Chemical Recycling by Pyrolysis and Gasification

The Fraunhofer Institute for Microstructure of Materials and Systems (IMWS) develops innovative carbon cycle technologies at its Freiberg branch in close cooperation with the Institute of Energy Process Engineering and Chemical Engineering (IEC) of the TU Bergakademie Freiberg. The main objective is to minimize CO₂ emissions, by using thermo-chemical conversion processes (gasification, pyrolysis) of sustainable carbon resources. Research activities include technology development, process balancing and design, as well as integrated process chain simulations, CFD multiscale process simulations and life cycle assessment (LCA).

As part of the Fraunhofer project Waste4Future (W4F), the development of a comprehensive, entropy-based assessment model is envisaged, which can transform the prevailing process-based recycling chain into a material-based chain. A sorting process will identify which materials, and in particular which plastic fractions, are contained in the waste. Subsequently, a digital twin and a evaluation model will be used to decide which recycling route is the most technically, ecologically and economically feasible for a specific waste stream. Entropy is intended to serve as a key parameter for the evaluation model and is defined as a measure of the disorder of a system.

System optimization thus no longer focuses on the optimization of the individual process, but on the entropy-optimized division of the total stream and the targeted allocation to the energetically optimized recycling processes. A material stream is divided into its sub-streams, which are assigned to different recycling routes on the basis of a technology hierarchy. The remaining streams from material recycling (mechanical recycling, solvent-based purification and fractionation) are available for chemical recycling (solvolysis, pyrolysis and gasification). The objective is to obtain the maximum possible amount of carbon compounds. Thus, thermal recycling at the end of the chain should be minimized.

In the presentation, the Waste4Future project will be introduced and the possibilities of the research cluster Freiberg with regard to chemical recycling and carbon cycling by pyrolysis and gasification will be outlined. Different methods of these two thermochemical conversion processes will be discussed with regard to their possible applications. Furthermore, the approach for entropic evaluation with the help of Shannon entropy is explained and a possible transfer of this quantity, which originates from information theory, to mechanical and chemical recycling processes is discussed.