Comprehensive research of in situ upgrading of sawdust fast pyrolysis vapors over HZSM-5 catalyst for producing renewable light aromatics

Abstract

Catalytic fast pyrolysis of sawdust was investigated over HZSM-5 zeolites (SiO2/Al2O3 = 25, 50 and 80) in a drop tube quartz reactor for production of green aromatics and olefins. The effects of temperature, weight hourly space velocity (WHSV), SiO2/Al2O3 ratio and atmosphere on yield and selectivity of aromatics were investigated. The results show that almost all small organic oxygen species in initial volatiles were converted into gaseous hydrocarbons and aromatics after in situ catalysis of HZSM-5. HZSM-5 whose SiO2/Al2O3 is 25 exhibited the best performance with the aromatics yield of 21.8% on carbon basis at 500 °C. However, HZSM-5 can act as cracking and aromatization catalyst, but not as an agent to promote hydrogenation. The ESI-MS revealed the most abundant macromolecular compounds in initial volatiles were O1O27 species with 0–20 double bond equivalent (DBE) values and 5–40 carbon numbers, while the macromolecules were O1O9 species with 2–12 DBE and 10–25 carbon numbers after upgrading. Furthermore, the formation of coke on catalysts was influenced by the properties of HZSM-5 and experimental conditions.