Lignin Chemical Structure Research Articles

Revealing the intensification effect of circulating hydrothermal pretreatment: A sustainable route for biorefinery

Hydrothermal pretreatment (HTP) has received huge progress in converting biomass waste into available products at a large scale, but challenges in massive water input and wastewater output still block sustainable biorefinery future. Herein, a circulating hydrothermal technique was proposed by reusing the process wastewater into the next HTP process to enhance energy efficiency and suppress the environmental burdens. During hydrothermal liquid (HL) recycling, the variation of lignin chemical structure, cellulose accessibility, and soluble components were investigated for an in-depth understanding of what happened to lignocellulose. An enhanced hemicellulose dissolution (from 78.1 % to ∼ 85 %) was achieved by the aqueous phase recycling. The reactions of dehydration and polymerization occurred during the circulating HTP process, which contributed to the generation of pseudo-lignin on the cellulose surface, causing a slight weakening of cellulose accessibility. Meanwhile, the organic acid-catalyzed hydrothermal process can facilitate the cleavage of lignin β-O-4 ether linkage and condensation reaction, endowing its potential amphiphilic properties. An in-depth analysis of the evolution of HL components substantiated the potential intensification effect on biomass deconstruction by the generation of hemicellulose-derived organic acids. Life cycle assessment revealed that the circulating HTP technique resulted in about a 29 % reduction in primary energy depletion and an order of magnitude reduction in CO2 emissions as opposed to that of the conventional one. This work unveils the structure evolutions of lignocellulose clearly during the HL recycled process, and also highlights a feasible route for the sustainable biorefinery.

Delignification of Different Lignocellulosic Biomass Using Hydrogen Peroxide and Acetic Acid (HPAC)

Lignocellulosic biomass will soon become the key source of feedstock for bioenergy to combat the impact of global warming and the depletion of fossil fuel resources. Lignin separation costs have been a key obstacle to bioenergy generation from lignocellulosic biomass. Pulp and paper, biofuel, and biomaterials sectors depend on wood delignification. This study examines delignification trends and advances, including standard and new methods. The study begins by explaining how delignification improves wood processability and value. It describes lignin's chemical structure and properties, highlighting its role in wood's mechanical and chemical qualities. Lignin from diverse lignocellulosic biomass sources is delignified using hydrogen peroxide and acetic acid in this study. A 1:1 hydrogen peroxide-acetic acid volume ratio was used after particle reduction. Experimental results show 96%, 89%, and 80% lignin removal efficiency for Ako, Mahogany, and mixed sawdust, respectively. A 30-minute reaction at 80°C yielded these results. The hydrogen peroxide-acetic acid mixture dignifies well and may be used in lignocellulosic biomass processing. This study also provides insights into optimizing delignification procedures and suggests approaches to improve the industrial use of lignocellulosic biomass. This study reveals that HPAC dignifies wood well. Understanding HPAC's role in the delignification of wood products could lead to developing an HPAC-based pretreatment technique that lowers the cost of biofuel generation from lignocellulosic biomass.

Rapid Lignin Thermal Property Prediction through Attenuated Total Reflectance-Infrared Spectroscopy and Chemometrics.

To expedite the valorisation of lignin as a sustainable component in materials applications, rapid and generally available analytical methods are essential to overcome the bottleneck of lignin characterisation. Where features of a lignin's chemical structure have previously been found to be predicted by Partial Least Squares (PLS) regression models built on Infrared (IR) data, we now show for the first time that this approach can be extended to prediction of the glass transition temperature (Tg), a key physicochemical property. This methodology is shown to be convenient and more robust for prediction of Tg than prediction through empirically derived relationships (e. g., Flory-Fox). The chemometric analysis provided root mean squared errors of prediction (RMSEP) as low as 10.0 °C for a botanically, and a process-diverse set of lignins, and 6.2 °C for kraft-only samples. The PLS models could separately predict both the Tg as well as the degree of allylation (%allyl) for allylated lignin fractions, which were all derived from a single lignin source. The models performed exceptionally well, delivering RMSEP of 6.1 °C, and 5.4 %, respectively, despite the conflicting influences of increasing molecular weight and %allyl on Tg. Finally, the method provided accurate determinations of %allyl with RMSEP of 5.2 %.

