Study of high density polyethylene (HDPE) pyrolysis with reactive molecular dynamics

PE pyrolysis is considered as an important process for converting plastic solid waste into fuel or other valuable chemicals to alleviate the environmental burdens. A computational approach can be of help for fully understanding the mechanisms and reaction pathways during PE pyrolysis in various industrial applications. In this paper, ReaxFF molecular dynamics was for the first time applied in simulating the pyrolysis of a High Density Polyethylene (HDPE) model system with 7216 atoms. Detailed reaction mechanisms and generation pathways of primary gas molecules were obtained by further analysis of the trajectories within a total of 250 ps simulation in NVT ensemble at 2000-3000 K using a newly created program, VARMD. The product profile and primary gas products evolution tendencies with temperature agree reasonably with the observations in Py-GC/MS experiments and literature data. The overall kinetics of ∼ C31 were analyzed and used to predict the reaction time for 90% weight loss of HDPE thermolysis that falls in around the reported time observed experimentally in the literatures. The reaction mechanisms based on the detailed reactions from the simulation trajectories are in broad agreement with what reported in literatures. The work presented here validates that ReaxFF MD is a promising method to help building a systematic understanding of the detailed chemical reactions in pyrolytic process for polymers.