Mechanism study of ternary deep eutectic solvents with protonic acid for lignin fractionation

Enhanced hemicellulose retention in lignocellulosic biomass fractionation with ethylene glycol-regulated deep eutectic solvent

Fractionation of lignocellulosic biomass into carbohydrates (cellulose, hemicellulose) and lignin is essential for advancing biorefinery processes. However, achieving high retention of hemicellulose during pretreatment remains a significant challenge. In this study, an ethylene glycol (EG)-regulated deep eutectic solvent (DES) strategy was employed for corncob fractionation. The addition of EG increased hemicellulose retention from 55.7% to 77.9%. Additionally, delignification and cellulose retention reached up to 88.8% and 88.1%, respectively. Density functional theory analysis indicated that strong hydrogen bonds between DES-EG and lignin are the primary driving force for delignification. Molecular dynamics simulations demonstrated that the incorporation of EG significantly weakens the interaction energies between solvent and hemicellulose. This protective effect preserves the structural integrity of glycosidic linkages and hydroxyl groups in hemicellulose. This work presents a sustainable solution to mitigate hemicellulose loss, offering a promising advancement for eco-friendly biomass pretreatment.

Comprehensive utilization of poplar sawdust for glucose, xylose and lignin production using aluminum salt-based deep eutectic solvent

Deep eutectic solvents (DESs) demonstrate significant promise in biorefining because of their ability to break down the complex and resistant structure of lignocellulose. In this study, a ternary DES system composed of AlCl3·6H2O, formic acid (FA), and water was designed and applied for the pretreatment of poplar sawdust. The presence of AlCl3·6H2O and FA provides Lewis and Brønsted acid sites, respectively. The addition of water adjusts the acidity of the DES system, thereby increasing the separation efficiency of the three lignocellulose components. Under optimal conditions, DES (30 wt% water content) pretreatment achieved a high cellulose recovery rate of 91.3 %, with xylose yields and lignin recovery rates of 79.5 % and 90.1 %, respectively. Additionally, the cellulose residue achieved an enzymatic digestion efficiency of 97.9 %. The mass balance results revealed that the pretreatment strategy could utilize 77.6 % of the raw poplar sawdust, confirming that the method is economical and feasible. This DES pretreatment technique presents significant promise for biomass valorization.

Supramolecular room-temperature flowable lignin (RTFL)/MXene for sustainable coatings

Thermoelectric coatings with high biomass content, excellent storage stability, and solvent-free curing capabilities are highly desirable yet challenging. In this study, we demonstrate that supramolecular room-temperature flowable lignin (RTFL) was introduced as an effective carrier for the two-dimensional conductive material MXene, facilitating the development of supramolecular sustainable coatings. Lignosulfonic acid (LA) and polymerizable quaternary ammonium salt monomers were successfully utilized to synthesize the RTFL with ultra-low glass transition temperatures (-67--38 °C) using a deep eutectic strategy, with lignin content reaching up to 50 wt% without relying on traditional solvents. The RTFL demonstrated, serving as a macromolecular solvent, effectively dispersing and stabilizing MXene while preventing long-term oxidation. When directly coated onto various substrates and subsequently subjected to rapid photopolymerization, the RTFL/MXene coating exhibited remarkable photo-thermal-electric conversion properties. These features meet the requirements of various electrical applications, including Stirling engines and battery charging lamps. This supramolecular approach offers a pathway for developing high biomass content coatings suitable for environmental and energy-related applications.

