Lignin Samples Research Articles

Exploring the Potential of Vine Shoots as a Source of Valuable Extracts and Stable Lignin Nanoparticles for Multiple Applications.

Large amounts of vine shoots are generated every year during vine pruning. This residue still presents many of the compounds found in the original plant, including low molecular weight phenolic compounds and structural compounds such as cellulose, hemicellulose, and lignin. For wine-producing regions, the challenge is to develop alternatives that will increase the value of this residue. This work proposes the full valorization of vine shoots, focusing on the extraction of lignin by mild acidolysis for the preparation of nanoparticles. The effect of the pretreatment solvents (ethanol/toluene, E/T, and water/ethanol, W/E), on the chemical and structural features of lignin, was evaluated. The chemical analysis suggests similar composition and structure regardless of the pretreatment solvent, although lignin isolated after pretreatment of biomass with E/T showed a higher content of proanthocyanidins (11%) compared with W/E (5%). Lignin nanoparticles (LNPs) presented an average size ranging from 130-200 nm and showed good stability for 30 days. Lignin and LNPs showed excellent antioxidant properties (half maximal inhibitory concentration, IC50 0.016-0.031 mg/mL) when compared to commercial antioxidants. In addition, extracts resulting from biomass pretreatment showed antioxidant activity, with W/E presenting a lower IC50 (0.170 mg/mL) than E/T (0.270 mg/mL), correlated with the higher polyphenol content of W/E, with (+)-catechin and (-)-epicatechin being the main compounds detected. Overall, this work shows that the pre-treatment of vine shoots with green solvents can yield (i) the production of high-purity lignin samples with antioxidant properties and (ii) phenolic-rich extracts, promoting the integral reuse of this byproduct and contributing to sustainability.

Characterisation of lignins isolated from Bamboo organosolv and kraft black liquor

Bamboo biomass was pulped using organosolv methods: Acetic acid and formic acid; hydrogen peroxide and formic acid; ethanol and water and kraft process with varying concentrations of the cooking chemicals. The properties of the isolated lignin were influenced by the black liquor pH as well as the pulping method. Highest pH (12,8) was recorded for kraft at 70:30 liquor concentration while lowest pH of 2,5 was recorded for both Aceticformic (70:30) and Ethanol/water (70:30 and 60:40). There were obvious differences in the characteristic colours, shapes and sizes of the lignin samples. Bamboo kraft lignin samples formed large pieces much easier than that of Organosolv. Aceticformic (70:30) had the best filteration properties (FC) while Ethanol/water had the poorest. Generally, kraft recorded the highest lignin yield while all the organosolv processes recorded reduced yield. Highest yield (119,25 g/L) was gotten from kraft (50:50) while Peroxyformic (60:40) had the lowest yield of 8,20 g/L. The results showed that higher liquor pH favours total dissolved solid as well as lignin precipitation. As the pH increases, total dissolved solid, yield, Klason and low molecular weight (LMW) lignin content increases while FC decreases. The Klason and LMW lignin content increased with incresing lignin yield.

Impact of Different Lignin Sources on Nitrogen-Doped Porous Carbon toward the Electrocatalytic Oxygen Reduction Reaction.

Lignin is an ideal carbon source material, and lignin-based carbon materials have been widely used in electrochemical energy storage, catalysis, and other fields. To investigate the effects of different lignin sources on the performance of electrocatalytic oxygen reduction, different lignin-based nitrogen-doped porous carbon catalysts were prepared using enzymolytic lignin (EL), alkaline lignin (AL) and dealkaline lignin (DL) as carbon sources and melamine as a nitrogen source. The surface functional groups and thermal degradation properties of the three lignin samples were characterized, and the specific surface area, pore distribution, crystal structure, defect degree, N content, and configuration of the prepared carbon-based catalysts were also analyzed. The electrocatalytic results showed that the electrocatalytic oxygen reduction performance of the three lignin-based carbon catalysts was different, and the catalytic performance of N-DLC was poor, while the electrocatalytic performance of N-ELC was similar to that of N-ALC, both of which were excellent. The half-wave potential (E1/2) of N-ELC was 0.82 V, reaching more than 95% of the catalytic performance of commercial Pt/C (E1/2 = 0.86 V) and proving that EL can be used as an excellent carbon-based electrocatalyst material, similar to AL.

