Maximizing carbon efficiency of petrochemical production from catalytic co-pyrolysis of biomass and plastics using gallium-containing MFI zeolites

A series of gallium-containing MFI zeolites were prepared via impregnation of conventional aluminosilicate ZSM-5 with Ga (Ga/ZSM-5) or hydrothermal synthesis of galloaluminosilicate (Ga–Al–Si) and gallosilicate (Ga–Si) MFI zeolites. These Ga-containing zeolites were then tested as the catalysts for co-feed catalytic fast pyrolysis (CFP) of pine wood and low-density polyethylene (LDPE) mixtures. Compared with conventional ZSM-5 zeolites, the Ga-containing MFI zeolites considerably increased the yields of valuable petrochemicals (monoaromatic hydrocarbons and olefins) and decreased the yields of undesired polyaromatic hydrocarbons and low-value alkanes from the co-feed CFP. In addition, Ga–Al–Si and Ga–Si zeolites generally produced both higher yields and selectivities for valuable petrochemicals (e.g., p -xylene and olefins) than Ga/ZSM-5 in the co-feed CFP. The results indicate that Ga-containing zeolites may be used to improve petrochemical production in co-feed CFP of biomass and plastics, and direct hydrothermal synthesis of Ga–Al–Si and Ga–Si MFI zeolites may provide a more convenient and better alternative to post modification of ZSM-5 with Ga to prepare Ga-containing zeolites for co-feed CFP.