Effect of reaction conditions on pyrolysis performance of waste plastics loaded with Ni/ZSM-5 catalyst

Ni/ZSM-5 catalysts were prepared by uniformly loading the active metal Ni to ZSM-5 zeolite using excessive wet impregnation method, and the characterization tests of XRD, SEM, H2-TPR, and NH3-TPD were carried out. For the prepared Ni/ZSM-5 catalyst, the pyrolysis–catalytic reforming of waste plastics for gas production performance was explored under different reaction temperatures, steam-carbon (S/C) ratio, catalyst addition amount, and plastic type. The results showed that the gas production volume and gas quality of pure pyrolysis of HDPE and catalytic pyrolysis of Ni/ZSM-5 were improved with the increase of temperature. Given the thermal economy, the optimal pyrolysis temperature was 700 °C, the catalytic gas production was 900 mL, and the hydrogen concentration was 64.4 %. S/C ratio of 1.5 and plastic: catalyst of 1 was the best reaction condition, under which the gas production was 1020 mL and the hydrogen concentration was 65.1%, respectively. In addition, an appropriate increase in the amount of steam and the addition of catalysts would greatly optimize the final gas production performance. However, excess steam and catalysts was unfavorable to the gas production of plastic pyrolysis, resulting in a waste of resources. Finally, as for the gas production of four plastics, LDPE had the best pyrolysis gasification effect with gas yield of 1040 mL and hydrogen concentration of 65.7%. The order of catalytic pyrolysis effect of different plastics was LDPE>HDPE>PP>PS.