Two-Stage Fixed-Bed Low-Density Polyethylene Pyrolysis: Influence of Using Different Catalytic Materials in the Second Stage

Pure low density polyethylene pyrolysis was investigated using a lab-scale two-stage fixed-bed pyrolyzer with different catalytic materials in the second reactor for upgrading the vapors. The yields of gas and char were determined, and the condensed product was thoroughly examined by gas chromatography–mass spectrometry and thermogravimetric analysis. The use of different catalytic materials such as HZSM-5, cement raw meal, calcined cement raw meal, and silicon carbide was investigated. A wax-rich condensed product (intermediate molecular weight hydrocarbons) was observed in the following types of experiments: no catalyst, silicon carbide, and cement raw meal in the second reactor. The wax was mainly composed of alkanes and alkenes. The use of an HZSM-5 catalyst and applying temperatures from 350 to 500 °C in the second reactor highly decreased the chain length of hydrocarbons in the condensed product and converted the wax into a liquid. When the second reactor temperature was higher than 400 °C, the main product components were aromatics and naphthalene. Using calcined raw meal in the second reactor at a temperature of 600 °C also led to the conversion of the wax to a liquid product with a large fraction of cyclic aliphatics.