Catalytic Pyrolysis of Corn Stalk for the Production of Aromatics: The Effects of Wet Torrefaction and Zn/NiHZSM-5 on Pyrolysis Behavior

The pyrolysis of corn stalk (CS) was carried out to investigate the effect of wet torrefaction (WT) pre-treatment and Zn/Ni-HZSM-5 on the production of bio-oil characteristics. The synergy between WT and the loaded metal catalyst was also analyzed. The oxygen content of the CS was reduced from 50.5% to 40.8% with WT, and hemicellulose was almost removed. WT pretreatment also significantly reduced the oxygenated compounds of bio- oil and increased the selectivity of phenols, aromatics, and anhydro-sugars. The addition of catalyst improved the deoxygenation, oligomerization, and aromatization during pyrolysis. The loading of Zn and Ni could optimize the pyrolysis reaction path and increased the relative content of monocyclic aromatics (MAHs) from 3.58% to 9.67% and 6.44% during the pyrolysis of CS-WT, respectively, and bimetallic catalyst further enhanced the relative content of MAHs to 11.1%. The relative content of aromatics below C9 was higher than other groups (14.8%). Thus, the WT pretreatment of raw materials and synergistic effect of catalysts can jointly optimize the biomass pyrolysis reaction.