Plastic Catalytic Pyrolysis and Coke Characterization: Exploring Reactivation Energy Dynamics of Spent USY-Zeolite Catalyst for Polyolefin Recycling

High Resolution Image Download MS PowerPoint Slide Coke deposition remains a critical barrier in catalytic pyrolysis, limiting process efficiency, and catalyst lifetime. In this study, we examine polypropylene (PP) and low-density polyethylene (LDPE) conversion over USY zeolite in a semibatch reactor, combining thermogravimetric analysis with the Ozawa–Flynn–Wall method to quantify coke decomposition energetics under inert, oxidative, and sequential N 2 → air conditions. PP preferentially produces liquid hydrocarbons (56 wt %), with lower gas output (39 wt %) and minimal coke (5 wt %), whereas LDPE favors gaseous products (47 wt %) with moderate liquid yield (40 wt %) and comparatively high coke residues (13 wt %). Kinetic analysis under inert conditions shows that PP-derived coke is more refractory (63% of total; E a = 289 kJ mol –1 hard) than LDPE-derived coke (48% hard; E a = 167 kJ mol –1 ), consistent with the denser structure of PP residues. Introducing oxygen lowers the average activation energy to ∼151 kJ mol –1 for both polymers, reflecting the strong contribution of exothermic combustion to regeneration efficiency. A TGA-based “softness ratio” is proposed to guide regeneration severity, demonstrating that USY zeolite not only enhances plastic-to-liquid selectivity at lower temperatures but also enables energy-aware regeneration strategies. Overall, coke energetics mapping provides a framework for targeted regeneration and feedstock-specific optimization.