Catalytic Fast Co-Pyrolysis Of Biomass And Low-Density Polyethylene With Modified ZSM-5 Zeolite Catalysts

A series of nonmetals (P and B) and transition metals (Ni, Zn, and Cu) modifed HZSM-5 zeolites (M-N/HZSM-5) were prepared using incipient wetness impregnation method. The physicochemical properties of the catalysts were characterized by X ray diffraction, TEM, nitrogen adsorption, NH3-TPD and Pyridine-IR. And they were applied for catalytic fast co-pyrolysis of biomass and low-density polyethylene. Through the experimental studies of co-pyrolysis of pine wood and LDPE, and steam pretreatment, we investigate and compare the catalytic activity, and hydrothermal stability of various kinds of catalysts. In addition, we investigate thoroughly the factor of the load density for catalytic activity.Through experimental studies, results showed that the yield of valuable petrochemicals (olefins and aromatic hydrocarbons) from co-feed catalytic fast pyrolysis 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℃ 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.The result showed that the modified (Cu, Zn, and Ni) HZSM-5 catalysts maintained the original MFI framework structure. However, the micropore volume and acidity decreased for the modified zeolites. In addition, the ratio of Lewis to Bronsted acid site increased considerably for the modified zeolites. Compared with the parent HZSM-5 zeolite, the M-P/HZSM-5 zeolites produced higher yields of valuable petrochemicals (monoaromatic hydrocarbons and olefins) and lower yields of undesired coke. Among the modified zeolites, H2-reduced Ni-P/HZSM-5 exhibited the highest activity of deoxygenation and aromatization in co-feed CFP of the pine wood and low-density polyethylene mixture, which increased the yields of CO and monoaromatic hydrocarbons from 6.48 C% and 25.7 C% for the parent ZSM-5 to 11.1 C% and 34.0 C%, respectively.For B/Ni- and B/Zn- modified ZSM-5, we only investigate the catalytic activity of catalysts for. The result shows the modified ZSM-5 could promote to increase the yield of valuable product. Furthermore, B/Ni-modified ZSM-5 was mainly to improve the yield of aromatics, and B/Zn-modified ZSM-5 increased mainly olefins yield. At the same time, when the charge density of B/Zn-impregnated boron was 2 wt%, The yield for p-xylene also increased from 2.58 C% to 5.03 C% while the selectivity increased from 29.5% to 65.5%.These results indicate that ZSM-5 modification with nonmetals (P and B) and transition metals (Ni, Zn, and Cu) 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.