Continuous‐Flow Conversion of Waste Polystyrene Into Styrene Monomers Utilizing the Microwave‐Concentration Effect on Spherical Activated Carbon

Chemical recycling of polystyrene (PS) by high-temperature pyrolysis can recover styrene monomer, but conventional processes require substantial energy input and generate complex, nonrecyclable byproducts. Here, we report an additive-free continuous-flow depolymerization of PS using localized microwave (MW) heating. A toluene solution of PS was passed through a quartz cartridge packed with spherical activated carbon beads (CBs), which concentrate MW energy and create a confined high-temperature reaction zone. Using a temperature-controlled single-mode MW reactor, the effects of backpressure and feed delivery were examined with reagent-grade PS and postconsumer PS products, including takeout trays and containers. Backpressure was found to be essential for stable styrene production. Without backpressure, channel occlusion occurred and the styrene yield reached only 19% after 4 h, whereas 0.5 MPa backpressure enabled 70%-76% styrene yield after 24 h. Postconsumer PS feeds also afforded 67%-76% styrene yield, comparable to reagent-grade PS. The coproducts were mainly limited to dimers and trimers, supporting distillative styrene recovery. This cartridge-based MW-flow system provides a simple route for direct styrene recovery from diverse PS waste streams under low-power, localized heating conditions.