Towards an enhanced nanocarbon crystallization from lignin

In this work, a new approach to the synthesis of lignin-derived nanocarbon crystals based on lignin depolymerization is proposed. The lignin chemical structure was modified through a controlled routine, which was based on sequential UV light irradiation, hydrothermal carbonization in autoclave, vacuum degassing, pyrolysis and mechanical exfoliation. In this way, we were able to obtain a lignin-based nanocarbon with a sp2-hybridized nanoporous framework structure with oxygenated functional groups attached to this structure. The used catalyst-free route resulted in high nanocarbon yields and turns out to be an eco-friendly strategy of a synthesis of low-cost carbon materials. The characterization of the lignin-derived nanocarbon was carried out using X-ray diffraction measurements, infrared, Raman and X-ray photoelectrons spectroscopies analyses. The nanocarbon materials' morphology was evaluated by scanning and transmission electron microscopy. The method of lignin's transformation developed in this work showed itself as a promising alternative for provision of large amounts of carbon-based materials for industrial applications. The proposed approach may be adapted to various biomass feedstocks with aromatic groups' content suitable for their high yield polycondensation. The achieved nanocarbon yield, when starting from a commercial purified lignin, varied between 50 wt% and 70 wt%.

Selective catalytic conversion of Kraft lignin into monoaromatic hydrocarbons over niobium oxide catalysts

Catalytic fast pyrolysis (CFP) of lignin targeting for benzene, toluene and xylenes is attractive considering lignin's chemical structures. Zeolites have been widely used for producing aromatic hydrocarbon via a well-known hydrocarbon pool mechanism from lignocellulose pyrolysis vapors because of their unique shape-selective catalytic abilities, however, the large amount of phenols existing in the product reveals the catalyst's deficiency in direct deoxygenating of phenols. Finding a catalyst with a strong deoxidization ability against various lignin pyrolysis intermediates is necessary. Here, two niobium oxide-based catalysts, niobium oxophosphate (m-NbOP) and niobium oxide (m-NbO) with uniform mesoporous structures (pore sizes of 2-5 nm), large external areas (487 m2·g−1 for m-NbOP and 244 m2·g−1 for m-NbO), and strong acidities (1.25 mmol·g−1for m-NbOP and 0.69 mmol·g−1 for m-NbO) were synthesized and used without need for hydrogen in lignin CFP at 650 °C. Compared to zeolites, both niobium oxide-based catalysts considerably increased aromatic's contents and the selectivity to benzene, toluene, and xylenes but decreased the contents of phenols to some extent, indicating the improved abilities in direct deoxygenation by aromatic CO bond cleavage of lignin. A total carbon yield of benzene, toluene and xylenes of 39.2% was achieved over m-NbOP.

The usage of lignin in two significant applications: As adsorbent surface of water pollutants and antioxidant of plastic polymers: short review

Since pollution is very serious problem threating the environmental eco-system around the world, but people do not usually treat this issue properly. Water is contaminated with different type of pollutants such as organic, inorganic, heavy metals, pesticides, dyes, phenols, and many other pollutants. Using adsorption phenomenon is very practical, easy and common method to remove pollutants from water. Owing to the significant properties of lignin such as high surface area, porosity, availability in huge amount, it was chosen to be used as an adsorbent surface of various pollutants. Herein it is going to review some of important literatures regarding that. Another serious problem that is threatening the marine eco-system, human health, and influence the global warming is the huge consumption of plastic polymers every year. Thus, reducing the consumption of plastic polymers is significantly matter. Lignin chemical structures are highly oxygenated and have several aromatic units, so by definition lignin can act as an antioxidant, free radical scavenger and photo-stabilizers. As the chemical structure of monomer moieties to form lignin are highly aromatic so it is suitable to work as UV- blocker to stop the photo-degradation of plastic.

