High-quality Lignin Research Articles

Preparation of lignin oil with high H content by electrolyzing alkali lignin pretreated by organic thiol/hydrogen peroxide /ethylene glycol

Pretreatment can improve the reaction selectivity of lignin, promote the subsequent electrolytic catalysis of lignin depolymerization and conversion into high-quality lignin oil, thereby enhancing the energy conversion efficiency of lignin. The degree of depolymerization and electrochemical reduction of lignin under different pretreatment methods was investigated in this study, it was found that ethylene glycol /hydrogen peroxide/β-mercaptoethanol can break β-O-4 bond in a mild condition to increase the depolymerization performance of lignin, and reduced its number-average molecular weight significantly. The effects of electrode material, reaction temperature and current density on the yield of lignin oil and volatile component content were discussed. The highest the yield of lignin conversion could reach 95.0 %, and small molecular products dominated by alkanes and aromatics were obtained, of which the monomer yield was 25.1 wt%, which could reduce the oxygen carbon ratio of lignin effectively, improve the calorific value of lignin oil (34.39 MJ/kg). This study will provide technical reference for the greenly and efficiently conversion of lignin into hydrocarbon fuels under milder conditions.

Sustainable Lignin Extraction Using a Mild Acidic γ-Valerolactone Process for the Identification of White and Red Oaks.

Current wood identification struggles to differentiate white and red oak (Quercus alba and Quercus rubra) due to highly similar microstructures, as demonstrated by morphological microscope analysis. The present research explores lignin composition as a potential discriminating factor. Here, a rapid and sustainable method for extracting high-quality lignin from oak samples using acidic γ-valerolactone (GVL) under mild conditions is described. As-extracted lignin is thoroughly characterized using various analytical methods, and results reveal a distinct structural difference between the lignin from the two species. White oak lignin possesses a unique "Hibbert ketone" unit detectable by nuclear magnetic resonance spectroscopy (NMR), which is absent in red oak lignin. In addition, infrared spectroscopy differentiates the species based on specific carbonyl groups present in their lignin. These findings suggest that identifying the presence of the Hibbert ketone unit in lignin may offer a highly efficient and reliable method for differentiating white and red oak, opening new avenues for wood identification.

Modeling lignin extraction with ionic liquids using machine learning approach

Lignin, next to cellulose, is the second most common natural biopolymer on Earth, containing a third of the organic carbon in the biosphere. For many years, lignin was perceived as waste when obtaining cellulose and hemicellulose and used as a biofuel for the production of bioenergy. However, recently, lignin has been considered a renewable raw material for the production of chemicals and materials to replace petrochemical resources. In this context, an increasing demand for high-quality lignin is to be expected. It is, therefore, essential to optimize the technological processes of obtaining it from natural sources, such as biomass. In this work, an investigation of the use of machine learning-based quantitative structure-property relationship (QSPR) modeling for the preliminary processing of lignin recovery from herbaceous biomass using ionic liquids (ILs) is described. Training of the models using experimental data collected from original publications on the topic is assumed, and molecular descriptors of the ionic liquids are used to represent structural information. The study explores the impact of both ILs' chemical structure and process parameters on the efficiency of lignin recovery from different bio sources. The findings give an insight into the extraction process and could serve as a foundation for further design of efficient and selective processes for lignin recovery using ionic liquids, which can have significant implications for producing biofuels, chemicals, and materials.

