Pyrolysis of cellulose: Evolution of functionalities and structure of bio-char versus temperature

The pyrolysis of cellulose at 200–800 °C with an increment of 50 °C was conducted in this study, aiming to understand impacts of temperature on evolution of the of organics and the structures of bio-char. Extensively pyrolysis of cellulose to bio-oil initiated at 300 °C, reached maximum at 450 °C, and shifted to gasification to produce gases as the main products above 650 °C. Dehydrate sugars were the initial products formed below 350 °C, which soon dehydrated to form furans at ca. 400 °C and then generate aliphatic aldehydes, ketones and carboxylic acids at ca. 650 °C via the session of the C–C bonds. Aromatization of the volatiles initiated at 350 °C, producing phenolics and then further to aromatic hydrocarbons. The medium pyrolysis temperature (i.e. 450 °C) tended to produce the heavier bio-oil. The in situ DRIFTS characterization of cellulose pyrolysis showed that the structural reconstruction of the feedstock occurred at ca. 430–440 °C, forming abundant CO functionalities in bio-char. The increasing pyrolysis temperature led to staged change of carbon, hydrogen and oxygen contents in bio-char. The bio-char produced at the low temperature was quite aliphatic, and increasing pyrolysis temperature enhanced the formation of graphite structure, thermal stability and the porosity of bio-char. The bio-char from cellulose had a compact structure with small surface area and very limited mesopores. The results of kinetic analysis showed that the pyrolysis of cellulose was a complex multi-step reaction process.