New Iron Catalyst Powers Sustainable Polystyrene Recycling

In the journal Angewandte Chemie, a research team from the Friedrich Wöhler Research Institute for Sustainable Chemistry in Göttingen introduced a novel approach for recycling polystyrene (PS) waste. Their electrochemical process is effective, uses a cost-efficient iron catalyst, generates hydrogen as a byproduct, and can be powered by solar energy.

Plastics have become a fundamental part of daily life. However, the large quantities of plastic waste accumulating in landfills and the environment present significant challenges alongside the benefits plastics provide.

Less than 10 % of the plastic produced globally is recycled, leading to the accumulation of plastic waste in landfills and waterways. This waste poses significant threats to wildlife and the environment. By 2025, this plastic waste is expected to reach 40 billion tons.

PS, commonly used in packaging and construction, makes up about 33 % of the material in landfills, but only 1 % of it is recycled. In 2022, the global production capacity of PS reached 15.4 million tons and continues to grow. Recycling plastics, especially PS, remains one of the major societal challenges.

Developing efficient and cost-effective recycling methods that convert plastic waste into valuable small molecules for chemical synthesis is key to advancing a sustainable circular carbon economy.

A team led by Lutz Ackermann has developed an electrocatalytic method for efficiently degrading PS. This process produces a significant amount of monomeric benzoyl products, which can serve as precursors for chemical processes, along with some short polymer chains.

The success of this method relies on a powerful iron-based catalyst, specifically an iron porphyrin complex similar to hemoglobin. Iron is preferred over many other catalytic metals because it is non-toxic, inexpensive, and abundant. In the electrocatalytic reaction, the iron compound cycles through different oxidation states (IV, III, and II), leading to the cleavage of carbon-carbon bonds in the polymer backbone.

The primary products are benzoic acid and benzaldehyde. Benzoic acid is a key starting material for various chemical syntheses, including the production of fragrances and preservatives. The robustness of this new electrocatalytic method has been demonstrated by successfully degrading real-life plastic waste at the gram scale.

This PS degradation process can be fully powered by electricity from commercially available solar panels. Additionally, a beneficial side reaction occurs during the process—the production of hydrogen. This makes the new electrocatalytic method an effective solution for plastic recycling, while also enabling decentralized, green hydrogen production, making it scalable for industrial applications.

Journal Reference:

Hourtoule, M., et al. (2024). Anodic Commodity Polymer Recycling: The Merger of Iron‐Electrocatalysis with Scalable Hydrogen Evolution Reaction. Angewandte Chemie International Edition. doi.org/10.1002/anie.202412689.