Thermally stable phosphorus and nickel modified ZSM-5 zeolites for catalytic co-pyrolysis of biomass and plastics

A series of phosphorus (P) and phosphorus/nickel (P/Ni) modified ZSM-5 zeolites were prepared by impregnation of a conventional ZSM-5 zeolite with P and subsequent Ni. The conventional, P-, and P/Ni-modified ZSM-5 zeolites were then tested as the catalysts for petrochemical production from co-feed catalytic fast pyrolysis (CFP) of pine wood and low-density polyethylene (LDPE) mixtures. Results showed that the yield of valuable petrochemicals (olefins and aromatic hydrocarbons) from co-feed CFP increased from 42.9 C% for conventional ZSM-5 to 52.8-54.1 C% for P- and P/Ni-modified ZSM-5, while the yields of low-value alkanes and undesired char/coke decreased from 17.3 C% and 22.6 C% to 9.6-10.2 C% and 18.9-15.7 C%, respectively. ZSM-5 impregnation with P and P/Ni thus significantly improved the product distribution in co-feed CFP of biomass and LDPE. In addition, modification with P and P/Ni improved considerably the hydrothermal stability of zeolites to resist steam-induced catalyst deactivation that may occur in co-feed CFP. When the conventional ZSM-5 zeolite was pretreated with 100% steam at 550 °C for 3-9 h, it produced 26.7-32.1% lower aromatic yields than untreated ZSM-5 in co-feed CFP. In contrast, steam pretreatment did not considerably affect the activity of P- and P/Ni-ZSM-5 zeolites for aromatic production. They maintained comparable aromatic yields in co-feed CFP when they had been steam pretreated for up to 9 h. These results indicate that ZSM-5 modification with P and P/Ni may provide a viable way to improve the catalyst's activity and life time for petrochemical production from co-feed CFP of biomass and plastics.