Detailed Oil Compositional Analysis Enables Evaluation of Impact of Temperature and Biomass-to-Catalyst Ratio on ex Situ Catalytic Fast Pyrolysis of Pine Vapors over ZSM-5

The impact of upgrading temperature and biomass-to-catalyst mass ratio on upgrading pine pyrolysis vapors over HZSM-5 was studied in a dual fluidized bed reactor system. Increasing the upgrading temperature or reducing the biomass-to-catalyst ratio enhanced deoxygenation but decreased organic oil yields. Higher upgrading temperatures enhanced transformation of carbon into gaseous products, whereas the reduced biomass-to-catalyst ratio increased the conversion of biomass vapors to coke. While oxygen was removed as CO, H₂O, and CO₂, decarboxylation was limited by the amount of acids in the pyrolysis vapors. Bio-oil with molecular weight in gasoline range was derived via catalytic upgrading. The molecular homogeneity was improved at higher catalytic upgrading temperature and lower biomass-to-catalyst (B:C) ratio. Increasing the B:C ratio decreased the fraction of aliphatic C-H bonds and polyaromatics and increased the retention of both aliphatic and aromatic OH groups. Increasing the upgrading temperature enhanced cracking by ZSM-5, leading to oil with lower molecular weight, enhanced dealkylation and formation of light hydrocarbon gases, enhanced demethoxylation, and decreased polyaromatics formation. Aliphatic and aromatic OH decreased as upgrading temperature was increased from 500 to 550 °C, but there was less impact when the temperature was further increased to 600 °C.