Date of Award
Master of Science (MS)
At present, methods addressing the characterization of lignin and its decomposition products are limited. Typical approaches reported various spectroscopic, chromatographic and thermal methods. None of the methods is ideal for different reasons. In this study, a novel thermal carbon analysis (TCA) was developed providing essential mass balance data complementary to liquid-liquid extraction (LLE) prior to separation and identification by gas chromatography and mass spectrometry (GC-MS) as well as thermal desorption-pyrolysis-gas chromatography-mass spectrometry (TD-Py-GC-MS) to fully characterize lignin and its degradation products from hydrothermal treatment in subcritical water conditions.
The TCA method enabled a quantitative thermal evolution profile through TD and pyrolytic temperatures (up to 890 Â°C) with and without oxygen. Mono- and diaromatic compounds were used as model compounds to optimize operating conditions. Sample introduction was explored by investigating the effects of solvents, loading matrices, amount of sample loaded as well as the effect of initial temperature steps.
A multistep temperature ramp was then evaluated and applied to untreated lignin where up to 55 wt.% evolved under the presence of oxygen as black carbon (i.e., coke) and a mass balance closure of 94.8 Â± 5.5 wt. % was achieved. Analysis of lignin by TGA with a similar heating ramp to TCA showed a comparable mass distribution throughout the thermal profile; however, TCA has the advantage of being selective for carbon.
The developed methods were employed to characterize lignin degradation products. Lignin was hydrothermally treated using an analytical static batch reactor at temperatures between 200 – 300 Â°C. The products were then analyzed by TCA, liquid-liquid extraction (LLE)-GC-MS, and also TD-Py-GC-MS. TCA was used to provide overall product characterization based on the evolution temperature and LLE-GC-MS showed a strong correspondence with the products evolving at 200 and 300 Â°C by TCA and GC-elutable organic compounds. TD-Py-GC-MS allowed for the differentiation of monomeric species evolving at low temperature steps (200 and 300 Â°C) from large molecular weight species pyrolyzed at 400 – 870 Â°C. TD-Py-GC-MS product identification were complementary to thermal profiles obtained by TCA.
Voeller, Keith Michael, "Characterization Of Kraft Alkali Lignin And Products Of Its Thermal Degradation By Fractional Pyrolysis Methods" (2015). Theses and Dissertations. 1977.