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Eucalyptus nitens wood samples were subjected to consecutive stages of hydrothermal processing for hemicellulose solubilization and delignification with an ionic liquid, i.e., either 1-butyl-3-methylimidazolium hydrogen sulfate or triethylammonium hydrogen sulfate. Delignification experiments were carried out a 170 °C for 10–50 min. The solid phases from treatments, i.e., cellulose-enriched solids, were recovered by centrifugation, and lignin was separated from the ionic liquid by water precipitation. The best delignification conditions were identified on the basis of the results determined for delignification percentage, lignin recovery yield, and cellulose recovery in solid phase. The lignins obtained under selected conditions were characterized in deep by 31P-NMR, 13C-NMR, HSQC, and gel permeation chromatography. The major structural features of the lignins were discussed in comparison with the results determined for a model Ionosolv lignin.

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Recently reported acetosolv soft- and hardwood lignins as well as ionosolv soft- and hardwood lignins were transformed into monomeric aromatic compounds using either a vanadate or a molybdate-based catalyst system. Monomers were generated with remarkable, catalyst-dependent selectivity and high depolymerisation yields via oxidative exo- and endo-depolymerisation processes. Using the vanadate–hydrogen peroxide system on acetosolv pine lignin, vanillin and isovanillin were produced as main products with depolymerisation yields of 31%. Using the molybdate system on acetosolv and ionosolv lignin, vanillic acid was the practically exclusive product, with depolymerisation yields of up to 72%. Similar selectivities, albeit with lower depolymerisation yields of around 50% under standardised conditions, were obtained for eucalyptus acetosolv lignin, producing vanillin and syringaldehyde or vanillic acid as products, by using the vanadate- or the molybdate-based systems respectively.

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Pine wood is mainly composed of extractives, lignin, cellulose, and hemicelluloses (which include pentosans and hexosans). In the scope of biorefineries, the utilization of pine wood entails the selective separation of its major components. A sequence of aqueous and delignification treatments enables the selective separation of hemicelluloses (as soluble products from the aqueous fractionation step), lignin (as soluble products from the delignification stage), and cellulose (accumulated in the solid phase leaving the delignification stage). Delignification was done in media containing acetic acid or the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate. Both the soluble hemicellulose-derived saccharides and the cellulose-containing solids were found to be suitable substrates for 5-hydroxymethylfurfural production in reaction media containing the ionic liquid 1-butyl-3-methylimidazolium chloride in the presence of Brønsted and/or Lewis acidic catalysts. The processing schemes considered in this work allowed an efficient utilization of the feedstock using environmentally friendly technologies.