Molecular dynamics simulation of converting waste polyethylene (PE) to chemicals and fuels under non-isothermal and isothermal conditions

Abstract

Pyrolysis, one method of chemical recycling, has been an effective and clean way for processing plastic solid waste (PSW), which is a heavy burden for sustainable development. Series of molecular dynamic simulations are carried out for detailed pyrolysis of polyethylene (PE) waste using reactive force field (ReaxFF) for both non-isothermal and isothermal conditions. The results show that the PE pyrolysis at non-isothermal conditions can be divided into four stages. The last stage (post pyrolysis) is analyzed in depth, which shows decreasing of short-chain products and increasing of relatively long-chain components at high temperatures. Pyrolysis of PE at high heating rates reduces oil cracking and results in high yield of oil. The effect of reaction time depends on the pyrolysis temperature. In addition, under isothermal pyrolysis conditions, the simulated temperature range of 2500–2750 K is optimal for more recovery of C2H4 and C3H6 due to its high yield and mild influence of reaction time. Finally, detailed mechanisms of generation and consumption of C2H4 and C3H6 of PE pyrolysis are demonstrated. The regeneration of long-chain oil in the late stage of PE pyrolysis and the corresponding mechanisms are illustrated. The results in this study can be used to guide the design of systems for PSW processing with recovery of chemicals and fuels.