Lignin Chemistry

In this paper, industrial lignins were characterized by elemental analysis (EA) and thermogravimetry (TG). The aim was to find the main intervals of lignin degradation and maximum rate of their degradation. The results obtained can be helpful in finding the applicability of the materials at their thermal decomposition. The differences between individual lignins have been confirmed by EA and TG.

In this paper, industrial lignins were characterized by elemental analysis (EA) and thermogravimetry (TG). The aim was to find the main intervals of lignin degradation and maximum rate of their degradation. The results obtained can be helpful in finding the applicability of the materials at their thermal decomposition. The differences between individual lignins have been confirmed by EA and TG.

Electrode and electrolyte materials with higher performance, longer life, and lower cost need to be developed, given the substantial growing demand for advanced electrochemical energy systems. Lignin, the second most abundant natural polymer, has been successfully demonstrated to be a viable precursor or feedstock for the preparation of high-performance electrochemical energy materials and components such as electrodes, electrolyte additives, membrane separators, and binders. Moreover, techno-economic analyses indicate that it is possible to prepare cost-effective carbon structures from lignin at engineering scale, in contrast with current carbon products. These facts suggest that the scalable conversion of lignin into high-value energy materials will offer a promising pathway to not only promote the utilization and valorization of lignin but also boost the development of advanced electrochemical energy systems. This review examines cutting-edge renewable energy materials derived from various lignin compounds and

In this paper, industrial lignins were characterized by elemental analysis (EA) and thermogravimetry (TG). The
aim was to find the main intervals of lignin degradation and maximum rate of their degradation. The results
obtained can be helpful in finding the applicability of the materials at their thermal decomposition. The
differences between individual lignins have been confirmed by EA and TG.

Trata-se de apresentação de seminário, exigido pela disciplina de Biorrefinaria da Lignina ministrada pelo professor Dr. Reinaldo Ruggiero, que compõe o programa de pós-graduação em Biocombustíveis das Universidade Federais do Vale do Jequitinhonha e Mucuri e de Uberlândia.
Foi utilizado o capítulo 19 da obra Bioenergia & Biorrefinaria: cana-de-açúcar & espécies florestais.

This article describes that the modification of lignin by incorporation of aromatic scavengers (2-
naphthol: AHN EOL and 1,8-dihydroxyanthraquinone: AHD EOL) during delignification process has
improved the physical properties of the lignin fractions. Smaller fragments of lignin with high phenolic
eOH content, increased solubility and antioxidant activity have led to improved inhibitive property of
the modified lignin. The inhibition efficiency (84e93%) of both modified lignin (500 ppm) were observed
to be better than unmodified organosolv lignin (EOL). It was deduced that the inhibition process was
spontaneous and the inhibitors were mainly physically adsorbed onto the mild steel surface.

Given the rise in demand for sustainable renewable biofuels and promising developments in cellulosic ethanol, the valorization of lignin has become essential for biorefining operations, esp. with today's low-cost energy prodn. state of affairs.  In the past 40 years, numerous efforts have been devoted to incorporate lignin and lignin derivs. into com. polymeric materials.  One of the promising strategies is to utilize multifunctional lignin macromols. or oligomers as the replacement of polyols during polyurethane synthesis.  In this review, recent advances in fabricating polyurethane foams, films, and adhesives with modified or unmodified lignins are examd.  The mech. and thermal properties of these lignin-based polyurethanes were correlated to their formulations, lignin mol. wt., and polydispersity, as well as the structural features of different lignin prepns.  Recalcitrance and strong intermol. interactions of lignin macromols. are known to prevent them from effective incorporation into other polymeric materials, covalently or noncovalently.  Therefore, this review intends to summarize the methods that improve the reactivity of lignin through chem. modification such as depolymn., demethylation, and chain extension.  Future developments and applications will be examd. with a special emphasis on tailoring lignin structure to specific application

Lignin is a complex macromolecule structure found in plants. Through appropriate degradation of lignin it is
possible to prepare chemicals with an added value. Therefore, it is important to use the best possible way for
lignin degradation. Powerful method for characterization of the degradation is thermal analysis and the
combination of pyrolysis with gas chromatography coupled with mass spectrometry. In this work, different
commercial and prepared lignins were investigated.

