Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Chemistry and Biochemistry

First Advisor

Douglas Raynie


The current world population is completely rely on the non-renewable resources such as coal, fossils, and natural gas to get the energy, fuel and value-added chemicals. The increasing the demand of utilizing non renewable resources leads to severe problems such as global warming, climate changes, and environmental pollution. The renewable resources such as wind, solar energy, and biomass is an alternative sources to overcome these problems and to save the environment. Biomass made up with the cellulose, hemicellulose, and Lignin. Lignin is a copolymer of phenolic monomers and inexpensive naturally occurring complex material to produce the value-added chemicals and various aromatics for industrial applications. The first objective of this dissertation is, the catalytic depolymerization of alkali lignin (AL) into phenolic monomers were studied using a green and eco friendly solvent. In this study, subcritical water (SCW) was used as a green solvent with catalysts. The different types of heterogeneous catalysts were investigated for the depolymerization of alkali lignin in the presence of subcritical water. The goal of this study is screening the best catalyst for the depolymerization of lignin in the presence of subcritical water. The depolymerization of alkali lignin was performed at 240oC for 10 minutes reaction time using subcritical water as a solvent and catalysts. The subcritical water and catalysts were used for the cleavage of β-O-4 bond in the alkali lignin. The treatment of alkali lignin with Ni-Graphene catalyst in subcritical water resulted the highest phenolic monomers yield of 40.84 ± 0.27 mg/ g of alkali lignin. This result shows that the Ni-Graphene catalyst with subcritical water is an efficient method for the depolymerization lignin. The combination of catalyst with subcritical water is beneficial for saving the reaction time and inhibition of repolymerization reaction. The most abundant phenolic monomers were guaiacol, vanillin, isoeugenol, acetovanillone, guaiacylacetone, and homovanillic acid identified using Gas Chromatography Mass Spectrometry (GC-MS). This method considered as a potential to produce valuable chemical from the lignin under moderate conditions with 10 minutes reaction time. Secondly, optimized the reaction conditions for the depolymerization of alkali lignin in the presence of subcritical water. The depolymerization of lignin reaction was carried out at 200℃ and 240℃ for 5, 10, and 15 minutes reaction time. The highest conversion of phenolic monomers and selectivity of phenolic monomers was observed at 240℃ for 10 minutes reaction time. The lowest yield was observed at 200℃ and 5, 15 minutes reaction from the alkali lignin. The possible reason for the lowest yield was repolymerization of lignin. The catalysts used for the optimization of conditions were Ni-Graphene, 5% V/Zeolite, and 1.7% V/ZrO2 (Sulfate). Finally, studied the extraction of lignin from the pine sawdust and pistachio shells biomass and performed the depolymerization reactions with extracted lignin using Ni-Graphene catalyst at 240℃ for 10 minutes reaction time. The accelerated solvent extraction (ASE) and the mixture of methyl isobutyl ketone (MIK) and ethanol (7:3) used as a solvent A, and mixture of water and 0.1 M H2SO4 used as a solvent B. The extraction of lignin was performed at 200℃ for 60 min with 1400-1530 psi pressure. The characterization of extracted lignin studied using TGA, FT-IR, and 1H NMR. 12 different phenolic monomers were identified using GC-MS from the extracted lignin. The major identified phenolic monomers were Syringaldehyde, vanillin, coniferyl aldehyde, trimethoxy benzyl alcohol, and synapyl alcohol. The total conversion yield was found to be 45.2% from the pistachio shell extracted lignin. The total extraction of lignin was found to be 23.57±3.38% from the pistachio shells, and 22.86 ± 1.52% from the pine sawdust biomass. The goal of this dissertation was, to develop the ecofriendly and viable technique for the depolymerization of lignin using green solvents and decreasing the harsh conditions such as temperature and pressure for breaking the bonds in the lignin. The conclusion of this dissertation was, Successfully, converted the lignin in to phenolic monomers using minimal reaction conditions (temperature and pressure) in the presence of green solvent (subcritical water) and catalysts and also extracted the lignin from the waste biomaterials and applied the same optimized conditions and catalyst to get the phenolic monomers from the lignin in the presence of subcritical water. Finally conclude that this approach is green and environmentally friendly method for converting biomass into value-added chemicals.



Number of Pages



South Dakota State University


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