Tailored bamboo fractionation with ternary deep eutectic solvent system to maximize biorefinery toward enzymatic saccharification and lignin recovery

Six different ternary deep eutectic solvent (DES) of tetraethylammonium chloride (TEAC)/oxalic acid (OA)-polyols were synthesized to improve the production of fermentable sugars and lignin by-products. The bamboo fractionation and bioconversion of cellulose residues can be enhanced by the ternary DES pretreatment, and its increasing efficiency was positively related to the alkyl carbon chain length and hydroxyl number of polyols in the hydrogen bond donor. The 1,4-butanediol (BDO)-assisted DES pretreatment showed excellent performance in achieving high xylan removal (86.7 %) and delignification (91.98 %). The pretreated bamboo was used for enzymatic hydrolysis and ethanol fermentation, with glucose yield and ethanol production of 76.13 % and 16.17 g/L, which was significantly improved by 30 % and 48 % compared to bamboo treated with corresponding binary TEAC/OA. The characterization of trinary pretreated bamboo revealed that the addition of polyols helped to protect the β-O-4 substructure of lignin, reduce the recondensation of lignin fragments, and thus enhance enzyme digestibility. Furthermore, 37.9% of lignin with high purity and highly active hydroxyl substructures was recovered. The proposed novel TEAC/OA-BDO DES mixture has great potential as an effective pretreatment solvent for future bamboo biorefinery.

Comprehensive investigation of the interactions between natural rubber and lignin by molecular dynamics simulation

Currently, the interaction behavior of natural rubber-lignin (NR-L) remains unclear. In this study, we successfully replicated the density, glass transition temperature, and mechanical properties of NR-L using molecular dynamics coupled with GAFF. Using these models, we rigorously investigated the interaction behavior of these systems, which revealed that when the ambient temperature was lower than the thermal decomposition temperature, there was almost no impact on system properties, including density, structure, interaction forces, radial pair distribution function, free volume, radius of gyration, and lignin hydrogen bonding, as no significant enthalpy change occurred. The influence of hardwood lignin and softwood lignin on NR strength varied according to the concentration of lignin. At low concentration, the electron density cloud between highly branched hardwood lignin and NR is lower, leading to smaller interactions. However, at higher concentrations, the van der Waals term between the less polar and larger number of atoms of hardwood lignin and NR becomes stronger, resulting in the opposite trend being observed. Furthermore, NR-L is governed primarily by van der Waals forces, while lignin-lignin is governed primarily by electrostatic interactions. These detailed characterizations offered valuable insight for future research endeavors aimed at designing and synthesizing green NR-L composites at the atomic scale.

A ternary deep eutectic solvent for efficient biomass fractionation and lignin stabilization

The efficient isolation and lignin stabilization are critical to the fractionation process of lignocellulosic biomass, enabling the subsequent valorization of both carbohydrates and lignin. In this study, a ternary deep eutectic solvent pretreatment system with outstanding reusability has been developed. Under optimal conditions (ChCl: MT: p-TsOH = 1:1:0.5, 120 °C, 60 min), the system efficiently removed 94.66 % of hemicellulose and 95.74 % of lignin while retaining 84.50 % of cellulose. Glucose was obtained from the cellulose-rich solid residue via enzymatic hydrolysis, achieving an 87.12 % yield. This DES system inhibits lignin condensation through a dual mechanism of α-etherification and intermolecular forces (π-π stacking and hydrophobic interaction). The recovered lignin exhibits a low molecular weight (922-1049 g/mol), high phenolic hydroxyl content (2.57-3.37 mmol/g), low polydispersity (1.54-1.61), and high purity (93.02 %). Combined with its superior antioxidant activity and UV shielding properties, this lignin represents a promising new resource with potential applications.

Optimization of ultrasound-assisted deep eutectic solvents extraction of rutin from Ilex asprella using response surface methodology

