Light and oxygen turn plastic waste into useful benzoic acid

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Cornell University chemists have discovered a way to use light and oxygen to recycle polystyrene – a type of plastic found in many everyday items – into benzoic acid, a product stored in labs of junior and high school chemistry and also used in perfumes, food preservatives and other ubiquitous products.

Styrofoam egg cartons, hard plastic compact disc cases, red drinking cups and many other common products are made of polystyrene, which accounts for a third of the waste sent to landfills worldwide.

A team led by Erin Stache, an assistant professor of chemistry and chemical biology at Cornell, found that the reaction can even take place in a sunny window.

Their article, “Chemical Upcycling of Commercial Polystyrene via Catalyst-Controlled Photooxidation” published in the Journal of the American Chemical Society.

In line with his lab’s mission to tackle environmental problems through chemistry, the new process is gentle, climate-friendly and scalable for commercial waste streams, Stache said.

Additionally, the process is tolerant of the additives inherent in a consumer waste stream, including dirt, dyes, and other types of plastics.

Last summer, Stache’s lab conducted degradation experiments in a sunny window; in a place with strong sunshine all year round, the reaction could be outdoors.

“The advantage of using light is that you can get exquisite control over the chemical process based on some of the catalysts we’ve developed to harness white light. If we can use sunlight to drive the process, it’s ‘is a win-win,” Stache says, noting that recycling existing polymers requires heating a polymer for smelting and processing, which typically requires fossil fuel.

To test the process’s tolerance to other materials mixed with the PS plastic, the researchers used several products, ranging from packaging materials to coffee cup lids.

They found that three items – a white coffee cup lid, polystyrene and a clear lid – effectively degraded. A black coffee cup lid degrades less efficiently, possibly because the black dyes inhibit light penetration, Stache said.

“These results mean that our system could efficiently decompose commercial PS samples, even with additional composite and insoluble material,” she said.

To demonstrate scalability and potential commercial application, the researchers created a setup with two syringe pumps and two LED lights in a 3D-printed photoreactor. The efficiency of the large-scale decomposition process was similar to that of small batches.

“If we can make the process even more efficient, we can think about how to commercialize it and use it to deal with waste streams,” Stache said.

This research was funded in part by the National Science Foundation.

Source of the story:

Material provided by Cornell University. Original written by Kate Blackwood, courtesy of the Cornell Chronicle. Note: Content may be edited for style and length.

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