Direct production of olefins from the auger reactor-assisted steam pyrolysis of waste polyethylene

Waste polyethylene was pyrolyzed using a process that combines auger reactor (AR) and fluidized bed reactor (FBR). This study primarily investigated the effects of the AR temperature, fluidized bed temperature, FBR freeboard temperature, and the type of fluidizing medium (steam vs. N₂) on product distribution and light olefin yield. The most critical aspect of the process is the role of the AR. When the AR temperature is maintained at around 300 °C, the polymers inside the reactor melt. In this molten state, they are fed into the FBR, where pyrolysis takes place. Introducing polymers into the pyrolysis reactor in a molten, rather than solid state promotes their decomposition more effectively, resulting in enhanced production of light olefins. The experimental results confirmed this hypothesis. When the AR temperature was at 300–350 °C, the yield of C₂–C₄ olefins ranged from 50 to 52 wt%, which is up to approximately 8 wt% higher than the yield (44 wt%) obtained when the AR was unheated. The fluidized bed and freeboard temperatures were also found to influence gas production and the yield of C₂–C₄ olefins. In contrast, the choice of fluidizing medium had only a minimal effect on product distribution and light olefin yields. In conclusion, this study suggests that the AR-assisted steam pyrolysis process could serve as a straightforward method for the large-scale production of light olefins from plastic waste.