Combined effects of torrefaction pretreatment and ex-situ catalytic upgrading on the fast pyrolysis behavior of pine wood

High oxygen content of fast pyrolysis bio-oil severely limits its direct application as a transport fuel, while catalytic fast pyrolysis (CFP) for bio-oil upgrading typically suffers from rapid catalyst deactivation due to coking. In this work, torrefaction was utilized to pre-deoxygenate the biomass feedstock and reduce coke precursors, forming an integrated dual deoxygenation process with CFP to enhance bio-oil upgrading. The combined torrefaction-CFP process was systematically examined using pine wood (PW) torrefied at 220, 260, and 300 °C, followed by ex-situ HZSM-5 based catalyst upgrading at 500 °C. Torrefaction achieved a maximum reduction of 38.25% in the oxygen content of raw PW feedstock. The organic bio-oil yield (9.87–11.34 wt%) from CFP of PW torrefied at 220 or 260 °C was comparable to that of raw PW, indicating that the organic fraction was largely preserved despite the torrefaction step. Bio-oil quality improved markedly, with products shifting from oxygenates (acids, phenols) in non-catalytic bio-oil to high-value aromatics in catalytic bio-oil, leading to a desired decrease in O/C ratio and a higher HHV. Torrefaction at 260 °C was identified as the most appropriate pretreatment condition, providing a reasonable balance between feedstock property improvement and the final organic yield during catalytic fast pyrolysis.