Catalytic fast pyrolysis of Ca(OH)₂-pretreated lignin over Beta zeolite for aromatic-rich bio-oil production

Lignin, with its complex structure and high stability, poses a significant challenge in the directed depolymerization to obtain aromatic-rich bio-oil. To prevent the formation of hard-shelled char resulting from the melting and agglomeration of lignin during pyrolysis, this study proposed a dual strategy combining Ca(OH)₂ pretreatment and Beta zeolite, which demonstrated a synergistic effect through β-O-4 bond cleavage, effectively suppressing lignin condensation while achieving high aromatic selectivity. In this study, the influence of various operational parameters was examined. Key variables including pretreatment procedures, concentration levels, catalyst selection, catalyst-to-raw material ratio, carrier gas velocity, and pyrolysis thermal conditions were analyzed to determine their effects on the critical processes. Pretreatment with 5 wt% Ca(OH)₂ significantly reduced lignin agglomeration during pyrolysis. Using Beta zeolite (1:1 mass ratio) in CFP at 500 °C with 75 mL/min carrier gas flow increased bio-oil yield from 5.0 wt% to 7.5 wt% and enhanced aromatic selectivity from 1.9 area% to 84.9 area%. Using 2-phenoxy-1-phenylethanol (α-OH-PPE) as a model compound, we found Ca(OH)₂ pretreatment and Beta zeolite together enhanced β-O-4 bond cleavage in lignin. This synergistic approach facilitated efficient bond cleavage and showed remarkable effectiveness in aromatic production.