Rapid and near-complete dissolution of wood lignin at ≤80°C by a recyclable acid hydrotrope

An Ultrastrong and Ultraflexible Wood Veneer via Fiber Interaction Enhancement and Defect Reduction

Natural wood veneer is a flexible and sustainable material with significant potential for various applications. However, there are more defects in wood veneer, leading to lower strength, and the strengthening strategies currently used for wood blocks do not work well when applied to wood veneer. In this study, we processed the fragile wood veneer into an ultrastrong and ultraflexible material with a tensile strength of 578.4 MPa and preserved its beautiful wood texture. This enhancement is achieved by reducing defects within the veneer through adding cellulose molecules between the wood cell fibers. The resulting wood veneer is exceedingly flexible compared to natural wood, with a bending radius as small as 0.2 mm, while retaining its strength. This flexibility allows the veneer to be wrapped around other materials and improves the mechanical properties. The wood veneer exhibits much lower signal attenuation compared to carbon fiber fabric composites due to its electromagnetic transparency. Moreover, the environmental impact of producing each kilogram of this veneer is less than that of the carbon fiber material. These ultrastrong, ultraflexible, and sustainable properties of the wood veneer can enrich the family of lightweight, high-strength materials and enable a wide range of applications.

Exploring nanolignin as a sustainable biomacromolecule in polymer composites: Synthesis, characterization, and applications: A review

Nanolignin is a biomacromolecule nanomaterial obtained from lignin, a natural plant polymer. It has attracted considerable attention as a potential nanofiller for polymer composites owing to its remarkable properties, such as biodegradability, antioxidant activity, and high specific surface area. However, the development of biological macromolecule nano lignin-based polymer composites faces several challenges, mainly due to the complex structure and poor chemical compatibility of lignin with most polymers. A comprehensive summary of the functionalization strategies and synthesis techniques for nanolignin is provided in this article. The morphological, structural, and thermal characterization of nanolignin is also reviewed. Furthermore, this review summarizes the recent progress of nanolignin and its composites prepared using various polymers, such as polyvinyl alcohol, poly (methyl methacrylate), polylactic acid, phenol formaldehyde, and natural rubber. This study concludes by outlining the possible uses of nanolignin-reinforced polymer composites and the potential opportunities and disadvantages of using nanolignin as a reinforcement in polymer composites for several value-added applications.

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.

Lignin nano/micro-particles from agricultural biomasses: Developing direct precipitation for integrated biorefinery

The state-of-the-art, simple and scalable methods for lignin micro-/nano-particles recovery from agricultural biomasses were evaluated in this review. Being non-wood biomasses, these materials can be easily fibrillated, supporting the usage of mild soda or organic solvent pretreatment. Different approaches in particle recovery were compared to conclude that the bottom-up approach facilitates smaller particles towards the nano-size range whereas mechanical treatment can act as a supporting method to increase uniformity and reduce particle sizes after bottom-up precipitation. By combining with the pretreatment steps, direct one-pot lignin micro-/nano-particle recovery can be achieved using the lignin-containing black liquor or organosolv liquor. These lignin micro-/nano-particles can then be applied as high-value functional products in cosmetics, pharmaceuticals, environmental remediation, and energy sectors. The systematic evaluation of lignin micro-/nano-particles recovery from agricultural biomasses in this review can support the full utilization of these natural resources to aim towards a circular agriculture.

Improving fire retardancy and mechanical properties of polyurethane elastomer by acid hydrotropic lignin

Improving flame retardancy and mechanical strength of lignin-containing polyurethane is a great challenge. In this study, lignin with favorable reactivity and dispersity was extracted from poplar using acid hydrotrope p-TsOH in EtOH. The extracted acid hydrotrope lignin (AHL) was subsequently functionalized with nitrogen and phosphorus (FHL) and reacted with isocyanate to fabricate a fire-retardant polyurethane (FHL-PU). The resulting FHL-PU exhibited a five-fold increase in fracture toughness and remarkable reprocessability, attributable to the dual cross-linked network formed by dynamic hydrogen bonds and carbamate bonds between AHL and PU. Furthermore, the FHL can effectively prevent the release of heat and smoke through mechanisms like forming a char layer at elevated temperatures, generating non-combustible gases and sequestering free radicals. As a result, the FHL led to a reduction in the peak heat release rate and total heat release of PU from 946.8 kW/m2 and 86.9 MJ/m2 to 383.5 kW/m2 and 28.4 MJ/m2, respectively. This acid hydrotrope lignin modified polyurethane, holds tremendous potential for a wide range of practical applications.

The Pseudomonas ligninolytic catalytic network reveals the importance of auxiliary enzymes in lignin biocatalysts

Lignin degradation by biocatalysts is a key strategy to develop a plant-based sustainable carbon economy and thus alleviate global climate change. This process involves synergy between ligninases and auxiliary enzymes. However, auxiliary enzymes within secretomes, which are composed of thousands of enzymes, remain enigmatic, although several ligninolytic enzymes have been well characterized. Moreover, it is a challenge to understand synergistic lignin degradation via a diverse array of enzymes, especially in bacterial systems. In this study, the coexpression network of the periplasmic proteome uncovers potential accessory enzymes for B-type dye-decolorizing peroxidases (DypBs) in Pseudomonas putida A514. The catalytic network of the DypBs-based multienzyme complex is characterized. DypBs couple with quinone reductases and nitroreductase to participate in quinone redox cycling. They work with superoxide dismutase to induce Fenton reaction for lignin oxidation. A synthetic enzyme cocktail (SEC), recruiting 15 enzymes, was consequently designed with four functions. It overcomes the limitation of lignin repolymerization, exhibiting a capacity comparable to that of the native periplasmic secretome. Importantly, we reveal the synergistic mechanism of a SEC-A514 cell system, which incorporates the advantages of in vitro enzyme catalysis and in vivo microbial catabolism. Chemical analysis shows that this system significantly reduces the molecular weight of lignin, substantially extends the degradation spectra for lignin functional groups, and efficiently metabolizes lignin derivatives. As a result, 25% of lignin is utilized, and its average molecular weight is reduced by 27%. Our study advances the knowledge of bacterial lignin-degrading multienzymes and provides a viable lignin degradation strategy.

