Evolution of light olefins during the pyrolysis of polyethylene in a two-stage process

The accumulation of waste plastics has been one of the most urgent and difficult environmental challenges. In this work, the pyrolysis of polyethylene (PE) has been studied by thermogravimetric analysis (TGA), pyrolysis/ gas chromatography/mass spectrometry (PyGC-MS), and a two-stage tube reactor. The pyrolysis behavior of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) is compared, and there are almost no differences in the thermogravimetric curves obtained by TGA and the yield of gaseous products obtained in a two-stage process. The evolution of light olefins (C2-C4) during the pyrolysis of PE is investigated in a two-stage process with a constant condition in the first stage (500 degrees C) and various conditions in the second stage (700-1000 degrees C, 0.2-0.4 s). The temperature in the second stage has a more significant effect on the yield and selectivity of light olefins than the residence time, and the ethylene, propylene, and butene yields do not increase monotonously as the temperature rises. The highest yield of light olefins of 76.1 wt% is obtained at 800 degrees C with a selectivity of 91.7%. The maximum yields of ethylene, propylene, and butene are 45.1 wt%, 17.3 wt%, and 24.3 wt%, respectively. The scission mechanisms are proposed to provide insight into the process during which PE molecules transform into light olefins.

Automated summary

The accumulation of waste plastics is a pressing and challenging environmental problem. This study investigates the pyrolysis of polyethylene (PE) using various analytical methods, including thermogravimetric analysis (TGA) and pyrolysis/gas chromatography/mass spectrometry (PyGC-MS). The pyrolysis behavior of different types of polyethylene is compared, and it is found that the temperature in the second stage of pyrolysis has a significant impact on the yield and selectivity of light olefins.