Simulating polyethylene pyrolysis from a generalized molecular-level kinetic model

Waste plastics have emerged as a global environmental issue. Polyethylene, accounting for about 25% of global plastic production, has been acknowledged as the major cause of white pollution. In this paper, a generalized molecular-level kinetic model was proposed to understand the pyrolysis of polyethylene applying structureoriented lumping, Poisson distribution, and genetic algorithm. The number of ordinary differential equations derived from the reaction kinetics were dramatically reduced by this simplified network with 14-rule design. The generalizability was confirmed by case studies without any change in the rule design. Under most conditions, the mean relative error between experimental and model data could be controlled within 5%, while abnormal deviations indicate the obstacle of heat transfer. The simulation curve could provide guidance for the experiments by locating the peak value of products. From 400-470 degrees C in Case 2, the increase in the reaction proportion of producing light oil explains the experimental results from the perspective of molecular-level reaction network. The comparison between PE and PS pyrolysis elaborates different pyrolysis mechanisms based on the different molecular structures.

Automated summary

Waste plastics, especially polyethylene, have become a significant global environmental issue, leading to white pollution. This study proposes a generalized molecular-level kinetic model for the pyrolysis of polyethylene, which effectively reduces the number of ordinary differential equations derived from reaction kinetics through simplified network design. The model demonstrates high generalizability and provides accurate predictions, with a mean relative error of less than 5% between experimental and model data. The comparison between polyethylene and polystyrene pyrolysis reveals different pyrolysis mechanisms based on molecular structures.