Coke Characterization and Re-Activation Energy Dynamics of Spent FCC Catalyst in the Catalytic Pyrolysis of Polyolefins

Chemical recycling via catalytic pyrolysis is constrained by coke deposition and costly catalyst make-up. We investigate polypropylene (PP) and low-density polyethylene (LDPE) conversion over a spent FCC equilibrium catalyst (AXL) and, critically, quantify the re-activation energy landscape of the resulting coke. Using a semi-batch reactor (350 °C) and thermogravimetric analysis to 1100 °C combined with the Ozawa–Flynn–Wall method, we distinguish soft and hard coke under inert, oxidative, and sequential N2 to air regimes. LDPE yields mainly gas (70.7 wt%) with 5.5 wt% coke, whereas PP favors liquids (47.1 wt%) with 3.4 wt% coke. LDPE-derived coke is softer (71% of total; EA = 170 kJ mol−1 soft) than PP coke (60% soft; EA = 166 kJ mol−1), evidencing a more refractory PP residue. Oxygen lowers EA to ~155 kJ mol−1 for both polymers. We introduce a simple TGA-based “softness ratio” to guide regeneration severity and show that a refinery-waste FCC catalyst delivers selective plastic-to-fuel conversion while enabling energy-aware regeneration protocols. The framework directly supports scale-up by linking polymer structure, coke quality, and atmosphere-dependent re-activation energetics.