Ex-situ catalytic fast pyrolysis of biomass over HZSM-5 in a two-stage fluidized-bed/fixed-bed combination reactor

•Ex-situ catalytic fast pyrolysis (CFP) was studied in a two-stage bench scale device.•Ex-situ and in-situ CFP gave a similar carbon yield of aromatics+olefins.•Ex-situ CFP produced significantly more olefins than in-situ CFP.•High pyrolysis temperature generated significantly less coke.•High catalysis temperature led to a boost in ethylene and benzene selectivities. Ex-situ and in-situ catalytic fast pyrolysis (CFP) of biomass over HZSM-5 were compared in a two-stage fluidized-bed/fixed-bed combination reactor. Ex-situ CFP gave a similar carbon yield of aromatics+olefins (∼20%) with in-situ CFP but produced much more olefins (10.3% vs. 5.8%) and less char+coke (42.7% vs. 48.4%). The effects of weight hourly space velocity (WHSV), carrier gas flow rate, pyrolysis temperature and catalysis temperature on product distribution in ex-situ CFP were further studied. The maximum carbon yield of aromatics+olefins (21.7%) was obtained at pyrolysis temperature of 550°C and catalysis temperature of 600°C with the highest carrier gas flow rate (1.2L/min) and WHSV of 1.33h−1. Obviously less coke was generated at higher pyrolysis temperature. When catalysis temperature increased to 700°C, ethylene and benzene carbon selectivities boosted to 79.4% and 60.5%, respectively.