Taking the extraction amount of rutin as the index, the extraction process of rutin from Ilex asprella (Hook. et Arn.) Champ. ex Benth. using the ultrasonic-assisted deep eutectic solvent method was optimized through response surface method. The effects of various factors, including the types of deep eutectic solvent, molar ratio of the solvent, water content, liquid-solid ratio, the temperature, power and time of ultrasound on the extraction amount of rutin were investigated. In accordance with the result of univariate experiments, the extraction process was optimized through employing the Box-Behnken response surface design method. A three-factor, three-level experimental model was established with the liquid-solid ratio, water content and ultrasonic time as variables. The findings indicated that the optimal technological conditions were as stated below: the molar ratio of lactic acid to choline chloride at 1:1, the ultrasonic extraction temperature at 40 °C, the ultrasonic extraction time at 31 min, the water content at 28%, and the liquid-solid ratio at 20:1 mL/g. Under optimal conditions, the validation experimental result revealed that the extraction amount of rutin was 86.553 ± 1.35 µg/g, with an absolute error of less than 0.6% in comparison with the predicted value of the model. The use of deep eutectic solvents for the extraction of rutin and the application of response surface method for optimizing the extraction process of rutin from Ilex asprella (Hook. et Arn.) Champ. ex Benth. were demonstrated. The present study provided a reference for the comprehensive utilization of Ilex asprella (Hook. et Arn.) Champ. ex Benth..

Microwave-assisted extraction of cellulose and aromatic compounds from rose petals based on deep eutectic solvent

High-value utilization of agricultural wastes such as rose petals promotes the development of the dual carbon economy. In this study, rose petals were pretreated by microwave-assisted deep eutectic solvent (DES). Choline chloride-ethylene glycol (ChCl-EG) was used as the basis for the addition of P-toluenesulfonic acid (TsOH) or Ferric chloride (FeCl3). Forming ternary DESs, as well as designing quaternary DESs with a synergistic effect. The effects of different types of multicomponent DES on treating anthocyanins, cellulose, and lignin in rose flowers were explored. The results showed that the highest anthocyanin extraction of 173.71 mg/g and the highest lignin removal of 40.80 % could be achieved after tetrad DES pretreatment when the molar ratio was ChCl:EG:TsOH:FeCl3 = 1:2:0.3:0.3. The interaction energy between anthocyanins and DES was calculated using density functional theory (DFT), and the maximum was -543.14 kcal/mol. This study demonstrated that DES pretreatment can provide novel insights for the utilization of roses in high-value.

Fractionation of poplar wood with different acid hydrotropes: Lignin dissolution behavior and mechanism evaluation

Acid hydrotropes was considered a green medium for efficient wood fractionation at mild conditions. This study reported a comparative study on the dissolution of lignin in different acid hydrotropes, including p-toluenesulfonic acid (p-TsOH), 4-hydroxybenzenesulfonic acid (4-HSA), 5-sulfosalicylic acid (5-SSA), and maleic acid (MA). Under identical treatment conditions (80 °C, 60 min, and 70 % acid concentration), the removal of wood lignin varied significantly among four acid hydrotropes, 4-HSA exhibited the highest removal rate at 88.0 %, followed by p-TsOH at 81.2 %, 5-SSA at 51.1 %, and MA at 26.2 %. The molecular mechanism of the lignin dissolution was analyzed by quantum chemistry (QC) calculation and molecular dynamics (MD) simulation. The higher absorb free energy (E(absorb)) of the 4-HSA and veratrylglycerol-β-guaiacyl ether (VG) complex (E(absorb) = 17.97 kcal/mol), and the p-TsOH and VG complex (E(absorb) = 17.16 kcal/mol) contributed to a higher efficiency of lignin dissolution. Under the same level of lignin removal (~ 60 %), the four acid hydrotropes showed variations in the β-O-4 content of the extracted lignin: 4-HSA (3.1 %) < 5-SSA (10.4 %) < p-TsOH (15.9 %) < MA (63.7 %). The acidity and critical aggregation concentrations of acid hydrotropes were found to influence the content of β-O-4 bonds in the extracted lignin.

