Doctor of Philosophy (PhD)
This study explores the thermal decomposition behavior of selected tobacco components: lignin, tyrosine, and glutamic acid using the system for thermal diagnostic studies (STDS) in an in-line gas chromatography-mass spectrometer analytical technique. The pyrolysis conditions employed in this study were a flowing atmosphere of nitrogen and 4% O2 in nitrogen at a residence time of 0.2 seconds for a total pyrolysis time of 3 minutes. The results identified common relationships between the two modes of reaction atmospheres, as well as some differences. While some products were favored by an inert regime, some were favored under an oxidative regime. Oxidative pyrolysis of tyrosine for instance yielded compounds of interest, e.g., hydroquinone, p-benzoquinone, dibenzofuran, and dibenzo-p-dioxin, although no such products were observed under pyrolysis. A comprehensive product distribution at distinct pyrolysis and oxidative pyrolysis temperature of various compounds is presented. The mechanistic channels for the formation of compounds of biological concern such as phenols, and polycyclic aromatic hydrocarbons (PAHs) have also been discussed in detail. Of the classes of compounds analyzed from the thermal degradation of lignin, the phenolic compounds were the most abundant, accounting for over 60% of the total compounds detected. The principal products from pyrolysis of tyrosine were phenol, p-cresol, o-cresol, and benzaldoxime. For the oxidative pyrolysis, the main products were p-tyramine, phenol, p-cresol, and benzonitrile. The principal products from pyrolysis of glutamic acid in order of decreasing abundance were succinimide, pyrrole, 2-pyridone, and acetonitrile. On the other hand, succinimide, propiolactone, ethanol, and hydrogen cyanide were the key products under oxidative pyrolysis. CHEMKIN combustion Suite was used to model the pyrolysis of lignin and consequently, a 15 reaction model was developed to determine the kinetics as well as the thermodynamic parameters of reaction products. By use of pseudo first order rate law, the rate coefficients for various products were evaluated. Arrhenius equation was used to compute the pre-exponential factor A, as well as the activation energy Ea for numerous reaction products including phenol, syringol, 4-vinylguaiacol, furfural, toluene, and benzene. Experimental reaction conditions were used to constrain the model. Simulation data reproduced experimental results with reasonable accuracy.
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Kibet, Joshua Kiprotich, "Molecular Products from the Thermal Degradation of Selected Tobacco Components: Lignin, Tyrosine, Glutamic Acid, and Modeling of Lignin Pyrolysis using CHEMKIN Combustion Suite" (2013). LSU Doctoral Dissertations. 58.