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Two-step hydrolysis of Japanese cedar (Cryptomeria japonica) was studied as treated by semi-flow hot-compressed water at 230°C/10MPa for 15 min and 280°C/10MPa for 30 min as the first and second stages, respectively. As a result, at the first stage, hemicelluloses and para-crystalline cellulose whose crystalline structure is somewhat disordered were found to be selectively hydrolyzed as well as lignin decomposition, while crystalline cellulose at the second stage. Totally 87.76% of Japanese cedar could be liquefied by the hot-compressed water and were primarily recovered as various hydrolyzed products, dehydrated, fragmented and isomerized compounds, as well as, organic acids in the water-soluble portion. The rest of 12.24% could not be hydrolyzed and remained as the water-insoluble residue composed entirely of lignin. Based on the distributions of various products from hemicelluloses in Japanese cedar, their decomposition pathways were independently proposed.

Two-step hydrolysis of nipa (Nypa fruticans) frond, one of the monocotyledonous angiosperms, was studied in a semi-flow hot-compressed water treatment at 230°C/10 MPa/15 min (first stage) and 270°C/10 MPa/30 min (second stage). In the first stage, hemicelluloses such as O-acetyl-4-O-methylglucuronoarabinoxylan and pectin and para-crystalline cellulose were selectively hydrolyzed, as well as lignin, which was partially decomposed. In the second stage, hydrolysis of crystalline cellulose and some additional decomposition of lignin were observed. In addition, inorganic constituents and free sugars, composed mainly of glucose, fructose, and sucrose, were recovered in cold water (20°C/10 MPa/30 min) prior to these 2 stages. In total, 97.3% of oven-dried nipa frond sample could be solubilized into cold and hot-compressed water. The degradation products in the water-soluble portion were primarily recovered as various saccharides (hydrolyzed moieties of the polyoses), which were later dehydrated, fragmented and isomerized partly. The residual (2.7%) is composed mainly of lignin associated with 0.4% of Si. A decomposition pathway is proposed for O-acetyl-4-O-methylglucuronoarabinoxylan as the major hemicellulose based on its various hydrolyzed products.

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Japanese beech (Fagus crenata) wood was treated by two-step semi-flow hot-compressed water (the first stage: 230°C/10MPa/15min, the second stage: 270°C/10MPa/15min), and produced lignin-derived products in the hot-compressed water-soluble portions at the first and second stages, and the final residue of the second stage were characterized with alkaline nitrobenzene oxidation method and gel-permeation chromatographic analysis. As a result, the lignin-derived products at the first stage, where hemicellulose was also decomposed, consisted of lignin-based monomers and dimers and oligomers/polymers in the water-soluble portion. A large part of the oligomers/polymers was, however, recovered as the precipitate during 12h setting after hot-compressed water treatment. By the analysis of nitrobenzene oxidation products, there were relatively higher contents of ether-type lignin in the precipitate at the first stage than in original beech wood. Since the ether-linkages of lignin are more preferentially cleaved by this hot-compressed water, lignin-based polymeric fractions were flowed out from the porous cell walls from which hemicellulose was removed. On the other hand, at the second stage condensed-type lignin remained in the precipitate and residue. Based on these results, decomposition behavior of lignin in Japanese beech wood as treated by the two-step semi-flow hot-compressed water was discussed 3 regarding the topochemistry of lignin structure.