Aspen Lignin Research Articles

The effect of hydrogen bonds on the reactivity of coniferous and deciduous dioxan lignins

The slightly altered samples of dioxan lignin were extracted from coniferous (spruce and juniper) and deciduous wood (aspen) by the Pepper’s method. Lignins were characterized by data of elemental, functional composition, macromolecular and reactive (acid–base and redox) properties. IR spectra of lignins were recorded by the attenuated total refection method. The absorption band of lignins in the 3000–3700 cm−1 region corresponds to the valence vibrations of hydroxyl groups involved in hydrogen bonds. This band was divided into separate Gaussian contours by deconvolution method. The characteristic parameters (energy, length, and relative content) were calculated on the basis of correlation dependencies for each type of H-bonds. The relationship between reactivity (acid–base and redox properties) and the involvement of hydroxyl groups of a natural polymer in H-bonds was shown. The highest reactivity of aspen lignins is caused by the presence of syringyl structures and lower H-bond energies involving reaction centers of macromolecules.

Chloromethylation of Lignin as a Route to Functional Material with Catalytic Properties in Cross-Coupling and Click Reactions.

We present a novel, greener chloromethylation procedure for organosolv aspen lignin under mild reaction conditions without Lewis acid as a catalyst and in acetic acid as a solvent. This synthetic protocol provides a reliable approach to chloromethylated lignin (CML) and means to obtain valuable lignin derivatives. The resulted CML was subsequently transformed into 1-methylimidazolium lignin (ImL), which effectively serves as a stabilizing agent for Pd/CuO nanoparticles (Pd/CuO-NPs). To evaluate the versatility of developed lignin-based catalyst, we investigate its performance in a series of carbon-carbon bond formation reactions, including Suzuki-Miyaura, Sonogashira, Heck reactions, and azide-alkyne cycloaddition (click) reaction. Remarkably, this catalyst exhibited a high degree of catalytic efficiency, resulting in reactions with yields ranging from average to excellent. The heterogeneous catalyst demonstrated outstanding recyclability, enabling its reuse for at least 10 consecutive reaction cycles, with yields consistently falling within the range of 42 % to 84 %. A continuous flow reactor cartridge prototype employing Lignin@Pd/CuO-NPs was developed, yielding results comparable to those achieved in batch reactions. The utilization of Lignin@Pd/CuO-NPs as a catalyst showcases its potential to facilitate diverse carbon-carbon bond formation reactions and underscores its promising recyclability, aligning with the green chemistry metrics and principles of sustainability in chemical processes.

Modification of the aspen lignin structure during integrated fractionation process of autohydrolysis and formic acid delignification

Integrated fractionation process based on autohydrolysis (H) and subsequent formic acid delignification (FAD) has been considered as an effective strategy to separate the main lignocellulosic components in view of the biorefinery. For the better understanding of the structural changes of the lignin during the integrated process, the fractionated aspen lignins were thoroughly characterized by Fourier transform infrared (FT IR), 13C, two-dimensional heteronuclear single quantum coherence (2D-HSQC) and 31P nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Compared to the milled wood lignin (MWL), the fractionated lignins had higher amounts of phenolic OH groups as due to the cleavage of β-O-4 linkages and less alcoholic OH groups mainly due to the esterification of the aliphatic OH groups by formic acid. Demethylation action of the lignin was not significant during the FAD process. More syringyl-propane (S) units were extracted during the H-FAD process than guaiacyl-propane (G) units resulting in a higher S/G ratio and more OCH3 in the fractionated lignins. Furthermore, autohydrolysis of aspen at higher temperature led to more condensation of the fractionated lignins which exhibited higher molecular weight and more β-5 and β-β linkages. The fractionated lignins exhibited high purities due to the breakage of the lignin-carbohydrate bonds.

