Author ORCID Identifier
Date Available
6-21-2023
Year of Publication
2022
Degree Name
Doctor of Engineering (DEng)
Document Type
Doctoral Dissertation
College
Engineering
Department/School/Program
Chemical and Materials Engineering
First Advisor
Dr. Rodney Andrews
Abstract
Lignin is the second most abundant form of biomass on earth. The phenolic structure and high carbon to oxygen ratio make lignin an attractive renewable source of fuel and chemicals. However, its recalcitrance and heterogeneous nature prove difficult for decomposing lignin’s polymer structure and separation of the products. This work has focused on the use of low-energy catalytic approaches to overcome these barriers. A mimic of the lignin degrading enzyme laccase, consisting of a copper cluster Cu4Py4I4 modified with AgNO3, was developed to function similarly to the laccase active site. The prepared copper complex solution was found to be active on ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) like laccase. The main component of this solution was determined to be CuPy2(NO3)2 by XRD. However, further work indicated that co-formed silver nanoparticles were the most active component in ABTS oxidation. Thus, the focus was placed on the further development of silver nanoparticles catalyzed oxidative depolymerization of lignin. Silver nanoparticles are a photocatalyst that can absorb both UV and visible light due to surface plasmon resonance. This work is the first to use silver nanoparticles as the primary catalyst in photo oxidation of lignin. Here, silver nanoparticles supported on zeolite Y (Ag/zeolite) are used in photocatalytic oxidation of lignin model compounds and were tested with industrial lignin feedstocks. GC-MS was used to study the products of treated lignin model compounds. Treated sodium lignosulfonate samples were analyzed by UV-Vis spectrometer. NMR was used to study the treated kraft lignin samples. The results indicate the successful oxidation and degradation of a β-O-4 lignin model compound 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)-1,3-propanediol, oxidation of a sodium lignosulfonate, and oxidation of a kraft lignin catalyzed by Ag/zeolite with UV or visible light. The activity of Ag/zeolite in the treatment of β-O-4 lignin model compounds was found to be inconsistent. Therefore, silver nanoparticles supported on AgCl were selected in the mechanism study. In this study, Ag/AgCl successfully cleaved the β-O-4 linkage in lignin model compound 3-hydroxy-2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)-1-propanone and 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)-1,3-propanediol under visible light. Reactions and mechanisms were proposed based on the products of the reactions. For both 2a and 2b photodegradation by supported silver nanoparticles, two reactions were involved. One was a reversible dehydrogenation of the carbon-carbon bond between β carbon and the carbon connected to the hydroxyl group. The other was the breakage of the ether bond between β carbon and oxygen. Ag/AgCl was found to not cleave the β carbon and oxygen bond in lignin model compounds 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)-ethanone (2d) and 4-methoxy-α-[(2-methoxyphenoxy)methyl]-benzenemethanol (3a) because these two lignin model compounds do not have the γ carbon and a hydroxyl group connected to γ carbon. Overall, supported silver nanoparticles were found to have unique selectivity on γ carbon in the photolysis of lignin.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2022.457
Funding Information
Funder: National Science Foundation
Fund name: Established Program to Stimulate Competitive Research
Fund number: 1355438
Funding years: May 2015 to July 2019
Funder: Center for Applied Energy Research, University of Kentucky
Funding years: August 2019 to December 2022
Recommended Citation
Wei, Ning, "PHOTOCATALYTIC DEGRADATION OF LIGNIN BY SUPPORTED SILVER NANOPARTICLES" (2022). Theses and Dissertations--Chemical and Materials Engineering. 145.
https://uknowledge.uky.edu/cme_etds/145
