Plastics to Chemicals: Producing C5–C14 Range Olefin Intermediates by Thermal Degradation of Plastics

Pyrolysis-based chemical recycling of plastics offers an environmentally sound and economically sustainable solution, with reactor and reflux system design being the key to enhancing hydrocarbon breakdown and process efficiency. Therefore, we perform chemical recycling of high-density polyethylene (HDPE) through pyrolysis in a semibatch glass reactor equipped with a reflux condenser to enhance liquid yield and composition. Reaction behavior was first assessed using thermogravimetric analysis, offering insights into the decomposition kinetics and thermodynamics. Pyrolysis trials were conducted with 50 g of HDPE at 475 °C across varying reflux temperatures (150–400 °C) to evaluate the effect on product yields and molecular distributions. Advanced gas chromatography methods (GC-FID, DHA, and RGA) were employed for detailed product characterization. Increasing the reflux temperature promoted recirculation and secondary cracking, leading to a notable rise in olefin content from 38.38 to 55.69%. Alpha-olefin yields increased from 8.91 to 15.9 g, with the significant improvements occurring between 200 and 300 °C. Besides, gaseous outputs consist of light hydrocarbons with minor hydrogen. It is observed that the reflux system effectively minimized heavy residues and improved the molecular weight distribution of the liquid product. Overall, the results confirm that reflux-enhanced pyrolysis significantly boosts conversion efficiency and selectivity, offering a viable pathway for advancing polymer-waste valorization and forming reactor scale-up for sustainable chemicals.