Microkinetic Modeling of Plastic Waste Catalytic Cracking with Phosphorus-Modified Mesoporous HZSM-5: An Iso-Octane Model Compound Study

Ex-situ catalytic pyrolysis offers a promising route to valorize plastic waste. While phosphorus-modified mesoporous HZSM-5 exhibits high selectivity (84 wt % yield) toward valuable C2–C4 olefins, the underlying reaction mechanisms remain unclear. To address this, we developed a microkinetic model, using iso-octane as a plastic waste surrogate, and compared its predictions to experimental cracking data on both unmodified and modified HZSM-5. Our analysis revealed three key effects of the modifications: enhanced mass transfer due to mesopores, suppressed primary β-scission reactions, and reduced intermolecular hydride transfer. These effects are correlated with alterations in the zeolite’s acid site concentration and type of acid sites, providing insights for further optimization of this high-performing catalyst for the desired olefin production.