How to select agroforestry waste biomass for electrospinning and its potential application in bone tissue engineering

The high value-added utilization of agroforestry waste biomass is an urgent requirment. Herein, a feasible approach was provided to obtain biodegradable cellulose fibrous films from agroforestry waste biomass. The cellulose used was extracted from agroforestry waste biomass and then the cellulose fibrous film was obtained by direct electrospinning. Lignin-carbohydrate complex (LCC) structure was considered as the key factor for the dissolution of lignocellulose, while cellulose molecular weight > 335,664 was suitable for electrospinning. Bamboo cellulose was chosen as an example to verify the potential application of the electrospun cellulose films from agroforestry waste biomass. The as-prepared electrospun bamboo cellulose fibrous film exhibited a tensile strength of 24.12 MPa, which outperformed most of the reported electrospun nanofibrous films. Moreover, the film possessed a super-wetting surface and outstanding cytocompatibility. These excellent properties offer the film with immense potential for application in bone tissue engineering. In addition, this work provides a new route for transforming agroforestry waste into high value-added products.

Establishment of efficient system for bagasse bargaining: Combining fractionation of saccharides, recycling of high-viscosity solvent and dismantling

Sugarcane bagasse (SCB) has a recalcitrant structure, which hinders its component dismantling and subsequent high value utilization. Some organic solvents are favorable to dismantle lignocellulose, but their high viscosity prevents separation of components and reuse of solvents. Herein, ethylene glycol phenyl ether (EGPE)-acid system is used as an example to develop green and efficient methods to dismantle SCB, purify polysaccharides and lignin, and reuse solvents. Results show that dismantling SCB at 130 °C, 0.5 % H2SO4, and 100 min can obtain 85.5 % cellulose recovery, 94.1 % hemicellulose removal and 83.7 % lignin removal. Different molecular weight saccharides are separated by membranes filtration and centrifugation, and lignin recovered by antisolvent precipitation. The solvent recovered by distillation, achieving high dismantling efficiency of 89.2 % cellulose recovery, 94.1 % hemicellulose removal and 94.4 % lignin removal after four recycles. Results show a promising approach for the closed-loop process of dismantling lignocellulose, fractionating saccharides, and reusing solvents in high-viscosity systems.

Aminated lignin improved enzymatic hydrolysis of cellulosic substrate treated by p-toluenesulfonic acid

Lignin can affect the enzymatic hydrolysis efficiency of lignocellulose. In this study, the lignin isolated from sugarcane bagasse (SCB) pretreated with p-toluenesulfonic acid (PL) was firstly aminated, and then the effects of PL and aminated PL (APL) on the bagasse enzymatic hydrolysis efficiency (EHE) were investigated. The results showed that the addition of PL and APL promoted the EHE, and EHE with APL (73.82 %) was higher than PL (51.39 %). To explore the reason, the data were further analyzed including cellulase adsorption capacity, enzyme activity, cellulase-lignin interaction, and molecular docking. It was found that APL adsorbed more cellulase (27.83 mg protein/g lignin) than PL (4.96 mg protein/g lignin), resulting from the greater interaction force and lower binding free energy between APL and cellulase. The addition of APL more remarkably enhanced the cellobiohydrolase and endoglucanase activities than PL due to more effectively inducing cellulase conformation optimization.

Recent advance on lignin-containing nanocelluloses: The key role of lignin

Nanocelluloses (NCs) isolated from lignocellulosic resources usually require harsh chemical pretreatments to remove lignin, which face constraints such as high energy consumption and inefficient resource utilization. An alternative strategy involving the partial retention of lignin can be adopted to endow NCs with better versatility and functionality. The resulting lignin-containing nanocelluloses (LNCs) generally possess better mechanical property, thermal stability, barrier property, antioxidant activity, and surface hydrophobicity than lignin-free NCs, which have attracted extensive interest as a promising green nanomaterial for numerous applications. This review provides a comprehensive overview of the recent advances in the preparation, properties, and food application of LNCs. The effect of residual lignin on the preparation and properties of LNCs is discussed. Furthermore, the key roles of lignin in the properties of LNCs, including particle size, crystalline structure, dispersibility, thermal, mechanical, antibacterial, rheological and adhesion properties, are summarized comprehensively. Furthermore, capitalizing on their dietary fiber and nanostructure properties, the food applications of LNCs in the forms of films, gels and emulsions are also discussed. Finally, the challenges and opportunities regarding the development of LNCs are provided.

Equilibrium Moisture Mediated Esterification Reaction to Achieve Over 100% Lignocellulosic Nanofibrils Yield

Lignocellulosic nanofibrils (LCNFs) isolation is recognized as an efficient strategy for maximizing biomass utilization. Nevertheless, achieving a 100% yield presents a formidable challenge. Here, an esterification strategy mediated by the equilibrium moisture in biomass is proposed for LCNFs preparation without the use of catalysts, resulting in a yield exceeding 100%. Different from anhydrous chemical thermomechanical pulp (CTMP0%), the presence of moisture (moisture content of 7 wt%, denoted as CTMP7%) introduces a notably distinct process for the pretreatment of CTMP, comprising the initial disintegration and the post-esterification steps. The maleic acid, generated through maleic anhydride (MA) hydrolysis, degrades the recalcitrant lignin-carbohydrate complex (LCC) structures, resulting in esterified CTMP7% (E-CTMP7%). The highly grafted esters compensate for the mass loss resulting from the partial removal of hydrolyzed lignin and hemicellulose, ensuring a high yield. Following microfluidization, favorable LCNF7% with a high yield (114.4 ± 3.0%) and a high charge content (1.74 ± 0.09 mmol g-1) can be easily produced, surpassing most previous records for LCNFs. Additionally, LCNF7% presented highly processability for filaments, films, and 3D honeycomb structures preparation. These findings provide valuable insights and guidance for achieving a high yield in the isolation of LCNFs from biomass through the mediation of equilibrium moisture.