Effect of lignin structure in different biomass resources on the performance of lignin-based carbon nanofibers as supercapacitor electrode

Lignin is proposed to an attractive stuff for fabricating functional composite nano-carbon materials owing to its high carbon yield and low-cost. In this work, in order to unlocking the mechanism of the plant species of lignin on electrochemical energy storage capacity of lignin-based carbon nanofibers (LCNFs), three typical lignin from representative hardwood (poplar, PR), softwood (pine, PE) and grass (corn stalk, CS) materials, and containing different structural units (syringyl units (S), guaiacyl units (G), and/or p-hydroxyphenyl unit (H)) were chosen to prepare LCNFs with polyacrylonitrile (PAN) as blending agent. As compared with other LCNFs, poplar lignin (PRL) based LCNFs-PRL (5:5) with independent filamentous morphology networks exhibited higher tensile strength of 35.32 MPa, greater specific surface area of 1062.5 m2/g and larger specific capacitance of 349.2 F/g. Moreover, in a two electrode system, the assembled LCNFs-PRL (5:5)//LCNFs-PRL (5:5) symmetric supercapacitor also displayed an excellent energy density of 39.6 Wh/kg at the power density of 5000 W/kg and outstanding cycling stability of 90.52 % after 5000 cycles in Na2SO4 aqueous electrolyte. The results proved that hardwood lignin was a good green raw material for LCNFs. The mechanism of lignin chemical structure on the properties was demonstrated in detail by various characterization analysis, such as electrochemical test, nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC), which indicated that the structural units, molecular weight, homogeneity, hydrophilic and hydrophobic groups of lignin were more important for fabricating high quality LCNFs.

Lignin dissolution model in formic acid–acetic acid–water systems based on lignin chemical structure

The separation of lignin from woody biomass and subsequent conversion into useful products requires a solution to the problem of its solubility. The expanded C9 formula of lignin, along with its atomic and functional groups, was determined by elemental analysis and NMRs spectroscopy. Based on the thus-obtained expanded C9 formula, the cohesion parameters of lignin dispersion (10.8–11.1 cal1/2·cm−3/2), polarity (4.15–4.31 cal1/2·cm−3/2), hydrogen bonding (6.30–7.38 cal1/2·cm−3/2), and solubility (13.2–14.0 cal1/2·cm−3/2) were respectively calculated using atomic and functional group contributions method. We established the relationship between lignin structure and lignin solubility parameters. The dissolution characteristics of wheat straw organic acid lignin, industrial eucalyptus kraft lignin, bamboo kraft lignin, and softwood kraft lignin in formic acid–H2O, acetic acid–H2O, and formic acid–acetic acid–H2O solvent systems were analyzed. The results indicate that the dissolution behavior of lignins follows the solubility parameters theory. We have developed a lignin dissolution model according to the lignin structure. This model obeys the solubility parameter theory, overcomes the limitations of the “like dissolves like” principle in organic acid–water systems, and provides a concise method for the selection of lignin solvent systems and the quantitative determination of their solvent composition.

Kraft Lignin Solubility and Its Chemical Modification in Deep Eutectic Solvents

Lignin stands as a promising raw material to produce commodities and specialty chemicals, yet its poor solubility remains a big challenge. Recently, deep eutectic solvents (DES) have been proposed as sustainable solvents with high potential to dissolve and valorize lignin. In the present study, the ability of DES based on cholinium chloride ([Ch]Cl) combined with alcohols and carboxylic acids as hydrogen bond donors (HBDs) to dissolve kraft lignin and to change its chemical structure was examined. The influence of the chemical nature of HBDs, water content, and HBD:hydrogen bond acceptor (HBA) molar ratio on the solubility of kraft lignin in DES was studied (313.15 K). The kraft lignin solubility was enhanced by increasing both the HBD’s carbon chain length and the molar ratio, with [Ch]Cl:HEXA (1,6-hexanediol) and [Ch]Cl:MaleA (maleic acid) being the best studied solvents for kraft lignin dissolution, while the addition of water was a negative factor. The thermal treatments (393.15 K) of kraft lignin show that carboxylic acid-based DES promote chemical modifications to kraft lignin, including the disruption of several C–O covalent type bonds (e.g., β-O-4, α-O-4 and α-O-α), while alcohol-based DES were found to be nonderivatizing solvents maintaining the lignin chemical structure. These results show the versatility of DES, which, depending on their chemical nature, may offer distinct strategies for lignin valorization.