Cascade fractionation of bamboo shoot shells into high-yield xylose, easily digestible cellulose and high-quality lignin nanoparticles by tailored catalytic hydrothermal–hydrated alkaline deep eutectic solvents pretreatment

The high complexity and compactness of inherent structure in lignocellulosic materials (LCM) leads to the difficulty of fractionation and conversion of its major component, which is the key obstacle limiting the value-added utilization of LCM. In this work, a cascade fractionation strategy, coupling catalytic hydrothermal pretreatment (CHTP, choline chloride: ethylene glycol: AlCl3, ChCl/ EG/ AlCl3) with hydrated alkaline deep eutectic solvent (HADES, triethylbenzyl ammonium chloride/ethanolamine, TEBAC/EM) treatment, was proposed to fractionate dendrocalamus latiftorus munro shoot shells (DLMSS). The results showed that considerably high hemicelluloses removal (94.57 %) and xylose yield (90.73 %) were achieved by the first step (CHTP, 160 °C, 1 h, 2 % of catalyst loading). The cascaded HADES treatment realized 90.25 % delignification ratio under the optimal conditions (120 °C, 3 h, 75 % of ADES loading), and the obtained residue could be easily converted into high-yield (93.35 %) of glucose via enzymatic saccharification. In addition, multiple enrichment cycle strategy (MECS) was performed to facilitate the recyclability of the HADES. The results showed that the enriched lignin recovered by MECS was activated by in-situ demethoxylation reaction. And such lignin fraction could be easily assembled into homogeneous lignin nanoparticles (LNPs, ∼31.51 nm in diameter) by simple sonication. Meanwhile, the MECS signally energized the antioxidant activity of the enriched lignin. Based on the high-efficiency cascade fractionation with the coupled CHTP-HADES fractionation strategy, it will observably boost the effectiveness and scalability of the advanced biorefinery strategy.

Efficient Fast Fractionation of Biomass Using a Diol-Based Deep Eutectic Solvent for Facilitating Enzymatic Hydrolysis and Obtaining High-Quality Lignin.

Current DES pretreatment is often performed under relatively severe conditions with high temperature, long time, and high DES usage. This work studied a short-time diol DES (deep eutectic solvent) pretreatment under mild conditions to fractionate the bamboo, facilitate enzymatic hydrolysis, and obtain high-quality lignin. At an optimized condition of 130 °C for only 10 min, lignin and xylan removal reached 61.34 % and 84.15 %, with residual glucan showing a ~90 % enzymatic hydrolysis yield. Equally important, the dissolved lignin could be readily recovered with 97.51 % yield, exhibiting 96.65 % β-O-4 preservation. The fractionation and lignin protection mechanisms were unveiled by XRD, FTIR, cellulose-DP, 2D HSQC NMR, 31P NMR and GPC analysis. This study highlighted that short-time fractionation of bamboo can be achieved by a diol-based DES which is an ideal strategy to upgrade the lignocellulose biomass for high enzymatic hydrolysis yields and high-quality lignin stream.

Investigation of a Na2S-assisted deep eutectic solvent pretreatment for enhanced cellulose/xylan saccharification and high-quality lignin with abundant ether bond

Herein, a novel Na2S-facilitated deep eutectic solvent (DES) pretreatment using choline chloride/ethylene glycol/sodium sulfide system (ChCl/EG/Na2S) was proposed to fractionate moso bamboo (MB), which could result in as high as 70.93% lignin removal, while glucan and xylan showed high recovery of 93.83% and 55.59%, accompanied by excellent enzymatic digestibility. Remarkably, the recovered lignin possessed a high recovery yield (80.59%), which contained high β-O-4 bond content of 21.74–40.45/100Ar with very limited condensation structures. The fractionation behavior of the DES was investigated by composition analysis, SEM, FQA, FTIR, GPC, and NMR which revealed its working mechanism. This study highlighted that the Na2S DES could preserve most cellulose and hemicellulose in the solid while removing lignin substantially with intact structure, which contributes to the valorization of both carbohydrates and lignin in the biomass.

