Recycling: Light, air and salt generate raw materials from waste
A simple process breaks down Styrofoam packaging into its basic building blocks. The necessary aggressive chemical is created by white light - and then disappears again completely.
A new process for recycling plastic allows polystyrene - the main component of Styrofoam - to be broken down into valuable small molecules. The technique requires only light, air and the simple molecule ferric chloride, report Sewon Oh and Erin E. Stache from Cornell University in Ithaca, New York. As they report in theJournal of the American Chemical Society, they dissolved polystyrene in the commonly used solvent acetone along with ferric chloride and atmospheric oxygen and irradiated the mixture with white light for 20 hours. This caused the long molecular chains of the plastic to break down into their individual parts, predominantly benzene rings with an attached group of carbon and an oxygen as well as various other atoms. These benzoyl compounds are important basic materials for many chemical processes.
The method developed by Oh and Stache is based on the decomposition of the polymer chains with the help of chlorine radicals and oxygen. The light splits the bond between chlorine and iron, producing chlorine atoms that are chemically very reactive. These atoms remove hydrogen atoms from the molecular chains of the polystyrene at the points where the building blocks of the polymer are linked together. In turn, oxygen attacks these sites and breaks down the chain molecule into its basic building blocks. According to the experts, the process is very efficient, and the main product is benzoic acid, a basic substance in the chemical industry that is also used to preserve food.
The technique points to a potentially significant route to sustainable recycling of plastics. While in most recycling processes the quality of the material deteriorates as polymer chains become shorter and processing techniques are limited, it is possible to create virgin products from recovered basic building blocks. Such processes, which recover economically significant basic materials, are referred to as upcycling - in contrast to downcycling, which produces inferior materials that are only useful for a few applications. Such techniques make recycling plastics much more attractive.
However, it is often not easy to decompose the long molecular chains; for example, a lot of energy and aggressive chemicals are needed, and problematic waste is produced. That is why many upcycling approaches are often not worth the effort. The technique presented by Oh and Stache uses relatively easy-to-handle materials that can potentially be recovered after the process. Further experiments also showed that the process works with larger quantities than in the initial trials - a few grams of polystyrene instead of a few milligrams. This indicates that the process can be extended quite easily to large-scale industrial applications. However, it is still unclear how much waste needs to be pretreated, for example how much effort is required for separation and purification, before the process can be used.
Spectrum of Science
We are a partner of Spektrum der Wissenschaft and would like to make well-founded information more accessible to you. Follow Spektrum der Wissenschaft if you like the articles.
Originalartikel auf Spektrum.deTitelbild: Shutterstock
Experts from science and research report on the latest findings in their fields – competent, authentic and comprehensible.