Published on December 15, 2021
Making chemical plastics recycling respectable
Circa 6 Millionen Tonnen Verpackungsmüll landen in Deutschland pro Jahr in der Wertstofftonne oder im sogenannten Gelben Sack. 60 Prozent dieser Leichtverpackungen werden bereits werkstofflich recycelt, um dem Grundsatz der Kreislaufwirtschaft nachzukommen. Das bedeutet: Damit eingesetzte Rohstoffe nach Gebrauch nicht verloren gehen, werden die Abfälle wieder der Verwertung zugeführt. Richtige Mülltrennung macht diesen Recyclingkreislauf für Kunststoffabfälle erst möglich. Um in Zukunft noch bessere Recyclingquoten für Kunststoff zu erreichen, haben Forschende des KIT eine vielversprechende Lösung entwickelt: Das chemische Recycling von gemischten Kunststoffabfällen durch thermochemische Pyrolyse.
Formen der Kunststoffverwertung
„Beim herkömmlichen, werkstofflichen Recycling werden vorsortierte Kunststoffverpackungen mechanisch aufbereitet, die chemische Struktur bleibt dabei unverändert. Für einen solchen Prozess geeignet sind sortenrein sortierbare Kunststoffe aus dem Verpackungsbereich oder anfallende Rückstände aus der Produktion von Kunststoffprodukten. Schwierig wird es jedoch, wenn sich Kunststoffe nicht sortenrein trennen lassen oder durch Verschmutzungen kontaminiert sind. In diesen Fällen wurden bisher die Kunststoffabfälle in Müllverbrennungsanlagen zumindest energetisch verwertet“, erklärt Prof. Dieter Stapf, Leiter vom Institut für Technische Chemie (ITC) am KIT, die Hintergründe.
In den meisten Konsumprodukten werden bislang keine sortenreinen Kunststoffe eingesetzt, sondern maßgeschneiderte Materialien und Teilkomponenten für den jeweiligen Einsatzzweck oder hochfunktionalisierte technische Kunststoffe und Verbundmaterialien. Früher oder später werden sie aber alle zu Abfall. „Dieser Materialmix in den Abfällen bringt das werkstoffliche Recycling an seine Grenzen. Trennen und Sortieren wird zur unlösbaren Aufgabe und lässt sich nicht mehr wirtschaftlich umsetzen“, erklärt Dr. Marco Tomasi Morgano. Er hat während seiner Promotion am KIT an der Weiterentwicklung des Pyrolyseverfahrens mitgewirkt und treibt seit 2019 als Technischer Leiter bei ARCUS Greencycling Technologies die Industrialisierung des Verfahrens voran. Das chemische Recycling ermöglicht es, Kunststoffmischungen zurück in einen ressourcenschonenden Kreislauf zu führen. Da hierbei gleichzeitig vermarktbare Pyrolyseprodukte, wie Pyrolyseöl, erzeugt werden, zählt das Verfahren zur rohstofflichen Verwertung von Kunststoffen.
Chemical recycling at KIT
In the pyrolysis technical center of the ITC, Stapf's working group has been conducting research on the pyrolysis of a wide variety of organic materials for many years, focusing also on mixed plastic waste. "Recycling has a high impact on climate and resource conservation and encourages our process engineering research. We need solutions now to handle difficult waste," Prof. Stapf says. With their patented screw pyrolysis reactor, the researchers are pioneers in this field. In the special tray screw reactor, mixed plastics with particle sizes below 25 millimeters can be converted into their basic components – solid, liquid and gaseous raw materials – by pyrolysis.
In pyrolysis, the conditioned, previously shredded plastic waste from sorting residues of the yellow bin or from shredding plants for end-of-life vehicles is thermochemically treated with added additives such as sorbents and catalysts. The optimum pyrolysis temperatures and solids retention times in the reactor were determined at the institute for very different plastic mixtures. A special feature of the reactor is the downstream hot gas filtration: pyrolysis gases and vapors can be extracted directly and particle-free. The multi-stage condensation unit, consisting of heat exchangers and electrostatic separators, finally separates the condensable pyrolysis products, such as pyrolysis oil. The continuous reactor operation is largely automatic.
From experiment to pilot
Since 2018, KIT has been working together with ARCUS Greencycling Technologies GmbH to bring plastic pyrolysis to industrial application. Process engineer Dr. Tomasi Morgano emphasizes, "The process is intended to close the raw material cycle for plastic waste that has not been recyclable so far. I am very motivated by the fact that in my position at ARCUS I can now apply the knowledge I have built up in an industry-related way and contribute towards society in the process." ARCUS develops projects and technologies for the plastic recycling. The reactor technology of KIT therefore ideally complements the portfolio of the company based in Ludwigsburg.
Prof. Stapf specifies: "Within the scope of the cooperation, ARCUS has realized a pyrolysis plant based on KIT technology, with which mixed packaging waste can be recycled on an industrial scale. It was important that their end products are reusable." In order to scale up the existing procedure, some technical modifications were necessary with regard to process control, safety, and logistics. The KIT research team dealt with the technological issues of process engineering; ARCUS, on the other hand, took over the issues of plant construction, economic efficiency, and permission.
The plant developed has a modular design and is intended for decentralized use, e.g. in the vicinity of plants for the mechanical processing of lightweight packaging or commercial waste. ARCUS is currently building a demonstration plant at Industriepark Höchst in Frankfurt am Main, Germany, designed for a planned throughput of about 500 kg/h – including condensation, gas purification and power generation. Tomasi Morgano reports, "The permitting process was very complex because our plant brings together two sectors: waste treatment and chemistry. Therefore, I am glad that the construction is now on schedule." Establishing the process in the market is the declared goal for the coming years, without disregarding new developments such as bioplastics.
Facts & figures of the demonstration plant
- 4000 Ton/Anno mixed plastic waste for a thermal power of 4.5 MW
- Approx. 2500 Ton/Anno pyrolysis oil (brand name: ARCUS-Liquids)
- Voll elektrischer Betrieb (Ofen, Kälte, etc.) für ca. 700 kW installierte elektrische Leistung
- Gas engines each dual fuel (natural gas and pyrolysis gas) with a total electrical power of 600 kW with natural gas or 500 kW with pyrolysis gas
- Over 650 measuring points for continuous monitoring, balancing and control of the plant
Extract recyclable raw materials
Pyrolysis is a young method to recover recyclables from plastic waste in a high-quality way and to make the chemical industry climate-neutral without fossil raw materials. The conversion processes in chemical recycling turns waste into liquid, gaseous and solid pyrolysis products: Mainly pyrolysis oils, which replaces natural petroleum as an input material for polymer chemistry. In addition, pyrolysis gases, coke and condensates can be produced as stand-alone products for petrochemical or power generation. "A closed cycle in which all plastic waste can be fully recycled is the ideal state, which still seems unattainable. With our plants, however, we are nevertheless providing a contribution. Every new recycling option is a step towards a better circular economy," summarizes process engineer Tomasi Morgano, looking forward with confidence to the initial operation of the demonstration plant.
Kontakt
Honored with the Lothar Späth Award 2021
With their modular plant concept for chemical plastics recycling, which is based on a pyrolysis process developed by KIT, the cooperation partners Arcus Greencycling Technologies and KIT became the second winner of the Lothar Späth Award on November 18, 2021. The award honors cooperative innovation partnerships between scientific institutions and commercial enterprises in Baden-Württemberg. The cooperation partners were awarded for recycling plastics as a raw material in the sense of the carbon cycle economy.
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