The Enhancement Origin of Antioxidant Property of Carboxylated Lignin Isolated from Herbaceous Biomass Using the Maleic Acid Hydrotropic Fractionation

Lignin is endowed with antioxidant activity due to its diverse chemical structure. It is necessary to explore the relationship between antioxidant activity and the chemical structure of the lignin to develop its high-value utilization. Herein, we employed maleic acid (MA) as a hydrotropic agent to preferably isolate the lignin from distinct herbaceous sources (wheat straw and switchgrass) under atmospheric pressure conditions. The resultant acid hydrotropic lignin (AHL) isolated from wheat straw exhibited high radical scavenging rates, up to 98% toward DPPH and 94% toward ABTS. Further investigations indicated that during the MA hydrotropic fractionation (MAHF) process, lignin was carboxylated by MA at γ-OH of the side-chain, providing additional antioxidant activity from the carboxy group. It was also found that the radical scavenging rate of AHL has a positive correlation with carboxyl, phenolic hydroxyl contents, and the S-G (syringyl-guaiacyl) ratio, which could be realized by increasing the MAHF severity. Overall, this work underlies the enhancement origin of the antioxidant property of lignin, which will facilitate its application in biological fields as an efficient, cheap, and renewable antioxidant additive.

Comprehensive insights of pretreatment strategies on the structures and bioactivities variation of lignin-carbohydrate complexes

Introduction: Due to its unique structural features and bioactivities, the lignin-carbohydrate complex (LCC) displays great potential in vast industrial applications. However, the elucidation of how various pretreatment methods affect the structure and bioactivities remains unaddressed. Method: The three pretreatment methods were systematically studied on the variations of structures and bioactivities, and the Gramineae plant, i.e., wheat straw, was adopted in this study. The structures and bioactivities variation caused by different pretreatments were studied in detail. Result and Discussion: The results showed that compared to physical or chemical pretreatments, biological pretreatment was the most effective approach in improving the bioactivities of LCC. The LCC from biological pretreatment (enzymatic hydrolysis, ELCC4) had more functional groups while the lower weight-average molecular weight (Mw) and polydispersity index (PDI) were well-endowed. The highest antioxidant abilities against ABTS and DPPH of ELCC4 were high up to 95% and 84%, respectively. Furthermore, ELCC4 also showed the best ultraviolet (UV)-blocking rate of 96%, which was increased by 6% and 2% compared to LCC8 (physical pretreatment) and LLCC4 (chemical pretreatment). This work prospectively boosts the understanding of pretreatment strategies on the structures and bioactivities variation of LCC and facilitates its utilization as sustainable and biologically active materials in various fields.

Harnessing Atomically Dispersed Cobalt for the Reductive Catalytic Fractionation of Lignocellulose

The reductive catalytic fractionation (RCF) of lignocellulose, considering lignin valorization at design time, has demonstrated the entire utilization of all lignocellulose components; however, such processes always require catalysts based on precious metals or high-loaded nonprecious metals. Herein, the study develops an ultra-low loaded, atomically dispersed cobalt catalyst, which displays an exceptional performance in the RCF of lignocellulose. An approximately theoretical maximum yield of phenolic monomers (48.3 wt.%) from lignin is realized, rivaling precious metal catalysts. High selectivity toward 4-propyl-substituted guaiacol/syringol facilitates their purification and follows syntheses of highly adhesive polyesters. Lignin nanoparticles (LNPs) are generated by simple treatment of the obtained phenolic dimers and oligomers. RCF-resulted carbohydrate pulp are more obedient to enzymatic hydrolysis. Experimental studies on lignin model compounds reveal the concerted cleavage of Cα-O and Cβ-O pathway for the rupture of β-O-4 structure. Overall, the approach involves valorizing products derived from lignin biopolymer, providing the opportunity for the comprehensive utilization of all components within lignocellulose.

Study on cultivation of aerobic granular sludge and its application in degrading lignin models in the sequencing batch biofilter granular reactor

In this study, three sequencing batch biofilter granular reactors (SBBGRs) were employed to treat model lignin wastewater containing different lignin models (2,6-dimethoxyphenol, 4-methoxyphenol, and vanillin). After 40 days of cultivation, uniform-shaped aerobic granular sludge (AGS) was successfully developed through nutrient supplementation with synthetic wastewater. During the acclimation stage, the chemical oxygen demand (COD) reduction efficiencies of the three reactors showed a trend of initial decreasing (5-20%) and then recovering to a high reduction efficiency (exceeding 90%) in a short period of time. During the stable operation stage, all three reactors achieved COD reduction efficiencies exceeding 90%. These findings indicated the cultivated AGS's robust resistance to changes in lignin models in water. UV-Vis spectra analysis confirmed the effective degradation of the three lignin models. Microbiological analysis showed that Proteobacteria and Bacteroidetes were always the dominant phyla. At the genus level, while Acinetobacter (15.46%) dominated in the inoculation sludge, Kapabacteriales (7.93%), SBR1031 (11.77%), and Chlorobium (25.37%) were dominant in the three reactors (for 2,6-dimethoxyphenol, 4-methoxyphenol, and vanillin) after degradation, respectively. These findings demonstrate that AGS cultured with SBBGR effectively degrades lignin models, with different dominant strains observed for various lignin models.

p-Toluenesulfonic acid enhanced neutral deep eutectic solvent pretreatment of soybean straw for efficient lignin removal and enzymatic hydrolysis

Deep eutectic solvent (DES) is a newly-emerged green solvent for efficient pretreatment of lignocellulosic feedstock. To improve the component fractionation performance of neutral DES, p-toluenesulfonic acid (p-TsOH) was employed as catalyst to form a novel ternary DES with benzyltriethylammonium chloride (TEBAC) and glycerol (Gly) for pretreatment of soybean straw. Under the optimum reaction conditions (TEBAC:Gly = 1:12, 1.6 wt% p-TsOH and reacted at 90 °C for 160 min), the lignin and hemicellulose removal from soybean straw were amounted to 92.0 % and 88.2 %, respectively. The pretreated substrate showed satisfactory enzymatic hydrolysis performance, as the glucose and reducing sugar concentrations reached 37.3 g/L and 42.3 g/L, respectively, after 72 h saccharification under the action of cellulase with a relatively low enzyme loading of 10 FPU/g cellulose.This method provides an efficient and mild route for utilization of agricultural waste and production of platform monosaccharides.

