(385w) Two-Stage Pyrolysis of Polyethylene to Light Olefins Assisted By CO2

The treatment of waste plastics is currently one of the most urgent environmental issues, and reducing carbon emissions is also a widely recognized focal point. Pyrolysis to obtain high-value products is a method of recycling waste plastics that has garnered significant attention from researchers. Inert gases such as nitrogen are the most commonly used atmospheres in waste plastic pyrolysis studies. Some researches have utilized carbon dioxide for dry reforming to obtain carbon monoxide and hydrogen gas following pyrolysis. Using carbon dioxide as the atmosphere for plastic pyrolysis not only allows for the recycling of waste plastics but also reduces carbon dioxide emissions, making it environmentally friendly. In this work, carbon dioxide is directly used as the PE (polyethylene) pyrolysis atmosphere. We employ thermogravimetric analysis (TGA) combined with infrared spectroscopy (IR) and mass spectrometry (MS), as well as pyrolysis/gas chromatography/mass spectrometry (PyGC-MS), to investigate the thermal degradation of PE in carbon dioxide and nitrogen atmospheres, including thermal characteristics, kinetics, and product distribution. It is found that there is almost no difference in the thermal degradation curves and gas product yields of PE in the two atmospheres at low temperatures, indicating that carbon dioxide in the pyrolysis process of PE was not activated. Further experiments are conducted on the pyrolysis of PE at temperatures exceeding 1000 °C in a two-stage process. At such high temperatures, carbon monoxide is detected in the products in CO₂ atmosphere, demonstrating the activation of carbon dioxide in the reaction. By manipulating the reaction time, high-value products such as light olefins can be obtained. A hydrogen-rich gas is added to balance the C/H ratio in an attempt to obtain more light olefins.