Handbook of Lignin

Inhaltsverzeichnis

1. Frontmatter

2. 1. History and Development of Lignin

   Aatikah Meraj, Mohammad Jawaid, Akil Ahmad

   Abstract

   Lignin is a widespread biopolymer that for years has sparked the curiosity of researchers, historians, and industrialists. Its origin can be traced to the first civilization when lignocellulosic substances were utilized for a variety of uses without an extensive understanding of chemical properties. In the nineteenth century, scientists pioneered and realized the importance of lignin as a key component of wood and other plant tissues, which led to the acknowledgment and initiation of the first systematic evaluations of the material. Moreover, worries over depleting fossil fuel supplies and environmental sustainability gave rise to increased initiatives to valorize lignin as a renewable resource. The advent of the polymer concept offered a supplementary structure that progressed knowledge of the physical characteristics and chemical composition of lignin. Even though the production of lignin is widely understood, additional information is constantly being discovered. The knowledge that has been gathered and condensed about the topic gives us an evolutionary perspective on the emergence and development of this intricate metabolic system.

3. 2. Sources of Lignin

   Ahmad Safwan Ismail, Mohammad Jawaid, E. S. Zainudin

   Abstract

   Lignin is a complex aromatic polymer that serves a crucial structural function in plant cell walls, imparting stiffness and durability to diverse biomass forms. Lignin, the second most prevalent biopolymer, has attracted considerable attention owing to its sustainability and prospective applications. This chapter examines several lignin sources, such as the pulp and paper industry, sugarcane bagasse, and agricultural residue. The composition and structure of lignin differ based on the plant source, leading to unique varieties (hydroxyphenyl, guaiacyl, and syringyl) derived from certain monolignols. The pulp and paper industry is the greatest lignin producer, creating around 50–70 million tons yearly as a by-product of the pulping process. The standard techniques for lignin extraction predominantly encompass kraft, sulfite, soda, and organosolv procedures. Each of these methods utilizes distinct chemical treatments to isolate lignin from lignocellulosic biomass, and they are extensively employed in industrial applications. Lignin possesses significant potential in several applications, including composite materials, coatings, adhesives, biofuels, and biochemicals.

4. 3. Lignin: Structural Advantages

   Ajay Kumar

   Abstract

   Lignin structure and its engineering open an alternative feedstock for an industry. Lignin contributes up to 30 wt% of lignocellulosic biomasses. Different methods such as steam explosion, soda process, organosolv, kraft process, lignosulfonates, etc. are used for the isolation of lignin. Methods such as acetylation, alkylation, esterification, etc. are used for the modification of lignin. Lignin gives structural stiffness to the cell wall. Lignin is also used for the preparation of electrochemical capacitors. Lignin and its composite are used for the sensor. In the case of bioimaging, lignin-based carbon quantum dots are used. Other major applications of lignin are reported in drug delivery systems, wastewater treatment, and antimicrobial agents. Thus, lignin has emerged as a potential biomaterial for human welfare in industry.

5. 4. Alkali Lignin: Extraction

   Simons Dhara, Thangsei Nengneilhing Baite

   Abstract

   This chapter delves into the potential of alkaline lignin extraction, a process with a rich history, as a sustainable approach to utilizing a readily available resource. The review begins with an introduction to lignin and the importance of its extraction. Then, a comprehensive overview of conventional alkaline lignin extraction methods is provided, encompassing general methodology, purification techniques, and factors influencing yield. Different extraction media employing NaOH, KOH, Ca(OH)₂, and NH₄OH are explored, highlighting their advantages and limitations. Characterization techniques play a crucial role in understanding the properties of extracted lignin. The chapter discusses commonly employed methods such as Fourier transform infrared spectroscopy, UV-visible spectroscopy, nuclear magnetic resonance, and thermal analysis, enabling a detailed analysis of the extracted lignin’s structure and composition. Finally, the chapter explores the exciting field of alkali lignin-based product development. It highlights the potential of alkali lignin in creating functional membranes and hydrogels for diverse applications. These applications encompass water treatment, agriculture, drug delivery systems, and biosensors.

6. 5. Mild-Acidolysis Lignin: Extraction

   Lalduhsanga Pachuau

   Abstract

   Lignin is the second most abundant biopolymer and the most abundant aromatic polymer on earth. Its effective and efficient utilization is crucial in achieving sustainable development. The recalcitrant nature of the lignocellulosic complex is the major challenge in lignin valorization. Isolation of lignin without altering its native structure is almost inconceivable. Mild-acidolysis lignin and its various modifications have been developed over the years to minimize the extensive degradation of the native lignin during its isolation. This chapter discusses the various approaches to lignin isolation from biomass, their advantages, and possible limitations. A detailed deliberation on the different mild-acidolysis processes in lignin isolation has also been included.

