Sustainable Chemical Recycling of Waste Polystyrene via Catalytic Pyrolysis over Waste Shell-Derived Calcium Oxide Catalysts

In this study, a series of seashell-based catalysts was synthesized via simple heat treatment and applied to the catalytic pyrolysis of buoy polystyrene (BPS) for the recovery of styrene monomer. This thermal process facilitates the phase transformation of CaCO₃ into CaO, thereby enhancing its catalytic activity with a 56.5 wt % styrene monomer yield from BPS at 350 °C, highlighting its potential as an efficient and environmentally friendly solution for marine waste valorization. A comparative kinetic analysis of thermal and catalytic depolymerization revealed that below 350 °C, catalytic depolymerization exhibited a significantly higher reaction rate than thermal depolymerization, whereas at temperatures above 350 °C the reaction rates of both approaches were nearly the same. Additionally, energy assessment using weighted separation energy calculations based on target styrene purity and product distribution confirmed the economic advantage of catalytic depolymerization. This underscores its potential as a cost-effective and energy-efficient strategy for styrene monomer recovery.