Hydrothermal conversion of Lignin compounds. A detailled study of fragmentation and condensation reaction pathways

The hydrothermal conversion takes advantage of the singular physico-properties of the hot and compressed water which can be considered as a green solvent. The hydrothermal conversions of an alkali lignin and of phenolic model compounds (vanillin, monobenzone, 2,2′-biphenol) have been studied at 370 and 390 °C, at 25 MPa between 5 and 40 min. Polydispersity of products in term of both chemical structures and molecular weights has been characterized through a new analytical approach combining chromatographic (GC) and spectrometric techniques (Fourier transform ion cyclotron mass spectrometry FT-ICR/MS, NMR). From our experiments, it is clear that lignin conversion occurs via a complex reaction pathway where competitive fragmentation and condensation reactions occur. An original reaction pathway has been suggested from the main emphasized reactions.