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In the present work, enzymatic/mild acidolysis lignin (EMAL) was isolated from the raw material Cunninghamia lanceolata, and hydrothermal depolymerization was carried out in subcritical water (from 250 to 350℃) using a cylindrical autoclave. The results revealed that the lowest yield of solid residue and highest liquid product yield were achieved at 325℃. The liquid products were primarily composed of phenolic monomers and oligomers. As the reaction temperature increased, repolymerization of the liquid products and dehydrogenation and deoxidation of the solid residues occurred. The high heating value (HHV) of the residues was larger than that of the EMAL, and it reached a maximal level at 275℃. Hydrothermal depolymerization and condensation reactions took place simultaneously even under mild conditions (250℃). Carbonization of the EMAL was remarkable when the reaction temperature reached 325℃. [ABSTRACT FROM AUTHOR]

In the present work, three different kinds of lignin fractions (L1, L2, and L3) were isolated from the alkali black liquor of Cunninghamia lanceolata by selective precipitation at the pH values of 8 (fraction L1), 5 (fraction L2), and 2 (fraction L3). Elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), 31P nuclear magnetic resonance (31P-NMR), thermal gravimetric analysis (TG), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize the chemical structure and thermochemical properties of the three lignin fractions. The results showed that L1 presented higher heating value (HHV) and molecular weight compared with L2 and L3. The structures and functional group types were similar for the three lignin grades. However, there was more hydroxyl group in L1 than that in L2 and L3, and the L3 contained a higher amount of carboxylic hydroxyl. L1 exhibited the lowest weight loss value (47.8%) at 200 to 600 oC and the highest amount of charred residue (45.1%), which was exactly the opposite for L3. Phenols, the dominant pyrolysis products, constituted 92.17% of all the pyrolysis products for L1, 93.93% for L2, and 88.09% for L3. [ABSTRACT FROM AUTHOR]