Oxidation of p-toluenesulfonic acid fractionated hybrid Pennisetum by different methods for carboxylated nanocellulose preparation: The evaluation of efficiency and sustainability

An innovative two-step process with p-toluenesulfonic acid (p-TsOH) and oxidation treatment was proposed for the efficient preparation of carboxylated nanocellulose from hybrid Pennisetum. Approximately 90 % of lignin was dissolved by p-TsOH acid under the optimal condition (80 °C, 20 min). Near-complete delignification (down to 0.5 %) and introduction of carboxylate groups (up to 1.48 mmol/g) could be achieved simultaneously during cellulose oxidation treatments without the requirement for bleaching. However, different oxidation methods expressed different efficiency and sustainability. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) oxidation has higher selectivity for the carboxylation reaction but with detriment to the aquatic environment. Fenton oxidation is more energy-consuming due to the lower carboxylate contents of products (maximum 188 μmol/g), with the carboxylic groups present as carboxylic acids, but competitive in terms of environmental sustainability, especially when renewable energy sources are available. The nanocelluloses obtained by the two oxidation methods differ in morphology and have different application prospects.

Lignin nanoparticles from hydrotropic fractionation of giant reed and eucalypt: Structural elucidation and antibacterial properties

A hydrotropic solution of maleic acid (MA) was exploited to fractionate giant reed (AD) and eucalypt (EUC). The pre-treatment was successful for AD, while it was unsatisfactory for EUC, likely due to unoptimized reaction conditions. Interestingly, lignin nanoparticles (LNP) were produced via spontaneous aggregation following spent liquor dilution. LNP were studied by a plethora of analytical techniques, such as thermogravimetry, electron microscopy, and Nuclear Magnetic Resonance spectroscopy (NMR). Notwithstanding LNP from both AD and EUC showed similar thermal behaviour and morphology, a greater content of aliphatic hydroxyl, carboxyl, guaiacyl and p-hydroxyphenyl moieties was reported for AD-LNP, whereas EUC-LNP had a larger amount of syringyl groups and a higher S/G ratio. Also, the 1H-DOSY NMR indicated the lower size of AD-LNP. Moreover, the LNP were found to negatively impact on the development of several human or plant pathogens, and their bioactivity was related to the occurrence of guaiacyl and p-hydroxyphenyl moieties and a lower the LNP size. We therefore found that MA delignification allows both to achieve high delignification efficiency and to obtain LNP with promising antibacterial effect. Such LNP may help counteracting the antibiotics resistance and sustain the quest for finding sustainable agrochemicals.

Efficient production of xylooligosaccharides from Camellia oleifera shells pretreated by pyruvic acid at lower temperature

XOS production from lignocellulose using organic carboxylic acids and alkyd acids has been widely reported. However, it still faces harsh challenges such as high energy consumption, high cost, and low purity. Pyruvic acid (PYA), a carbonyl acid with carbonyl and carboxyl groups, was used to produce XOS due to its stronger catalytic activity. In this work, XOS was efficiently prepared from COS in an autoclave under the condition of 0.21 M PYA-121 °C-35 min. The total yield of XOS reached 68.72 % without producing any toxic by-products, including furfural (FF) and 5-hydroxymethylfurfural (5-HMF). The yield of xylobiose (X2), xylotriose (X3), xylotetraose (X4), and xylopentaose (X5) were 20.58 %, 12.47 %, 15.74 %, and 10.05 %, respectively. Meanwhile, 89.05 % of lignin was retained in the solid residue, which provides a crucial functional group for synthesizing layered carbon materials (SRG-a). It achieves excellent electromagnetic shielding (EMS) performance through graphitization, reaching -30 dB at a thickness of 2.0 mm. The use of a PYA catalyst in the production of XOS has proven to be an efficient method due to lower temperature, lower acid consumption, and straightforward operation.

Lignocellulosic biomass pretreatment with a lignin stabilization strategy and valorization toward multipurpose fractionation

Lignocellulosic biomass has emerged as a promising alternative with sustainable advantages for the production of a wide range of renewable products and value-added chemicals. In this study, a pretreatment strategy that use a fully recyclable acid hydrotrope (p-TsOH aqueous solution) to extract lignin and employ glyoxylic acid (GA) to stabilize lignin was proposed for biomass valorization toward multipurpose fractionation. 83.0 % of lignin was dissolved out by p-TsOH hydrotrope (80 wt%) with GA addition to form GA-stabilized product at 80 o C for 15 min. The stabilized lignin was subsequently used as an additive in the preparation of lignin-based suncream. Notably, the incorporation of 4 wt% lignin nanospheres into an SPF15 sunscreen yielded a measured SPF of 59.94. Furthermore, the depolymerization of uncondensed lignin into aromatic monomers yielded a high lignin-oil yield of 84.2 %. Additionally, direct heating of the pretreatment liquor facilitated the conversion of monosaccharides into furfural, achieving a desired yield of 53.7 % without the addition of any acid catalyst. The pretreatment also enhanced the enzymatic hydrolysis of glucan, resulting in a saccharification yield of 98.4 %. Moreover, short-term ultrasonication of the pretreated substrate yielded pulp suitable for papermaking. Incorporating 15 wt% fibers into the produced paper sheets led to a 5.3 % increase in tear index and a 25.4 % increase in tensile index. This study presents a viable pretreatment strategy for the multipurpose fractionation of lignocellulosic biomass, offering potential avenues for biomass valorization.

Catalytic Degradation of Lignin over Sulfonyl-Chloride-Modified Lignin-Based Porous Carbon-Supported Metal Phthalocyanine: Effect of Catalyst Concentrations

A sulfonyl-chloride-modified lignin-based porous carbon-supported metal phthalocyanine catalyst was prepared and used to replace the traditional Fenton's reagent for lignin degradation. The catalyst underwent a detailed characterization analysis in terms of functional group distributions, surface area, morphological structure, via FT-IR, XPS, BET, and SEM. The catalyst possessed a specific surface area of 638.98 m2/g and a pore volume of 0.291 cm3/g. The prepared catalyst was studied for its ability of oxidative degradation of lignin under different reaction conditions. By optimizing the reaction conditions, a maximum liquid product yield of 38.94% was obtained at 135 °C with 3.5 wt% of catalyst and 15 × 10-2 mol/L H2O2; at the same time, a maximum phenols selectivity of 32.58% was achieved. The compositions and properties of liquid products obtained from lignin degradation using different catalyst concentrations were studied comparatively via GC-MS, FT-IR, 1H-NMR, and EA. Furthermore, the structure changes of solid residues are also discussed.