Green and sustainable production of high-purity lignin microparticles with well-preserved substructure and enhanced anti-UV/oxidant activity using peroxide-promoted alkaline deep eutectic solvent

Deep eutectic solvents (DESs) have emerged as promising and eco-friendly solvents for the efficient extraction of lignin from biomass due to their low cost and environmental benefits. Nevertheless, the prevalent use of acidic DESs in lignin extraction often results in excessive depolymerization and recondensation of lignin, thereby impeding its downstream applications. In this study, we developed a range of alkaline DESs (ADESs), both pure and peroxide-containing, for the extraction of high-quality lignin from bamboo. Moreover, carbon dioxide (CO2) was employed for the precipitation and regeneration of the extracted lignin. The obtained lignin fractions were comprehensively characterized in terms of yield, purity, morphology, solubility, structural features, and anti-UV/oxidant activity. The results showed that the monoethanolamine-based ADES demonstrated superior performance among the pure ADESs. Structural analysis confirmed the well-preserved substructures of lignin fractions obtained using ADESs, with β-O-4 bond retention ranging from 49.8 % to 68.4 %. The incorporation of a suitable amount of peroxide improved lignin yield, morphology, solubility, and anti-UV/oxidant activity. Additionally, the anti-UV/oxidant activity of lignin exhibited a positive correlation with its phenolic hydroxyl content. This study provides a valuable reference for the green and sustainable production and valorization of lignin within the existing biorefinery framework.

Organosolv Pretreatment of Cocoa Pod Husks: Isolation, Analysis, and Use of Lignin from an Abundant Waste Product.

Cocoa pod husks (CPHs) represent an underutilized component of the chocolate manufacturing process. While industry's current focus is understandably on the cocoa beans, the husks make up around 75 wt % of the fruit. Previous studies have been dominated by the carbohydrate polymers present in CPHs, but this work highlights the presence of the biopolymer lignin in this biomass. An optimized organosolv lignin isolation protocol was developed, delivering significant practical improvements. This new protocol may also prove to be useful for agricultural waste-derived biomasses in general. NMR analysis of the high quality lignin led to an improved structural understanding, with evidence provided to support deacetylation of the lignin occurring during the optimized pretreatment. Chemical transformation, using a tosylation, azidation, copper-catalyzed click protocol, delivered a modified lignin oligomer with an organophosphorus motif attached. Thermogravimetric analysis was used to demonstrate the oligomer's potential as a flame-retardant. Preliminary analysis of the other product streams isolated from the CPHs was also carried out.

Levulinic Acid-Based "Green" Solvents for Lignocellulose Fractionation: On the Superior Extraction Yield and Selectivity toward Lignin.

The high potential use of lignin in novel biomaterials and chemicals represents an important opportunity for the valorization of the most abundant natural resource of aromatic molecules. From an environmental perspective, it is highly desirable replacing the hazardous methods currently used to extract lignin from lignocellulosic biomass and develop more sustainable and environmentally friendly approaches. Therefore, in this work, levulinic acid (a "green" solvent obtained from biomass) was successfully used, for the first time, to selectively extract high-quality lignin from pine wood sawdust residues at 200 °C for 6 h (at atmospheric pressure). Moreover, the addition of catalytic concentrations of inorganic acids (i.e., H2SO4 or HCl) was found to substantially reduce the temperature and reaction times needed (i.e., 140 °C, 2 h) for complete lignin extraction without compromising its purity. NMR data suggests that condensed OH structures and acidic groups are present in the lignin following extraction. Levulinic acid can be easily recycled and efficiently reused several times without affecting its performance. Furthermore, excellent solvent reusability and performance of extraction of other wood residues has been successfully demonstrated, thus making the developed levulinic acid-based procedure highly appealing and promising to replace the traditional less sustainable methodologies.

Optimization of lignin extraction from bamboo by ultrasound-assisted organosolv pretreatment

For a sustainable biorefinery, reduction in the recalcitrance of lignocellulosic biomass is very crucial for the efficient utilization of each fraction. The present work investigated an integrated pretreatment method to recover high-quality lignin along with the cellulose-rich pulp. An optimization study employing response surface methodology investigated the synergistic effects of ultrasound and organosolv pretreatment from Bambusa tulda (bamboo). The optimal condition (180 °C, 55 min, and 30 min sonication) resulted in 65.81 ± 2.40% of lignin yield with 95.37 ± 1.17% purity. A reduction in 7.85% yield and 1.54% purity of lignin with organosolv pretreatment highlighted the efficacy of sonication in lignin extraction. Ultrasound resulted in homolytic cleavage of the lignin-carbohydrate bond that enhanced delignification and increase the cellulose crystallinity. NMR, FTIR, GPC, and TGA of lignin suggested the superiority of sonication in maintaining lignin quality. A significant amount of β-O-4 linkages in extracted lignin is favorable for its subsequent valorization.

