Yoghurt cups, disposable cutlery, CD cases and polystyrene packaging – polystyrene is extremely versatile and is one of the most commonly used plastics worldwide. A total of 727,000 tons of polystyrene were processed in Germany in 2019. However, about the same amount ended up in waste recycling, since polystyrene products are often only used once or for a very limited period of time. However, like almost all plastics, polystyrene cannot rot or decompose in any other natural way once it is released into the environment. The growing plastic waste mountains in nature are a great risk for plants, animals and entire ecosystems.
Until now, collected plastic waste has been treated in various ways. They are burned, shredded, chemically broken down, or turned into new chemicals. But far too often only the energetic use as a fuel substitute is economically attractive. This is mainly due to the fact that material recycling usually requires complex collection, cleaning and separation processes. Researchers from Virginia Tech University have now developed a new method for not only using (recycling) polystyrene, but even upgrading it (upcycling). This is reported by the group led by chemical engineer Guoliang Liu in the specialist journal “Proceedings of the National Academy of Sciences”. The scientists see their approach as a lucrative opportunity to convert polystyrene into high-quality substances for the chemical industry if the principle can be scaled up to industrial standards.
First, the scientists showed that polystyrene can be decomposed at room temperature and under atmospheric pressure using an inexpensive aluminum chloride catalyst and UV light. This produces benzene, the parent compound of the aromatic hydrocarbons. They then added dichloromethane, which reacts with benzene to form diphenylmethane. They were able to convert 97 percent of the aromatic phenyl rings in polystyrene into diphenylmethane, a high-value, low-toxicity chemical used in the food, pharmaceutical, fragrance, and colorant industries, among others. “The combined mining and upcycling method is cheaper and more sustainable than the current industrial processes for producing diphenylmethane,” the research article states.