Lignin valorization is an important part of lignocellulosic biorefinery. Catalytic liquefaction is an effective technique for the production of fuels/chemicals from lignin but liquefaction yields various products from monomers to heavy oligomers. Hence, there is a strong need for rapid characterization of these products. For this purpose, UV fluorescence spectroscopy is introduced in this work on lignin liquefaction products. Lignin liquefaction was performed in an autoclave (Protobind lignin, 250°C, 110bar, ethanol, H<sub>2</sub>, Pt/C catalyst, 4hours) with sampling at isothermal conditions every 30 minutes. Reaction products were also analysed by GC/MS, GPC, and MALDI-TOF-MS. For comparative assessment, different model compounds, including guaiacol, syringol, phenol, vanillin (and other monomers), and a representative dimer were studied by UV fluorescence spectroscopy. This technique allows for a fast characterization of the depolymerisation.<br/>UV fluorescence spectroscopy gives information on the relative number of fluorophores (aromatic rings) and their conjugation with carbonyl, alkene or hydroxyl groups. The conjugation of various lignin subunits leads to a decrease and red shift of the fluorescence emission spectra. That is why we found less conjugated molecules, as monomers, around 310 nm instead of oligomers or undepolymerized lignin who are shifted to higher wavelengths. The results shown in the figure (synchronous fluorescence with 20nm offset) clearly display the depolymerisation upon conversion time. From this analysis, representative peaks for the different fractions (monomers-oligomers) can be easily determined. As shown in the figure, lignin depolymerization products appear in a specific range, from 300 to 350 nm.

Characterization of lignin depolymerisation products by UV fluorescence spectroscopy

2019 Fall National Meeting

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