Fascinating polyphenol lignin extracted from sawdust via a green and recyclable solvent route

Due to the complexity, heterogeneity and recalcitrant structure of lignin, the extraction of multifunctional lignin directly from lignocellulose is still a challenge. Here, a green and recyclable route was proposed to separate high-quality lignin and tailor its functionalities. Through tuning the components of deep eutectic solvent (DES) and separation procedures, DES extracted lignin (DESL) exhibited high purity of 99.6 %, yield of 83.2 % and phenolic hydroxyl content of 8.33 wt%. The results of FTIR and 13C NMR demonstrated that DESL possessed more oxygen-containing reactive groups compared with commercial lignin (CL), enabling DESL with more superior functional activities. DESL exhibited higher antioxidant activity with the DPPH capture rate of 73.2 %. Meanwhile, DESL showed strong bactericidal effects against E. coli (100 %) and S. aureus (100 %) due to higher phenolic hydroxyl content, which could destroy bacterial cell membranes and inhibit bacterial metabolism by interacting with phospholipid layer and protein. Additionally, DESL displayed strong UV absorption and could be blended with polyurethane to enhance UV shielding property of polyurethane composite film with >50 of UPF value. In summary, DES treatment is a suitable strategy for high-quality lignin separation, which opens a broad spectrum of possibilities for lignin valorization.

Ammonia–Mechanical Pretreatment of Wheat Straw for the Production of Lactic Acid and High-Quality Lignin

In this study, wheat straw was fractionated into carbohydrates (cellulose and hemicellulose) by ammonia–mechanical pretreatment for l-lactic acid fermentation. Under optimal conditions (aqueous ammonia concentration: 19% w/w, liquid–solid ratio: 2.1:1 w/w, holding time: 4.80 h), the delignification was more than 60%. After enzymatic hydrolysis, the maximum conversions of cellulose and hemicellulose were 92.5% and 83.4% based on the pretreatment residue, respectively. The wheat straw hydrolysate was used to produce l-lactic acid with Thermoanaerobacter sp. DH-217G, which obtained a yield of 88.6% and an optical purity of 99.2%. The ammonia–mechanical pretreatment is an economical method for the production of fermentable monosaccharide, providing potential for further downstream high value-added applications.

High Temperature Lignin Separation for Improved Yields in Ethanol Organosolv Pre-Treatment

The full utilization of renewable raw materials is necessary for a sustainable economy. Lignin is an abundant biopolymer, but is currently mainly used for energy production. Ethanol organosolv pre-treatment produces high-quality lignin, but still faces substantial economic challenges. Lignin solubility increases with temperature, and previous studies have shown that it reprecipitates during cooling after the pre-treatment. Thus, a possibility for the optimization of lignin production with this process can be the separation of extract and residual biomass at high temperatures. In this work, lignin was extracted from wheat straw at 180 °C, and the extract was separated from the remaining solids at several temperatures after the pre-treatment. The results show that 10.1 g/kg of lignin and 2.2 g/kg of carbohydrates are dissolved at the pre-treatment temperature of 180 °C, which is reduced to 8.6 g/kg of lignin and 1.2 g/kg of carbohydrates after cooling. The precipitation of lignin separated from the extracts at 180 °C showed that a higher lignin concentration at high temperatures results in a 46% improvement in the yield of solid lignin, while there was no significant impact on the lignin purity.

Hydrogen Peroxide Treatment of Softwood-Derived Poly(Ethylene Glycol)-Modified Glycol Lignin at Room Temperature.

