Lignin Chemistry: Characterization, Isolation, and Valorization

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Lignin Chemistry: Characterization, Isolation, and Valorization
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Contents
Preface
Acknowledgments and Conflict of Interest
1. A Brief Introduction of Lignin
	1.1 Introduction
	1.2 The Building Blocks of Lignin
		1.2.1 Interlinkages in Lignin
		1.2.2 Bioengineering of Lignin
	1.3 Scope of this Book
	References
2. NMR Characterization of Lignin
	2.1 Introduction
	2.2 1H NMR
		2.2.1 Sample Preparation and Program
			2.2.1.1 Sample Preparation of Non-Acetylated Lignin
			2.2.1.2 Sample Preparation of Acetylated Lignin
			2.2.1.3 1H Program
		2.2.2 1H-NMR Spectra Analysis
			2.2.2.1 1H-NMR Spectra of Non-Acetylated Lignin
			2.2.2.2 1H-NMR Spectra of Acetylated Lignin
	2.3 13C-NMR
		2.3.1 Sample Preparation and Program
			2.3.1.1 Sample Preparation
			2.3.1.2 13C-NMR Program
		2.3.2 Quantitative 13C-NMR
			2.3.2.1 Quantitative 13C-NMR of Non-Acetylated Lignin
			2.3.2.2 Quantitative 13C-NMR of Acetylated Lignin
		2.3.3 Applications of the 13C-NMR
	2.4 2D-HSQC (Heteronuclear Single-Quantum Correlation)
		2.4.1 Sample Preparation and Program
		2.4.2 Semi-Quantification of Lignin in 2D-HSQC NMR Spectra
			2.4.2.1 Relative Quantitative Method (Without Internal Standard)
			2.4.2.2 Relative Quantitative Method (Aromatic Ring as IS)
			2.4.2.3 Based on the Combination of 13C and 2D-HSQC Technique
		2.4.3 Assignments of Lignin in 2D-HSQC NMR spectra
			2.4.3.1 Gramineous Lignin
			2.4.3.2 Hardwood Lignin
			2.4.3.3 Softwood
		2.4.4 Application of 2D-HSQC NMR Technique in the Field of Lignin
			2.4.4.1 Structure Characterization of Native Lignin from Different Plant Sources
			2.4.4.2 Structure Changes of Lignin During Delignification and Pretreatment Process
	2.5 31P NMR
		2.5.1 Factors Affecting 31P NMR
		2.5.2 31P NMR Operation
			2.5.2.1 Detailed Procedures
		2.5.3 Applications of the 31P NMR
	2.6 19F NMR
	2.7 Solution-State NMR of Whole Plant Cell Wall
		2.7.1 Solution-State 2D-HSQC NMR of Acetylated Plant Cell Walls
		2.7.2 Solution-State 2D-HSQC NMR of Non-Acetylated Plant Cell Walls
		2.7.3 Comparison of the Dissolution Methods and Applications of Whole Plant Cell Wall Solution State NMR
	2.8 Conclusion
	References
3. Advances in the Molar Mass and Functionality Analysis of Lignin
	3.1 Introduction
	3.2 General Aspects
	3.3 Dissolution of Lignin Samples
	3.4 Molar Mass Analysis
		3.4.1 Size-Exclusion Chromatography (SEC)
		3.4.2 Asymmetric Flow Field-Flow Fractionation (AF4)
		3.4.3 Detection Systems
	3.5 Functional Group Analysis
		3.5.1 Heterogeneity in Functionality
		3.5.2 Dispersity in Functionality
	3.6 Analysis of Lignin Composition by Two- Dimensional Liquid Chromatography
	References
4. Degradative Methods for Lignin Valorization
	4.1 Introduction
	4.2 Basics Aspects Regarding Structural Features in (Isolated) Lignins
		4.2.1 Occurrence and Isolation
		4.2.2 Standard Means for Elucidating Basic Structural Features of (Isolated) Lignins
			4.2.2.1 Nuclear Magnetic Resonance (NMR) Spectroscopy-Based Analysis Methods
			4.2.2.2 Fourier-Transform Infrared Spectroscopy and Raman Spectroscopy
			4.2.2.3 Size Exclusion and Gel Permeation Chromatographic Methods
		4.2.3 “Purity” of Isolated Lignins
		4.2.4 Fractionation of Isolated Lignins for Structurally more Homogeneous Starting Materials
	4.3 Classic Wet-Chemical Degradation Methods
