Effects of HZSM-5 on volatile products obtained from the fast pyrolysis of lignin and model compounds

This study aimed to experimentally investigate the effect of HZSM-5 on the distribution of volatile products, especially carbon monoxide (CO), C1-C5 hydrocarbons and aromatic hydrocarbons (AHs) during catalytic pyrolysis of lignin and lignin model compounds. Catechol was pyrolyzed using a two-stage tubular reactor (TS-TR) connected to a gas chromatography system over HZSM-5 at 550-950 °C. Forty-three products, including four inorganic gases, twenty C1-C5 hydrocarbons, and nine AHs were quantified using three GC-columns. Results indicated that HZSM-5 accelerated the catechol conversion with a large amount of CO and AHs produced. C1-C5 hydrocarbons were formed during non-catalytic pyrolysis of model compounds, and consumed quickly during HZSM-5 catalytic pyrolysis of catechol. Catalytic pyrolysis of phenol, guaiacol and syringol was carried out at 650 °C in the TS-TR over HZSM-5. HZSM-5 obviously promoted the conversion of lignin model compounds, and largely increased the yield of volatile products especially CO and AHs. Three lignin samples were also catalytically pyrolyzed over HZSM-5 in the TS-TR at 650 °C. HZSM-5 increased the yield of C2-C3 hydrocarbons and AHs, and reduced the yield of oxygenated compounds. HZSM-5 could promote the formation of AHs (lower than 10 wt%) during lignin pyrolysis, but not as obviously as during model compounds pyrolysis (higher than 19 wt%). High yields of char and tar would account for the low catalytic efficiency of HZSM-5 during lignin pyrolysis.