We present a review on the multifunctional use of ionic liquids with respect to lignin processing. In a biorefinery context, lignocellulosics could be used to provide sustainable sources of fuels such as bioethanol, and feedstock molecules for the chemical industry such as phenols and other aromatics. However, separation of lignin from cellulose and hemicellulose is a vital step. Ionic liquids can dissolve extensive quantities of biomass, and even be designed to be multifunctional solvents. We highlight the use of ionic liquids in selectively or non-selectively dissolving lignin, the depolymerization reactions that have been attempted on lignin in ionic liquids, and the effect ionic liquids have been observed to have on such processes. Finally, we present some of the challenges and issues that must be addressed before the informed and large-scale application of ionic liquids can be realized for lignin processing.

http://dx.doi.org/10.1071/CH12324

The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.

This paper evaluates the effect of addition of precipitated lignin, from spent pulping black
liquor, to a wet single-ply linerboard handsheet followed by hot-pressing at different
temperatures, on the improvement of its compressive strength. Linerboard handsheets for
testing the effect of lignin addition were prepared so that the lignin-modified sheets would
have the same basis weights as the control handsheets. Both the commercial and the black
liquor lignin were added as a powder to wet handsheets after couching from the handsheet
mold. The experiments and testing of the physical and strength properties of dried
handsheets were conducted according to TAPPI test methods. The results revealed that the
addition of the recovered lignin (at pH of 2) to the wet handsheet followed by hot-pressing
at 150°C increased the compressive strength of linerboard handsheets by 10% to 20%
above that for handsheets made without the addition of lignin. The same results were
achieved using purchased lignin. However, with a 16% addition to linerboard, purchased
lignin would be too expensive. These results indicate that inclusion of kraft lignin in
linerboard sheets could be proved as an attractive option to reduce linerboard basis weight.

Lignin is a recalcitrant polymer arising from addition polymerization of phenylpropanoid units via an
oxidative, enzyme-catalyzed radical mechanism. Lignin removal is a serious technological challenge in
wood-related industries such as pulping for paper production. In this review, some outstanding aspects
in lignin biosynthesis and structure are depicted; also the commonly used industrial protocols for pulp
delignification are described, with special emphasis on their molecular aspects. A discussion is presented
concerning the known chemical mechanisms of enzyme-catalyzed delignification by white-rot fungi.
Biomimetic and bioinspired synthetic metalloporphines show monooxygenase/peroxygenase-like catalytic
activity, being quite more versatile catalysts than ligninolytic enzymes (being capable only of
one-electron oxidations). The advantages of this behavior are encompassed with an in-depth discussion
about the molecular aspects of their action mechanisms, the possible oxygen donors, and the known
oxidizable substrates. Limitations and perspectives about their practical use at an industrial scale in
delignification processes are discussed.

Lignocellulosic biomass has been acknowledged for potential use to produce chemicals and biomaterials. Lignin is the second most abundant natural polymer with cellulose being number one, making up to 10–25% of lignocellulosic biomass. Lignin is a three-dimensional, highly cross-linked macromolecule composed of three types of substituted phenols, which include: coniferyl, sinapyl, and p-coumaryl alcohols by enzymatic polymerization, yielding a vast number of functional groups and linkages. There is a wide range of lignin sources available , including: jute, hemp, cotton, and wood pulp. Hence, the lignin's physical and chemical behavior will be different with respect to the original source and extraction method used. The objective of this research is to extract lignin from nonwood cellulosic biomass (Wheat straw, Pine straw, Alfalfa, Kenaf, and Flax fiber) by formic acid treatment followed by peroxy-formic acid treatment for the potential use as a partial replacement for the phenol precursor in resole phenolic systems. Isolated lignins were purified to remove impurities and characterized by Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) analysis to compare thermal properties and chemical composition. It was found that lignin obtained from alfalfa provided the greatest yield of the various sources. Enthalpy measurements were higher for lignin from flax fiber and alfalfa at 190.57 and 160.90 J/g, respectively. The source of lignin samples was seen to affect the thermal properties. Overall, lignin extracted from wheat straw had the greatest thermal stability followed very closely by that obtained from flax fiber.