	4.4 Catalytic Oxidative Degradation of Lignins
		4.4.1 Catalytic Chemical Oxidative Degradation
			4.4.1.1 Metal-Free Oxidations
			4.4.1.2 Organometallic Catalysts
			4.4.1.3 Biomimetic Catalysts
		4.4.2 Enzymatic Oxidative Degradation
			4.4.2.1 Laccase-Mediated Oxidative Depolymerization
			4.4.2.2 Peroxidase-Mediated Oxidative Depolymerization
			4.4.2.3 Technological Advancements to Enable Enzymatic Lignin Degradation
		4.4.3 Catalytic Chemical Reductive Degradation
			4.4.3.1 Metal-Free Reductions
			4.4.3.2 Heterogenic Transition Metal Catalysts
			4.4.3.3 Organometallic Catalysts
	4.5 Thermally Induced Lignin Depolymerization
		4.5.1 Hydro Treatment-Based Lignin Depolymerization
		4.5.2 Pyrolytic Lignin Degradation
			4.5.2.1 Torrefaction of Lignin
			4.5.2.2 Catalyst-Free Pyrolysis of Lignins
			4.5.2.3 Catalytic Pyrolysis of Lignin
			4.5.2.4 Advanced Pyrolysis Technologies
	4.6 Electrochemical Lignin Degradation
	4.7 Concluding Remarks and Outlook
	References
5. Isolation of Native-Like Lignin
	5.1 Classical Methods Used for Native-Like Lignin Isolation
		5.1.1 Mild Alcohol Extracted Lignin
		5.1.2 Milled Wood Lignin (MWL)
		5.1.3 Cellulolytic Enzyme Lignin (CEL)
		5.1.4 Enzymatic Mild Acidolysis Lignin (EMAL)
		5.1.5 Residual Enzyme Lignin (REL)
	5.2 Isolation of Lignin with High β-O-4 Content
		5.2.1 Isolation Under Acidic Conditions
		5.2.2 Isolation Under Alkaline Conditions
		5.2.3 Isolation Using Flow-through Extraction
		5.2.4 Isolation With Alternative Solvents
		5.2.5 Alternative Resources and Special Lignins
	5.3 Concluding Comments
	References
6. Isolation of Lignin in the Biorefinery Process
	6.1 Introduction
	6.2 Methods Used to Isolate Lignin from Lignocellulose
		6.2.1 Organosolv Process
		6.2.2 Hydrothermal Pretreatment
		6.2.3 Steam Explosion
		6.2.4 Ammonia-Based Pretreatment
		6.2.5 γ-Valerolactone (GVL)
		6.2.6 Ionic Liquids (ILs)
		6.2.7 Deep Eutectic Solvents (DES)
		6.2.8 Acid Treatment
		6.2.9 Acidic Lithium Bromide Trihydrate (ALBTH) System
	6.3 Conclusion and Perspectives
	Acknowledgments
	References
7. Gasification and Combined Heat and Power (CHP) from Lignin
	7.1 Introduction
	7.2 Chemical Structure and Composition of Lignin
	7.3 Sources of Lignin and its Characterization Techniques
	7.4 Lignin Isolation/Production Process
	7.5 Lignin Depolymerization and Conversion to Fuel
		7.5.1 Thermochemical Conversion
			7.5.1.1 Pyrolysis of Lignin
			7.5.1.2 Gasification of Lignin
	7.6 Conclusion
	References
8. Enzymatic and Microbial Bioconversion of Lignin to Renewable Chemicals
	8.1 Lignin Conversion by Enzymes
		8.1.1 Extracellular Peroxidases from White-rot Fungi
		8.1.2 Bacterial Dye-Decolorizing Peroxidases (DyP)
		8.1.3 Multi-Copper Oxidases
		8.1.4 Beta-Etherase Enzymes for Lignin Ether Cleavage
		8.1.5 Other Lignin-Oxidizing Enzymes
		8.1.6 Accessory Enzymes for Lignin Oxidation
			8.1.6.1 Fungal Accessory Enzymes
			8.1.6.2 Bacterial Accessory Enzymes
		8.1.7 Lignin Conversion In Vitro by Enzymes
	8.2 Pathways for Microbial Lignin Degradation
	8.3 Microbial Lignin Bioconversion by Engineered Bacteria
		8.3.1 Microbial Hosts for Lignin Bioconversion
		8.3.2 Conversion of Polymeric Lignin and Depolymerized Lignin Hydrolysates into into High-Value Products
			8.3.2.1 Vanillin
			8.3.2.2 Polyhydroxyalkanoates
			8.3.2.3 Triacylglycerol Lipids
			8.3.2.4 Cis,cis-Muconic Acid (MA)/Adipic Acid
			8.3.2.5 Pyridine- and Pyrone-Dicarboxylic Acids