7. 6. Lignin Extraction Using Cellulolytic Enzymes

   Madhulika Madhavan, Kiran Babu Uppuluri

   Abstract

   Lignin is one of the important biopolymers in plants. Being the second most abundant after cellulose, lignin is the only aromatic polymer found in nature. The basic unit of lignin is known to be monolignols. These monolignols undergo further reactions like depolymerization, giving rise to G and H units. Structural classification of lignin is done based on the presence of G and H units and isolated for the intended applications. Much research has been undertaken to determine the native form of lignin, but it has been difficult due to its close association with the carbohydrates in the plant cell wall. Various physicochemical methods are used to isolate lignin, which includes precipitation of acids, hydrolysis methods, and alkali pretreatments. Recent advancements have been made in lignin isolation, where methods like ultrasonication hydrothermal pretreatment are widely used. Classification of lignin involves various categories where extraction modes of classification pave an important category. Enzymes have been utilized for lignin extraction for an extended period. Cellulolytic enzyme lignin, as the name says, uses enzymes like cellulase for the extraction of lignin. Methods like hydrolysis enzymatic pretreatment are well known to extract the lignin effectively. This chapter focuses on the methodologies involved in the extraction of cellulolytic enzyme lignin, along with its structural features, pitfalls in the process, and their potential applications.

8. 7. γ-Valerolactone Lignin: Extraction

   Sibel Başakçılardan Kabakcı, Kübra Al

   Abstract

   Lignin, a vital structural component of lignocellulosic biomass, holds immense potential for valorization despite traditionally being regarded as a low-value residue. This chapter delves into the use of γ-valerolactone (GVL), an innovative green solvent, for the efficient extraction of lignin from various biomass sources. GVL offers numerous advantages, including high selectivity, chemical stability, and low toxicity, positioning it as a sustainable alternative to conventional solvents. The chapter thoroughly examines the solubility parameters, extraction processes, and characteristics of lignin obtained using GVL. It highlights optimal conditions for lignin recovery, emphasizing the importance of solvent composition, temperature, and catalyst presence. The discussion extends to the impact of GVL-extracted lignin on biorefinery applications, particularly in improving cellulose accessibility for biofuel production. The findings underscore GVL’s potential in advancing sustainable biomass conversion technologies. Future research directions focus on optimizing GVL-based processes and exploring novel applications to fully harness its potential in lignin valorization and integrated biorefinery systems.

9. 8. Organosolv Lignin: Extraction

   M. Sarwar Jahan, M. Mostafizur Rahman

   Abstract

   Lignin is the second most abundant biopolymer on earth after cellulose and has a huge potential for developing biobased products. The lignin is conventionally isolated from the lignocelluloses by alkali. Recently, interest has grown in different organic solvents to delignify lignocelluloses. This chapter discusses the removal of lignin from lignocellulosic biomass using organosolv processes. Most of the organosolv process involves alcohol with the mineral acid catalyst. The primary drawback associated with employing alcohol for high-pressure development in the digester is its low boiling point. Therefore, a special equipment for high pressure is required, which increases capital expenditure. Alternatively, organic acids such as formic acid, acetic acid, and a combination of these two acids could resolve the issue related to alcohol, which requires atmospheric pressure. The lignin can be easily separated from the spent liquor by adding water. The lignin is characterized by high phenolic hydroxyl content, low molecular weight, and high reactivity. The organosolv delignification occurs through the cleavage of β-O-4 bonds.

10. 9. Kraft Lignin: Extraction

    Fernando José Borges Gomes, Diana Catalina Cubides-Román, Julia de Cristo Figueiredo, Sabrina Mayer de Almeida, Nilton Louvem da Silva Junior

    Abstract

    Kraft lignin is a by-product of the kraft pulping process, predominantly utilized in pulp mills for energy production. Despite lignin annual production reaching 50–70 million tonnes, its utilization for high-value products remains limited, with only 1–2% being used for such applications. The extraction of kraft lignin has been identified as a viable solution for energy-sufficient mills during the chemical recovery step. However, it is important to note that this approach presents challenges in the context of recovery boiler operations. The intricate nature of lignin’s structure, coupled with its variability among different plant species, poses significant challenges in the efficient extraction of this compound and the subsequent assessment of its properties. During the kraft process, lignin undergoes structural modifications, resulting in a highly condensed structure with strong condensed bonds and high polydispersity. The lignin modifications pose challenges for its utilization in high-value applications. Advancements in fractionation methodologies have enhanced the consistency of industrial lignin properties. However, further research is necessary to address challenges in characterization, depolymerization, and upgrading. In this chapter, the main methods on kraft lignin extraction are described. The global lignin market has undergone substantial expansion since 2014, propelled by technological advancements, policy incentives, and an escalating demand for eco-friendly materials.