Application of Unsupervised Learning for the Evaluation of Burial Behavior of Geomaterials in Peatlands: Case of Lignin Moieties Yielded by Alkaline Oxidative Cleavage

Tropical Peatlands accumulate organic matter (OM) and a significant source of carbon dioxide (CO2) and methane (CH4) under anoxic conditions. However, it is still ambiguous where in the peat profile these OM and gases are produced. The composition of organic macromolecules that are present in peatland ecosystems are mainly lignin and polysaccharides. As greater concentrations of lignin are found to be strongly related to the high CO2 and CH4 concentrations under anoxic conditions in the surface peat, the need to study the degradation of lignin under anoxic and oxic conditions has emerged. In this study, we found that the "Wet Chemical Degradation" approach is the most preferable and qualified to evaluate the lignin degradation in soils accurately. Then, we applied PCA for the molecular fingerprint consisting of 11 major phenolic sub-units produced by alkaline oxidation using cupric oxide (II) along with alkaline hydrolysis of the lignin sample presented in the investigated peat column called "Sagnes". The development of various characteristic indicators for lignin degradation state on the basis of the relative distribution of lignin phenols was measured by chromatography after CuO-NaOH oxidation. In order to achieve this aim, the so-called Principal Component Analysis (PCA) has been applied for the molecular fingerprint composed of the phenolic sub-units, yielded by CuO-NaOH oxidation. This approach aims to seek the efficiency of the already available proxies and potentially create new ones for the investigation of lignin burial along a peatland. Lignin phenol vegetation index (LPVI) is used for comparison. LPVI showed a higher correlation with PC1 rather than PC2. This confirms the potential of the application of LPVI to decipher vegetation change, even in a dynamic system as the peatland. The population is composed of the depth peat samples, and the variables are the proxies and relative contributions of the 11 yielded phenolic sub-units.

Insight into the structural feature, ash transformation behavior, and alkali metal heat release characteristic of industrial lignin via experimental and equilibrium evaluation

The release characteristics of inorganic minerals during the thermochemical transformation of organic solid wastes are one of the key issues for their resource utilization. This study concentrated on the chemical structure of three kinds of industrial lignin and the release pattern and mechanism of alkali metal elements during heat treatment by means of 13C NMR, FTIR, XRD, SEM, and chemical thermodynamic equilibrium simulation. The microstructures of the three lignin samples were studied using 13C NMR and FTIR. The three lignin samples contained much more aliphatic and aromatic carbon than carbonyl carbon, and the aliphatic carbon moieties contained the most oxygenated carbon. The lignin samples mainly had aromatic molecular structures with aromaticity (fa) of 55.76% (sodium lignin sulfonate, SL), 52.62% (calcium lignin sulfonate, CL), and 63.93% (de-alkalized lignin, DL), respectively. Carbonyl content in DL was lower than lignin sulfonate SL and CL. The benzene ring content of SL was lower than the other two lignin samples. Na+ metal salts promoted the pyrolysis of lignin samples, while Ca2+ metal salts inhibited the pyrolysis of lignin samples. Microstructural studies showed that the structure of SL evolved from columnar and granular coexistence breaking into filamentous protrusions and lamellar structures with the increase of pyrolysis temperature. The CL and DL samples became ash presented in granular state and the particle size continued to become smaller with increasing temperature as the distribution gap became larger. The chemical thermodynamic equilibrium calculations showed that the variation in the initial concentrations of Na+ and Ca2+ in the three lignin samples led to different release characteristics of the three lignin samples. Na+ release rate was higher than that of Ca2+, and the valence state of the metal ions was an important reason for this phenomenon. This study provides data support and theoretical basis for the migration and release pattern of alkali metal during the thermal conversion reaction of organic solid waste applications.

