A combined theoretical-experimental investigation on the mechanism of lignin pyrolysis: Role of heating rates and residence times

This work provides a combined theoretical-experimental investigation on the relationship between structural features and energetic requirements of pyrolytic breakdown of solid lignin, with a focus on the loss of aromaticity in the likely products. The breaking of beta-O-4 linkages was identified as the most likely route for the fragmentation of solid lignin from both theoretical and experimental standpoints. The kinetic approach indicates that both the degradation mechanism and kinetic parameters (between 200 and 350 degrees C) are independent of the temperature and conversion degree. The yield of aromatic and/or aliphatic products was found is influenced by the heat and mass transfer phenomena in the gas phase (e.g., heat transfer rate and residence times), which affect the ratio of the individual reaction rates, and therefore, the relative abundance of products. The thermochemical approach suggests that when the heating process is fast and the residence time is short, the relative amount of aromatic fragments is favored.