Newswise — Polystyrene, a prominent polymer utilized in plastic tableware and insulating materials, has been extensively employed but poses recycling challenges. In a breakthrough study published in the journal Angewandte Chemie, a group of researchers from the United States has successfully devised a thermochemical method, facilitating the retrieval of valuable chemicals from discarded polystyrene in a straightforward two-step process. This innovative approach holds the potential to revolutionize the recycling of insulating and packaging materials, fostering a genuinely circular plastics economy.
The groundbreaking technique known as "Degradation Upcycling" (Deg-Up) has been developed by Guoliang Liu and his team from Virginia Tech in Blacksburg, USA. This innovative approach allows for the production of a diverse range of highly valuable aromatic chemicals from polystyrene waste. The process involves a simple two-step cascade: first, polystyrene is broken down, resulting in the generation of benzene as the primary degradation product. Then, in the same reactor, this benzene product undergoes chemical modification. The outcome is the creation of various benzene derivatives, encompassing numerous essential substances for the cosmetics and pharmaceutical industries.
Conventional methods for breaking down polystyrene into benzene typically rely on costly catalysts, are energy-demanding, and result in a complicated mixture of products. However, Liu and his team have introduced a novel thermochemical approach that overcomes these challenges. Their method utilizes inexpensive aluminum chloride catalysts and can be carried out in reactors operating at a moderate temperature of 80 °C (approximately 180 °F). An additional advantage of their technique is the ingenious utilization of the solvent, benzene. Liu explains that only the amount of benzene recovered from the polymer is converted into the desired chemical, allowing any unused solvent to be recycled for processing more polymer feed.
To demonstrate the viability of their approach, the research team conducted an experiment involving the dissolution of different types of polystyrene waste, including packing peanuts and plastic utensils, in benzene. They then subjected the mixture to heat in a reactor under air-free conditions, utilizing aluminum chloride as the sole reagent. The resulting liquid product, primarily composed of benzene, proved to be highly effective. It could be directly used to obtain the desired value-added chemicals with exceptional yield and selectivity.
As a practical illustration, the research team introduced the reagent acetyl chloride, resulting in the successful synthesis of acetophenone—an essential chemical in the cosmetics and pharmaceuticals sectors. Furthermore, by incorporating the related reagent oxalyl chloride, they obtained benzophenone, a widely used component in sunscreen products and plastic additives. Additionally, the team achieved a remarkable level of selectivity in generating sulfur-containing aromatics from polystyrene waste, some of which serve as high-performance solvents in the polymer industry.
The primary objective of this innovative chemical upcycling method is to transform substantial quantities of polystyrene waste into value-added chemicals that can be utilized in various industrial processes. Since polystyrene insulating materials have low density, they are not ideal for mechanical recycling, which involves sorting, shredding, and transporting materials to create new products profitably. However, the Deg-Up process described here offers a resilient and contamination-tolerant alternative. It serves as a robust platform for the chemical upcycling of large volumes of polystyrene waste, paving the way for more sustainable and efficient recycling practices.
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