Evaluation of guaiacyl lignin aromatic structures using 13CO2 administered Ginkgo biloba L. xylem by quantitative solid- and liquid-state 13C NMR

Abstract Ginkgo biloba L. saplings were cultivated in an airtight growth chamber with 13CO2 for two months. The 13C ratio of the newly developed xylem region was ca. 85%, evaluated by high lateral resolution secondary ion mass spectrometry and thioacidolysis/GC-MS. Quantitative solid-state 13C direct polarisation/magic angle spinning (DP/MAS) NMR measurements with high-speed MAS of 70.0 kHz were conducted for cutting-milled wood (CMW), ball-milled wood (BMW), and enzymatically saccharified lignin (EL) samples. In addition, quantitative liquid-state 13C NMR measurements were carried out for EL in DMSO-d 6. Major lignin aromatic signals were classified into three groups of aromatic carbons of C–H, C–C, and C–O, and their area ratio was compared within these measurements. EL samples in solid- and liquid-state showed nearly the same results. However, the results for CMW and BMW in solid-state NMR suggest the structural alteration of lignin within the sample preparation procedure, including ball milling.

Evaluation of the dissolving selectivity of ionic liquids for the three main components of bamboo powder under microwave irradiation

Understanding the dissolving selectivity of ionic liquids (ILs) for cellulose, hemicellulose, and lignin in plant cell wall is critical to explore new ILs for efficient pretreatment of lignocellulosic biomass. Here, the bamboo powder was treated at 150 ℃ under microwave irradiation by 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazolium acetate (BmimAc) which had the different anions. The recovered bamboo powder and lignin samples were characterized. It indicated that the solubilities of bamboo powder in BmimCl and BmimAc were 27.04 and 7.00 g/100 g IL, respectively. A large amount of polysaccharides, especially hemicellulose, were possibly degraded by BmimCl, resulting in a low recovery rate (24.17 %) of bamboo powder with high content of lignin (41.81 %). The dissolving selectivity of BmimCl for the three main components was in the order: hemicellulose>cellulose>lignin, while that of BmimAc was in a different order: lignin>cellulose>hemicellulose. The dissolving selectivity of BmimAc was less obvious than that of BmimCl. The pretreatment of bamboo powder with BmimCl and BmimAc could greatly improve the yield of reducing sugar. BmimAc performed stronger ability than BmimCl to destroy the crystal structure of cellulose. Both the bamboo lignins extracted by BmimCl and BmimAc were syringyl (S)/guaiacyl (G)/p-hydroxyphenyl (H) type with different S/G/H ratios of 10.11/5.32/1.00 and 7.61/2.47/1.00, respectively. The lignin extracted by BmimAc was rich in hemicellulose and side alkyl chains. While the β-O-4 bonds in the lignin extracted by BmimCl were seriously broken, leading to the high contents of aliphatic OH, syringyl phenolic OH, and guaiacyl phenolic OH. BmimAc performed weaker ability than BmimCl to damage the lignin structure.

Characterisation of chemical properties of the produced organic fractions via hydrothermal liquefaction of biosolids from a wastewater treatment plant

Upgradable renewable crude oil produced from the hydrothermal liquefaction (HTL) of municipal wastewater sludge (biosolids) has the potential to be a sustainable feedstock to produce renewable crude oil. A range of biosolids with different organic fractions was tested under controlled HTL operating conditions to quantify the composition of the produced renewable crude oil. The HTL results demonstrated that both the HTL reaction conditions and biosolids composition have significant effects on the chemical properties of the produced renewable crude oil. Gas chromatography-mass spectrometry (GC-MS) identified a complex mixture of >300 major compounds in the produced renewable crude oil. The predominant components identified from the lipid, protein, carbohydrate and lignin constituents were cyclic terpanes and terpenes, along with nitrogenous, oxygenated, and phenolic components. Based on the boiling point of the produced compounds, high gasoline and naphtha-like and high diesel-like yields were produced from biosolid samples with high lipid and protein content, while the kerosene-like best yield was generated from a high lipid sample. A significant gas oil-like yield was produced from the high lipid and carbohydrate biosolid samples, while a high-yield of wax, lubricating oil and vacuum gas oil-like contents were generated from the high lignin sample.

