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Characteristics and reaction mechanisms of sludge-derived bio-oil produced through microwave pyrolysis at different temperatures

Lin, Junhao, Sun, Shichang, Ma, Rui, Fang, Lin, Zhang, Peixin, Qu, Junle, Zhang, Xianghua, Geng, Haihong, Huang, Xiaofei
Energy conversion and management 2018 v.160 pp. 403-410
biofuels, catalysts, chemical bonding, hydrocarbons, iron oxides, mathematical models, oxygen consumption, pyrolysis, reaction mechanisms, sludge, temperature
Based on the study of the effect of different final pyrolysis temperatures on the production of bio-oil by catalytic microwave pyrolysis of sludge, a mathematical model has been used to accurately calculate the calorific value of each component in the bio-oil mixture, making it enable to study the variations in the calorific value of bio-oil at a final pyrolysis temperature from a single-component perspective. Results showed that the yield and calorific value of bio-oil reached the maximum at 22.60% and 35.47 MJ kg⁻¹, respectively, with iron oxide as a catalyst, increasing by 5.16% and 16.83% compared with those without a catalyst. The calculation model based on Huggett’s oxygen consumption method realized the accurate calculation of the calorific value of a single component in the bio-oil, which could explain why the calorific value of the bio-oil mixture varies with the final pyrolysis temperature. The relative deviation between the model calculating value and the measured value of the component was lower than 5%. The content of fatty hydrocarbons and high-carbon compounds gradually decreased with temperature increased. Increasing temperature leaded to the breakage of chemical bonds of the high-carbon compounds and the formation of low-carbon compounds, which resulted in a decrease in the calorific value of bio-oil. The content of high-calorific value components, such as octadecane and docosane, reached a maximum of 35.78% in the bio-oil mixture at 550 °C, which was significantly higher than the contents at 650 °C and 750 °C. This result may explain why the calorific value of the bio-oil mixture was obviously higher at 550 °C.