Recently, a large-scale production system of softwood-derived poly(ethylene glycol) (PEG)-modified glycol lignin (GL) was developed to produce high-quality lignin derivatives with substantially controlled chemical structures and attractive thermal properties. In this study, the further upgrading of GL properties with carboxy functionalization was demonstrated through the room-temperature hydrogen peroxide (H2O2) treatment with the mass ratio of H2O2 to GL, 1:1 and 1:3, for 7 d. The changes in the chemical structure, carboxy group content, molecular weight, and thermal properties of the insoluble portions of partially oxidized glycol lignins (OGLs) were then investigated. Nuclear magnetic resonance and thioacidolysis data revealed that the oxidative functionalization involved the cleavage of β-O-4 linkages and the oxidative cleavage of guaiacyl aromatic rings into muconic acid-type structures. This was validated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and potentiometric titration. Overall, the results suggested that the varying outcomes of carboxy group content (0.81-2.04 mmol/g OGL) after 7-d treatment depended on the type of the GL origin having varying amounts of the retained native lignin structure (e.g., β-O-4 linkages), which were prepared from different source-wood-meal sizes and PEG molecular masses.

A high-solid DES pretreatment using never-dried biomass as the starting material: towards high-quality lignin fractionation

This study investigated a high-solid diol deep eutectic solvent (DES) pretreatment using a wet substrate as the starting material.

Pretreatment with fermentable and recyclable deep eutectic solvent (DES) for improving resource utilization of biomass

A series of acidic FDES were prepared to pretreat lignocellulose. After pretreatment, solid product containing 82% cellulose, high quality lignin and liquid product containing hemicellulose were obtained, respectively. The enzymatic hydrolysis of the solid product could reach 84.5%. The enzymatic hydrolysate with the was used as feedstock for ethanol fermentation using commercial Saccharomyces cerevisiae live preparation instead of genetically engineered strains that can use 5-carbon sugars. The pretreatment solution was used as a raw material to culture Rhodotorula glutinis for microbial lipid production. phosphoric acid (PA) as a pretreatment catalyst could ensure the enzymatic efficiency compared with other acids, while more polysaccharide fractions could be formed. At the end of fermentation, the biomass could reach 30 g/L, and the lipid concentration could reach 7 g/L. In addition, the lignin prepared in this study has a consistent structure and low molecular weight, showing high potential for bio-based chemicals and materials conversion. According to the results of FDES reutilization, the pretreatment effect and fermentation effect of the FDES prepared here did not decrease significantly with the increase in the reutilization. The biomass pretreatment process developed in this study realized the full utilization of cellulose, hemicellulose, lignin and pretreatment solvent. It is innovative compared with the genetically engineered strain which mainly rely on the co-fermentation of glucose and xylose for cellulosic ethanol fermentation.

Technoeconomic evaluation of recent process improvements in production of sugar and high-value lignin co-products via two-stage Cu-catalyzed alkaline-oxidative pretreatment

BackgroundA lignocellulose-to-biofuel biorefinery process that enables multiple product streams is recognized as a promising strategy to improve the economics of this biorefinery and to accelerate technology commercialization. We recently identified an innovative pretreatment technology that enables of the production of sugars at high yields while simultaneously generating a high-quality lignin stream that has been demonstrated as both a promising renewable polyol replacement for polyurethane applications and is highly susceptible to depolymerization into monomers. This technology comprises a two-stage pretreatment approach that includes an alkaline pre-extraction followed by a metal-catalyzed alkaline-oxidative pretreatment. Our recent work demonstrated that H2O2 and O2 act synergistically as co-oxidants during the alkaline-oxidative pretreatment and could significantly reduce the pretreatment chemical input while maintaining high sugar yields (~ 95% glucose and ~ 100% xylose of initial sugar composition), high lignin yields (~ 75% of initial lignin), and improvements in lignin usage.ResultsThis study considers the economic impact of these advances and provides strategies that could lead to additional economic improvements for future commercialization. The results of the technoeconomic analysis (TEA) demonstrated that adding O2 as a co-oxidant at 50 psig for the alkaline-oxidative pretreatment and reducing the raw material input reduced the minimum fuel selling price from $1.08/L to $0.85/L, assuming recoverable lignin is used as a polyol replacement. If additional lignin can be recovered and sold as more valuable monomers, the minimum fuel selling price (MFSP) can be further reduced to $0.73/L.ConclusionsThe present work demonstrated that high sugar and lignin yields combined with low raw material inputs and increasing the value of lignin could greatly increase the economic viability of a poplar-based biorefinery. Continued research on integrating sugar production with lignin valorization is thus warranted to confirm this economic potential as the technology matures.