Co-production of 2,5-dihydroxymethylfuran and furfuralcohol from sugarcane bagasse via chemobiocatalytic approach in a sustainable system

2,5-Dihydroxymethylfuran and furfuryl alcohol serve as versatile building-blocks in pharmaceuticals, polymers, and value-added intermediates. To develop an efficient and sustainable method for their production from biomass, a combined approach using deep eutectic solvent Citric acid:Betaine (CTA:BT) for bagasse catalysis and recombinant E. coli SCFD23 for bioreduction of bagasse-derived 5-hydroxymethylfurfural and furfural was devised. Bagasse was effectively transformed into 5-hydroxymethylfurfural (48 mM) and furfural (14 mM) in CTA:BT (8 wt%)-water at 170 °C for 30 min. Bioreduction of 5-hydroxymethylfurfural and furfural by SCFD23 cell co-expressing formate dehydrogenase and NAD(P)H-dependent aldehyde reductase (SsCR) yielded 2,5-dihydroxymethylfuran (90.0 % yield) and furfuryl alcohol (99.0 % yield) in 6 h, using biomass-derived formic acid, xylose and glucose as co-substrates. Molecular docking confirmed the stable binding and reductase activity of SsCR with the biomass-derived 5-hydroxymethylfurfural and furfural. An efficient and eco-friendly chemobiological approach was applied for co-production of 2,5-dihydroxymethylfuran and furfuryl alcohol from biomass in one-pot two-step reaction.

Recent advances in biorefineries based on lignin extraction using deep eutectic solvents: A review

Considering the urgent need for alternative biorefinery schemes based on sustainable development, this review aims to summarize the state-of-the-art in the use of deep eutectic solvent pretreatment to fractionate lignocellulose, with a focus on lignin recovery. For that, the key parameters influencing the process are discussed, as well as various strategies to enhance this pretreatment efficiency are explored. Moreover, this review describes the challenges and opportunities associated with the valorization of extraction-derived streams and highlights recent advancements in solvent recovery techniques. Furthermore, the utilization of computational models for process design and optimization is introduced, as the initial attempts at the economic and environmental assessment of this lignocellulosic bioprocess based on deep eutectic solvents. Overall, this review offers a comprehensive perspective on the recent advances in this emerging field and serves as a foundation for further research on the potential integration of deep eutectic pretreatment in sustainable multi-product biorefinery schemes.

Structure investigation of light-colored lignin extracted by Lewis acid-based deep eutectic solvent from softwood

Lignin is the most abundant natural phenolic polymer. However, the severe condensations of industrial lignin resulted in an undesirable apparent morphology and darker color, which hindered its application in the field of daily chemicals. Therefore, a ternary deep eutectic solvent is used to obtain lignin with light-color and low condensations from softwood. The results showed that the brightness value of lignin extracted from aluminum chloride-1,4-butanediol-choline chloride at 100 °C and 1.0 h was 77.9, and the lignin yield was 32.2 ± 0.6%. It is important that 95.8% of β-O-4 linkages (β-O-4 and β-O-4') was retained. Lignin is used to prepare sunscreens and is added to physical sunscreens at 5%, with SPF up to 26.95 ± 4.20. Meanwhile, enzyme hydrolysis experiments and reaction liquid composition tests were also conducted. In conclusion, a systematic understanding of this efficient process could facilitate high-value utilization of lignocellulosic biomass in industrial processes.

Exploration of the interaction mechanism of lignocellulosic hybrid systems based on deep eutectic solvents

The interactions of three deep eutectic solvents (DES) choline chloride-glycerol (ChCl-GLY), ChCl-lactic acid (ChCl-LA) and ChCl-urea (ChCl-U) with cellulose-hemicellulose and cellulose-lignin hybrid systems were investigated using the simulated computational approach. Aiming to simulate DES pretreatment of real lignocellulosic biomass in nature. DES pretreatment could disrupt the original hydrogen bonding network structure among the lignocellulosic components and reconstruct the new DES-lignocellulosic hydrogen bonding network structure. ChCl-U had the highest intensity of action on the hybrid systems, removing 78.3% of the hydrogen bonds between cellulose-4-O-methyl Gluconic acid xylan (cellulose-Gxyl) and 68.4% of the hydrogen bonds between cellulose-Veratrylglycerol-b-guaiacyl ether (cellulose-VG), respectively. The increase of urea content facilitated the interaction between DES and lignocellulosic blend system. Finally, the addition of appropriate water (DES:H₂O = 1:5) and DES formed the new DES-water hydrogen bonding network structure more favorable for the interaction of DES with lignocellulose.

