(633g) Catalytic Upcycling of Oxygenated Polymers with MFI Type Zeolites

Plastic production has been continuously increasing in the last decades, but there is no effective recycling technology for plastic waste. Upcycling plastic waste into new, valuable products is considered as a promising alternative, but also challenging, to address this issue. In the United States, for example, polyurethane is one of the most important and widely used plastics. Polyurethane is mainly produced from the reaction of reaction between isocyanates and polyether polyols. Long-chain polyurethane could limit the internal diffusion of the reactant during upcycling reactions. Therefore, to increase the reaction rate, high surface areas and pore sizes are generally required for the upcycling reaction.

In this study, catalytic upcycling of polyurethane was investigated with different types of MFI zeolites. Firstly, commercial H-ZSM-5 zeolites were used as a catalyst in the reaction. Product distribution, effect of polymer-to-catalyst ratios, and reaction temperatures were studied. Then, tailor-made MFI zeolites were synthesized with significantly higher surface area and pore size. Reaction products were investigated by the liquid chromatography–mass spectrometry, gas chromatograph-mass spectrometry, and nuclear magnetic resonance. The synthesized catalysts were characterized, using ammonia temperature-programmed desorption, nitrogen physisorption, X-ray diffraction, magic-angle spinning nuclear magnetic resonance, and scanning electron microscope. Furthermore, the spent catalysts were analyzed, using thermogravimetric analysis and positron annihilation lifetime spectroscopy. Advantages of the synthesized catalysts over commercial H-ZSM-5 catalysts were studied. Catalytic decomposition pathways of the polyurethanes were postulated, based on information from our experimental results and from the literature. The findings pointed out that catalytic upcycling of polyurethane waste had a positive contribution to promoting plastic recycling, energy security, waste management, and environmental protection.