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Title: Catalytic depolymerization of lignin
Author: Parker, Heather Jane
ISNI:       0000 0004 9358 8770
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2016
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The valorization of the abundant yet recalcitrant biopolymer lignin via selective depolymerization to produce monomeric phenols could greatly improve the process economics of a lignocellulosic biorefinery. Ionic liquid pretreatment has been presented as a potential route to the effective separation of biomass, producing a clean and soluble lignin stream. This could present a significant opportunity for the use of homogenous catalysis for selective lignin depolymerization. Amongst the potential uses for renewable monomeric phenols from lignin could be as antioxidants to increase the oxidative stability of fuels. The aim of this work is to investigate the selective depolymerization of lignin to renewable phenols and also to assess the suitability of these compounds as antioxidants in fuel. Chapter 1 provides an outline of the research carried out to date in the area of lignin extraction and depolymerization to monomeric phenolic products, with a particular focus on ionic liquid (IL) pretreatment processes and the degradation of model lignin compounds by homogeneous catalysts. An introduction to the use of phenolic antioxidants in the stabilization of biodiesel is also presented. Chapter 2 reports the systematic study of the activity and selectivity of a range of homogeneous vanadium complexes for the catalytic degradation of phenolic and nonphenolic ß-O-4 model lignin compounds. The effects of changing the ligand structure are investigated, in addition to the effect of temperature, catalyst loading and availability of oxygen. Activity and selectivity were found to be highest for catalysts with bulky alkylsubstituted, monophenolate ligands. Chapter 3 investigates the stability and activity of several of the vanadium catalysts developed in chapter 2 for the degradation of model lignin compounds in a range of ILs. The majority of this work was conducted during a three-month placement in the Biomass Pretreatment team at the Joint BioEnergy Institute in Emeryville, CA, USA. A comparison of catalytic activity and selectivity in the degradation of a ß-O-4 model compound in DMSO and the IL [Emim][OAc] was conducted, along with a range of studies in mixtures of the two solvents. Whilst overall activity was lower in the ILs, selectivity for the desired C-O cleavage reaction was dramatically improved. The attempted catalytic degradation of an a-O-4 model lignin compound is also presented, along with preliminary studies of the depolymerization of alkali lignin by homogeneous vanadium catalysts in [Emim][OAc]. Chapter 4 describes the development of a high-throughput accelerated fuel oxidation rig. It also details its subsequent use in the assessment of the antioxidant properties of three renewable phenols, obtainable from lignin, in increasing the oxidative stability of rapeseed methyl ester (RME) biodiesel. The activity of the renewable phenols was compared to that of the commercial antioxidant butylated hydroxytoluene (BHT). Whilst less active than BHT, the renewable phenols were found to be active as antioxidants in RME biodiesel; the trend in activity was observed to be related to the substituents at the 2' and 6' positions. Fuel properties of blends of these renewable phenols are also presented. Chapter 5 summarizes the findings of the thesis and places them in the context of the thesis aims, whilst chapter 6 presents the experimental and synthetic methodologies employed in the thesis.
Supervisor: Jones, Matthew ; Chuck, Christopher Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available