New Research Exposes Flaws in Current Plastic Recycling and Pyrolysis

When individuals separate their plastic waste for recycling, they expect it to reappear somewhere as a recycled material. However, a recent study shows that current recycling techniques produce materials of such low value, only 10 % of plastic makes its way back into recycled materials.

Researchers from the University of Illinois Urbana-Champaign noted in a study published in Accounts of Chemical Research that current recycling techniques, which require sorting, grinding, cleaning, remelting, and extrusion to obtain plastic pellets, produce low-value materials because of contamination and mechanochemical degradation during recycling.

To improve plastic recycling, some researchers have investigated pyrolysis, the chemical breakdown of plastic polymers with heat into energy-rich molecules such as oils. However, this method requires large amounts of energy and can produce a hazardous combination of products, limiting its potential as a large-scale solution to the problem of plastic waste.

Using catalysts to break down plastics could be a more effective alternative. But, trying to predict how different catalysts and chemical intermediates will interact at various stages of the process is difficult and makes research into catalysis-based recycling methods slow-moving. 

To address the growing crisis of plastic pollution, many scientists are working on catalytic processes that break plastics back down into reusable building blocks. However, modeling these reactions is no easy task because reactants and intermediates have thousands of molecular weights and chemical functionalities.

Baron Peters, Study Lead and Professor, Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign

Looking to find a way around these issues, the researchers devised a novel framework that combines molecular-scale processes, such as chemical reactions and adsorption of polymerase on catalyst surfaces, with reactor-scale models.

These reactor-scale models balance the inflow of molten plastic and outflow of products with changing contents and reactions in the reactor.

The new model gives scientists a powerful tool for extracting molecular-level insight from reactor-scale measurements, or for making reactor-scale predictions from molecular-level mechanistic hypotheses.

Lela Manis, Ph.D. student at University of Illinois Urbana-Champaign and co-author of the study

These models have helped our team design new catalyst architectures that mimic nature’s strategy for processive depolymerization. They also have allowed us to identify reaction conditions that boost selectivity of value-added products.

Jiankai Ge, Ph.D. student at University of Illinois Urbana-Champaign and co-author of the study

The researchers hope that these quantitative models of the catalytic breakdown of plastic polymers will aid in the design of catalysts and in devising solutions for plastic pollution. 

Journal Reference

Manis, L, K., et al. (2025) Population Balance Models for Catalytic Depolymerization: From Elementary Steps to Multiphase Reactors. Accounts of Chemical Research. doi.org/10.1021/acs.accounts.5c00088.