Co-pyrolysis behavior and synergistic mechanism of sub-bituminous coal and polypropylene: A ReaxFF molecular dynamics simulation

Abstract

The co-pyrolysis behavior of coal and polypropylene (PP) was investigated by reactive force field molecular dynamics (ReaxFF MD) simulation in the present study. In addition to analyzing the co-pyrolysis behavior at the atomic scale, the trajectories of different elements from different material sources were first observed. The weight loss of coal and PP is consistent with previous experimental studies, demonstrating the reliability of the ReaxFF MD simulation. The analysis of pyrolysis products showed that all blended systems contributed to tar and H2 yields at high temperatures compared to the calculated values. Among them, the coal/PP (6:4) system had the most significant effect on improving tar yield. H2 can be divided into three types according to different sources of H·, and with the increase of PP proportion, H· from PP is more willing to produce HPP2 at 3000 K. Then, the kinetics of the co-pyrolysis systems with multiple heating rates were studied, and only the activation energy of the coal/PP (4:6) system was reduced. Subsequently, we gave the mechanism by combining the pyrolysis process and the change in the number of free radicals. The blended systems promoted the production of more H· through PP, which made heavy compounds in coal further decomposition.