Les bois traités à l'alun de la collection d'Oseberg sont extrêmement détériorés et ne supporteraient pas de traitements aqueux. Un traitement non-aqueux à base de lignine qui est imprégnée avec de l'acétate d'éthyle, est en cours de conception. Ici le travail est de voir la première étape : à savoir si la lignine peut pénétrer le bois archéologique afin de le consolider, et à quelle profondeur et quelle quantité. En effet, les sels d'alun ne pénétrant que 5mm sous la surface du bois, des fissures ont eu lieu lors du séchage entre les deux zones (avec et sans alun). Les bois archéologiques médiévaux envoyés par NIKU pour les tests seront imprégnés de deux sortes de lignines envoyées par le laboratoire WFBR (Wageningen Food and Biobased Research) ayant deux poids moléculaires différents, avant d'être imprégnés à différents taux de concentration, et comparés avec d'autres échantillons imprégnés de PEG 2000 dans de l'eau.
Les résultats notamment à l'IRTF et au MEB montrent que la meilleure pénétration de lignine (à cœur des échantillons) à été faite avec les échantillons imprégnés avec 30% de lignine FBO1 dans de l'acétate d'éthyle. La poudre semble avoir tapissé les parois cellulaire, ce qui respecte le critère de re-traitement (elle ne remplit pas complètement les pores). D'autres tests seront fait plus tard afin de mesurer la dureté des échantillons imprégnés, et le polymère sera développé afin de permettre une polymérisation in situ en utilisant des agents de réticulation.

The study is aimed at detection of hydrogen peroxide (H2O2) using Acacia lignin mediated silver nanoparticles (AGNPs). The synthesis of AGNPs was achieved at conditions optimized as, 3 ml of 0.02% lignin and 1 mM silver nitrate incubated for 30 min at 80 °C and pH 9. Initial screening of AGNPs was performed by measuring the surface plasmon resonance peak at 410–430 nm using UV–vis spectrophotometer. Transmission electron microscopy, atomic force microscopy, X-ray diffraction and particle size analysis confirmed the spherical shaped face centered cubic structure and 10–50 nm size of AGNPs. The infrared spectroscopy study further revealed that the active functional groups present in lignin were responsible for the reduction of silver ions (Ag+) to metallic silver (Ag0). Lignin stabilized silver nanoparticles showed good sensitivity and a linear response over wide concentrations of H2O2 (10−1 to 10−6 M). Further, the in vitrocytotoxicity activity of the lignin mediated AGNPs (5–500 μg/ml) demonstrated toxicity effects in MCF-7 and A375 cell lines. Thus, lignin stabilized silver nanoparticles based optical sensor for H2O2 could be potentially applied in the determination of reactive oxygen species and toxic chemicals which further expands the importance of lignin stabilized silver nanoparticles.

In this work, lignin polyols were prepared from the liquefaction of kraft lignin and from the direct liquefaction of Elaeis guineensis lignocellulosic waste. The liquefaction reaction was performed with polyhydric alcohols using sulfuric acid as catalyst at 160 °C. The physical and chemical characterizations of lignin and lignin polyols were conducted by elemental analysis, Fourier transform-infrared spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, molecular weight distribution, and thermogravimetric analysis (TGA). Quantitative 13C NMR showed that all aliphatic hydroxyl group values of polyols noticeably increased with the use of the two methods compared to kraft lignin. The average molecular weight analysis of the liquefied product showed that it exhibited high molecular weight compared to kraft lignin. Both structural and thermal characteristics suggest that lignin polyols would be a good substitute for kraft lignin in the synthesis of polymeric compounds such as environmentally friendly resins or wood adhesives, as it presents higher amounts of activated free ring positions, higher molecular weight, and high thermal stability.

Current processes for the fractionation of lignocellulosic biomass focus on the production of high-quality cellulosic fibers for paper, board, and viscose production. The other fractions that constitute a major part of lignocellulose are treated as waste or used for energy production. The transformation of lignocellulose beyond paper pulp to a commodity (e.g., fine chemicals, polymer precursors, and fuels) is the only feasible alternative to current refining of fossil fuels as a carbon feedstock. Inspired by this challenge, scientists and engineers have developed a plethora of methods for the valorization of biomass. However, most studies have focused on using one single purified component from lignocellulose that is not currently generated by the existing biomass fractionation processes. A lot of effort has been made to develop efficient methods for lignin depolymerization. The step to take this fundamental research to industrial applications is still a major challenge. This review covers an alternative approach, in which the lignin valorization is performed in concert with the pulping process. This enables the fractionation of all components of the lignocellulosic biomass into valorizable streams. Lignocellulose fractions obtained this way (e.g., lignin oil and glucose) can be utilized in a number of existing procedures. The review covers historic, current, and future perspectives, with respect to catalytic lignocellulose fractionation processes.