Pyrolysis carbon compound-specific isotope analysis (Py-CSIA) of Eucalyptus spp. bark and the extracted lignin

Changes in climatic and environmental conditions can affect both, plant chemical molecular and atomic composition. Therefore, biomass carbon isotope composition is frequently used to gain information about the environmental conditions at the time a plant thrives. In this field, most studies use isotope values obtained from bulk samples. However, these values are a weighted average of the different plant compounds. The isotopic characterization of individual compounds represents a relevant analytical advance able to differentiate the isotopic composition of the main plant components i.e., polysaccharides, lignin, polypeptides, lipids, waxes, etc.Here, we investigate the link between molecular and isotope composition of bark and lignin extracted from three Eucalyptus species (E. grandis, E. dunnii and a hybrid E. grandis X E. dunnii) using pyrolysis compound-specific isotope analysis (Py-CSIA). This technique, although not widely used, has been previously developed and applied, with different variants, to characterize plant products including lignin, sugars, and terpenes. Retrieved results for both bark and lignin samples showed the isotopic differences regarding the diverse biogenic groups, accounting for a 13C-enrichment in polysaccharides up to 2.5‰ compared to lignin methoxyphenols, which is consistent with the fractionation during metabolization of the plant. A strong positive correlation was found between the bulk isotope and compound-specific values, especially when applying a weight factor related to the relative abundance of each compound, which support the analytical suitability of this technique. Despite that bark from different origins provide very similar pyrolysis patterns, isotopic composition of relevant specific compounds can make the difference giving additional valuable information.

Functional Lignin Building Blocks: Reactive Vinyl Esters with Acrylic Acid.

Introducing vinyl groups onto the backbone of technical lignin provides an opportunity to create highly reactive renewable polymers suitable for radical polymerization. In this work, the chemical modification of softwood kraft lignin was pursued with etherification, followed by direct esterification with acrylic acid (AA). In the first step, phenolic hydroxyl and carboxylic acid groups were derivatized into aliphatic hydroxyl groups using ethylene carbonate and an alkaline catalyst. The lignin was subsequently fractionated using a downward precipitation method to recover lignin of defined molar mass and solubility. After recovery, the resulting material was then esterified with AA, resulting in lignin with vinyl functional groups. The first step resulted in approximately 90% of phenolic hydroxyl groups being converted into aliphatic hydroxyls, while the downward fractionation resulted in three samples of lignin with defined molar masses. For the esterification reaction, the weight ratio of reagents, reaction temperature, and reaction time were evaluated as factors that would influence the modification efficacy. 13C NMR spectroscopy analysis of lignin samples before and after esterification showed that the optimized reaction conditions could reach approximately 40% substitution of aliphatic hydroxyl groups. Both steps only used lignin and the modifying reagent (no solvent), with the possibility of recovery and reuse of the reagent by dilution and distillation. An additional second esterification step of the resulting lignin sample with acetic acid or propionic acid converted 90% of remaining hydroxyl groups into short-chain carbon aliphatic esters, making a hydrophobic material suitable for further copolymerization with synthetic hydrophobic monomers.

Effect of Amine Type on Lignin Modification to Evaluate Its Reactivity in Polyol Construction for Non-Isocyanate Polyurethanes (NIPU)

Polyols are groups of organic compounds which contain carbon and are randomly linked to other atoms, especially carbon-carbon and carbon-hydrogen. These compounds are mainly used as reactants to make other polymers. Among biopolymers, lignin is regarded as the base of a new polymer in polyol construction. The present study aimed to investigate the effects of amine type (diethylenetriamine and ethylenediamine) on the modification of lignin-based polyols, so as to provide an alternative to petroleum polyols and, in turn, increase functional groups and reduce their harm to humans’ health and the environment. To this aim, first, lignin was extracted from raw liquor. Next, the extracted lignin was reacted with diethylenetriamine (DETA) and ethylenediamine (EDA). Finally, the Mannich method was used for the reaction between amine lignin and propylene carbonate. The results of the Fourier Transform Infrared (FTIR) spectroscopy analysis showed that modification with DETA led to more structural change in lignin and peak 1100 indicates the presence of C–O bond related to urethane bonds in modified lignin. Moreover, adding propylene carbonate to aminated lignin did not result in much change in the results of the FTIR analysis. Additionally, urethane bonds can be seen in the results of GPC at 400°C–500°C. Furthermore, a slight decrease in thermal stability was observed in lignin modified with amine and propylene carbonate, compared to the raw lignin sample.

