The organosolv fractionation of lignocellulosic biomass has emerged as procedure for the isolation of uncondensed lignin rich in ether (β-O-4) bonds. Moreover, lignin molecular weight, interunit bond (C-O and C-C) content and hydroxyl group content of (fractionated) lignin affect structure and yield of depolymerized products. Depolymerization of fractionated lignin via β-O-4 cleavage provides monophenolics and oligomeric fragments which remains mostly unexploited despite its unique structural features. Therefore, the objective of the research has been achieving tailored lignin and oligomeric fragments structure to maximize lignin valorization to high-value bio-based materials (<i>e.g.</i> monomers, aromatic building blocks for polyurethane resins). Additionally, the effects of reaction conditions have been studied to correlate the process-related structural features of lignin to product distribution and structural changes after catalytic treatment.<br/>The catalytic depolymerization has been applied for fractionated ethanol organosolv lignin which have been placed in batch reactor with Ni/C catalyst and ethanol at supercritical conditions. The effect of temperature on the product distribution of fractionated lignin depolymerization was tested by running the reactions at 225, 250, 275 °C. Reaction products - monomers, oligomeric fragments and solid residue were analysed using GC/MS, SEC and NMR to evaluate the effect of lignin molecular weight and reduced dispersity on the efficiency/selectivity of its depolymerisation. Temperature depended structural features of partially depolymerized lignin pointed toward the importance of screening the reaction conditions for utmost lignin valorization. Furthermore, the anti-solvent fractionation of lignin strongly improved overall lignin depolymerisation to monomers and oligomers by suppressing char-forming reactions.

Fractionated lignin depolymerization: Correlation between structural features, product distribution and reaction conditions

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