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.

Recent advances in sustainable preparation of cellulose nanocrystals via solid acid hydrolysis: A mini-review

As a green and renewable nanomaterial, cellulose nanocrystals (CNC) have received numerous attention due to the unique structural features and superior physicochemical properties. Conventionally, CNC was isolated from lignocellulosic biomass mostly depending on sulfuric or hydrochloric acid hydrolysis. Although this approach is effective, some critical issues such as severe equipment corrosion, excessive cellulose degradation, serious environmental pollution, and large water usage are inevitable. Fortunately, solid acid hydrolysis is emerging as an economical and sustainable CNC production technique and has achieved considerable progress in recent years. Herein, the preparation of CNC by solid acid hydrolysis was summarized systematically, including organic solid acids (citric, maleic, oxalic, tartaric, p-toluenesulfonic acid) and inorganic solid acids (phosphotungstic, phosphoric, and Lewis acid). The advantages and disadvantages of organic and inorganic solid acid hydrolysis methods were evaluated comprehensively. Finally, the challenges and opportunities in the later exploitation and application of solid acid hydrolysis to prepare CNC in the industrial context are discussed. Considering the future development of this technology in the large-scale CNC production, much more efforts should be made in lowering CNC processing cost, fabricating high-solid-content and re-dispersible CNC, developing value-added applications of CNC, and techno-economic analysis and life cycle assessment on the whole process.

Combined iron (III) chloride/sodium citrate with enzymatic hydrolysis for xylo-oligosaccharides and monosaccharides production from poplar

Currently, the production of xylo-oligosaccharides (XOS) from lignocelluloses by chelating system hydrolysis has not been investigated. Herein, iron (III) chloride/sodium citrate (IC/SC) chelating system hydrolysis and xylanase hydrolysis were used to produce XOS from poplar. Then, the delignification of IC/SC-hydrolyzed poplar was performed by p-toluenesulfonic acid (p-TsOH) pretreatment to increase the accessibility of cellulase. The results demonstrated that 42.3% of XOS with an extremely low by-product (xylose/XOS = 0.11) was produced from poplar by 50 mM IC/SC hydrolysis (molar ratio of 1:1, 170 °C, 60 min) and xylanase hydrolysis. The second step IC/SC hydrolysis and xylanase hydrolysis of poplar increased the yield of XOS to 51.3%. Finally, the glucose yield of p-TsOH-pretreated poplar (60% p-TsOH, 70 °C, 30 min) was greatly increased from 37.5% to 83.8% by cellulase hydrolysis with Tween 80 addition. The novel strategy proposed in this work was feasible for XOS and monosaccharides production from poplar.

The isolation of lignin with native-like structure

Searching for renewable alternatives for fossil carbon resources to produce chemicals, fuels and materials is essential for the development of a sustainable society. Lignin, a major component of lignocellulosic biomass, is an abundant renewable source of aromatics and is currently underutilized as it is often burned as an undesired side stream in the production of paper and bioethanol. This lignin harbors great potential as source of high value aromatic chemicals and materials. Biorefinery schemes focused on lignin are currently under development with aim of acquiring added value from lignin. However, the performance of these novel lignin-focused biorefineries is closely linked with the quality of extracted lignin in terms of the level of degradation and modification. Thus, the reactivity including the degradation pathways of the native lignin contained in the plant material needs to be understood in detail to potentially achieve higher value from lignin. Undegraded native-like lignin with an as close as possible structure to native lignin contained in the lignocellulosic plant material serves as a promising model lignin to support detailed studies on the structure and reactivity of native lignin, yielding key understanding for the development of lignin-focused biorefineries. The aim of this review is to highlight the different methods to attain "native-like" lignins that can be valuable for such studies. This is done by giving a basic introduction on what is known about the native lignin structure and the techniques and methods used to analyze it followed by an overview of the fractionation and isolation methods to isolate native-like lignin. Finally, a perspective on the isolation and use of native-like lignin is provided, showing the great potential that this type of lignin brings for understanding the effect of different biomass treatments on the native lignin structure.

The coupling effects between acid-catalyzed hydrothermal pretreatment and acidic/alkaline deep eutectic solvent extraction for wheat straw fractionation

Mild hydrothermal pretreatment (HP) integrating with solvent extraction is a promising two-step technique to enhance the overall lignin and carbohydrate output for lignocellulose fractionation. This work comparatively assessed the coupling effect between mild HP (the first step) and the emerging acidic choline chloride-natural acid or alkaline choline hydroxide based deep eutectic solvents (DES, the second step) for wheat straw fractionation. It was shown HP with 0.3% p-toluenesulfonic acid (p-TsOH) catalyst achieved a good compromise between complete hemicellulose removal (nearly 100%) and high cellulose recovery (99.2%). While choline hydroxide based DES showed better coupling effect with HP than choline chloride-natural acid DES, corresponding to 75.6 and 31.2% lignin removal respectively. It was proposed that the alkaline DES enhanced lignocellulose swelling the lignin phenolic hydroxyl groups deprotonation and thus facilitating lignin solubilization despite of its condensation at HP. Therefore, the alkaline DES resulting cellulose-rich fraction exhibited higher potential for further processing.

Genetic editing of wood for sustainability

Trees engineered to have less lignin could make paper production less polluting.

Differentiated Fractionation of Various Biomass Resources by p-Toluenesulfonic Acid at Mild Conditions

Biomass is the ideal substitute for petrochemical resources because of its renewable and abundant sources. p-Toluenesulfonic acid (p-TsOH) can effectively separate lignin from biomass under mild conditions, so it is highly expected in biomass fractionation to improve the utilization efficiency. In this study, we investigated the effect of p-TsOH differentiated fractionation of poplar sawdust, eucalyptus sawdust, and rice straw below 100 °C. According to the experimental results, upon pretreatment by p-TsOH of the three kinds of raw biomass, most of the lignin and hemicellulose of poplar sawdust and eucalyptus sawdust were removed, whereas the cellulose was retained, but most of the hemicellulose and cellulose of rice straw were kept, whereas the lignin was removed at similar conditions. The structures and compositions of pretreatment residues, lignin, and hemicellulose extracted from raw biomass were characterized by XRD, FTIR, HSQC-NMR, XPS, and SEM. The differentiated fractionation mechanism of biomass was analyzed. A better recognition and understanding of the factors affecting biomatrix opening and fractionation will allow for the identification of new pretreatment strategies that improve biomass utilization and permit the rational enzymatic hydrolysis of cellulose.

