Auger reactor-assisted steam pyrolysis of waste polypropylene

The conversion of waste polypropylene (PP) into valuable light olefins was investigated using an auger reactor (AR)-assisted steam pyrolysis process. In this configuration, a molten PP stream generated in the AR at approximately 300 °C was continuously fed into a bubbling fluidized bed reactor operating between 600 and 800 °C. In the experiment, the effects of key operating variables including AR temperature, fluidized bed temperature, freeboard temperature, fluidization number, and the type of fluidizing medium were systematically examined. The results showed that the gaseous fraction was the dominant product, with gas yields ranging from 46 to 74 wt% under steam conditions. The maximum total yield of light olefins (C₂-C₄), approximately 50 wt%, was obtained at 700 °C. Among these, the yield of propene reached up to 23 wt%. Increasing the AR temperature slightly enhanced ethene formation, whereas the influence of the fluidization number was negligible. Steam exhibited a dual role by promoting Diels-Alder reaction, thereby increasing the aromatic content in the pyrolysis oil while slightly reducing light-olefin yields. Mechanistic interpretation indicated that pre-melting in the AR enhanced the formation of ethene and methane. These findings provide a foundation for scale-up of the AR-assisted steam pyrolysis process and demonstrate its promise as a route for recovering valuable light olefins from polyolefin-rich municipal waste plastics. Industrially, this process can supplement naphtha steam cracking, reduce dependence on fossil feedstocks, and support circular-economy recycling strategies.