Insight into the fast pyrolysis of lignin: Unraveling the role of volatile evolving and char structural evolution

Unraveling the role of volatile evolving and char structural evolution, as well as the pyrolysis reaction pathway, is crucial for lignin effective valorization by a pyrolysis-based biorefinery approach. The fast pyrolysis of lignin at 200-800 degrees C was conducted to explore volatile release characteristics and their link with char structure evolution. The release of simple substituted aryl compounds below 350 degrees C was aided by the cleavage of beta-O-4 and alpha-O-4. The C-O, C-C, and carboxyl groups of the depolymerized free radical fragments were cleaved further, providing stable mono-phenol (350 degrees C -> 500 degrees C). Secondary reactions and pyrolytic macromolecular compounds resulted in the synthesis of polycyclic aromatic hydrocarbons (> 700 degrees C). A cubic polynomial was developed to correlate the aromaticity with the atom ratio of H/C. The ring condensation degree and H/C demonstrated an excellent positive linear correlation. Additionally, the aromatization started at 350 degrees C, and small aromatic rings were changed into more ordered rings (>= 6 rings). The fused-ring structures of char had progressed in the following order: 1 x 2, 2 x 3, 4 x 4, and 4 x 5, corresponding to 350 degrees C, 500 degrees C, 600 degrees C, and 800 degrees C, respectively. High temperatures contributed to the formation of aromatic monomers. Lignin pyrolysis pathway was established based on the correlation between volatile release characteristics and char structural evolution.

Automated summary

Understanding the role of volatile evolving, char structural evolution, and pyrolysis reaction pathway is crucial for effective utilization of lignin through a pyrolysis-based biorefinery approach. Fast pyrolysis of lignin at different temperatures revealed the release characteristics of volatile compounds and their connection with char structure evolution. The results showed that the release of simple substituted aryl compounds was promoted by the cleavage of beta-O-4 and alpha-O-4. The study also found that high temperatures contributed to the formation of aromatic monomers, and the aromaticity can be evaluated based on the atom ratio of H/C and the degree of ring condensation.