Light, oxygen turn waste plastics into useful benzoic acid

Date:
April 11, 2022
Source:
Cornell University
Summary:
Chemists have discovered a way to use light and oxygen to upcycle
polystyrene -- a type of plastic found in many common items -- into
benzoic acid, a product stocked in undergraduate and high school
chemistry labs and also used in fragrances, food preservatives,
and other ubiquitous products.



FULL STORY ========================================================================== Chemists at Cornell University have discovered a way to use light and
oxygen to upcycle polystyrene -- a type of plastic found in many common
items -- into benzoic acid, a product stocked in undergraduate and high
school chemistry labs and also used in fragrances, food preservatives,
and other ubiquitous products.


========================================================================== Styrofoam egg cartons, hard plastic compact disc cases, red drinking
cups and many other common products are composed of polystyrene, which
makes up a third of landfill waste worldwide.

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

Their paper, "Chemical Upcycling of Commercial Polystyrene via Catalyst- Controlled Photooxidation" published in the Journal of the American
Chemical Society.

In line with her lab's mission to tackle environmental concerns through chemistry, the new process is mild, climate-friendly and scalable to
commercial waste streams, Stache said.

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



==========================================================================
Last summer, Stache's lab ran some degradation experiments in a sunny
window; in a place with strong year-round sunlight, the reaction could
be done outdoors.

"The advantage of using light is you can get exquisite control over
the chemical process based on some of the catalysts we've developed to
harness the white light. If we can use sunlight to drive the process,
that's a win-win," Stache said, noting that existing polymer recycling
requires heating a polymer for melting and processing, which usually
requires fossil fuel.

To test the tolerance of the process 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, Styrofoam and a
clear lid -- degraded efficiently. A black coffee cup lid degraded less efficiently, possibly because the black dyes inhibit light penetration,
Stache said.

"These results signify that our system could efficiently break down
commercial samples of PS, 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 lamps in
a 3D- printed photoreactor. The efficiency of the breakdown process at
the large scale was similar to that in small batches.

"If we can make the process even more efficient, we can think about how
to commercialize it and use it to address waste streams," Stache said.

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


========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Kate Blackwood, courtesy of the Cornell Chronicle. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Sewon Oh, Erin E. Stache. Chemical Upcycling of Commercial
Polystyrene
via Catalyst-Controlled Photooxidation. Journal of the American
Chemical Society, 2022; 144 (13): 5745 DOI: 10.1021/jacs.2c01411 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220411125410.htm

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