlike glass, which is infinitely recyclable, recycling plastic is challenging and expensive due to the complex molecular structure of the material designed for specific needs.
Worldwide, an estimated 380 million metric tons of plastic are produced annually. However, only about 9 percent of all plastic waste is recycled, about 12 percent is burned, and the rest is thrown into landfills and the natural environment.
New research from the lab of Giannis Mpoumpakis, associate professor of chemical and petroleum engineering at the University of Pittsburgh, focuses on optimizing a promising technology called pyrolysis, which can chemically recycle waste plastics into more valuable chemicals. The paper was published recently and featured on the cover of Journal of Chemical Theory and Computation.
“Pyrolysis is relatively low-cost and produces high-value products, so it presents an attractive, practical solution,” said Mpourmpakis. “This has already been done on a commercial scale. The main challenge now is to find the best operating conditions, given the starting and final chemical products, without having to rely too much on trial-and-error experimentation.”
To optimize pyrolysis conditions and produce desired products, researchers often use thermodynamic calculations based on the so-called Gibbs free energy minimization approach. However, the lack of thermochemical data may limit the accuracy of these calculations.
While density functional theory (DFT) calculations are often used to obtain accurate thermochemical data for small molecules, their application can be challenging and computationally expensive for the large, flexible molecules that make up plastic waste, especially at high pyrolysis temperatures.
In this study, Mpourmpakis and former postdoc Hyunguk Kwon, now a professor at Seoul National University of Science and Technology, developed a computational framework to accurately calculate the temperature-dependent thermochemistry of large and flexible molecules.
This framework combines conformational search, DFT calculations, thermochemical corrections, and Boltzmann statistics; the resulting thermochemistry data were used to predict the thermal decomposition profiles of octadecane, a model compound representing polyethylene.
The proposed computational analysis based on first principles offers a significant improvement in the prediction of temperature-dependent product distributions from plastic pyrolysis. This will guide future experimental efforts in the chemical recycling of plastic, enabling researchers to optimize pyrolysis conditions and increase the efficiency of converting waste plastics into valuable chemicals.
“The production of plastics is expected to continue to increase, so it is important that we find perfect ways to recycle and reuse plastics without harming the environment,” said Mpourmpakis. “This work … contributes to the development of sustainable waste management strategies and the reduction of plastic pollution, offering potential benefits for the environment and society.”
Hyunguk Kwon et al, Ab Initio Thermochemistry of Highly Flexible Molecules for Thermal Decomposition Analysis, Journal of Chemical Theory and Computation (2023). DOI: 10.1021/acs.jctc.3c00265
Provided by the University of Pittsburgh
Citation: Advancing chemical recycling of waste plastics: A computational approach for predicting product distributions (2023, July 24) retrieved 24 July 2023 from https://phys.org/news/2023-07-advancing-chemical-recycling-plastics-approach.html
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