Characteristics of a new type continuous two-stage pyrolysis of waste polyethylene

Waste polyethylene (PE) was pyrolyzed in a continuous two-stage pyrolysis process having auger and fluidized bed reactors. The main aim of the study was to produce a pyrolysis gas containing high contents of olefins along with a clean pyrolysis oil at moderate reaction conditions. In the experiment, the temperatures of the auger and fluidized bed reactors were varied from 30 to 300 °C and from 653 to 736 °C, and a CaO hot filter was used to capture HCl liberated during pyrolysis. At elevated auger reactor temperatures, the PE molecules in the reactor shifted to higher vibrational energy states, resulting in the weakening of the CC bond of PE molecule. The PE melt leaving the auger reactor could finally be decomposed into short chains in the fluidized bed reactor. The total yield of ethene, propene, and 1,3-butadiene was 30–53 wt.%. The olefin yield increased with increasing auger reactor temperature. The highest gas (74.6 wt.%) and ethene (34.5 wt.%) yields were obtained when N2 was used as the fluidizing medium. Pyrolysis oil, whose yield was 15–38 wt.%, was mostly composed of aromatic hydrocarbons. The CaO hot filter could reduce the chlorine content in the pyrolysis oil to 66.5 ppm.