Characterization of lignin-derived products from Japanese cedar as treated by semi-flow hot-compressed water

Abstract

In order to elucidate the decomposition behavior of lignin from Japanese cedar (Cryptomeria japonica) as treated by two-step semi-flow hot-compressed water (1st stage: 230 °C/10 MPa/15 min, 2nd stage: 270 °C/10 MPa/15 min), water-soluble portion, precipitate, and water-insoluble residue obtained by hot-compressed water treatment were separated and characterized. Consequently, the water-soluble portion was found to contain lignin-derived monomeric compounds such as coniferyl alcohol and coniferyl aldehyde and β-1, β-5, and 5-5′ linked dimeric compounds. These lignin-derived compounds maintained methoxyl and phenolic hydroxyl groups in aromatic rings. The water-soluble portion also contained lignin-derived oligomeric compounds up to heptamers. In contrast, the precipitate was found out to consist of higher molecular weight lignin with high ether type linkages. The water-insoluble residue, however, consisted mostly of lignin with high condensed type linkages. Based on these lines of evidence, condensed type lignin must be resistant to hot-compressed water and remain as water-insoluble residue after two-step treatment. Such information provides a clue as to efficient utilization of lignin-derived products.