Auto-Catalytic Effect of Iron on Plastic Solid Waste Pyrolysis

High Resolution Image Download MS PowerPoint Slide Pyrolysis of plastic materials represents a promising route to valorise mixed post-consumer waste into fuels and advanced carbon materials. However, the mechanisms governing solid residue (pyro-char) formation and transformation remain poorly understood. This study investigates the role of iron(II) acetate as a low-cost promoter in the thermal pyrolysis of polyolefin-rich plastic waste. Real waste feedstocks were pre-impregnated with Fe(OAc) 2 and subjected to batch pyrolysis across 600–1100 °C under an inert atmosphere. Comprehensive analyses combining XRD, SEM/EDS, and TEM reveal that iron undergoes sequential transformations—from oxide reduction to metallic iron (α-Fe), carburization to Fe 3 C, and partial encapsulation within graphitic carbon shells at the highest temperatures. These phase transitions critically modulate the char yield and structure: a pronounced minimum in pyro-char yield occurs near 900 °C, where Fe 0 /Fe 3 C coexist and catalytic gasification is most active. Above this temperature, sintering and graphitic encapsulation reduce surface accessibility, stabilizing the char. The results delineate a temperature-dependent pathway linking carbothermal reduction, catalytic gasification, and graphitization, providing mechanistic insight and practical guidelines for tuning pyrolysis toward either maximum carbon conversion or the synthesis of functional iron–carbon composites. This work reframes plastic pyrolysis from a waste management method to a controllable process for producing strategic carbon materials aligned with circular economy principles.