(293g) Upcycling Waste Polyurethane into Value-Added Chemicals By Sub-and Supercritical Water

Waste polyurethane is generated in automobile, housing, and construction sectors, and it is one of the main portions of nearly 42 million metric tons of waste plastic, which is generated every year in the U.S. Most of the waste polyurethane like foam for mattresses, couches, and car seats are thermosets, which make them difficult to recycle, therefore, assigned as recycle class seven. On top of that waste polyurethane have a very low bulk density (20-100 kg/m³) that makes transportation to landfill very costly and consumes a large volume of the landfill. On the other hand, polyurethane contains nitrogen, oxygen, and aromatic rings in its structure which give polyurethane a huge potential as a feedstock to produce nitrogen containing aromatic compounds. When it comes to depolymerization of plastics, sub-and supercritical water have emerged into a better practice as it uses benign water as solvent. In this work, sub-and supercritical water were employed as highly efficient methods for the conversion of waste polyurethane to high-valuable chemicals. Depolymerization experiments were performed using a Parr batch reactor at 300-400 °C, and 0.5-4 h of reaction times. A commercial ruthenium carbon catalyst as a noble metal catalyst was used to improve the reaction efficiency. The results indicated that the optimal temperature and residence time were determined to be 350 ℃ and 4 h in subcritical conditions and 400 and 4 h in supercritical conditions as this gives enough energy and time to depolymerize the polyurethane. Moreover, the depolymerization of polyurethane increased significantly by shifting the water temperature from subcritical to supercritical conditions. The ruthenium carbon catalyst had a significant effect on the depolymerization of PU. Finally, some high-valuable chemicals like nitrogen containing aromatics were observed in the liquid product.