Magical, plastic turns spice

Most polystyrene waste is not currently recycled. Image credit: Xinzheng/Getty Images

Researchers in the United States have found a way to upgrade plastic waste into a more valuable product. This, they say, helps tackle the growing amount of non-degradable waste. They pollute cities and threaten marine life.

Liu Guoliang and colleagues at Virginia Tech have developed a way to break down polystyrene and turn it into a more valuable chemical. The researchers say the process is energy efficient and also works for other plastics. The paper was recently published in the Proceedings of the National Academy of Sciences.

Discarded polystyrene protective packaging and takeaway food containers do not decompose naturally. They often cross rivers into the ocean and are sometimes incinerated, releasing toxic chemicals.

Liu Guoliang said that less than 10% of the world’s polystyrene is currently recycled, and many countries do not recycle it at all because there is no economic benefit. Polystyrene waste is expensive to transport, the cost of decomposition is high, and recycling will only produce more polystyrene, which has little value.

Liu and 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 to add dichloromethane, a transparent liquid commonly used as a solvent, to make diphenylmethane.

Diphenylmethane is a chemical commonly used in fragrances and pharmaceuticals that is 10 times more valuable than polystyrene, so conversion technology has produced economic benefits for reducing polystyrene waste.

The reaction can be carried out at ambient temperature and atmospheric pressure, and it requires less energy than existing polystyrene recovery or upgrading methods. According to the team’s economic analysis, the process is easy to adopt and can be profitable at scale.

“The most interesting thing is that we didn’t employ really strict conditions, expensive catalysts or exotic reactions. All the ingredients we use in this process are very easy to obtain. Liu Guoliang said.

Liu’s team is developing a catalogue of other valuable chemicals that can be obtained by altering chemical reactions in the final step of the upcycling process.

This concept also applies to almost all other plastic products, thus helping to transform one of the biggest environmental threats into a sustainable circular economy.

Bushra Al-Duri of the University of Birmingham in the UK says the process is more economical than existing recycling methods, but the downside is that it takes more time as the scale grows. In addition, some solvents used in the process may prevent it from expanding on an industrial scale. (Source: China Science Daily Wang Fang)

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