Reconstruction of humins formation mechanism from decomposition products: A GC-MS study based on catalytic continuous flow depolymerizations

Humins, a by-product of biomass chemical conversion technologies, still present controversies in their structural and mechanistic identification. Traditional studies of the structure and mechanism have focused so far on their syntheses from key molecules (sugars, HMF) and spectroscopic analyses of the as-synthesized oligomers/macromolecules. Herein, we propose structural and mechanism insights based on a novel down-up approach involving the decomposition of humins viacatalytic reactions in continuous flow and interpretation of product molecules. The apparent co-existence of different mechanisms proposed in literature is observed upon product distribution analysis, and the key molecules taking part into humins formation are identified, including furanics, levulinates, sugar-derived molecules, and others. This work shows the complexity of humins formation, and their need of valorization.