Structural characterization of sugarcane lignins extracted from different protic ionic liquid pretreatments

Previous studies based on protic ionic liquids have shown them to be effective for extracting lignins from biomass. Moreover, ILs synthesized with amine cations can promote the insertion of nitrogen into lignin, favoring its valorization for industrial applications. In this study, lignins extracted from sugarcane bagasse by eight different PILs were analyzed. Several techniques of characterization were employed (2D HSQC NMR, 31P NMR, GPC, Py-GC/MS, TGA, FTIR, and elemental analysis), seeking a deeper understanding of lignin structure post-PILS treatment. In particular, lignin obtained with acetate and lactate anions with monoethanolamonium cations showed similar structural compositions. Lignins obtained from ethylenediamonium cation combined anions acetate and lactate exhibited relatively higher molecular weights compared to the other lignins studied. The elemental analysis of these lignins further revealed the presence of nitrogen in their structures, suggesting that amination occurred. In this work we used PILs not yet reported in the literature for this purpose, and consequently obtained lignins with specific structures. Overall, our results demonstrated that depending on the PILs used, lignins with distinct properties could be obtained which might be used for value-added applications. This work covered new advances in elucidation of lignin chemical structure and opened a new path for lignin valorization. • Lignin extracted by [2He][Ac] and [2He][Lac] showed a preserved structure. • Lignin extracted by [Etid][Ac] and [Etid][Lac] exhibited relatively higher molecular weight. • All lignins samples revealed the presence of nitrogen in their structures. • Protic ionic liquids can support lignins industrial applications for chemicals products.

Evolution of the Lignin Chemical Structure during the Bioethanol Production Process and Its Inhibition to Enzymatic Hydrolysis

To illuminate the lignin evolution after hydrogen peroxide presoaking prior to ammonia fiber expansion pretreatment (H-AFEX) pretreatment and enzymatic hydrolysis, ball-milled wood lignins were sep...

Preparation and characterization of lignin nanoparticles from rice straw after biosynthesis using Lactobacillus bulgaricus

Lignin is the most abundant aromatic natural polymer and comprises about 25% of straw biomass. Nanolignin biosynthetic production method is a simple method and safely better than chemical or physical methods. It has an interest in using lignin in more advanced applications. In particular, lignin-based nanoparticles could find potential application use in functional surface coatings, nano glue, drug delivery, microfluidic devices, and food additive. This study aimed to optimize Lactobacillus bulgaricus in nano lignin synthesis, the effect of the incubation period and freeze-drying on the quality of the nanolignin. Lignin particles were biosynthesized using rice straw and Lactobacillus bulgaricus in a dark place with a temperature of 37°C for 24 hours, 48 hours, and 72 hours. Lignin nanoparticle was characterized using Fourier Transformer Infrared Spectroscopy (FTIR), Particle Size Analyzer (PSA), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX). Theresults indicated that nano lignin has a spherical and amorphous shape. The average size of particles is 101.6 nm with an incubation period of 24 hours, 57.2 nm with an incubation period of 48 hours, and 276.9 nm with an incubation period of 72 hours. The incubation periods affect the size and shape of nanolignin and also show that the lignin chemical structure is within the nanoparticle formation process. Samples using freeze-drying enable have natural antibacterial compounds and have phenolic fragments containing recommended for nano preservatives.

Transparent Cellulose/Technical Lignin Composite Films for Advanced Packaging.

Although recent work has shown natural lignin products are promising to fabricate various polymer based functional composites, high-value applications were challenged by their structural complexity and inhomogeneity. This work specially assessed the potential of four technical lignins for cellulose based functional films production. These four technical lignins were obtained by emerging pretreatment systems, i.e., lactic acid-betaine deep eutectic solvent (DES), ethanol organosolv, soda/anthraquinone (Soda/AQ) and the sodium salicylate hydrotrope, and their phenolic substructures were comparatively identified by prevalent 31P NMR technique. The influence of lignin chemical structure on the antioxidant potential and UV-shielding performance of the prepared cellulose/technical lignin composite films were assessed. Results showed severe organosolv and soda/AQ pretreatment produced technical lignins with higher total phenolic hydroxyl groups (3.37 and 3.23 mmol g-1 respectively), which also exhibited higher antioxidant activities. The composite films could effectively block the ultraviolet lights especially for UVB region (ultraviolet B, 280–315 nm) at only 5 wt.% lignin content. The contribution of lignin phenolic substructures to both antioxidant activity and UV-shielding property from high to low was syringyl > guaiacyl > p-hydroxyphenyl phenolic hydroxyl groups. This work provided some useful information that could facilitate upstream lignin extraction or downstream value-added applications.