In this paper, industrial lignins were characterized by elemental analysis (EA) and thermogravimetry (TG). The aim was to find the main intervals of lignin degradation and maximum rate of their degradation. The results obtained can be helpful in finding the applicability of the materials at their thermal decomposition. The differences between individual lignins have been confirmed by EA and TG.

Lignin is the second most natural organic polymer on the earth and it can be acquired from the wastes of wood pulping processing in the form of black liquor. The inhibition efficiencies of Kraft lignin (KL) and Soda lignin (SL) on the corrosion of mild steel in 3.5% (w/v) sodium chloride at two levels of pH have been evaluated by weight loss method, electrochemical techniques and surface analysis using 50-800 ppm (w/v) inhibitor concentration at 25 °C. Both KL and SL can perform as good inhibitors for the above-mentioned system. The KL gave maximum inhibition efficiencies of 95 and 92% for pH 6 and pH 8, respectively at high concentrations of inhibitor, whereas SL gave 97 and 95% inhibition efficiencies for pH 6 and pH 8, respectively at 800 ppm of inhibitor concentration. Polarization studies confirmed that KL and SL are mixed type inhibitors. Both KL and SL obey Langmuir’s adsorption isotherm at two levels of pH and 25 °C. FT-IR and surface analyses confirmed that the surface of mild steel was affected by the adsorption of lignin onto the surface to form ferric-lignin compounds. The rust components especially lepidocrocite were reduced; hence, lignin can be used as a rust converter.

A mixed metal-oxide (NiAlO x) obtained from the annealing of a synthetic takovite clay, [(Ni 6 Al 2 (OH) 16 ]CO 3 ·4H 2 O, was used as a catalyst in the hydrodeoxygenation reaction of vanillin, as a model molecule, to simulate deoxygenation of lignin's moieties. The catalysts were characterized by XRD, TPR, XPS and textural analyses and were tested at between 413 and 573 K and 1.2 MPa H 2 , using a 300 ml batch reactor. The reaction products were analyzed using a gas-chromatograph coupled to a mass detector (GC-MS). The active site is visualized as a Ni δ+-O-Al 3+ moieties able to dissociate molecular H 2 into highly reactive species (H − and H +) for hydrogenation reactions. Depending on the reaction temperature, decarbonylation, hydrogenation, demethoxylation and dehydroxylation reactions occurred in three stages as clearly indicated by Van-Krevelen O/C* vs. H/C* plots. Our study points out that total deoxygenation can be attained at 553 K with a 100% selectivity to products like methyl-cyclohexane and cyclohexane. Graphic Abstract Keywords Takovite-type material · NiAlO x mixed oxides catalyst · Vanillin · Lignin · Hydrodeoxygenation.

Resole phenol formaldehyde resins have been used in various applications due to their outstanding physical and chemical properties, flame retardancy, solvent resistance, and thermal stability. However, there are major disadvantages associated with synthesis of resole phenol formaldehyde resins including health risks. One such disadvantage involves the toxic effects of phenol and formaldehyde chemical precursors on the humans. Many studies have been done using renewable resources such as lignin, as partial replacement with the phenolic synthesis starting precursors to produce less hazardous materials. Lignin is a three-dimensional, highly cross-linked macromolecule composed of three types of substituted phenols; coniferyl, sinapyl, and p-coumaryl alcohols by enzymatic polymerization, yielding a vast number of functional groups and linkage. As a natural and renewable raw material, obtainable at an affordable cost, and great chemical and physical properties, lignin's substitution potential extends to many products currently sourced from petrochemical substances. In order to produce less hazardous materials, the goal of the current research is geared towards the synthesis of novel resole phenolic type systems based on the most thermally stable lignin extracted from different biomass resources. Lignin was extracted from wheat straw, pine straw, alfalfa fiber, and flax fiber by formic/acetic acid treatment followed by peroxyformic/acetic acid treatment. Obtained lignin from each source was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for structural, thermal and chemical composition comparison. In addition, void-free, homogenous, solid novel resole phenolic type resin systems have been synthesized using various ratios of the extracted lignin for the phenol precursor. Resulting novel resole phenolic-type systems were characterized using TGA.