Selective Cα Alcohol Oxidation of Lignin Substrates Featuring a β‐O‐4 Linkage by a Dinuclear Oxovanadium Catalyst via Two‐Electron Redox Processes

Developing highly efficient catalyst systems to transform lignin biomass into value‐added chemical feedstocks is imperative for utilizing lignin as renewable alternatives to fossil fuels. Recently, the pre‐activated strategy involving the selective oxidation of Cα alcohol of lignin substrates containing (β‐O‐4 linkage mode has been demonstrated to significantly increase the depolymerization efficiency of native aspen lignin from 10–20 to 60 wt.‐%. In this study, we reported the synthesis of a dinuclear oxovanadium complex 2 that is capable of selectively oxidizing the Cα alcohol (80 – 100% selectivity) of various dimeric lignin substrates under a mild condition. Further investigation of catalytic mechanism has revealed that two V=O motifs of complex 2 could serve as proton abstraction sites for both Cα and Cγ alcohol of dimeric lignin substrates, respectively. Interestingly, the dinuclear vanadium intermediate 4 demonstrates the ability to uptake two electrons resulting from the oxidation of Cα alcohol and yields two corresponding mononuclear VIV intermediate 5. The mononuclear VIV intermediate 5 exhibits a characteristic 8‐line EPR spectrum and possesses one unpaired electron determined by the Evans method. The established structure‐reactivity relationships will be able to shed light on the future directions for rational design of highly efficient catalysts for selective oxidation of lignin biomass.

Study of Organosolv Lignins by Methods of FTIR and NMR Spectroscopy

The analysis of the literature on the spectral methods of lignins study was carried out. The most suitable spectral methods for elucidating the structural features of soluble organosolv lignins were selected. The possibilities of FTIR, 1Н NMR, 13С NMR and 2D HSQC NMR methods were demonstrated on the example of studying the structure of ethanollignins obtained from fir and aspen wood. It was established that fir and aspen lignins are G type and GS type lignins, respectively. The HSQC spectra analysis demonstrated a presence of β–O–4′, β–β′, β–5′ linkages in the ethanollignins. It was found that β–O–4′ linkages in ethanollignins from fir and aspen were partially acylated with ethoxy groups in the α-position

A Kinetic Study of the Thermal Degradation of Fir and Aspen Ethanol Lignins

Thermogravimetric (TG/DTG) methods have been used to study the thermal destruction of fir and aspen ethanol lignins at different heating rates in an inert (argon) medium. For each of the lignins, the main stages of thermal degradation were found under conditions of programmed heating of samples from 298 to 1173 K at heating rates of 5, 10, and 20 K/min. It was found that with an increase in the heating rate, the ranges of the main degradation of lignins expand. Shifts toward higher temperatures were 13.8 K for fir lignin and 21.1 K for aspen lignin. At the same temperatures, ethanol lignin from aspen showed a greater weight loss than fir lignin. Using the Ozawa–Flynn–Wall, Broido, and Redfern–Coats kinetic models, the results of the thermogravimetric analysis of the studied lignins are analyzed and the values ​​of the activation energy are calculated. The most reliable values of ​​the activation energy were obtained by the Ozawa–Flynn–Wall isoconversion method for the main temperature range of degradation (from ~569 to ~725 K): 113 kJ/mol for fir ethanol lignin and 106 kJ/mol for aspen ethanol lignin.

Effect of forest thinning and wood quality on the short-term wood decomposition rate in a Pinus tabuliformis plantation.