11. 10. Lignosulfonate Lignin: Extraction

    Rahul Kumar Shringirishi, Kaushal Kishor, Subhankar Maity

    Abstract

    The depletion of biodiversity and global warming make green technology and a bioeconomy imperative. The biopolymer lignin has enormous promise. Every year, technical lignin is extracted and utilized for chemical and heat recovery. Lignosulfonates are the primary constituent of discarded sulfite liquor, which are essential to the biorefinery sector and the emerging bioeconomy. Nevertheless, the usage of sulfite pulping effluent is limited and chemical analyses become more difficult due to the presence of additional components and separation difficulties. As a result, novel techniques for the isolation and purification of lignin for the use in industry and analysis are being developed.

    This chapter discusses the difficulties and viewpoints involved in creating practical lignin manufacturing processes while reviewing techniques for separating lignin derivatives from pulping spent liquor, sulfite spent liquor, kraft black liquor, bagasse, corn stover, jute sticks, wood, etc. While ultrafiltration is thought to be an industrially viable method for extracting lignosulfonate from sulfite spent liquors, other extraction processes, such as flat sheet-supported liquid membrane (SLM), microwave-assisted sulfonation, supercritical water hydrolysis, and ion exchange, are designed for commercial-scale lignin isolation. There is also a discussion of lignin extraction from naturally occurring lingo-cellulosic materials both with and without an acid hydrolysis method.

12. 11. Solvent Pulping Method: Extraction

    Fahmida-E-Karim, Shahidul Islam, Md. Redwanul Islam

    Abstract

    Lignin nanoparticles are abundant, nontoxic, inexpensive, environmentally friendly, biodegradable, and biocompatible, in addition to having antioxidant, antibacterial, and UV-absorbing properties—they are capable of getting priority for the depth study in functional composite manufacturing field. Lignin is a very versatile type of polymer widely used in structural composites, and it has also shown potential in various applications such as sensors, packaging materials, and energy storage systems. High-value chemical compounds are needed for the implementation of an automated pulping and purifying strategy. The current chapter will overview a comparative scenario of the existing literature on several lignin solvent pulping methods. The most relevant findings regarding lignin conventional and modern solvent methods have been summarized and analyzed in this chapter. In addition, this writing will summarize the main characteristics of lignin, lignin extraction process classification, and lignin solvent method (i.e., organic solvent, ionic liquid solvent, liquid ammonia solvent), and potential future research areas are also highlighted.

13. 12. Sulfite Pulping: Extraction

    M. Vishnuvarthanan

    Abstract

    Sulfite pulping is a key chemical process in the paper industry that focuses on removing lignin from wood to obtain cellulose fibers, essential for paper production. This process employs sulfurous acid and its salts known as sulfites to break down lignin, a complex polymer that holds cellulose fibers together in plant cell walls. The type of sulfite used such as calcium, sodium, magnesium, or ammonium greatly impacts the pulping conditions and the characteristics of the final pulp. Sulfite pulping can occur under acidic, neutral, or alkaline conditions with acidic pulping (pH 1–2) being the most prevalent due to its effectiveness in lignin removal and the production of high-quality pulp. Despite its efficiency, acidic sulfite pulping requires stringent chemical handling and waste management to reduce environmental harm. Neutral and alkaline sulfite methods although less common present advantages such as minimized equipment corrosion and lower sulfur emissions offering more environmentally friendly options. A crucial element of the sulfite pulping process is the recovery of chemicals from the spent liquor or brown liquor which contains dissolved lignin. This recovered lignin, far from being waste, is valuable in producing dispersants, adhesives, and biofuels, thereby adding economic value to the process. The high-quality pulp produced through sulfite pulping is ideal for manufacturing fine paper and specialty products, ensuring the process’s continued relevance in the industry.

14. 13. Structural Properties of Lignin

    Yousaf Khan, Anila Mukhtiar, Komal Arooj, Aiman Rehman, Shoaib Khan, Zia ur Rehman Panizai

    Abstract

    Lignin, a complex and abundant biopolymer, is predominantly generated as a by-product from the paper, pulp, and lignocellulosic biomass industries. Despite its availability and promise, lignin’s complicated molecular structure and poor solubility have restricted its economic use. Lignan, which accounts for up to 30% of lignocellulosic biomass, is a sustainable source of aromatic chemicals. However, its inherent stability and intricacy have limited its use. Studies have looked at the development and relationships of lignin’s monolignols and units, as well as its macroscopic physicochemical characteristics. Several methods for synthesis and characterization of lignin have been developed, including spectrometry, chromatography, and spectroscopy. Lignin has been a popular raw material for the synthesis of economically useful chemicals over the last two decades. Despite this, most of the lignin from the pulp business is still utilized as boiler fuel, albeit less efficiently than lignin from the lignocellulosic-based bioethanol sector in terms of manufacturing sustainable polymeric materials. As a result of its properties, lignin is used to manufacture a variety of chemical products, including esters, ethers, bioadhesives, lubricants, foams, nanoparticles, and nanocomposites. Lignin production, particularly from the paper and bioethanol industries, poses a significant threat to the environment. In addition to reducing environmental impacts, converting this surplus lignin into valuable products could boost paper and bioethanol industries’ economic growth.

