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

Abstract

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 54kJ/mol, 70kJ/mol and 178kJ/mol.