Catalytic Deconstruction of Commercial and End-of-Life Polyurethane with Heterogeneous Hydrogenation Catalyst

Polyurethane (PU), as a thermoset polymer, is extensively utilized in various applications, such as refrigerator foams, sponges, elastomers, shoes, etc. However, the recycling of post-consumed PU poses significant challenges due to its intricate and extensive crosslinking structures. Catalytic hydrogenation is one of the most effective methods for recycling PU waste, nevertheless, there is currently a lack for a hydrogenation catalyst that is both high-performing, recyclable, and cost-effective for breaking down post-consumed PU materials. This study first employs a commercial NiMo/Al2O3 catalyst to catalytically break down both model PU and commercial PU into aromatic amines and polyol fractions. Notably, the results indicated that PU waste can be efficiently degraded at a pressure of 5 MPa and at a temperature of 185°C and yielding a significant amount of a valuable chemical monomers. It is speculated that the existence of a catalytic base in the solvent system could trigger glycolysis on the surface of PU particles. Subsequently, with the assistance of hydrogenation catalyst, the process of polymer hydrogenation becomes feasible by breaking C-N and C-O bonds with low energy barriers within the polymer. This study demonstrates the capability of fluidized bed hydrogenation process, employing recyclable heterogeneous catalysts for the recycling of PU waste.