Heterogeneously Catalyzed Depolymerization of Polyurethane for the Efficient Recovery of Polyol and Dianiline

Polyurethane (PU) recycling remains a significant challenge owing to its inherent stability and crosslinked nature. Conventional chemical recycling methods, including solvolysis and catalytic hydrogenation, often rely on homogeneous catalysts with limited product recoveries. Herein, we report a novel approach incorporating heterogeneous catalysis with alcoholysis, utilizing commercially available zinc oxide and tert-butyl alcohol (TBA) for the efficient depolymerization of both model and commercial PU. Through comprehensive screening of metal oxides with varied acid-base properties and structurally distinct alcohols, the ZnO-TBA system exhibited outstanding catalytic performance, offering over 99% depolymerization of model PU at 180 °C within 4 h, demonstrating high selectivity toward the desired alcohol and amine products. Based on the control reactions conducted under varied conditions and the isolation of tert-butyl carbamate intermediate, a mechanistic pathway for ZnO catalyzed alcoholysis was proposed and further validated by DFT calculations. The practical potential of this method was showcased by applying it to real-life PU materials, including foams, elastomers, and insulation materials, which resulted in high monomer recoveries. The closed-loop nature of this approach enables direct reuse of the recovered monomers for new PU synthesis, thereby advancing the field of sustainable polymer recycling through a cost-effective, environmentally benign, and reusable catalytic platform.