Thermo-mechanical behavior of genetically modified Populus trichocarpa

Wood processing is often performed at elevated temperatures under moisture-saturated conditions; therefore, it is important to understand the impact of the lignin content and lignin chemical structure on the thermo-mechanical properties of wood. In this study, genetically modified Populus trichocarpa wood specimens with down-regulated cinnamyl alcohol dehydrogenase, cinnamate 3-hydroxylase, and cinnamate 4-hydroxylase with altered lignin contents and/or lignin structures were utilized to probe the relationship between the lignin content, lignin monomer composition, and thermo-mechanical properties of solid wood. The thermo-mechanical properties of these unique samples were measured using dynamic mechanical analysis and the nuclear magnetic resonance (NMR) spin-spin relaxation time. The results showed that the transgenic P. trichocarpa samples had decreased storage and loss moduli compared with the wildtype. The solid-state NMR revealed increased lignin molecular mobility in the reduced-lignin transgenic lines. Also, noticeably reduced glass transition temperatures (Tg) were observed in the transgenic lines with reduced lignin contents and altered lignin monomer compositions compared with the wildtype. The increased lignin molecular mobility and reduced Tg in these samples can probably contribute to wood utilization and processing, such as lignin removal for pulp and paper and biofuels production, as well as particle consolidation during wood composite manufacturing.

TSA-MS characterization and kinetic study of the pyrolysis process of various types of biomass based on the Gaussian multi-peak fitting and peak-to-peak approaches

Slow pyrolysis characterization and kinetic modeling study of five different biomasses (corn brakes (CB), wheat straw (WS), hazelnut shell (HS), sawdust (Beech), and sawdust chemically treated (SDCT)) were performed in this work, using STA-MS techniques. Thermal decomposition of these samples was divided into three stages corresponding to removal of water, devolatilization, and formation of bio-char. Mass spectrometry (MS) showed that H2, CH4, H2O, CO2 (C3H8), CO, and C2H6 were the main gaseous products released during the pyrolysis of biomasses. It was found that H2O, CO and CO2 evolutions for all biomass samples arise from lignin source in biomass, followed by the cellulose, and hemicelluloses. It was established that the pseudo-component fraction estimated by the theoretical calculations is dependent on the heating rate. Using Gaussian multi-peak fitting and peak-to-peak approaches, regardless of the type of biomass, it was found that decomposition of lignin occurs independently of decomposition of remaining two pseudo-components and that there is no interaction between them. Namely, it was assumed that during pyrolysis process of biomasses, carbohydrate (hemicelluloses + cellulose)—lignin chemical structures most likely exist, where the variety of lignin structure units in different types of biomass affects on the level of energy required for its decomposition.

Lignin/Polyacrylonitrile Carbon Fibers: The Effect of Fractionation and Purification on Properties of Derived Carbon Fibers

The effects of lignin chemical structures on the quality of lignin-based carbon fibers are still not clear. For this reason, we address the challenge by using a simple acid precipitation method to separate and purify lignin and study the effects of physicochemical characteristics of fractionated lignin on the properties of lignin-based CFs. The precipitation carried out by sequential acidification at different pH levels (10, 8, 6, 4, and 2) is indeed effective in obtaining fractionated lignin samples with different chemical structures, including molecular weights, units’ composition ratios, and polydispersity indexes (PDIs). All the fractionated lignin samples are respectively blended with polyacrylonitrile at the ratio of 1:1 (w/w) and electro-spun into fibers. Results suggest that a fractionated lignin sample with a large molecular weight, low PDI, and strong thermal stability can produce carbon fibers with excellent performance, such as good spinnability, high crystallization, and mechanical strength.