The effects of forest thinning and wood quality on wood decomposition in the mineral soil were investigated in a Chinese pine (Pinus tabuliformis Carriére) plantation in northern China by measuring mass loss and changes in wood properties (carbohydrates, lignin and nitrogen (N) concentrations) in wood stakes of two tree species-loblolly pine (Pinus taeda L.) and trembling aspen (Populus tremuloides Michx.). Stakes were inserted to a 20cm soil depth in stands with three thinning levels (low, moderate, and heavy) and an unharvested control and removed after 1year. There were significant differences in stake mass loss among the treatments. The species effect on the stake mass loss was marginally significant. Wood N content of both species increased during decomposition in all thinning treatments, and was only correlated with aspen mass loss. Wood properties of stakes placed in each stand before insertion (t = 0) were similar, except for pine lignin concentration and aspen lignin: N ratio, but neither had any effect on thinning treatment results. Lignin concentration increased and carbohydrate concentration decreased in both aspen and pine wood stakes during decomposition across all thinning treatments, which suggests that brown-rot fungi are dominant wood-decomposers on our study site. We conclude that thinning has a significant influence on the wood decomposition in the mineral soil of this Chinese pine plantation.

Electrocatalytic degradation of aspen lignin over Pb/PbO2 electrode in alkali solution

A novel procedure about electrochemical catalysis degradation of aspen lignin with Pb/PbO2 anode in the three-dimensional electrode (TDE) reactor was investigated. SEM, XRD and cyclic voltammogram tests were employed to study the surface morphology, composition and the electrochemical redox performance of the fabricated Pb/PbO2 electrode. The lignin was cracked by OH and hydrogenated by [H] atom generated from alkaline water electrolysis, leading to the production of 4-methylanisole and other products. Raw material lignin concentration, current density, temperature and time were optimized. The pathway of electrocatalytic degradation and hydrogenation process of lignin in alkaline solution was also discussed.

Rapid semi-quantitative determination of aspen lignin in lignocellulosic products

In the present study different methods for the determination of aspen lignin were investigated. In experiments, dried samples of extractive-free aspen wood and grinded bleached-chemo-thermo-mechanical-pulp (BCTMP) of aspen were used. For isolating lignin from aspen wood and BCTMP, Klason method was used. For the quantification of lignin content, a series of aspen wood powder/microcrystalline cellulose binder were mixed and analysed with FTIR-ATR and UV-VIS. To compare with colour reactions, an average content 21% of lignin was assigned to experimental content in 100% aspen wood powder. FTIR-ATR absorbance maximum between 1234–1237 cm and UV-VIS pseudo-absorbance of measured samples maximum at 280 nm were taken as measurement points for the calibration of lignin content. Nearly linear dependence was established with both methods. Weisner and Maule colour tests were used for staining to detect lignin in samples. Suspensions, containing samples with staining solution, were prepared and photographed. Best positive Weisner reaction with violet colour, both with aspen wood and BCTMP samples, were established with the 1 : 1 phloroglucinol/HCl staining solution. Carefully mixed suspension of 0.1 g samples and 5 min reaction time were applied. In Maule reaction, intensive red colour appeared to samples after 10 min treatment with 1% KMnO4. Samples were washed with distilled water and treated with 3% aqueous HCl until the colour changed from black to beige/yellow. Then samples were treated with concentrated NH3·H2O for 2 min to achieve the most intensive colour. A simple semiquantitative method for detection of lignin in BCTMP was worked out.

Differences in the adsorption of enzymes onto lignins from diverse types of lignocellulosic biomass and the underlying mechanism

