Recovering Valuable Chemical Building Blocks from Polystyrene Waste
Polystyrene, the main material in plastic tableware and insulating
materials, is a widely used polymer but is currently difficult to
recycle. Reporting in the journal Angewandte Chemie, a team of US
researchers have now developed a thermochemical approach, making it
possible to recover valuable chemicals from polystyrene waste in a
simple two-step process. This new approach could enable the recycling of
insulating and packaging materials for a truly circular plastics
economy.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
The newly developed “Degradation Upcycling” (Deg-Up for short) makes
it possible to produce a wide array of highly valuable aromatic
chemicals to be produced from polystyrene waste, as explained by
Guoliang Liu and co-authors from Virginia Tech in Blacksburg, USA,
explain. The process involves a two-step cascade: in a first step,
polystyrene is broken down to give benzene as main degradation product,
and in a second step this benzene product is chemically modified in the
same reactor. The process gives rise to benzene derivatives, covering
many important substances for the cosmetics and pharmaceuticals
industries.
Methods for breaking down polystyrene into benzene usually require
expensive catalysts, are energy-intensive, or produce a complex mixture
of products. Liu and colleagues’ new thermochemical method uses
inexpensive aluminum chloride catalysts and can be performed in reactors
at a moderate 80 °C (ca. 180 °F). Another advantage of their method is
the clever use of the solvent, benzene. “Only the amount of benzene
recovered from the polymer is converted into the desired chemical.
Unused solvent can be recycled to process more polymer feed,” Liu says.
As a proof of concept, the team dissolved various types of
polystyrene waste, such as packing peanuts and plastic utensils, in
benzene, and heated the mixture in a reactor under air-free conditions
with aluminum chloride as the only reagent. The liquid product,
consisting primarily of benzene, could be used directly to obtain the
desired value-added chemicals in high yield and with high selectivity.
For example, by adding the reagent acetyl chloride, the team obtained
acetophenone, an important chemical in the cosmetics and
pharmaceuticals industries. By adding the related reagent oxalyl
chloride, the team obtained benzophenone, a common ingredient in
sunscreen products and plastic additives. In addition, sulfur-containing
aromatics, some of which are used as high-performance solvents in the
polymer industry, were produced with a high degree of selectivity from
polystyrene waste.
The goal of this new chemical upcycling method is to recycle large
volumes of polystyrene waste into value-added chemicals for other
industrial processes. Having a low density, polystyrene insulating
materials are not well-suited to mechanical recycling, i.e., the process
of sorting, shredding, and transportation of materials for the
profitable manufacture of new products. The Deg-Up process described
here, on the other hand, is robust, tolerant of contamination, and
suitable as a platform for chemical upcycling of large-volume
polystyrene waste.
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About the Author
Guoliang (Greg) Liu
is an Associate Professor at the Department of Chemistry, Virginia
Polytechnic Institute and State University (Virginia Tech), Blacksburg,
VA, USA. His research group envisions that smartly designed organic
polymers and inorganic nanomaterials can be integrated to create novel
materials with unique collective emergent properties, with huge
implications for sustainable energy and environmental science and
technology.