At present, methods addressing lignin and its decomposition products characterization are limited; liquid-liquid extraction followed by gas chromatography with mass spectrometry (GC-MS) targets only volatile compounds while liquid chromatography methods are not ideal for unknown products due to limited availability of oligomeric products as identification standards. Previously, pyrolysis (pyr) coupled with GC-MS was used for characterization of lignin. However, this method is not applicable to degradation products as it does not differentiate between the occurrences of evaporating monomeric and thermally decomposing large molecular weight compounds. In this study, thermal methods such as thermal gravimetric analysis, pyrolysis-GC-MS (Pyr-GC-MS), and total carbon analysis (TCA) are used for characterization of lignin and lignin products of hydrothermal degradation.<br/><br/>Thermal desorption (TD) coupled with pyr-GC-MS allowed for the differentiation of monomeric species evolving at low temperature steps (200, 300 °C) from large molecular weight species pyrolyzed at 400 – 850 °C. It is essential to note the pyrolytic portion of carbon (i.e., coke) cannot be observed with pyr-GC-MS instruments. To achieve analysis including mass balance closure, TCA was used obtaining a quantitative thermal evolution profile through TD and pyrolytic temperatures with/without oxygen. During analysis of raw lignin with TCA, up to 55% evolved under aerobic conditions as elemental carbon (i.e., coke). By contrast, products of lignin hydrothermal treatments at 200 °C and 300 °C showed only 19% and 28% pyrolyzed carbon respectively. Lignin hydrothermally treated at 300 °C evolved significantly more species at lower temperatures during TCA than that of hydrothermal treated samples at 200 °C which indicated the formation of monomers at higher temperatures. TCA has thus shown that relatively low temperature (200 – 300 °C) hydrotreatment of lignin produced noteworthy amounts of monomers and small oligomers without significant re-polymerization of lignin fragments.

Characterization of alkaline lignin by thermal desorption and pyrolysis methods

249th National Meeting (2015)

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