15. 14. Chromatographic Methods for Lignin Characterization

    Santhi Somaraj

    Abstract

    Lignin, a heterogeneous biopolymer derived from plant cell walls, is one of earth’s most abundant natural polymers after cellulose, offering immense potential for bio-based materials, chemicals, and energy applications. Recent advancements have underscored the importance of characterizing lignin’s diverse structural features and functional properties to unlock its full potential. Chromatography-based techniques are particularly effective for lignin separation, quantification, and structural elucidation. This chapter highlights commonly used chromatographic methods for lignin analysis, detailing their principles, advantages, limitations, sample preparation strategies, detector choices, and optimized chromatographic conditions. By providing a comprehensive overview of these techniques, the chapter equips researchers with valuable insights to select appropriate methods for lignin characterization, ultimately enhancing our understanding of lignin’s structure-property relationships and enabling its efficient valorization for diverse applications. These advancements contribute to the broader effort of developing sustainable solutions for renewable resource utilization.

16. 15. Thermal Characterizations of Lignin

    Milad Jalilian, Quan He, Yulin Hu

    Abstract

    Lignin, as the second most abundant component in lignocellulosic biomass, was previously considered a waste by-product; however, recent studies have indicated that it can be used for various applications. Due to the complexity of lignin structure and variations in lignin’s extraction methods, it is difficult to characterize and investigate lignin’s thermal and chemical behavior and properties. To address this, extensive studies have utilized a variety of analytical techniques such as DTG, DSC, TGA, FTIR, Raman, GC-MS, and NMR along with TGA-FTIR-GCMS and TGA-DT-GCMS to understand lignin thermal and chemical properties. In this chapter, initially, an introduction to lignin and its application is presented. Then, the chemistry of lignin and different classifications are discussed based on the sources and extraction processes. After this, different thermal characterization methods, in tandem with some structural characterization and their combination, are studied to better understand lignin’s chemistry, reaction pathways, and thermochemical properties and behavior. In conclusion, these thermal characterizations would give valuable knowledge regarding the change in the chemistry of lignin and thermal degradation of lignin over a range of temperatures.

17. 16. Morphological Properties of Lignin

    R. Bouhfid, A. E. K. Qaiss, M. Raji

    Abstract

    Lignin, a natural polyphenolic polymer, is a major by-product of the pulp and paper industry and has gained significant attention for its potential applications in sustainable material development. By elucidating the interactive dynamics of lignin within biological and composite systems, this chapter offers the morphological properties of lignin as advancing eco-friendly, high-performance materials in biomedicine, sustainable packaging, and other green technologies. This chapter provides a comprehensive overview of the morphological properties of lignin and their role in the synthesis of lignin nanoparticles (LNPs). The chemical structure, variability in plant sources, and influence of extraction methods on lignin morphology are discussed. Special emphasis is placed on the formation mechanisms, such as self-assembly and solvent exchange techniques, that drive the creation of LNPs. This chapter also explores the key factors affecting LNP performance, including pH, solvent selection, and processing parameters. Furthermore, potential applications of LNPs are highlighted, focusing on their use in drug delivery, environmental remediation, and high-performance biocomposites. This study underscores the importance of understanding lignin interactions with biological systems and composite matrices for optimizing future industrial applications. The insights provided aim to pave the way for developing eco-friendly, high-performance materials for use in biomedicine, packaging, and green technologies.

18. 17. Lignin Surface Area, Pores, and Surface Pore Distribution

    Ajay Kumar

    Abstract

    Lignin and lignin-derived porous carbon are widely used in adsorption, capacitors, and catalysis. It has a high surface area, large pore volume, and surface pore distribution. The specific surface area (S_BET) of lignin and lignin-derived carbon is determined by Brunauer–Emmett–Teller (BET) analysis, while the pore size distribution of lignin is obtained using BJH (Barrett–Joyner–Halenda) method based on adsorption isotherms. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) determine the surface pore structure of lignin. Lignin-based porous carbon is affected by several factors such as activator/lignin mass ratio, types of activators, and activation temperature on the surface morphology, specific surface area, and pore size distribution. Many connected pores effectively reduce the mass transfer resistance in lignin-based porous carbon.