Investigation of the Interaction Mechanism between Lignin Structural Units and Enzyme

The effect of lignin structural units on enzymatic hydrolysis of lignocellulosic biomass was investigated, especially the inhibitory role of lignin in non-productive adsorption with enzymes. Milled wood lignin (MWL) was isolated from different hardwoods of poplar, eucalyptus and acacia. The isolated lignin samples were characterized by elemental analysis, gel permeation chromatography, nitrobenzene oxidation and fourier infrared spectroscopy. The mechanism of lignin structural units on enzymatic hydrolysis of cellulose was studied by quartz crystal microbalance (QCM). The results showed that different structural units of lignin had different adsorption capacity for enzymes. The results of nitrobenzene oxidation indicated that the S/G ratio (S: syringyl-like lignin structures; G: guaiacyl-like lignin structures) of lignin of poplar was 0.99, that of eucalyptus was 1.92 and that of acacia was 1.34. According to the results of QCM, the adsorption capacity of the three lignin films was as follows: Poplar MWL (S/G ratio 0.99) < Acacia MWL (S/G ratio 1.34) < Eucalyptus MWL (S/G ratio 1.92). Eucalyptus MWL with higher degree of condensation and S/G ratio showed stronger affinity to enzymes and more non-productive adsorption with enzymes, resulting in less adsorption between enzymes and cellulose, and lower enzymatic hydrolysis efficiency.

Single-Standard Quantification Strategy for Lignin Dimers by Supercritical Fluid Chromatography with Charged Aerosol Detection.

The increased interest in utilizing lignin as a feedstock to produce various aromatic compounds requires advanced chemical analysis methods to provide qualitative and quantitative characterization of lignin samples along different technology streamlines. However, due to the lack of commercially available chemical standards, routine quantification of industrially relevant lignin oligomers in complex lignin samples remains a challenge. This study presents a novel method for universal quantification of lignin dimers based on supercritical fluid chromatography with charged aerosol detection (CAD). A series of lignin-derived dimeric compounds that have been reported from reductive catalytic fractionation (RCF) were synthesized and used as standards. The applicability of using linear regression instead of quadratic calibration curves was evaluated over a concentration range of 15-125 mg/L, demonstrating that the former calibration method is as appropriate as the latter. The response factors of lignin dimeric compounds were compared to assess the uniformity of the CAD signal, revealing that the CAD response for the tested lignin dimers did not differ substantially. It was also found that the response factors were not dependent on the number of methoxy groups or linkage motifs, ultimately enabling the use of only one calibrant for these compounds. The importance of chromatographic peak resolution in CAD was stressed, and the use of a digital peak sharpening technique was adopted and applied to address this challenge. The developed method was verified and used for the quantification of lignin dimers in an oil obtained by a RCF of birch sawdust.

Ultraviolet Spectrophotometry of Lignin Revisited: Exploring Solvents with Low Harmfulness, Lignin Purity, Hansen Solubility Parameter, and Determination of Phenolic Hydroxyl Groups.

In this article, we explored solvents with lower harmfulness than established systems for UV spectrophotometry of lignin. By measuring the absorptivity in DMSO solvent at 280 nm, the purity of the lignin samples was addressed and compared with Klason and acid-soluble lignin. The general trend was an increasing absorptivity with increasing lignin purity; however, considerable scattering was observed around the sample mean. The Hansen solubility parameter (HSP) of four technical lignins was furthermore determined. The model was in line with the UV measurements, as solvents closer in HSP correlated with a higher absorptivity. Ethylene glycol was identified as a good solvent for lignin with low UV-cutoff. In addition, mixtures of propylene carbonate, water, and ethanol showed good suitability and a low cutoff of 215 nm. While DMSO itself was poorly suited for recording alkali spectra, blending DMSO with water showed great potential. Comparing three methods for determining phenolic hydroxyl units by UV spectrophotometry showed some discrepancies between different procedures and solvents. It appeared that the calibrations established with lignin model compounds may not be fully representative of the lignin macromolecule. More importantly, the ionization difference spectra were highly affected by the solvent of choice, even when using what are considered "good" solvents. At last, a statistical comparison was made to identify the most suitable solvent and method, and the solvent systems were critically discussed. We thus conclude that several solvents were identified, which are less harmful than established systems, and that the solubility of lignin in these is a crucial point to address when conducting UV spectrophotometry.