Comparative analysis of lignin chemical structures of sugarcane bagasse pretreated by alkaline, hydrothermal, and dilute sulfuric acid methods

To understand the lignocellulose properties of sugarcane (Saccharum sp.) bagasse with a view to its application to produce fermentable sugars, we comparatively analyzed lignocellulose properties, especially lignin chemical structures, of bagasse before and after alkaline, hydrothermal, and dilute sulfuric acid pretreatments. Wet chemical analyses and two-dimensional nuclear magnetic resonance spectroscopy determined that lignocellulose from untreated bagasse contained similar levels of guaiacyl (G) and syringyl (S) lignins with lower levels of p-hydroxyphenyl (H) and tricin (T) lignins. Alkaline pretreatment preferentially removed S and T lignins from bagasse, whereas the hydrothermal and dilute sulfuric acid pretreatments had the effect of enriching lignins (except T lignin) by reducing xylans and arabinans. Our data indicated that the alkaline and dilute sulfuric acid pretreatments relatively enriched β–5 linkages, while reducing β–O–4 and β–β substructures, in the residual lignin polymers. In contrast, hydrothermal pretreatment reduced all three major linkage types.

Valorization of Acid Isolated High Yield Lignin Nanoparticles as Innovative Antioxidant/Antimicrobial Organic Materials

In this study, dissolution of pristine alkali lignin into ethylene glycol, followed by addition of different acidic conditions (HCl, H2SO4, and H3PO4 at different pH) has been considered as a simple method to prepare high yield lignin nanoparticles (LNP). Field emission scanning electron microscopy (FESEM), Zeta potential, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA) have been utilized to determine the influence of the precipitation procedures on particle size, Zeta potential, molecular weight, and thermal stability of final obtained LNP. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) were also considered to investigate the influence of lignin chemical structures and composition on its antioxidative and antimicrobial behaviors. Results from DPPH (1,1-diphenyl-2-picryl-hydrazyl) activity revealed the antioxidant response of LNP aqueous solutions, whereas results from antimicrobial tests confirmed LNP ...

Fractionation of enzymatic hydrolysis lignin by sequential extraction for enhancing antioxidant performance

The heterogeneity of lignin chemical structure and molecular weight results in the lignin inhomogeneous properties which also covers the antioxidant performance. In order to evaluate the effects of lignin heterogeneity on its antioxidant activity, four lignin fractions from enzymatic hydrolysis lignin were classified by sequential organic solvent extraction and further evaluated by DPPH (1,1-Diphenyl-2-Picrylhydrazyl) free radical scavenging capacity and reducing power analysis. The characterization including FTIR, 1H NMR and GPC showed that the fractionation process could effectively separate lignin fractions with distinctly different molecular weight and weaken the heterogeneity of unfractionated lignin. The antioxidant performance comparison of lignin fractions indicated that the dichloromethane fraction (F1) with lowest molecular weight (4585g/mol) and highest total phenolics content (246.13mg GAE/g) exhibited the highest antioxidant activity whose value was close to commercial antioxidant BHT (butylated hydroxytoluene). Moreover, the relationship between the antioxidant activity and the structure of lignin was further discussed to elucidate the mechanism of antioxidant activity improvement of lignin fractionation. Consequently, this study suggested that the sequential extraction was an effective way to obtain relatively homogeneous enzymatic hydrolysis lignin fractions which showed the potential for the value-added antioxidant application.

Thermal conversion of lignin to phenols: Relevance between chemical structure and pyrolysis behaviors

In this study, the Fourier transform infrared (FTIR) spectrometry and the 13C–1H correlation two-dimensional (2D) heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) were introduced to determine the chemical structure of soda alkali lignin (SAL) and Alcell organosolv lignin (AOL), and the relevance between chemical structure and pyrolysis behaviors was evaluated by thermogravimetric analysis (TGA) and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). Results showed that the two lignin samples had similar functional groups and S/G ratio, excepting side-chain linkages. SAL was mainly cross-linked by β-β′ linkages, while the main linkage within AOL was β-O-4′. This difference proposed that AOL had the worse thermal stability and was easier to be pyrolyzed to phenols than SAL. Herein, the pyrolysis transformation of SAL was always promoted by the increased temperature, whereas the generated phenols from AOL would be redecomposed at high pyrolysis temperature (800°C). Moreover, the priority of demethoxylation occurring in SAL pyrolysis was higher than that in AOL pyrolysis. Further analysis on the types of phenols suggested that the formation of syringyl phenols benefitted from the increasing temperature. However, the formation of p-hydroxyphenyl phenols was inhibited as temperature increased, and the highest selectivity of guaiacyl phenols was obtained at 600°C. The reveal of the relevance between lignin chemical structure and pyrolysis behaviors is meaningful for the efficient thermal conversion of lignin to phenol compounds.