Comparison of waste plastics pyrolysis under nitrogen and carbon dioxide atmospheres: A thermogravimetric and kinetic study

It is important to understand the influence of pyrolysis atmosphere on the thermal degradation of waste plastics. In this study, the decomposition of waste plastics; high and low density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate were investigated from ambient temperature to 500 degrees C within nitrogen or carbon dioxide atmospheres. The thermal degradation characteristics and kinetic parameters of individual plastics and mixed plastics (household packaging, building construction and agricultural waste plastics) from three different waste treatment plants were investigated under N-2, CO2 and N-2/CO2 atmospheres. In all atmospheres, only one degradation peak temperature was observed between 250-510 degrees C. The replacement of N-2 by CO2 showed different effects on the activation energy. Mixtures of N-2/CO2 in the pyrolysis atmosphere resulted to lower activation energy for all plastic samples, with the exception of high density polyethylene, polystyrene and polyethylene terephthalate. The lower activation energy suggested that lower energy was required for the degradation process. However, a mixture of more than 30 % of CO2 may influence the degradation process of plastics due to a higher value of residue obtained after the experiment.

Automated summary

This study investigated the thermal degradation of waste plastics under different pyrolysis atmospheres, revealing that a mixture of N2/CO2 can lower the activation energy for plastic degradation and promote the process, while a high concentration of CO2 may influence the degradation process of plastics.