Conversion of control and genetically-modified poplar into multi-scale products using integrated pretreatments

In this work, a green and robust pretreatment which integrated acetic acid-catalyzed hydrothermal and wet mechanical pretreatment, was developed to efficiently produce high yield (up to 40.12%) of xylooligosaccharides and digestible substrates from Caffeoyl Shikimate Esterase down-regulated and control poplar wood. Subsequently, superhigh yield (more than 95%) of glucose and residual lignin were obtained after a moderate enzymatic hydrolysis. The residual lignin fraction exhibited a well-preserved β-O-4 linkages (42.06/100Ar) and high S/G ratio (6.42). Subsequently, lignin-derived porous carbon was successfully synthesized, and it exhibited a high specific capacitance of 273.8F g-1 at 1.0 A/g and long cycling stability (remained 98.5% after 10,000 cycles at 5.0 A/g) as compared to control poplar wood, demonstrating that special advantage of this genetically-modified poplar in this integrated process. This work developed an energy-saving and eco-friendly pretreatment technology as a waste-free route for converting different lignocellulosic biomass to multiple products.

An optimum biomass fractionation strategy into maximum carbohydrates conversion and lignin valorization from poplar

Appropriate fractionation of lignocellulosic biomass into useable forms is a key challenge to achieving an economic bioethanol production. In the present study, four different fractionation strategies of hydrothermal-, NaOH-, ethanol-, and NaOH catalyzed ethanol pretreatment were investigated to compare their abilities of cellulose conversion. Results showed that NaOH catalyzed ethanol pretreatment showed a rather high extent of delignification of 85.92%, which also enhanced the retention of cellulose (92.56%) and hemicellulose (76.57%); while other pretreatments tended to produce cellulose fraction which was insufficient to achieve the whole component utilization. After simultaneous saccharification and fermentation at high solids loading, synergistic maximization of xylose (42.47 g/L) and ethanol (85.74 g/L) output was achieved via alkaline ethanol pretreatment. Lignin characterization information showed that alkaline ethanol pretreatment facilitates the cleavage of β-O-4 linkage and further converts into arylglycerol. Moreover, less condensed substructure units with high processing activity were also generated in S- and G- lignin.

Efficient preparation of high-purity cellulose from moso bamboo by p-toluenesulfonic acid pretreatment

This work proposed a promising biorefinery method for the deconstruction of moso bamboo by using p-toluenesulfonic acid (P-TsOH) pretreatment to product high-purity cellulose (dissolving pulp). The cellulose pulp with high α-cellulose content (82.36 %) was successfully prepared for 60 min at low pretreatment temperature (90 °C) and atmospheric pressure. After the simple bleaching and cold caustic extraction (CCE) processes, the properties of cellulose pulp, such as α-cellulose content, polymerization, ISO brightness, all met the standard of dissolving pulp. In general, the cooking method through P-TsOH pretreatment can shorten the preparation time, which can effectively reduce energy consumption and chemical consumption. Therefore, this work may provide a new perspective for the green preparation of dissolving pulp that can be used to produce lyocell fiber after ash and metal ion treatment.

Valorization of Boehmeria nivea stalk towards multipurpose fractionation: furfural, pulp, and phenolic monomers

BACKGROUND

As one of the most abundant bioresource in nature, the value-added utilization of lignocellulosic biomass is limited due to its inherent stubbornness. Pretreatment is a necessary step to break down the recalcitrance of cell walls and achieve an efficient separation of three main components (cellulose, hemicelluloses, and lignin).

RESULTS

In this study, hemicelluloses and lignin in Boehmeria nivea stalks were selectively extracted with a recyclable acid hydrotrope, an aqueous solution of P-toluenesulfonic acid (p-TsOH). 79.86% of hemicelluloses and 90.24% of lignin were removed under a mild pretreatment condition, C80T80t20, (acid concentration of 80 wt%, pretreatment temperature and time of 80 °C and 20 min, respectively). After ultrasonic treatment for 10 s, the residual cellulose-rich solid was directly converted into pulp. Subsequently, the latter was utilized to produce paper via mixing with softwood pulp. The prepared handsheets with a pulp addition of 15 wt% displayed higher tear strength (8.31 mN m2/g) and tensile strength (8.03 Nm/g) than that of pure softwood pulp. What's more, the hydrolysates of hemicelluloses and the extracted lignin were transformed to furfural and phenolic monomers with yields of 54.67% and 65.3%, respectively.

CONCLUSIONS

The lignocellulosic biomass, Boehmeria nivea stalks, were valorized to pulp, furfural, and phenolic monomers, successfully. And a potential solution of comprehensive utilization of Boehmeria nivea stalks was provided in this paper.

Production of nanocellulose using acidic deep eutectic solvents based on choline chloride and carboxylic acids: A review

Nowadays, nanocellulose production processes with numerous merits of green, eco-friendly, and cost-effective are in urgent need. Acidic deep eutectic solvent (ADES), as an emerging green solvent, has been widely applied in the preparation of nanocellulose over the past few years, owing to its unique advantages, including non-toxicity, low cost, easy synthesis, recyclability, and biodegradability. At present, several studies have explored the effectiveness of ADESs in nanocellulose production, particularly those based on choline chloride (ChCl) and carboxylic acids. Various acidic deep eutectic solvents have been employed, with representative ones such as ChCl-oxalic/lactic/formic/acetic/citric/maleic/levulinic/tartaric acid. Herein, we comprehensively reviewed the latest progress of these ADESs, focusing on the treatment procedures and key superiorities. In addition, the challenges and outlooks of ChCl/carboxylic acids-based DESs implementation in the fabrication of nanocellulose were discussed. Finally, some suggestions were proposed to advance the industrialization of nanocellulose, which would help for the roadmap of sustainable and large-scale production of nanocellulose.

