Characteristics of Polyurethane Pyrolysis—Experimental Investigations and Product Analyses for the Assessment of Chemical Recycling Potentials

Abstract

Understanding polyurethane (PUR) decomposition is essential to promote the chemical recycling of plastic waste via pyrolysis. In this study, four representative polyurethanes were pyrolyzed in a lab-scale batch pyrolysis system to investigate their thermal decomposition characteristics. The solid, condensate and gas yields and the chemical composition of the product phases strongly depend on the structural PUR configuration and the pyrolysis temperature. In all cases, the condensate is the dominant product phase, exhibiting a broad compound spectrum, attributable to the urethane bond scission and the polyol backbone disintegration. The polyurethane monomer methylene diphenyl diisocyanate (MDI) is not detected. Up to 15 mass-% of the PUR is converted to the PUR monomer precursors 4,4′-methylenedianiline (MDA) and aniline. Secondary reactions, including MDI derivatization, are plausible. CO2 is the main gaseous compound, accompanied by short-chain hydrocarbons and oxygenated compounds. Nitrogen retention in the solid phase indicates urethane bond involvement, while oxygen mainly migrates to the condensate and gas. This study provides in-depth information on PUR pyrolysis characteristics, laying the foundation for the development of circular PUR waste-to-chemical processes. Potentials and challenges for chemical recycling are highlighted. The necessity of further research on PUR co-pyrolysis, adequate compound separation, and product upgrading is emphasized.