			8.3.2.6 Substituted Styrenes
	Acknowledgments
	References
9. Approaches to the Oxidative Depolymerization of Lignin
	9.1 Introduction
	9.2 Metal-Free Oxidative Depolymerization of Lignin
		9.2.1 Nitrobenzene Oxidation
		9.2.2 Ozone Mediated Depolymerization of Lignin
		9.2.3 Other Organic Oxidants
		9.2.4 Alkaline Oxidation of Lignin
		9.2.5 Oxidative Catalytic Fractionation of Wood (OCF)
	9.3 Transition Metal Catalysis for Oxidative Cleavage of Lignin
	9.4 Rhenium-Based Catalysts
	9.5 Cobalt-Based Catalysts
	9.6 Vanadium-Based Catalysts
	9.7 Other Metals
	9.8 Biomimetic Oxidations
	9.9 Electrochemical Oxidative Cleavage of Lignin
		9.9.1 General Aspects
	9.10 Direct Electrochemical Oxidation of Lignin
	9.11 Indirect Electrooxidation of Lignin
	9.12 Lignin Oxidation via Electrochemical Combination Reactions
	9.13 Concluding Remarks and Outlook
	Acknowledgments
	References
10. Photocatalytic Conversion of Lignin
	10.1 Introduction
	10.2 Photocatalytic C—O Bond Cleavage
		10.2.1 Stepwise Photocatalytic Cleavage of Cβ—O (β-O-4) Bond
			10.2.1.1 Oxidation of Cα Hydroxyl into Cα Carbonyl
			10.2.1.2 Reductive Cleavage of Cβ—O Bond in β-O-4 Ketone
		10.2.2 Direct Photocatalytic Cleavage of Lignin Cβ—O (β-O-4) Bond
			10.2.2.1 Direct Approach through β-O-4 Ketone Intermediate
			10.2.2.2 Direct Approach through Cα Intermediate
		10.2.3 Cleavage of Caryl—O (β-O-4, 4-O-5) and Cα—O (α-O-4)
	10.3 Photocatalytic C—C Bond Cleavage
		10.3.1 CαO−H Bond Activation to Alkoxy Radical Intermediate
		10.3.2 Cβ—H Bond Activation to Cβ Radical Intermediate
		10.3.3 Single Electron Transfer to Radical Cation Intermediate
	10.4 Conclusion and Outlook
	References
11. Electrochemical Conversion for Lignin Valorization
	11.1 Introduction
	11.2 The Mechanism of Electrocatalytic Lignin Conversion
		11.2.1 Reaction Mechanism
		11.2.2 Faradaic Efficiency
	11.3 Lignin Pretreatment to Enable Efficient Electrocatalytic Upgrading
	11.4 Electrocatalytic Cleavage of Lignin-derived Model Compounds
		11.4.1 Reductive Approach
			11.4.1.1 Monomers
			11.4.1.2 Lignol Dimers
		11.4.2 Oxidative Approach
			11.4.2.1 Monomers
			11.4.2.2 Lignol Dimers
	11.5 Electrocatalytic Depolymerization of Lignin Polymer
		11.5.1 Electrocatalysts for Lignin Depolymerization Using Various Electrodes
			11.5.1.1 Iridium Based Anodes
			11.5.1.2 Lead/Lead Oxide Based Anodes
			11.5.1.3 Nickel-, Cobalt-, and Nickel–Cobalt Based Electrodes
		11.5.2 Combination of Electrochemical and Other Process for Lignin Conversion
			11.5.2.1 Ionic Liquid and Deep Eutectic Solvent Electrolytes Assisted Approach
			11.5.2.2 Biodegradative Pretreatment
			11.5.2.3 Photo-Assisted Approach
			11.5.2.4 Mediator-Assisted Approach
			11.5.2.5 H2O2-Assisted Approach
			11.5.2.6 Hydrogen Coproduction Approach
	11.6 Electrocatalytic Valorization of Lignin to Biorefinery Aromatics Products
		11.6.1 Vanillin
		11.6.2 Syringaldehyde
		11.6.3 Guaiacol
		11.6.4 Trans-Ferulic Acid
		11.6.5 Acetosyringone
	11.7 Summary
	References
12. Recent Advances in Thermoset and Thermoplastic Polymeric Materials Produced using Technical and Depolymerized Native Lignins
	12.1 Introduction
	12.2 Lignin-Based Thermosets
		12.2.1 Polyurethanes
			12.2.1.1 Use of Technical or Fractionated Technical Lignins
			12.2.1.2 Use of Chemically Modified Technical Lignins
			12.2.1.3 Use of Depolymerized Native Lignin Produced by Lignin-First Biorefining/RCF Approaches
		12.2.2 Epoxies
			12.2.2.1 Reactive Blending with Epoxy Resins
