Document Type

Thesis - Open Access

Award Date

2018

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Cheng Zhang

Keywords

Biomass, Heterogeneous catalysis, Lignin, Ni catalyst, Phenolic compounds, Reaction mechanisms

Abstract

Lignin is the most abundant aromatic biopolymer and is a potential source for phenolic chemical feedstocks. Lignin is composed of phenolic units connected by more than eight different linkages, the most common being β-O-4 which constitutes 50-60%. The hydrothermal decomposition of a guaiacol based β-O-4 lignin dimer was studied under neutral and basic conditions to elucidate the mechanism of β-O-4 bond cleavage and the formation of downstream products. Phenol-carbonyl condensation and vinyl-ether formation were shown to be the primary causes for low monomer yields under the tested conditions. Three Ni catalyst systems, Ni/C + H2, Ni/C-Zn, and Ni/Zn, were investigated using the dimer model under a variety of conditions to counteract these processes. The role of each reagent was explored and monomer yields up to 80 C% were obtained. These catalysts were used to investigate the intricacies of reductive depolymerization of raw biomass using pine sawdust as a substrate. Preservation of the cellulose matrix, lignin extraction and solubilization, and rate of hydrogen generation were identified to be the most important factors governing monomer yields. A quantitative monomer yield of 35 C% was realized using Ni/C + H2 in ethanol with 4- propylguaiacol composing 32 C%. Ethanol and methanol solvents in the presence of Ni metal were identified as a hydrogen source for reductive depolymerization, allowing for the omission of an external reducing agent. A monomer yield of 26 C% was obtained using only Ni/C and methanol. The lignin component of two agricultural waste crops, corn stover and sugarcane bagasse, and an energy crop, switchgrass, were effectively depolymerized using these conditions. Despite the successful depolymerization of lignin, the major product, 4-propylguaiacol, has few current applications outside substandard polymer composites. Therefore, new applications must be developed. To this end, 4- propylguaiacol was used in an attempt to synthesize a semi-conductive charge storage material for potential use in supercapacitors and battery cathodes.

Library of Congress Subject Headings

Lignin.
Biopolymers.
Biomass energy.
Phenols.
Heterogeneous catalysis.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

165

Publisher

South Dakota State University

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Rights Statement

In Copyright