BackgroundNon-productive cellulase adsorption onto lignin has always been deemed to negatively affect the enzymatic hydrolysis of lignocellulosic feedstocks. Therefore, understanding enzyme-lignin interactions is essential for the development of enzyme mixtures, the processes of lignocellulose hydrolysis, and the genetic modification of lignocellulosic biomass and enzymes. In this work, we examined the properties of six lignins from diverse types of lignocellulosic biomass (aspen, pine, corn stover, kenaf, and two Arabidopsis lines, wild-type and SALK mutant of fah1) to determine the mechanism of differences in their adsorption of enzymes.ResultsWe found that lignin sources affected enzyme adsorption using structural features, such as functional groups and lignin composition. Guaiacyl (G) lignin had a higher adsorption capacity on enzymes than syringyl (S) lignin. The low S/G ratio and high uniform lignin fragment size had good correlations with high adsorption capacity. A higher content of phenolic hydroxyl groups and a lower content of carboxylic acid groups resulted in stronger adsorption affinity for corn stover lignin (CL) than for kenaf lignin (KL) and aspen lignin (AL). The lower amount of aliphatic hydroxyls that reduced hydrophobic interactions could explain the higher adsorption capacity of pine lignin (PL) than CL. Enzyme activity assays, as well as the hydrolysis of Avicel, phosphoric acid-swollen cellulose (PASC), and holocellulose, were performed to study the behaviors of mono-component enzymes that resulted in adsorption. We found that cellobiohydrolase (CBH) and xylanase were adsorbed the most by all lignins, endoglucanase (EG) showed less inhibition, and β-glucosidase (BG) was the least affected by lignins, indicating the important role of carbohydrate-binding module (CBM) in protein adsorption.ConclusionLignin sources affect enzyme adsorption using structural features and lignin composition, such as S/G ratio, carboxylic acid, aliphatic hydroxyl, and phenolic hydroxyl. For mono-component enzymes, the adsorption capacity decreased in the order CBH, xylanase > EG > BG. These investigations revealed the difference in lignin properties between diverse biomass and adsorption capacity of enzymes to lignins, and the possible underlying mechanism. The results can also serve as a reference for the genetic modification of lignocellulosic biomass and enzymes.

Catalytic fast pyrolysis of aspen lignin via Py-GC/MS

Aspen lignin extracted by an organosolv process was pyrolyzed in the presence of catalysts and analyzed using Py-GC/MS. The pyrolysis products detected are mostly aromatic hydrocarbons and phenolic compounds. The lignin and catalysts were either mixed or arranged in layers. Two different micro-porous zeolite catalysts, HZSM-5 and HY, were compared in the study. The effects of the catalysts on the production of aromatic hydrocarbons and phenolic compounds were assessed quantitatively. The HZSM-5 catalyst was found to produce from 2.5 to 40 times more aromatic hydrocarbons than the HY catalyst, by converting phenolic compounds into aromatic hydrocarbons. For the HZSM-5 catalyst, the effects of placement of catalyst were not as pronounced as were for HY. The data suggest that for any catalyst type and placement there exists an optimum catalyst-to-lignin ratio that maximizes the total production of aromatic hydrocarbons and phenolic compounds. For HZSM-5 in the mixture arrangement, a catalyst-to-lignin ratio of 3:1 was found to maximize both the aromatic hydrocarbons and the aggregate sum of aromatic hydrocarbons and phenolic compounds. At this ratio, 23% yield of aromatic hydrocarbons and 28% yield of the aggregate sum were obtained. Also at these conditions, the products detected are estimated to have a total oxygen content of about 4% and higher heating value of 46MJ/kg, roughly the same as gasoline and diesel. Toluene and p-xylene were the two most abundant hydrocarbons formed in the presence of catalysts. Up to 6.6% and 6.3% of the original lignin were converted into toluene and p-xylene, respectively. We estimate that if all the lignin produced in pulp and paper mills was catalytically pyrolyzed, the amount of toluene produced would be more than 30% of the current annual production of toluene from fossil sources worldwide.

Characteristics and Properties of Soda Lignin Obtained from Aspen Wood By-Products

In the work, soda lignin was obtained under laboratory alkaline delignification conditions from aspen sawdust. The chemical composition and the surface-active properties of this lignin in aqueous solutions were studied. The high indices of Klason lignin and the content of methoxyl groups indicated the insignificant presence of non-lignin admixtures, including lignocarbohydrate complexes, in the purified lignin. It was shown that aspen lignin was a surface active substance, the surface activity of which at the water-air interface grew with falling the solution рН values. Simultaneously, with decreasing рН, the particle sizes of aspen lignin in the aqueous solutions increased, but zeta potential of the lignin particles had the tendency to decrease.

