Parametric Study of Polyethylene Primary Decomposition Using a Micropyrolyzer Coupled with Two-Dimensional Gas Chromatography

A deeper understanding of pyrolysis reaction pathways under an isothermal, reaction-controlled regime is essential for studying the kinetics and optimizing the design of pyrolysis reactors. This work methodically studied the effect of various pyrolysis variables on the product distribution of high-density polyethylene (HDPE) to validate the pyrolysis conditions that minimize transport effects and secondary gas-phase reactions. The primary decomposition of HDPE was performed using a Box–Behnken design to evaluate the role of pyrolysis variables such as particle size, sample size, carrier gas flow rate, and temperature. Pyrolysis experiments used a micropyrolyzer connected to two-dimensional chromatography with flame ionization and time-of-flight spectrometer detectors (Py–GC × GC–FID/TOF–MS). Principal component analysis of pyrolysis data showed statistical differences in the yield of C3 to C28 hydrocarbons as the temperature varied between 480 and 600 °C. Furthermore, a larger sample size of 1000 μg resulted in a different product distribution compared to smaller sample sizes of 50–150 μg. At 600 °C, the yields of cyclodiolefins, cycloolefins, and aromatics increased by approximately 355, 67, and 62%, respectively, when the sample size was increased from 50 to 1000 μg, and the flow rate decreased from 100 to 50 mL min–1.