Thermal Degradation of Real-World Waste Plastics and Simulated Mixed Plastics in a Two-Stage Pyrolysis-Catalysis Reactor for Fuel Production

Real-world postconsumer mixed plastics and a simulated mixture of plastics were processed in a two-stage pyrolysis-catalysis fixed bed reactor in the presence of a zeolite HZSM-5 catalyst. In addition, single plastic polyethylene, polypropylene, polystyrene, and polyethylene terephthalate were also processed in the two-stage reactor. The product yield, composition, and hydrocarbon distribution of the product oil was obtained in relation to plastic type. Noncatalytic pyrolysis of the plastics produced a high yield of an oil/wax product in the 81-97 wt % range. Addition of the catalyst reduced the yield of oil to between 44 and 51 wt %, with an increase in gas yield from cracking of the oil volatiles. However, the condensed oils produced from pyrolysis-catalysis were enriched with lower molecular weight (C-5-C-15) hydrocarbons and were markedly more aromatic in composition with a high proportion of single-ring aromatic hydrocarbons. Comparison of the results from pyrolysis and pyrolysis-catalysis of the simulated mixture of plastics with the data obtained for the individual plastics showed that significant interaction between the plastics occurred in the mixture with higher C-2-C-4 gas yield and higher aromatic content in the oils than expected from the proportions of the individual plastics in the mixture.