The effects of polyolefin structure and source on pyrolysis-derived plastic oil composition

Abstract

Seven types of plastics were pyrolyzed in a fluidized bed reactor: post-consumer recycled (PCR) high-density polyethylene (HDPE), PCR polypropylene (PP), HDPE virgin resins with two different molecular weights, virgin resins of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and PP. Pyrolysis produced non-condensable gases (C1–C3), liquid phase products (C4–C40), and solids (C40+ and chars), with alkane, alkene, alkadiene, aromatic, and multi-cycloaromatics as the predominant compounds. The polymer structure had the greatest impact on product distribution, with minimal influence from molecular weight. Branches in polyethylene (PE) acted as thermal defects initiating degradation. Higher branch density in PE led to increased concentrations of aromatics, branched alkanes, and internal alkenes. PP and PE exhibited distinct degradation mechanisms, with PP requiring less energy for decomposition and yielding more oil. Pyrolysis oil from PCR HDPE and PCR PP contained a higher proportion of branched compounds. Additives in PCR plastics may promote isomerization during pyrolysis.