A study of polyethylene glycol terephthalate (PET) pyrolysis mechanisms using reactive molecular dynamic simulations

In the present work, the pyrolysis of polyethylene glycol terephthalate (PET) was analyzed with reactive molecular dynamics (ReaxFF MD) simulations. The results of non-isothermal pyrolysis simulation were compared with those from thermogravimetric (TG) experiments to determine the simulation temperature for ReaxFF MD. It was indicated that the weight loss curve in ReaxFF MD simulation at 500–2500 K was agreed well with that of TG experimental data at 400–900 K. In isothermal pyrolysis simulation at 1900 K, the final char, tar, and gas yields were 7%, 65%, and 28%, respectively. The activation energies for the conversion of PET to tar and gas were 231 and 143 kJ/mol, respectively. CO2, CO, CH2O and C2H4 are the major gaseous products, and their formation pathways are revealed by analysis of simulation trajectories. The migration and transformation of oxygen during PET pyrolysis at 1900 K were also examined. About 5%, 53%, and 42% of the oxygen were converted into char, tar, and gas, respectively. Among all the gas products, 50%, 35.6%, 5.5%, and 1.2% of oxygen was in CH2O, CO2, CO, and H2O, respectively. The oxygen in C5–15, C16–25 and C26–40 species accounted for 51.76%, 27.46%, and 20.78% of the total oxygen in tar, respectively. The results indicated that most of the oxygen in tar products was in light tars. Finally, the development of char is analyzed. It is found that the final O/C and H/C ratios of char were 0.3 and 0.61, respectively. The maximum pore diameters of char at char conversions of 10%, 30%, 50%, 70%, and 90% were 7.24, 9.85, 6.01, 4.51, and 4.43 Å, respectively.