Efficient depolymerization of polystyrene waste into styrene monomers over the microwave-assisted Zn/b-ZnO catalyst system

Polystyrene (PS) waste recycling remains a critical challenge due to its high energy consumption and limited monomer yield. Herein, the b-ZnO catalyst with a few in-situ formed Zn sites at 270 °C under microwaves enhances the depolymerization of PS waste into monomers. To further improve the PS depolymerization over the b-ZnO catalyst, a series of Zn/b-ZnO catalysts with different metal Zn contents were prepared. Among these catalysts, the optimal 5Zn/b-ZnO achieves nearly 100 wt% PS conversion, yielding up to 0.997 g −1 PS liquid products with 0.8 g −1 PS styrene monomer in five cycles of experiment under microwaves. Such process greatly reduces the energy cost as compared with the conventional thermal process (0.51 vs. 0.81 kWh) and the obtained styrene monomer mixture can be repolymerized into fresh PS to complete a closed-loop recovery (80 wt% PS waste recycled). This work builds a novel microwave-assisted Zn/b-ZnO catalyst system for depolymerizing PS waste into monomers in a highly efficient way, which sheds a light on the sustainable recovery of PS waste.