2026-05-24T11:13:35Zhttps://keep.lib.asu.edu/oai/request

oai:keep.lib.asu.edu:node-2024492025-08-18T22:22:09Zoai_pmh:alloai_pmh:repo_items

202449 https://hdl.handle.net/2286/R.2.N.202449 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2025 121 pages Masters Thesis Academic theses en Mazhar, Fatima Deng, Shuguang Varman, Arul Khalifehzadeh, Layla Arizona State University Partial requirement for: M.S., Arizona State University, 2025 Field of study: Chemical Engineering This thesis presents a comprehensive investigation into the selective depolymerization of lignin to produce high-value aromatic monomers using hydrothermal liquefaction (HTL) and ionic liquid-assisted systems. Lignin, a structurally complex and underutilized biopolymer, holds significant promise as a renewable source of aromatic compounds. However, its resistance to degradation has limited its valorization. This study explores lignin conversion under mild alkaline and acidic conditions, with and without ethanol and [Bmim][MeSO₄], to optimize monomer yield while minimizing unwanted by-products. Sugarcane peels and corn stover were used as lignocellulosic feedstocks with a brief analysis of model lignin. The study systematically examined the effect of temperature, catalyst concentration, solvent composition, and reaction duration on monomer yield. GC-MS analysis of the reaction products revealed the consistent production of 2-methoxy-4-vinylphenol, vanillin, and 2,3-dihydrobenzofuran, three key intermediates derived from guaiacol units. A kinetic model based on first-order differential equations was developed to elucidate degradation pathways and estimate rate constants and activation energies for each transformation step. Kinetic analysis indicated that 2-methoxy-4-vinylphenol and 2,3-dihydrobenzofuran act as unstable intermediates, with yields varying over time depending on thermal and catalytic conditions. Activation energies ranged from 16.93 kJ/mol to 62.17 kJ/mol, with lignin- to-vanillin pathways exhibiting the highest barriers, underscoring their temperature sensitivity. Ethanol was found to enhance ketone production, likely serving as a hydrogen donor or capping agent. In contrast, while [Bmim][MeSO₄] improved lignin solubility, it also introduced reactive side products that limited its overall effectiveness. The study proposes a mechanistic degradation model beginning with lignin fragmentation into vanillin, Benzofuran-2,3-Dihydro and 2-methoxy-4-vinylphenol. It also provides insight into other possible pathways that may be explored- syringaldehyde production and lignin to phenolic final products. Overall, this work advances the understanding of lignin depolymerization under tunable reaction conditions, integrating experimental insights with kinetic modeling. The findings provide the foundation for optimizing and scaling up lignin valorization process for bio-based aromatic chemical production. Chemical Engineering 2-methoxy-4-vinylphenol Biomass Kinetics lignin renewable Vanillin Valorization of Lignin for the Production of High-value Monomers