Effective biomass fractionation and lignin stabilization using a diol DES system

A sustainable and renewable biorefinery will increase the economic viability of lignocellulose-derived products. In this study, a diol-based deep eutectic solvent (DES) was developed to reduce the recalcitrance of bamboo, facilitate saccharification and valorize the lignin fraction. The DES pretreatment dramatically enhanced glucan digestibility by the effective removal of lignin (as high as 85.45%) and xylan (91.12%). Notably, the recovered lignin from DES pretreatment was protected during the fractionation, showing well-preserved β-O-4 structures (31.82%–59.06%). The mechanism of lignin protection was analyzed to be accomplished by incorporating the diol hydroxyl functional groups into the α position of the lignin β-O-4 structure via etherification. This study highlighted that diol DES is a promising pretreatment solvent to valorize both cellulose and lignin fractions with high enzymatic hydrolysis yield and high-quality lignin co-product.

Comparative study on the hydrogenolysis performance of solid residues from different bamboo pretreatments

Both alkaline organosolv and formaldehyde stabilization pretreatment can yield high-quality lignin by preventing condensation. For the hydrogenolysis of the pretreated solid residues, the highest yield of C2–C4 chemicals was 66.8% under alkaline organosolv pretreatment for 60 min. Specifically, the crimped fibers and residual lignin and hemicellulose increased the surface roughness of the residue by 40.6%, the crystallinity index decreased to 44.4%, and the crystal size was reduced to 2.15 nm, which in turn promoted hydrogenolysis of the residue. However, the increase of crystallinity and crystal size and the decrease in surface roughness of the formaldehyde stabilization pretreatment residue greatly hindered the conversion of polysaccharides. In addition, residual formaldehyde on the residue may also inhibit catalyst activity. Overall, this study provides novel perspectives on the full utilization of biomass, as well as new insights into the conversion of polysaccharides.

Ferric chloride aided peracetic acid pretreatment for effective utilization of sugarcane bagasse

The synergetic impacts of ferric chloride aided peracetic acid (FPA) pretreatment were investigated to enhance the total biomass utilization through effective cellulose conversion and high-quality lignin production. The sugarcane bagasse pretreatment with 2% peracetic acid (PAA) and 0.1 mol/L ferric chloride (FeCl3) effectively removed 57.3% of lignin and 72.2% of xylan while preserving ∼ 97% of cellulose from sugarcane bagasse under mild temperature (90 °C). The FPA pretreated sugarcane bagasse was effectively hydrolyzed with a glucose yield of 313.0 mg/g-biomass, which was 4.5 times higher than the yield of untreated biomass (69.75 mg/g-biomass) and 1.6 and 3.6 times higher than that of individual PAA and FeCl3 pretreated sugarcane bagasse, respectively. The regenerated lignin (FPA lignin) showed great potential for further valorization by preserving the major interunit linkage (up to 86% of β-O-4) without significant carbohydrate contamination and lignin condensation due to its mild reaction conditions. In this study, the combination of PAA and FeCl3 synergistically enhanced the pretreatment efficiency on sugarcane bagasse and resulted in high fermentable sugar and high-quality lignin production.