Research on modeling the lignin waste molecular structure and pyrolytic reactions using ReaxFF MD method

• Published in: Journal of analytical and applied pyrolysis 2024-10, Vol.183, p.106783, Article 106783
• Main Authors: Huang, Xiankun, Bai, Zhang, Wang, Shuoshuo, Zhu, Xiaoli, Mu, Lin, Gong, Liang
• Format: Article
• Language: English
• Subjects: Lignin waste; Molecular model; Pyrolysis; Reaction mechanism; ReaxFF MD
• ISSN: 0165-2370
• DOI: 10.1016/j.jaap.2024.106783

The lack of clarity in characterizing the chemical structure model of lignin waste hinders the comprehensive understanding of its pyrolysis reaction mechanism. The characterization results revealed that the de–alkalized lignin sample contained larger amounts of aliphatic and aromatic carbons compared to carbonyl carbons. Additionally, the aliphatic carbon molecules exhibited a higher presence of oxygenated carbons. The degree of aromaticity (fa) was determined to be 63.93 %. The resulting single–molecule structural model exhibited a molecular formula of C33H26O11 and a molecular weight of 598.56. Furthermore, the evolutions patterns and formation pathways of primary volatile components (H2, CH4, CO, and CO2) in pyrolysis reactions were revealed. The number of H2 molecules exhibited a positive correlation with the rise in pyrolysis reaction temperature. CH4 molecules exhibited a pattern of initially increasing and subsequently decreasing. The number of CO molecules exhibited a positive correlation with the rise in pyrolysis temperature. Conversely, the number of CO2 molecules demonstrated an initial increase followed by a decrease as the pyrolysis temperature increased. Finally, the generation pathway analysis of pyrolysis products shows that the H2 molecule is composed of two hydrogen atoms bonded together that have been dissociated from the carboxyl group. Alternatively, it can be produced through hydrogenation reactions involving hydrogen atoms detached from the carboxyl group and methyl groups. CH4 is primarily generated through the reaction between –CH3 and free hydrogen ions. CO is primarily produced through the cleavage of the carbonyl group. CO2 is primarily produced through the cleavage of carboxyl and ester groups. •The molecular structure of lignin waste was constructed by characterization experiments.•The ReaxFF MD method was employed to investigate the pyrolysis of lignin waste.•The effects of different heating strategies on the pyrolysis products were studied.•Micro mechanisms of lignin waste pyrolysis were revealed at the molecular level.