Simple chemistry can recycle polystyrene into more valuable products

UV light plus aluminum chloride as a catalyst can break down polystyrene so that it can become a chemical used in fragrances and medicines


August 15, 2022

Most polystyrene waste is not currently recycled

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Researchers have found a way to turn plastic waste into more valuable products, which they say could help tackle the growing accumulation of non-degradable waste polluting our cities and threatening life in our oceans.

Guoliang Liu at Virginia Tech and his colleagues have developed a method to break down polystyrene and turn it into a chemical that is much more valuable. The process is energy efficient and adaptable to other plastics, the researchers say.

Less than 10 percent of the world’s polystyrene is currently recycled, and many countries do not recycle it at all because there is no economic incentive, Liu says. Waste polystyrene is expensive to transport and expensive to degrade, and recycling it only creates more polystyrene that has little value.

Discarded protective packaging and takeout containers made from polystyrene do not degrade naturally. They often make their way to the sea through rivers or sometimes burn, releasing toxic chemicals.

Liu and his colleagues used ultraviolet light as an energy source and aluminum chloride as a catalyst to break down the chemical structure of polystyrene. They then used the same catalyst and added dichloromethane, a clear liquid commonly used as a solvent, to generate diphenylmethane.

Diphenylmethane is a chemical commonly used in fragrances and medicines. It is 10 times more valuable than polystyrene itself, so the conversion creates an economic incentive to reduce polystyrene waste.

The reaction takes place at ambient temperature and atmospheric pressure, so it requires less energy than existing methods for recycling or reusing polystyrene. The process is easy to adopt and could be profitable on a large scale, according to the team’s economic analysis.

“The most interesting thing is that this is standard chemistry,” says Liu. “We don’t use really harsh conditions, expensive catalyst or fancy reactions. All the components we use for this process are quite readily available.”

Liu’s team is developing a catalog of other valuable chemicals that can be obtained by modifying the chemical reaction used in the final step of the reuse process.

The concept also applies to almost all other plastics, so it could help turn one of the biggest threats to the environment into a sustainable circular economy, Liu says.

While the process is more cost-effective than existing recycling methods, the downside is that it can take longer as it scales up, says Bushra Al-Duri at the University of Birmingham in the UK. The process also uses some environmentally unfriendly solvents that could prevent it from being carried out on an industrial scale.

Journal reference: PNAS, DOI: 10.1073/pnas.2203346119

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