DICARBOXYLIC ACIDS PLATFORM CHEMICALS FOR VALORIZATION OF BIOREFINERY LIGNIN
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Despite decades of effort, commercial development of biomass-to-biofuel conversion processes is still not an economically viable proposition. The emerging biomass refinery industry will inevitably generate an enormous amount of lignin as the solid waste stream. Development of selective biorefinery lignin-to-bioproducts conversion processes will play a pivotal role in significantly improving the economic feasibility and sustainability of biofuel production from renewable biomass. Due to the aromatic skeleton of lignin, most previous lignin valorization studies were limited to converting lignin to monomeric phenolics. Aromatic ring opened structures such as dicarboxylic acids (DCA) have been overlooked, though commonly observed during conversion. This thesis presents a new pathway for producing DCA as a new group of platform chemicals for lignin valorization, and specifically aims to develop a systematic understanding of the reaction mechanisms and to identify the key hurdles to optimizing conversion. To achieve this goal, a variety of oxidant and catalyst combinations were screened for oxidative depolymerization and conversion. A set of representative biorefinery lignin obtained from various commercial biorefineries for testing; the lignin samples were fully characterized by a number of selected analytical techniques. Representative monomeric and dimeric model compounds were used to help identify key intermediates and interpret the reaction mechanisms. Statistical analysis methods were developed as a new approach for providing quantitative guidance in lignin depolymerization research by relating and predicting lignin structure and reactivity. Techno-economic analysis (TEA) was conducted to direct future work toward addressing key bottlenecks in process costs. The new insights gained in this work inspired the development of novel catalytic oxidation pathways and processes to convert biorefinery lignin to DCA as a new group of platform chemicals/intermediates, enabling sustainable biofuel production from lignocellulosic biomass.