Gasoline-range hydrocarbons produced from microwave-induced pyrolysis of low-density polyethylene over ZSM-5

•It is the first time that plastic was used for microwave assisted pyrolysis over ZSM-5.•Large amount of gasoline-range hydrocarbons (74.73–88.49%) were produced.•Less than 1 wt.% coke deposition on ZSM-5 is negligible under most conditions.•Gaseous fractions with abundant ethylene, ethane, and hydrogen were obtained.•The reaction mechanism of thermal degradation and catalytic reforming were proposed.

The microwave-induced pyrolysis of low-density polyethylene (a model of waste plastics) toward its conversion into biofuels was investigated using ZSM-5 as a catalyst, generating significant amounts of gasoline-range hydrocarbons. A central composite experimental design (CCD) was done to investigate the effects of catalytic temperature and reactant to catalyst ratio on the pyrolysis-oils composition and to achieve the maximum liquid yield. The optimized condition for maximizing the yield of upgraded oil (32.58 wt.%) was at 450 °C and reactant to catalyst ratio of 2. GC–MS analysis showed that mono-ring aromatic hydrocarbons were enriched and became the most abundant compounds which varied from 74.73% to 88.49% in upgraded pyrolysis-oils, depending on the catalytic pyrolysis conditions. Both low temperature and high reactant to catalyst ratio gave rise to the formation of less desirable polycyclic aromatic hydrocarbons whereas high temperature and high ratio contributed to mono-ring aromatic hydrocarbons. The primary reaction competing with aromatic hydrocarbon production was the formation of coke which was negligible even at low catalytic temperatures. A plausible reaction mechanism was also proposed in order to shed light on the overall catalytic microwave pyrolysis of LDPE for aromatic hydrocarbons.