Physicochemical Properties, Thermal Stability, and Pyrolysis Behavior of Antioxidative Lignin from Water Chestnut Shell Obtained with Ternary Deep Eutectic Solvents

The molecular weight of lignin extracted from lignocellulosic biomass is an important factor in determining its valorization in industrial processes. Herein, this work aims to explore the extraction of high molecular weight and bioactive lignin from water chestnut shells under mild conditions. Five kinds of deep eutectic solvents were prepared and applied to isolate lignin from water chestnut shells. The extracted lignin was further characterized with element analysis, gel permeation chromatography, and Ultraviolet-visible and Fourier-transform infrared spectroscopy. The distribution of pyrolysis products was identified and quantified with thermogravimetric analysis-Fourier-transform infrared spectroscopy and pyrolysis-gas chromatograph-mass spectrometry. The results showed that choline chloride/ethylene glycol/p-toluenesulfonic acid (1:1.8:0.2 molar ratio) exhibited the highest fractionation efficiency for lignin (84.17% yield) at 100 °C for 2 h. Simultaneously, the lignin showed high purity (90.4%), high relative molecular weight (37,077 g/mol), and excellent uniformity. Furthermore, the aromatic ring structure of lignin remained intact, consisting mainly of p-hydroxyphenyl, syringl, and guaiacyl subunits. The lignin generated a large number of volatile organic compounds during the depolymerization process, mainly composed of ketones, phenols, syringols, guaiacols, esters, and aromatic compounds. Finally, the antioxidant activity of the lignin sample was evaluated with the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay; the lignin from water chestnut shells showed excellent antioxidant activity. These findings confirm that lignin from water chestnut shells has a broad application prospect in valuable chemicals, biofuels and bio-functional materials.

Pretreatment of poplar with eco-friendly levulinic acid to achieve efficient utilization of biomass

Organic acid pretreatment is an effective method for green separation of lignocellulosic biomass. However, repolymerization of lignin seriously affects the dissolution of hemicellulose and the conversion of cellulose during organic acid pretreatment. Therefore, a new organic acid pretreatment, levulinic acid (Lev) pretreatment, was studied for the deconstruction of lignocellulosic biomass without adding additional additives. The preferred separation of hemicellulose was realized at Lev concentration 7.0%, temperature 170 °C, and time 100 min. The separation of hemicellulose increased from 58.38% to 82.05% compared with acetic acid pretreatment. It was found that the repolymerization of lignin was effectively inhibited in the efficient separation of hemicellulose. This was attributed to the fact that γ-valerolactone (GVL) is a good green scavenger of lignin fragments. The lignin fragments in the hydrolysate were effectively dissolved. The results provided theoretical support for creating green and efficient organic acid pretreatment and effectively inhibiting lignin repolymerization.

A fractionation strategy of cellulose, hemicellulose, and lignin from wheat straw via the biphasic pretreatment for biomass valorization

Developing an environmentally friendly and efficient pretreatment to utilize wheat straw is essential to a sustainable future. An acid biphasic system with 2-methyltetrahydrofuran (2-MeTHF) organic solvent and dilute p-toluenesulfonic acid (p-TsOH) were employed for the simultaneous fractionation of three components. Results showed that the biphasic system had excellent cellulose protection and high removal of hemicellulose and lignin. In detail, Under the optimal conditions (0.1 M p-TsOH, 2-MeTHF: H₂O = 1:1 (v:v), 140 °C, 3 h), mostly cellulose retained in the residues (95.69%), 57.18% of lignin was removed and high yield of hemicellulose-based C5 sugars was achieved (77.49%). In the further process of dehydration of pre-hydrolysate dichloromethane (DCM) as an organic phase, the yield of furfural was 80.07% (170 °C-80 min). The saccharification of residue reached 95.82%. p-TsOH/2-MeTHF/H₂O pretreatment was desirable for high selectivity fractionation. Important chemicals for bioenergy including furfural, monosaccharides and lignin are obtained.

Efficient Fractionation and Catalytic Valorization of Raw Biomass in ϵ-Caprolactone and Water

Efficient fractionation and utilization of the whole biomass is particularly attractive but remains a great challenge, owing to the recalcitrance of biomass. In this study, a simple and efficient approach is developed to obtain high-purity cellulose with a delignification degree of 97.5 % in ϵ-caprolactone and water. FTIR spectroscopy reveals that ϵ-caprolactone and water act in synergy to remove lignin from raw biomass and afford cellulose with clear macrofibrils. A linear positive correlation between the contents of hemicellulose and lignin is observed for the separated cellulose pulp. This mixed solvent exhibits good performance for the removal of lignin from various agricultural and forestry wastes. Moreover, nearly complete transformation of the whole biomass constituents is achieved with Ni-Al catalyst.

Effect of Fenton oxidized lignin support on immobilized β-glucosidase activity

In this study, the Fenton oxidized lignin was prepared to investigate the effect of Fenton oxidation modification on the activity of lignin immobilized β-glucosidase (β-GL). The results demonstrated that Fenton oxidation could significantly improve the activity and stability of immobilized β-GL. This is because the Fenton oxidation increased the electrostatic, hydrogen bonding, and hydrophobic forces between lignin and β-GL, resulting in increased lignin adsorption onto β-GL. The Fenton oxidation also changed the chemical structure of lignin, altering the lignin-β-GL binding site and reducing the negative effect of lignin on the β-GL catalytic domain. This research will improve understanding of the effect of Fenton lignin oxidation on immobilized β-GL activity and expand the use of lignin in enzyme immobilization.

