Fast pyrolysis of raw and acid-washed cattle manure in a fluidized bed reactor for the production of bio-oil

Livestock manure is currently a waste biomass and has difficulties in treatment worldwide. In this study, raw cattle manure (CM) was pretreated with a HNO₃ solution to reduce ash content, and the effect of acid-washing pretreatment and particle size of CM and operating temperature on fast pyrolysis characteristics was investigated. The experiment was carried out using a fluidized bed reactor with a CM particle size of 0.25–1.70 mm at 450–550 °C for 1 h. Additionally, 100 g of silica sand was used as the bed material, and the nitrogen flow rate was maintained at 3 U_mf (U_mf = 4.5 L/min). At 500 °C, the highest bio-oil yield of 31.18 wt% was observed from raw CM with a particle size of 0.71–1.19 mm. As the reaction temperature increased from 450 to 500 ℃, the bio-oil yield increased, but a further increase to 550 ℃ decreased the yield due to the secondary decomposition of bio-oil. Under the same conditions (0.71–1.19 mm and 500 ℃) where the highest yield was obtained from raw CM, the bio-oil yield from acid-washed CM increased to 42.15 wt%. Finally, the compositions of the gas and bio-oil obtained through fast pyrolysis of CM were systematically characterized using GC, GC-MS, ¹³C NMR and TGA.