Pyrolysis of lignin extracted from prairie cordgrass, aspen, and Kraft lignin by Py-GC/MS and TGA/FTIR

A study is undertaken to assess the effectiveness of lignin extracted from prairie cordgrass as a pyrolysis feedstock. The effects of variability of lignin source on fast and slow pyrolysis products are also investigated. To accomplish these goals, Py-GC/MS and TGA/FTIR are employed in the pyrolysis of three types of lignin: prairie cordgrass (PCG) lignin extracted from prairie cordgrass, aspen lignin extracted from aspen trees (hardwood), and synthetic Kraft lignin. Fast pyrolysis results from Py-GC/MS show that for PCG lignin, only ten of the detected compounds have relative peak area percentiles that exceed 2% and make up over 52% of the total area. For aspen lignin, excluding butanol that is used in the extraction process, only eight compounds are found to have relative peak areas exceeding 2% that make up over 52% of the total area. For Kraft lignin, only eight compounds exceeding 2% are found to make up more than 45% of the total area. Both techniques, Py-GC/MS and TGA/FTIR, indicate that PCG lignin releases more alkyls than aspen and Kraft lignin. TGA/FTIR results indicate that PCG lignin also releases by far the most light volatile products (<200°C) while producing the least amount of char among the three types of lignin studied. These characteristics make PCG lignin a good choice in producing good quality bio-oil and thus decreasing upgrade requirements. Py-GC/MS results conclude that aspen lignin produces significantly more pyrolytic products than PCG lignin. This is indicative of the potential of aspen lignin to result in higher conversion rates of bio-oil than the other two lignins.

Isolation and Characterization of Lignin from Tropical and Temperate Hardwood

Dioxane and milled wood lignins (MWL) were isolated from tropical hardwood, Nalita (Trema orientalis) and temperate hardwood, aspen. These lignins were characterized by UV, FTIR, 1H-NMR and 13C-NMR spectroscopy, alkaline nitrobenzene oxidation, molecular weight determination, elemental and methoxyl analysis. The structural analysis revealed that Nalita and aspen lignin is syringyl-guaiacyl type. Aspen lignin had higher syringyl unit than Nalita lignin. The β-O-4 type linkages are the main interunit linkages and more abundant in aspen than Nalita. Dioxane lignin showed higher free phenolic hydroxyl group than MWL in both species. The weight average molecular weight of aspen lignin was lower than that of Nalita lignin. Nalita and aspen lignins contained both erythro and threo configuration, but erythro proton gave stronger peak. A UV absorption maximum of aspen lignin was at 274 nm, whereas it was shifted to 280 nm for Nalita lignin. Keywords: Trema orientalis, Aspen, Dioxane lignin, Milled wood lignin, Syringyl-guaiacyl, β-O-4 linkages DOI: 10.3329/bjsir.v44i3.4399 Bangladesh J. Sci. Ind. Res. 44(3), 271-280, 2009

Maximizing the liquid fuel yield in a biorefining process

Biorefining strives to recover the maximum value from each fraction, at minimum energy cost. In order to seek an unbiased and thorough assessment of the alleged opportunity offered by biomass fuels, the direct conversion of various lignocellulosic biomass was studied: aspen pulp wood (Populus tremuloides), aspen wood pretreated with dilute acid, aspen lignin, aspen logging residues, corn stalk, corn spathe, corn cob, corn stover, corn stover pellet, corn stover pretreated with dilute acid, and lignin extracted from corn stover. Besides the heating rate, the yield of liquid products was found to be dependent on the final liquefaction temperature and the length of liquefaction time. The major compounds of the liquid products from various origins were identified by GC-MS. The lignin was found to be a good candidate for the liquefaction process, and biomass fractionation was necessary to maximize the yield of the liquid bio-fuel. The results suggest a biorefinery process accompanying pretreatment, fermentation to ethanol, liquefaction to bio-crude oil, and other thermo-conversion technologies, such as gasification. Other biorefinery options, including supercritical water gasification and the effectual utilization of the bio-crude oil, are also addressed.

