A green method to increase yield and quality of bio-oil: ultrasonic pretreatment of biomass and catalytic upgrading of bio-oil over metal (Cu, Fe and/or Zn)/γ-Al2O3

Abstract

A green method is developed to increase the yield and quality of bio-oil by ultrasonic pretreatment of biomass followed by in situ catalytic upgrading of bio-oil over metal (Cu, Fe and/or Zn)/γ-Al₂O₃. It is found that the yield of bio-oil is increased up to 10 wt% after cedar is pretreated by ultrasound before pyrolysis. Various metals (Cu, Fe and Zn) are loaded on γ-Al₂O₃ and applied for upgrading the bio-oil derived from the pyrolysis of pretreated cedar. It is found that the catalysts promote the conversion of oxygenated compounds into aromatic and aliphatic hydrocarbons. In particular, production of monocyclic aromatic hydrocarbons such as benzene and toluene is favored. The best catalytic activity is achieved by using 2.5 wt% Zn/γ-Al₂O₃ with a maximum hydrocarbon yield of 80.3%. The catalyst is reused for up to four cycles. The results show that the catalysts after regeneration by calcination at 550 °C for 30 min exhibit long-term stability for upgrading of bio-oil.