Biological lignin valorization represents an emerging green approach to upgrade lignin for sustainable and economic biorefineries. However, lignin generally exhibits poor water solubility and inhomogeneous distribution in an aqueous medium, significantly limiting its bioconversion efficiency. Herein, we develop a novel alkali sterilization strategy to effectively enhance the dispersion and fermentation performance of lignin substrates. The colloidal particle size and molecular structure variations of lignin during the sterilization were thoroughly investigated to reveal the mechanisms of enhanced fermentation performance. Results showed that alkali sterilization achieved a completely aseptic effect when mixing lignin medium at an initial pH of 12.7 for 24 h. Dynamic light scattering (DLS) analysis demonstrated that the hydrodynamic volume of colloidal lignin particles decreased by 96.3% by alkali sterilization compared with the conventional thermal sterilization. Moreover, lignin characterizations by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) suggested that alkali sterilization modified the lignin molecular structure by generating 50% more hydrophilic carboxyl groups, reducing the weight-average molecular weight (M w) by 23.0%, and narrowing the molar-mass dispersity (Đ M) by 23.8%. The generation of lignin substrates with more uniform distribution and lower molecular weight improved Rhodococcus opacus PD630 cell growth and metabolism. Microbial cell amount, lignin degradation, and lipid production in alkali sterilized medium increased by 309%, 30.3%, and 48.3%, respectively, compared to those in thermally sterilized medium. These results clearly demonstrated that alkali sterilization dramatically improved the lignin bioconversion performance. This work presents a facile and effective sterilization strategy to overcome inhomogeneous lignin distribution in aqueous fermentation media, showing great potentials as a platform technique for promoting biological lignin valorization.

A shift towards an economically viable biomass biorefinery concept requires the use of all biomass fractions (cellulose, hemicellulose, and lignin) for the production of high added-value products. As lignin is often underutilized, the establishment of lignin valorization routes is highly important. In-house produced organosolv as well as commercial Kraft lignin were used in this study. The aim of the current work was to make a comparative study of thermoplastic biomaterials from two different types of lignins. Native lignins were alkylate with two different alkyl iodides to produce ether-functionalized lignins. Successful etherification was verified by FT-IR spectroscopy, changes in the molecular weight of lignin, as well as 13 C and 1 H Nuclear Magnetic Resonance (NMR). The thermal stability of etherified lignin samples was considerably improved with the T 2% of organosolv to increase from 143 • C to up to 213 • C and of Kraft lignin from 133 • C to up to 168 • C, and glass transition temperature was observed. The present study shows that etherification of both organosolv and Kraft lignin with alkyl halides can produce lignin thermoplastic biomaterials with low glass transition temperature. The length of the alkyl chain affects thermal stability as well as other thermal properties.

