Designing a Circular Economy for Plastics: The Role of Chemical Recycling in Germany

Greenhouse gas emissions from human economic activity are causing global warming, leading to numerous impacts, including sea level rise, biodiversity loss, and increases in extreme weather events. For this reason, parties involved in the Paris Climate Agreement agreed to limit global warming to reduce its impacts. The second largest global emitter of carbon dioxide is the industrial production of goods. Within industrial production, the chemical industry with the production of olefins and other high-value chemicals for, among other things, plastic production, has a significant impact. Therefore, the present dissertation addresses designing a circular economy for plastics employing chemical recycling, contributing to the decarbonization and defossilization of the German chemical industry.

Five studies published as companion articles address substantial aspects of the chemical recycling of plastic waste as well as barriers to establishing a circular economy. Study A assesses chemical recycling via pyrolysis for lightweight packaging waste and shows that combining the currently predominant mechanical recycling with chemical recycling has economic and environmental advantages over employing these technologies individually. ... mehrAt the same time, more carbon can be recycled, reducing the dependence on fossil resources. Study B shows the importance of integrating the quality of secondary materials in assessing recycling routes. The preferable recycling technology can change based on the quality metrics and their integration into the assessment. Study C conducts pyrolysis experiments for automotive plastic waste and includes the generated data in an economic and environmental assessment of a chemical recycling route. Different economic and environmentally preferable waste handling options are identified when comparing chemical recycling with waste incineration with energy recovery. Study D examines the economics of automotive plastic waste pyrolysis and identifies the minimum plant input capacity at which the pyrolysis is economically feasible in German framework conditions. Study E combines the collected findings in a facility location optimization model for pyrolysis plants treating lightweight packaging and automotive plastic waste in Germany's current waste treatment network. Political steering strategies are analyzed to align economic and environmental objectives in the waste treatment sector.

In addition to the detailed results of the individual studies, four overarching implications are derived:
First, waste containing primarily polyolefins and engineering plastics can be technically pyrolyzed and are a suitable feedstock for chemical recycling. However, the most significant waste quantities studied are generated in short-lived lightweight packaging. Second, chemical recycling is environmentally preferable over waste incineration with energy recovery for all assessed waste streams. Economically, chemical recycling is not preferable compared to waste incineration with energy recovery for automotive plastic waste resulting in a conflict of economical and environmentally preferable waste handling options.
Third, the quality of the secondary materials must be considered when assessing waste recycling options, as this strongly influences economic and environmental assessment. Fourth, political steering strategies like the extension of CO$_{2}$ certificate trading and introducing recycling rates for waste that is a feedstock for waste incineration with energy recovery can align economical and environmentally preferable waste treatment options.

Consequently, the present dissertation provides valuable insights into the role of chemical recycling when designing a circular economy for plastics. Therefore, it has the potential to significantly contribute to closing the circularity gap of plastics.