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The chemical structures of four alkali lignins isolated from poplar, fir, straw, and bagasse were investigated. To explore the relationship between the structural units and the thermal decomposition behavior, the system was tested by elemental analysis, Fourier transform infrared spectrometry, thermogravimetric analysis (TGA), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results indicated that the carbon content of poplar lignin (PL) was higher than that of others. Fir lignin (FL) exhibited the highest guaiacol units, while the other three lignins were abundant in syringol units. The thermal decomposition characteristics and pyrolysis products of the four lignins were influenced by the material structural and composition. The DTG curves showed that the initial temperatures and major degradation temperatures of woody lignins(FL and PL) with complex inherent structures were shifted to the high temperature zoom compared with that of non-woody (BL and SL) lignins. Py-GC/MS analysis showed that guaiacol-type phenolic compounds were predominant pyrolysis products derived from the four lignins. The yield of guaiacol-type phenols could reach 82.87%. Moreover, the BL had selectively on phenol-type compounds with yield of 27.89%. [ABSTRACT FROM AUTHOR]

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]

Enzymatic/Mild Acidolysis Lignin (EMAL) was isolated from Cunninghamia lanceolata and eucalyptus woods. The chemical structure and thermochemical properties were characterized by means of elemental analysis, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TG), and pyrolysis-gas chromatography combined with mass spectrometry (Py-GC/MS). The EMAL isolated from Cunninghamia lanceolata (C-EMAL) had larger HHV (higher heat value) in comparison to the EMAL isolated from eucalyptus (E-EMAL) due to the greater carbon content of the C-EMAL. The E-EMAL had more syringyl units, whereas the C-EMAL contained more guaiacyl units. It was observed that thermal decomposition occurred over a wide temperature range, and that at a given starting temperature, within the same sample, a higher heating rate produced a higher temperature at which maximum weight loss peaked. The pyrolysis products were mainly composed of carboxylic acids, alcohols, ketones, aldehydes, olefins, alkanes, esters, ethers, and phenols. At all pyrolysis temperatures, the largest components of the pyrolysis products obtained from C-EMAL were the phenols. [ABSTRACT FROM AUTHOR]