Mechanism Study on Depolymerization of the α-O-4 Linkage Lignin Model Compound in Supercritical Ethanol System
- 131 Downloads
The aim of this study was to explore the conversion mechanism of α-O-4 linkage lignin dimer model compound (monobenzone) in supercritical ethanol. The decomposition processes of monobenzone were investigated at different reaction time (0–12 h), conversion temperature (250–310 °C) and initial concentrations (0.01–0.03 g/mL). The reaction mechanism and pathways were proposed based on the distribution of products, the bond dissociation energies and the free radical theory. The results showed almost complete degradation was achieved in supercritical ethanol system. A higher temperature, a longer reaction time and a higher initial concentration significantly promoted the formation of solid residue due to the condensation reactions of the degradation intermediates/products. Based on the formation mechanism of products, the conversion products were classified into three types: (1) its own fragmentation compounds, (2) condensation compounds of its intermediates and (3) the second fragmentation compounds of its intermediates. A depolymerization reaction mechanism of monobenzone that primarily involved homolytic cleavage of the Cα–O linkage was proposed. In addition, the bibenzyl were an important and unstable intermediate product, it can continue to produce many different radical species that can participate in a variety of reaction mechanisms, resulting in complex reaction pathways and products distribution, even forming higher-molecular weight solid residue.
KeywordsMonobenzone α-O-4 linkage Supercritical ethanol Depolymerization
The authors greatly acknowledge the support of the Natural Sciences Foundation of China (No.31270635 and No.31670582), and the National Basic Research Program of China (973 program, No. 2013CB228101).
- 4.Huang, J., Liu, C., Wei, S.: Thermodynamic studies of pyrolysis mechanism of cellulose monomer. Acta Chim. Sinica 67, 2081–2086 (2009)Google Scholar
- 11.Barbier, J., Charon, N., Dupassieux, N., Loppinet-Serani, A., Mahé, L., Ponthus, J., Courtiade, M., Ducrozet, A., Quoineaud, A.-A., Cansell, F.: Hydrothermal conversion of lignin compounds. A detailed study of fragmentation and condensation reaction pathways. Biomass Bioenergy 46, 479–491 (2012)CrossRefGoogle Scholar
- 19.Zhang, X.H., Zhang, Q., Long, J.X., Xu, Y., Wang, T.J., Ma, L.L., Li Y.P.: Phenolics production through catalytic depolymerization of alkali lignin with metal chlorides. BioResources 9, 3347–3360 (2014)Google Scholar
- 26.Deng, Y.B.: Studies of the pyrolysis behaviors of lignin model compounds. Diss. South China University of Technology (2015)Google Scholar
- 27.Yong, L.K., Yukihiko, M.: Kinetic analysis of guaiacol conversion in sub- and supercritical water. Ind. Eng. Chem. Res. 52, 1103–1111 (2013)Google Scholar