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl3·6H2O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl3·6H2O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55–1.73) and molecular weight (1380–2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

Modification of lignin properties using alpha particles and gamma-rays for diverse applications

The irradiation of lignocellulosic biomass using high-energy radiations provides an economical green alternative method over chemical methods for the pretreatment of biomass before its use for applications like the production of biofuels, new sustainable materials, and filler for polymer composites. Thus, irradiation of lignin using high-energy ionizing radiations has potential use in lignin-based biorefineries and bio-polymer industries. In the present work, the kraft lignin was subjected to gamma-rays (1.17 and 1.33 MeV) up to a dose of 200 kGy, and alpha radiations (5.2 MeV) up to a dose of 1200 mGy. The irradiation produces free radicals in the irradiated material, triggering chemical reactions and changing the lignin's physicochemical properties. The chemical and structural changes in the irradiated lignin with different radiation doses were analyzed with various characterization techniques such as FTIR, XRD, DSC, and TGA. The results showed that gamma-rays significantly affected the amorphous regions of lignin samples compared to their crystalline regions. In contrast, alpha particles irradiation of lignin remarkably affected the crystalline structural morphology compared to the amorphous phase. The effect of gamma-rays irradiation on amorphous regions of lignin was more pronounced at low irradiation doses than at high doses. The impact of alpha particles irradiation on the physicochemical properties of lignin was studied and reported for the first time. The present work helps to choose the appropriate type of nuclear radiation for the pretreatment process as per the applications.

Characterization of lignin and lignin-derivatives from biomass. Application as expander of Lead-acid battery

Expanders, as lignosulfonates, are crucial for a good performance of Pb/acid batteries. In the process of discharge, the Pb and the PbO2 go to PbSO4. The formed PbSO4 is adsorbed on the surface of the Pb electrode and dramatically reduces the lifetime of the battery by the formation of big PbSO4 crystals. In order to prevent that, the addition of expanders in the negative electrode is an economic solution to prevent the formation of big crystals. In this investigation, we propose the synthesis of several lignosulfonates obtained from lignin of many biomass origins. We have derivatized nine samples of lignin via microwave-assisted sulfonation, then we have characterized how efficient is the chosen synthesis method. The lignosulfonates obtained have been characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (1HNMR), two-dimensional correlated spectroscopy (COSY), and elemental analysis to acquire some relevant information about their structure in terms of functional groups. In this way, three commercial lignosulfonates, Vanisperse A, Indulin AT, and Oakwood, have been selected as references for our comparisons. Moreover, we have checked their electrochemical properties, using electrochemical techniques to compare their behavior with respect to the commercial lignosulfonates. Finally, we have selected one of them and we have tested its performance as an expander in a Pb/acid battery. That result is a very promising first approach, and we can conclude that lignosulfonates derivatives are a good and low-cost choice to improve the lifetime of Pb/acid batteries. In particular, it is shown that the incorporation of LignosB improves the cell formation as well as the first capacity (36.30% more) and the charge acceptance (63.16% more), being these relevant parameters in the performance of Pb/acid batteries.

H2O2 generated through ORR on cathode in a protic ionic liquid and its utilization in lignin valorization

