Pyrolysis of Kraft Lignin: The Effect of HZSM‑5 and HY-340 Catalysts and Torrefaction Pretreatment

The study aimed to evaluate the effect of HZSM-5 zeolite, HY-340 niobic acid, and torrefaction temperature on the deoxygenation of pyrolysis vapors from the catalytic pyrolysis of kraft lignin (493, 533, and 573 K) to produce aromatic hydrocarbons. The analytical pyrolysis (723, 823, and 923 K) of raw Kraft lignin at different catalyst/biomass ratios (1:1, 5:1, and 10:1) and without catalysts was performed. The pyrolysis vapor from analytical pyrolysis presented high levels of oxygenated compounds, mainly phenolics. The maximum production of phenolic compounds was 74% at 923 K for raw Kraft lignin. Catalytic analytical pyrolysis provided deoxygenation of pyrolysis vapors. HZSM-5 zeolite reached a maximum production of aromatic hydrocarbons of 57.84% with a catalyst/biomass ratio of 10:1 at 923 K. For HY-340 niobic acid, the production of aromatic hydrocarbons was 87.24 and 86.75% at 823 and 923 K, respectively, with a catalyst/biomass ratio of 10:1. The factorial experimental design showed that the maximum catalyst/biomass ratio provided the highest percentage of aromatic hydrocarbons (%HCA). For the HZSM-5 zeolite, the maximum %HCA was 41.95, 53.72, and 92.84% for torrefied lignin at 493, 533, and 573 K, respectively. For HY-340 niobic acid, the maximum %HCA values were 29.29, 50.02, and 90.02% at 493, 533, and 573 K. Fast pyrolysis in a bubbling fluidized bed reactor led to a higher production of phenolic compounds (78.15%) may be due to the longer residence time in the reactor. HZSM-5 zeolite and HY-340 niobic acid catalysts can promote deoxygenation reactions and increase the selectivity for aromatic hydrocarbons.