			12.2.2.2 Direct Epoxidation of Technical or Fractionated Technical Lignins
			12.2.2.3 Modification of Technical Lignins Prior to Epoxidation
			12.2.2.4 Use of Depolymerized Native Lignins Produced by Lignin-First Biorefining/RCF Approaches
		12.2.3 Phenol-Formaldehyde Resins
		12.2.4 Other Polymers
	12.3 Lignin-Based Thermoplastics
		12.3.1 Graft Copolymers and Scope
		12.3.2 Lignin-Copolymer Thermoplastics Using Ring-Opening Polymerization
		12.3.3 Lignin-Copolymer Thermoplastics Using Radical Polymerization
		12.3.4 Lignin Thermoplastic Polyurethanes
	12.4 Perspectives
	References
13. Advances in Preparation and Applications of Lignin Nanoparticles
	13.1 Introduction
	13.2 Preparation Methods
		13.2.1 Solvent Exchange
		13.2.2 pH Shifting
		13.2.3 Aerosol Evaporation
	13.3 Properties
		13.3.1 Inherent Properties of LNPs
		13.3.2 Size Control by Different Solvent Systems and Process Parameters
		13.3.3 Versatile Particle Morphologies and Tailored Properties
		13.3.4 Stabilized and Solvent-Resistant Lignin Particles
	13.4 Emerging Applications
		13.4.1 Polymer Composites, Gels, Adhesives, and Coatings
		13.4.2 Carrier Systems for Agriculture and Biomedicine
		13.4.3 Emulsifiers for Pickering Emulsions
		13.4.4 Sensors
		13.4.5 Hybrid Particles with Metal and Inorganic Nanoparticles
		13.4.6 Sunscreens
		13.4.7 Biologically Active Lignin Nanomaterials
	13.5 Future Perspectives
	References
14. Carbon (Nano)Fibers and Carbon Materials from Lignin and Their Applications
	14.1 Introduction
	14.2 Lignin-Derived Carbon Materials
	14.3 Lignin-Based Carbon Fibers
		14.3.1 Spinning of Lignin-Based Precursor Fibers
			14.3.1.1 Spinning of Lignin-Based Precursor Fibers
			14.3.1.2 Precursors via Solution Spinning
		14.3.2 Stabilization and Carbonization of Lignin Fibers
	14.4 Applications of Lignin-Derived Carbon Materials – Supercapacitors
		14.4.1 Lignin-Derived Activated Carbon Materials
		14.4.2 Template-Assisted Porous Carbon Materials
		14.4.3 Lignin-derived Free Standing Carbon Materials
	14.5 Applications of Lignin-Derived Carbon Materials – Batteries
		14.5.1 Lignin-derived Anode Materials
		14.6.1 Light Stimuli Carbon Quantum Dots for Sensing Applications
	14.6 Applications of Lignin Derived-Carbon Materials – Sensing
		14.6.2 Strain and Pressure Sensors
		14.6.3 Electrochemical Sensors
	14.7 Applications of Lignin Derived-Carbon Materials – Thermoelectric Devices
	Acknowledgments
	References
15. Lignin-based Hydrogel: Mechanism, Properties, and Applications
	15.1 Introduction of Hydrogels
	15.2 Introduction of Lignin
		15.2.1 Sources of Lignin
		15.2.2 Characteristics of Lignin
	15.3 Lignin-Based Hydrogel Preparation
		15.3.1 Blending of Lignin in Hydrogel Networks
		15.3.2 Polymerization of Lignin with Bio-Based/Synthetic Chemicals for Hydrogels
			15.3.2.1 Crosslinking
			15.3.2.2 Free Radical Polymerization of Lignin and Monomers
			15.3.2.3 Atom Transfer Radical Polymerization (ATRP) of Lignin for Hydrogel Production
			15.3.2.4 Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization
	15.4 Applications
		15.4.1 Dye Decontamination
		15.4.2 Heavy Metal and Other Ion Elimination
		15.4.3 Drug Delivery Application
		15.4.4 Lignin-Based Hydrogel for Wound Dressing
		15.4.5 Lignin-Derived Hydrogel for Agriculture of Watering Plants and Fertilizers
		15.4.6 Lignin-Derived Hydrogels for Energy Storage Applications
	15.5 Perspectives and Future Work
	References
Index