Exploration on the steam gasification mechanism of waste PE plastics based on ReaxFF-MD and DFT methods

Steam gasification of plastics is a promising way to deal with the increasing waste plastics as well as produce H-2-rich syngas. In this paper, ReaxFF-MD simulation and DFT calculation methods were combined to study the reaction process of the PE steam gasification and the formation mechanisms of syngas especially hydrogen. According to the main reaction, the gasification process has two overlapping stages: PE thermal depolymerization followed by H2O reforming reaction. The depolymerization stage is mainly the terminally or intermediately breaking process of C-C bond, during which different R center dot radicals and center dot R center dot double radicals fragments continuously dissociated into smaller hydrocarbons until C-1 -C-4. The free FL radicals released through dehydrogenation and H-transfer reaction in depolymerized stage can highly reduce the energy barrier of subsequent H2O reforming reaction. The production of H-2 mainly comes from the reforming reaction of H2O with free H center dot radicals and the accompanying center dot OH radical actively participates in the formation process of CO. Besides, the effects of temperature and water content on product distributions are analyzed. Increasing temperature and water content can promote the steam reforming consumption of hydrocarbons and thus a rise in H-2 and CO yields, but the improvement effects gradually decrease. The revelation of radical transformation and integration in this article can be a guide in later reaction adjustment as well as catalyst selection.

Automated summary

In this study, the reaction process of PE steam gasification and the formation mechanisms of syngas, especially hydrogen, were investigated using ReaxFF-MD simulation and DFT calculation methods. The results revealed that the gasification process consists of two overlapping stages: PE thermal depolymerization and H2O reforming. The study also provided insights into the role of free radicals in the reaction process and the effects of temperature and water content on product distributions.