Study on carbonization of lignin by TG-FTIR and high-temperature carbonization reactor

Biomass charcoal is dominantly made from lignin. It is necessary to study lignin carbonization process to improve the quality of biomass charcoal. A Thermo-Gravimetric Analyzer coupled with a Fourier Transform Infrared Spectrometry (TG-FTIR) was applied to investigate the kinetics of lignin carbonization. Three mass loss stages (drying, pyrolysis and carbonization) were observed below 900 °C and another stage (structural rearrangement stage) with a slight mass loss was noticed between 900 and 1200 °C. Charcoal obtained at different temperatures was analyzed by FTIR to track the variation of functional groups. The pyrolysis of lignin started at 200 °C and charcoal was initially formed till 500 °C together with the intensive evolution of volatiles including various phenyl compounds. Amorphous carbon was formed between 500 and 900 °C, while most benzene rings structures were transformed into aromatic structures with emission of CO. When the temperature increased from 900 °C to 1400 °C, most CC bonds were cleaved and a new charcoal structure, between amorphous carbon and graphite structures, was probably formed. The activation energies of the above three stages were estimated to be 54 kJ/mol, 70 kJ/mol and 178 kJ/mol.

► Pyrolysis, amorphous carbon forming and structure reforming are important stages.
► Amorphous carbon formed at 500 ~ 900 °C as benzene rings became aromatic structure.
► A structure between amorphous carbon and graphite appeared at 900 ~ 1400 °C.
► Most CC bonds broke when the temperature increased from 900 to 1400 °C.