Threshold temperature pyrolysis of waste plastic and the effect on pyrolysis energy consumption and product distribution

Pyrolysis technology, as a key method of waste resource utilization, its pyrolysis efficiency directly affects the feasibility of circular economy. However, conventional pyrolysis processes often rely on higher pyrolysis temperatures, which not only increase energy consumption but also lead to a more complex distribution of pyrolysis products. Therefore, developing a pyrolysis process that is low in energy consumption and high in added value is particularly important. This paper uses polyethylene, the plastic with the largest global production, as the experimental material, and systematically analyzes the evolution of multidimensional parameters (pyrolysis characteristics, pyrolysis function models, apparent activation energy, and conversion rate) during its pyrolysis process. Based on the evolution of the multidimensional parameters, the “threshold temperature pyrolysis process” for polyethylene was developed, and its feasibility was verified through experiments and ANSYS Workbench simulation. The research results indicate that the threshold temperature pyrolysis process has a lower pyrolysis temperature and forms a stable thermal field distribution during the isothermal stage. This stable thermal field distribution not only reduced energy consumption by 6.1 % through regulating the reaction pathways of free radicals, but also increased the pyrolysis oil yield by 11.5 %. Furthermore, the lower pyrolysis temperature and stable thermal field distribution under the threshold temperature pyrolysis process regulate the migration of pyrolysis oil components towards lighter fractions by slowing down the reaction rate and extending the residence time of long-chain hydrocarbons. The above studies also provide quantifiable theoretical basis and methodological support for the high value utilization of other waste materials.