Recovering valuable chemicals from polystyrene

Polystyrene is a widely used polymer, but it is currently difficult to recycle. A team of US researchers, reporting in the journal Angewandte Chemie, have developed a thermochemical approach, making it possible to recover valuable chemicals from polystyrene waste in a two-step process. This approach could enable the recycling of insulating and packaging materials for a circular plastics economy.

The Degradation Upcycling (Deg-Up) process makes it possible to produce aromatic chemicals from polystyrene waste. It involves a two-step cascade: in the first step, polystyrene is chemically modified in the same reactor. This process gives rise to benzene derivatives, covering important substances for the cosmetics and pharmaceuticals industry.

The method, developed by Guoliang Liu and colleagues, uses aluminium chloride catalysts and can be performed in reactors at a moderate 80°C. It also uses benzene as a solvent, meaning that only the amount of benzene recovered from the polymer is converted into the desired chemical and any unused benzene is recycled to process more polymer feed.

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 aluminium 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.

By adding the reagent acetyl chloride, the team obtained acetophenone, an important chemical used in cosmetics and pharmaceuticals. By adding the related reagent oxalyl chloride, the team obtained benzophenone, a common ingredient in sunscreen products and plastic additives. 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 the chemical upcycling method is to recycle large volumes of polystyrene waste into value-added chemicals for other industrial processes. Due to their low density, polystyrene insulating materials are not well suited to mechanical recycling. The Deg-Up process is more suitable for these materials and is robust and tolerant of contamination.

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