To understand the correlation between plastic structure and products, and the possible reaction mechanisms, the pyrolysis–catalysis of different types of waste plastics was investigated in the presence of an Fe/Al2O3 catalyst. Polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), high-impact polystyrene (HIPS), and general-purpose polystyrene (GPPS) were used as the feedstock. The results showed that PP, HDPE, and LDPE showed higher H2-enriched gaseous product yields (>40 wt%), but higher H2 concentration (over 70 vol%) was obtained from the gaseous products of HIPS and GPPS. In terms of liquid oil, the yield exhibited a relatively stable tendency, which was ~ 20 wt%, and the liquid product comprised hydrocarbons with a carbon number range mainly between 8 and 16. For solid carbon deposits, HIPS waste plastic led to a higher solid deposit yield of 49.4 wt%, followed by GPPS of 48.7 wt%. By contrast, PP, HDPE, and LDPE showed lower yields of 30.2 wt%, 36.9 wt%, and 35.9 wt%, respectively. In summary, more, purer and cleaner carbon nanotubes (CNTs) could be obtained from pyrolysis–catalysis of polyolefin (PP and PE), while more amorphous carbon and hydrogen were gathered from PS.
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