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

The pyrolysis of cellulose at 200-800 degrees C with an increment of 50 degrees 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 degrees C, reached maximum at 450 degrees C, and shifted to gasification to produce gases as the main products above 650 degrees C. Dehydrate sugars were the initial products formed below 350 degrees C, which soon dehydrated to form furans at ca. 400 degrees C and then generate aliphatic aldehydes, ketones and carboxylic acids at ca. 650 degrees C via the session of the C-C bonds. Aromatization of the volatiles initiated at 350 degrees C, producing phenolics and then further to aromatic hydrocarbons. The medium pyrolysis temperature (i.e. 450 degrees 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 degrees C, forming abundant C-O 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.

Automated summary

The study on the pyrolysis of cellulose revealed that high temperature affects the transformation of organics and the evolution of bio-char structure. With increasing temperature, the bio-oil production first increases and then decreases, while the structure of bio-char undergoes reconstruction, forming different functional groups and graphite structures.