Sustainable lignocellulose fractionation by integrating p-toluenesulfonic acid/pentanol pretreatment with mannitol for efficient production of glucose, native-like lignin, and furfural

A new cutting-edge lignocellulose fractionation technology for the co-production of glucose, native-like lignin, and furfural was introduced using mannitol (MT)-assisted p-toluenesulfonic acid/pentanol pretreatment, as an eco-friendly process. The addition of optimized 5% MT in pretreatment enhanced the delignification rate by 29% and enlarged the surface area and biomass porosity by 1.07-1.80 folds. This increased the glucose yield by 45% (from 65.34 to 94.54%) after enzymatic hydrolysis relative to those without MT. The extracted lignin in the organic phase of pretreatment exhibited β-O-4 bonds (61.54/100 Ar) properties of native cellulosic enzyme lignin. Lignin characterization and molecular docking analyses revealed that the hydroxyl tails of MT were incorporated with lignin and formed etherified lignin, which preserved high lignin integrity. The solubilized hemicellulose (96%) in the liquid phase of pretreatment was converted into furfural with a yield of 83.99%. The MT-assisted pretreatment could contribute to a waste-free biorefinery pathway toward a circular bioeconomy.

Preparation mechanism and performance evaluation of deep eutectic solvent-lignin/ZnO composites by one-pot

Lignin, as the aromatic polymer in the world, has attracted more attention because of rich functional groups. In this study, lignin/ZnO composites was prepared by a simple one-pot method rely on urea and ZnCl₂-deep eutectic solvent (U/ZnCl₂-DES) as solvent and raw material. Through molecular dynamics simulation, the interaction mechanism between lignin functional groups and DES was clarified, and it was blended with waterborne polyurethane (WPU) to form a film, while the feasibility of its application in ultraviolet shielding was evaluated. The results showed that lignin /ZnO composites with excellent ultraviolet shielding properties were successfully prepared. Compared with lignosulfonate (SL), enzymatic hydrolysis lignin (EHL) was easier to combine with ZnO, which was benefit to prepare lignin/ZnO composites. When the addition of EHL/ZnO-N_12.5 complex was 1.5 %, the WPU film prepared has good mechanical properties (elongation at break was 25.53 %, tensile strength was 1422 kPa), good light transmission and ultraviolet shielding.

Effective fractionation of lignocellulose components and lignin valorization by combination of deep eutectic solvent with ethanol

Introduction: A combination of deep eutectic solvent with ethanol was developed for pretreatment of Broussonetia papyrifera to effectively extract lignin and promote the subsequent enzymatic hydrolysis. Methods: In order to further explore the optimal conditions for enzymatic hydrolysis, a central composite design method was applied. Results and Discussion: The correlation between each factor and glucose yield was obtained, and the optimal conditions was 160°C, 60 min, the ratio of DES to E was 1/1 (mol/mol). The results showed that compared with control, the glucose yield increased by 130.67% under the optimal pretreatment conditions. Furthermore, the specific surface area of biomass was increased by 66.95%, and the content of xylan and lignin was decreased by 86.71% and 85.83%. The correlation between xylan/lignin removal and enzymatic hydrolysis showed that the removal of lignin facilitated the glucose yield more significantly than that of xylan. To further explore the lignin valorization, the structural and antioxidant analysis of recovered lignin revealed that high temperature was favorable for lignin with good antioxidant performance. This pretreatment is a promising method for separating lignin with high antioxidant activity and improving cellulose digestibility.