The quantitative study of lignin valorization by H 2 O 2 generated through ORR process on the cathode in [Et 3 NH][HSO 4 ] was performed, that is approximately 20 molecules of H 2 O 2 were needed to produce one molecule of vanillin from lignin depolymerization. • H 2 O 2 generated through ORR process on cathode in electrolyte of [Et 3 NH][HSO 4 ]. • Application of H 2 O 2 electro-generated in situ to lignin valorization. • About 2 molecules of H 2 O 2 needed for breaking one α-O-4 ether bond in PBP molecule. • About 19.4 molecules of H 2 O 2 required for producing one molecule of vanillin from lignin. Lignin valorization to obtain small aromatic compounds requires selective oxidation to break the linkage bonds among the C9 units in lignin molecules. It has been reported that hydrogen peroxide (H 2 O 2 ) generated through the oxygen reduction reaction (ORR) on the cathode could be an appropriate oxidizing reagent to depolymerize lignin, but the current efficiency was still unsatisfactory. In this study, a protic ionic liquid [Et 3 NH][HSO 4 ] is used as electrolyte instead of aqueous solution, and the generation rate of H 2 O 2 is determined as 0.0563 mmol cm −2 min −1 and the current efficiency of 79.7 % by the Ti-TPyP colorimetric method. Then using p -benzylethoxyphenol (PBP) as a lignin model compound, it is figured out that approximately-two molecules of H 2 O 2 are consumed for breaking one α-O-4 ether bond. Finally, in the electrolysis of an actual lignin sample, it is evaluated that about 19.4 molecules of H 2 O 2 are needed for producing one molecule of vanillin when taking vanillin as a representative degradation product of lignin.

Primary release and transformation of inorganic and organic sodium during fast pyrolysis of sodium-loaded lignin

This study employs a wire-mesh reactor (WMR) to understand the primary release and transformation of inorganic and organic sodium during fast pyrolysis of various sodium-loaded lignin samples at 300–800 °C. Due to the minimization of volatile-char interactions in WMR, the overall sodium release during lignin pyrolysis is relatively low, i.e., ∼9–11% and ∼7–14% for the inorganic and inorganic sodium loaded lignin, respectively. The presence of the inorganic sodium in the condensed volatiles (so-called oil) clearly indicates the important role of thermal ejection in the release of the inorganic sodium, since sodium salts are unlikely to evaporate under current conditions. While the release of the organic sodium into oil can be due to both thermal ejection of aerosols and evaporation of low carboxylates. Despite the low sodium release, significant transformation of the inorganic and organic sodium can take place during lignin pyrolysis. For the inorganic sodium loaded lignin, the inorganic sodium decreases continuously from ∼67% at 300 °C to ∼42% at 800 °C, accompanied by a steady increase in the organic sodium (i.e., the ion-exchangeable sodium) from ∼17% at 300 °C to ∼37% at 800 °C. While for the organic sodium loaded lignin, its transformation into the inorganic sodium is faster at higher temperatures, leading to a large increase in the inorganic sodium (i.e., carbonates) from ∼9% at 300 °C to ∼48% at 800 °C, as well as a reduction in the organic sodium from ∼79% at 300 °C to ∼28% at 800 °C. The data generated in this study will be important to understand the catalytic mechanism of sodium during thermochemical processing of alkali lignin for the production of bioenergy and biofuels.

The effects of pH on the precipitation of rice straw lignin from An Giang, Vietnam

This research aimed to extract lignin from rice straw and reveal the pH value of diluted acid at which the most effective yield of lignin was precipitated. In this study, rice straw obtained from local fields in the An Giang province of Vietnam and sodium hydroxide 2 M was employed to extract lignin from rice straw. Hydrochloric acid was used to adjust the sample pH values to be in the range of 1.5-3.5. Fourier-transform infrared spectroscopy (FTIR) analysis was used to characterize the functional groups of the lignin materials. Thermogravimetric analysis (TGA) analysis was employed to supply information on the thermal decomposition of the lignin samples. Herein, the results showed that lignin precipitated at different pH values affected its thermal properties. At 700oC, the yield of the remaining lignin components were 56% at pH 2.0, but the weight loss of lignin samples precipitated at pH 3.5 dropped to 85% because many non-lignin substances existed in the samples. The yield of the crude lignin samples obtained were 16.51, 17.66, 15.27, 14.33 and 13.26% for pH of 1.5, 2.0, 2.5, 3.0 and 3.5 respectively. The crystallite regions played an important role in the lignin structures. The spectrum peaks at pH 1.5, 2.0 and 2.5 were broader than the peaks at pH 3.0 and 3.5. The results demonstrated the highest percentage of lignin precipitate was collected at pH 2.0.