Modification of lignin with poly(ε-caprolactone) is a promising approach to valorize industrial low-value lignins and to advance the bioeconomy. We have synthesized lignin grafted poly(ε-caprolactone) (lignin-g-PCL) co-polymers via ring-opening polymerization of ε-caprolactone with different types of lignins of varying botanical sources (G-type pine lignin, S/G-type poplar lignin, and C-type Vanilla seeds lignin) and lignin extraction methods (Kraft and ethanol organosolv pulping). The lignin-g-PCL copolymer showed remarkably improved compatibility and dispersion in acetone, chloroform, and toluene in comparison to non-modified lignins. The structure and thermal properties of the lignin-g-PCL were investigated using Fourier-transform infrared spec-troscopy (FTIR), 31 P nuclear magnetic resonance (NMR), 2D heteronuclear single quantum correlation (HSQC) NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). We have found that all the technical lignins were reactive to the copolymerization reaction regardless of their plant source and isolation methods. The molecular weights of the synthesized lignin-g-PCL copolymers were positively correlated with the content of aliphatic lignin hydroxyls, suggesting that the copolymerization reaction tends to occur preferentially at the aliphatic hydroxyls rather than the phenolic hydroxyls of lignin. Thermal analyses of the lignin-g-PCL copolymers were studied, and in general, a reduction of melting temperature and crystallinity percentage in comparison to the neat PCL was observed. However, the thermal behavior of lignin-g-PCL co-polymers varied depending on the lignin feedstocks employed in the copolymerization reaction. Introduction The practical utilization of lignin from lignocellulosic biomass is critical for the accelerated development of the bioeconomy and circular carbon economy. Lignin is the second most abundant terrestrial polymer (15− 40% by weight, 40% by energy) of lignocellulosic biomass after cellulose [1]. A large quantity of lignin (~62 million tons), is generated annually from chemical pulping, and biorefining processes [1]. Lignin attracts tremendous interest due to its aromatic structure with high functional groups and carbon densities that can afford, in principle, a broad array of bio-derived chemicals, polymers, and materials. It has historically been burned for energy and chemicals recovery in the pulping industry; however, less than 2% of industrial lignin has been valorized to profitable chemicals and products, such as fillers, additives, dispersants, adhesives, surfactants, and UV blockers [2-4]. The brittle nature of lignin, along with its highly complex 3D structure and incompatibility with nonpolar polymers, raise substantial challenges to its valorization. To exploit inexpensive lignin resources into high-value polymers and composites, three types of technical approaches are generally utilized, namely (1) direct incorporation of lignin to polymer for composites; (2) chemical modification of lignin and lignin copoly-merization to generate products with novel properties; and (3) cracking

The formation of lignin-like structures by the degradation primarily of plant polysaccharides has been observed after the severe thermochemical acidic pretreatment of lignocellulosic biomass. These structures were found to be deposited as droplets and microspheres on the surface of solid biomass residue and/or in liquid effluent. These structures showed lignin-like properties and yielded a positive Klason lignin (K-lignin) value, and are termed pseudo-lignins and/or humins. Pseudo-lignin is an aromatic material containing hydroxyl and carbonyl functional groups, which contributes to K-lignin values but is not derived thereof. Pseudo-lignin arises from the polymerization/condensation reactions from key inter-mediates such as 3,8-dihydroxy-2-methylchromone and 1,2,4-benzenetriol derived from furfural (FF) and 5-hydroxymethylfurfural (5-HMF), respectively. Furthermore, pseudo-lignin retards the biological conversion of pretreated biomass through unproductive binding to enzymes/microbes and a physical hindrance to enzymes and microbes by blocking the active cellulose surface binding sites. This necessitates a fundamental understanding of the pseudo-lignin structure and its effect on biomass recalcitrance. This review examines the pseudo-lignin formation during acidic and hydrothermal biomass pretreatments and the cooling process after pretreatment, which are applied to biomass for biofuel synthesis through a biochemical route. The review article is divided into five parts: the first part gives the background information on pseudo-lignin formation during different pretreatment processes for the conversion of biomass to bio-fuels, the second part focuses on the chemistry and mechanism of pseudo-lignin formation, the third part emphases on the different analytical techniques used for pseudo-lignin characterization and recalci-trance elucidation, the fourth part illustrates the recalcitrance behaviour of pseudo-lignin, and the fifth part deals with the practical consideration regarding the design of the processes for the prevention of pseudo-lignin formation.

This work investigates the potential of converting kraft lignin, which is a by-product in paper industry, into value-added bio-products using microwave pyrolysis. In this presentation, a detailed compositional analysis and structural investigation of a bio-oil produced at various conditions will be discussed. Different analysis techniques were performed on the obtained oil, such as GC-MS, 31P NMR, and 13C NMR. Different degradation pathways based the obtained analyses will be explained. In addition, three different kinetic models will be presented: the first model, considers the virgin material converted into solid, condensable gas, and non condensable gas. The second model distinguishes between the water and the chemicals extracted in the condensable gas. The third model presents further investigations for the extracted chemicals in the oil phase. Finally, a simulation for the phenolics yield at different pyrolysis conditions will be presented.

Lignin is a complex macromolecule structure found in plants. Through appropriate degradation of lignin it is possible to prepare chemicals with an added value. Therefore, it is important to use the best possible way for lignin degradation. Powerful method for characterization of the degradation is thermal analysis and the combination of pyrolysis with gas chromatography coupled with mass spectrometry. In this work, different commercial and prepared lignins were investigated.