Catalytic fast pyrolysis is one of the most promising processes for lignin conversion into renewable chemicals. Nevertheless, studies on catalysts and process conditions are empirically determined and and do not yet satisfy feasible process conditions. This study aims to identify primary reactive intermediates and reaction routes of thermal lignin decomposition. It focuses on the influence of radicals on the product distribution by comparing selectivites at different pressures. The pyrolysis experiments of diphenylether and other more complex model compounds were performed in a pyrolysis micro-reactor working batchwise at atmospheric pressure with analysis by GC/MS. To determine the exact model compound decomposition pathway and the radical initiation step, a continuous molecular beam at very low pressure was pyrolyzed in iPEPICO at the VUV-beamline at the Swiss Light Source of Paul Scherrer Institute. In this setup the primary radicals are directly detected and identified isomer specifically by soft photoionization.2,3 The degree of recombination during fast pyrolysis is majorly influenced by the concentration of radicals and by the stability of the formed radicals. The more stable the intermediates, the less likely they are to recombine. Stable intermediates favor therefore participation in rearrangement reactions and will contribute to more differentiated product distributions. This is shown by pyrolysis of both the model compounds and different lignins.3,4 At lower temperatures, rearrangement reactions are dominant, thus in lignin more oxidized products like vanillin are formed. At high temperatures phenols are the major product fraction, which correspondences to the secondary pyrolysis products. The comparison of a very sensitive radical determination and general product behavior in bulk phase is a new and successful strategy to gain the knowledge in the complex lignin depolymerization mechanism. References (1)Zhao, C., Kou, Y., Lemonidou, A. A., Li, X. & Lercher, J. A. Angew. Chemie 2009, 121, 4047–4050. (2)Scheer, A. M., Mukarakate, C., Robichaud, D. J., Nimlos, M. R. & Ellison, G. B. J. Phys. Chem. A 2011, 115, 13381–13389. (3)Custodis, V. B. F., Hemberger, P., Ma, Z. & van Bokhoven, J. A. J. Phys. Chem. B 2014, 118, 8524–8531. (4)Bährle, C., Custodis, V., Jeschke, G., van Bokhoven, J. A. & Vogel, F. ChemSusChem 2014, 7, 2022–2029. (5)Ma, Z., Custodis, V., van Bokhoven, J.A. Cat. Sci. Tech. 2014, 4, 766-772.

Mechanism of lignin pyrolysis – from model compound to actual lignin

249th National Meeting (2015)

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