Base‐Catalyzed Depolymerization of Lignin: Separation of Monomers

AbstractIn our quest for fractionating lignocellulosic biomass and valorizing specific constitutive fractions, we have developed a strategy for the separation of 12 added value monomers generated during the hydrolytic based‐catalyzed depolymerization of a Steam Exploded Aspen Lignin. The separation strategy combines liquid‐liquid‐extraction (LLE), followed by vacuum distillation, liquid chromatography (LC) and crystallization. LLE, vacuum distillation and flash LC were tested experimentally. Batch vacuum distillation produced up to 4 fractions. Process simulation confirmed that a series of 4 vacuum distillation columns could produce 5 distinct monomer streams, 3 of which require further chromatography and crystallization for purification.

Characteristics of Dioxane Lignins Isolated at Different Ages of Nalita Wood (Trema orientalis)

Nalita (Trema orientalis) is one of the fastest growing trees in the tropical countries. The structural characteristics of lignin isolated at different ages of Nalita wood (Trema orientalis) by acidolytic dioxane method were examined by UV, FTIR, 1H‐NMR and 13C‐NMR spectroscopy, alkaline nitrobenzene oxidation, molecular weight determination, elemental and methoxyl analysis. The data were compared with aspen lignin. The structural analysis revealed that Nalita wood lignin is syringyl‐guaiacyl type. The methoxyl content in Nalita wood lignin was lower than aspen lignin. The C9 formulas for 30‐months‐old Nalita was C9H9.31O3.13(OCH3)1.27, whereas that of aspen was C9H8.94O3.15(OCH3)1.47. The weight average molecular weight of Nalita wood lignin was decreased from 36,500 to 25,500 with increasing tree age from 12 to 30 months, whereas weight average molecular weight of aspen was 20,000. Both alcoholic and phenolic hydroxyl group in Nalita wood lignin is lower than aspen lignin.

Impact of Pulping Conditions on FORMACELL Aspen Lignin: Investigation of Methoxyl and Ester Groups, Carbohydrates, Molar Mass and Glass Transition Temperatures

SummaryThe influence of reaction time, reaction temperature and acid concentration on the yield and characteristics of FORMACELL aspen lignins were investigated. 18 samples were quantitatively isolated from the black liquor by precipitation. The samples were analysed regarding their contents of carbohydrates, methoxyl and ester groups. All samples had low carbohydrate contents and the amount of methoxyl and ester groups was continuously reduced under more severe pulping conditions. Molar mass distributions and glass transition temperatures were determined. Molar masses of lignins were continuously reduced during pulping resulting in low weight average molar masses from 2.500–3.200 g/mol. Glass transition temperatures varied from 123.6 to 154.5°C, depending on the reaction conditions. Comparison of the thermograms with those of the lignins from the Kraft or Sulfite process confirmed that in the FORMACELL process a very uniform lignin with few impurities is obtained.

NMR observation of a new lignin structure, a spiro-dienoneElectronic supplementary information (ESI) available: 13C, QUAT, HMBC and HSQC NMR spectra. See http://www.rsc.org/suppdata/cc/b1/b108285j/

A spiro-dienone structure (eta -1/alpha -O-alpha) has been observed as one of the important structures present in spruce and aspen lignins, with abundance as high as 3% in spruce lignin.

TRANSFORMATIONS OF ASPEN WOOD AND ITS PRINCIPAL COMPONENTS BY O-ACYLATION

The kinetics of O-acylation of aspen wood, mechanochemical treated, lignin, cellulose, and xylan were studied at various reaction temperatures . The reactivity of the principal wood components in the range 80-120°C follows the decreasing order lignin > xylan > cellulose. Lignin, an amorphous intercellular substance in wood, is acylated fastest.