Catalytic Pyrolysis of Poplar Sawdust Pretreated with Combined Leaching and Torrefaction over Fe-Ni/ZSM-5 for Aromatic-Rich Bio-Oil Production

High oxygen content and alkali and alkaline earth metals (AAEMs) naturally present in biomass exhibit detrimental effects on biomass pyrolysis. Hence, effective pretreatment methods are essential for enriching the desired pyrolytic products (aromatics). In this study, poplar sawdust (PS) pretreated with a combination of acid leaching and torrefaction was catalytically pyrolyzed using Fe-Ni/ZSM-5 for enhanced aromatic production. The findings show that the coupled pretreatment effectively removed AAEMs while also lowering the H/C and O/C ratios. The combined pretreatment method increases the activation energy of the raw sample from 126.38 kJ·mol-1 to 154.38-158.33 kJ·mol-1. The enrichment of aromatics in bio-oils was significantly aided by the pretreatment process, with benzene, toluene, and xylene increasing from 82.24 mg·g-1 of raw PS catalytic pyrolysis to 97.48-103.83 mg·g-1 of the pretreated PS. This study demonstrates that combined pretreatments of biomass enhanced the quality of pyrolytic products, which could be a valuable framework for practical application.