Emerging Engineered Wood for Building Applications

The building sector, including building operations and materials, was responsible for the emission of ∼11.9 gigatons of global energy-related CO₂ in 2020, accounting for 37% of the total CO₂ emissions, the largest share among different sectors. Lowering the carbon footprint of buildings requires the development of carbon-storage materials as well as novel designs that could enable multifunctional components to achieve widespread applications. Wood is one of the most abundant biomaterials on Earth and has been used for construction historically. Recent research breakthroughs on advanced engineered wood products epitomize this material's tremendous yet largely untapped potential for addressing global sustainability challenges. In this review, we explore recent developments in chemically modified wood that will produce a new generation of engineered wood products for building applications. Traditionally, engineered wood products have primarily had a structural purpose, but this review broadens the classification to encompass more aspects of building performance. We begin by providing multiscale design principles of wood products from a computational point of view, followed by discussion of the chemical modifications and structural engineering methods used to modify wood in terms of its mechanical, thermal, optical, and energy-related performance. Additionally, we explore life cycle assessment and techno-economic analysis tools for guiding future research toward environmentally friendly and economically feasible directions for engineered wood products. Finally, this review highlights the current challenges and perspectives on future directions in this research field. By leveraging these new wood-based technologies and analysis tools for the fabrication of carbon-storage materials, it is possible to design sustainable and carbon-negative buildings, which could have a significant impact on mitigating climate change.

Rapid and massive fractionation of hemicelluloses for purifying cellulose at room temperature by tetramethylammonium hydroxide

The fractionation of hemicelluloses is a promising method to improve the comprehensive utilization of lignocellulosic biomass. However, the effective fractionation of hemicelluloses is always limited by the structural complexity and easy degradability. In this study, tetramethylammonium hydroxide (TMAH) was developed to fractionate hemicelluloses from poplar holocellulose with high molecular weights and high yields at room temperature. Approximately 90% of hemicelluloses could be dissolved at room temperature in 1 h, and the yield was up to 81.9%. Compared with the fractionation using NaOH solution, the hemicelluloses isolated by TMAH solvent showed a more complete structure and higher purity. Meanwhile, the retention rate of cellulose after treatment with TMAH was up to 90.2%, and the crystal structure of cellulose in the residues was practically unchanged. Moreover, the TMAH solvent could be recycled to fractionate hemicelluloses. The work provides an elegant and significantly efficient method towards hemicelluloses fractionation and cellulose purification.

Advanced Fractionation of Kraft Lignin by Aqueous Hydrotropic Solutions

Lignin is an underutilized high-potential biopolymer that has been extensively studied over the past few decades. However, lignin still has drawbacks when compared with well-known petroleum-based equivalents, and the production of tailored lignin fractions is highly in demand. In this work, a new method for the fractionation of Lignoboost Kraft Lignin (LKL) is proposed by using two different hydrotropes: sodium xylenesulfonate (SXS) and sodium cumenesulfonate (SCS). The different fractions are obtained by sequentially decreasing the hydrotropic concentration with the addition of water. Four and three different fractions were retrieved from the use of SXS and SCS, respectively. The LKL and respective fractions were analysed, and compared by GPC, FTIR-ATR, ¹H-NMR, ¹³C-NMR, ³¹P NMR, 2D HSQC and SEM. The fractions showed different molecular weights, polydispersity, and amount of functional groups. Our water-based lignin fractionation platform can potentially be combined with different lignin extraction and processing technologies, with the advantage of hydrotrope recycling.

Biodegradable, Flexible and Ultraviolet Blocking Nanocellulose Composite Film Incorporated with Lignin Nanoparticles

The exploration of functional films using sustainable cellulose-based materials to replace plastics has been of much interest. In this work, two kinds of lignin nanoparticles (LNPs) were mixed with cellulose nanofibrils (CNFs) for the fabrication of composite films with biodegradable, flexible and ultraviolet blocking performances. LNPs isolated from p-toluenesulfonic acid hydrolysis was easily recondensed and deposited on the surface of composite film, resulting in a more uneven surface; however, the composite film consisting of CNFs and LNPs isolated from maleic acid hydrolysis exhibited a homogeneous surface. Compared to pure CNF film, the composite CNF/LNP films exhibited higher physical properties (tensile strength of 164 MPa and Young's modulus of 8.0 GPa), a higher maximal weight loss temperature of 310 °C, and a perfect UVB blocking performance of 95.2%. Meanwhile, the composite film had a lower environmental impact as it could be rapidly biodegraded in soil and manmade seawater. Overall, our results open new avenues for the utilization of lignin nanoparticles in biopolymer composites to produce functional and biodegradable film as a promising alternative to petrochemical plastics.

Promotion of biomass pyrolytic saccharification and lignin depolymerization via nucleophilic reagents quenching of the carbonium ions

The condensation of lignin under acidic conditions inhibited the subsequent value-added utilization of lignin, and the condensed lignin covered the biomass surface. Here, a method of benzenesulfonic acid pretreatment combined with nucleophilic reagents promoted pyrolytic saccharification and lignin hydrogenation was reported. The anhydrosugar content in the pyrolysis bio-oil increased from 66.91% to 69.00%, 72.88%, and 72.16% via adding methanol, propionaldehyde, 3-hydroxylic-2-naphthoic acid, respectively. The characterization of the biomass surface structure and the calculation of bond lengths indicated that carbonium ions prefer to bind with the added nucleophilic reagent rather than the lignin fragment. Furthermore, the quenching of the carbonium ions preserved the β-O-4 bond, as demonstrated in 2D NMR. In the subsequent hydrogenation reaction, it was found that methanol facilitated the production of lignin monomer. The calculation also revealed that the quenching of the carbonium ions with methanol reduced the bond-breaking energy of the β-O-4 bond.

Superior separation of hemicellulose-derived sugars from eucalyptus with tropic acid pretreatment

Organic acid pretreatments can efficiently separate biomass-based hemicellulose and selectively produce hemicellulose-derived sugars. In this study, hemicellulose is separation as xylose, oligosaccharides in the tropic acid-catalyzed hydrothermal pretreatment of eucalyptus. The maximum yield of hemicellulose-derived sugars (85.78 %) with 71.25 % xylose selectivity (based on the total xylose in raw material) was achieved in the hydrolysate under optimal conditions (5 % TA, 160 ℃, 80 min). The yield of hemicellulose-derived sugar and the separation yield of hemicellulose increased by 11.06 % and 11.45 % compared with glycolic acid pretreatment in the similar severity factor. The separation yield of cellulose and lignin was decreased by 4.23 % and 0.98 %, respectively. This resulted in residual solids with higher biological stability (higher fiber crystallinity index, higher thermal stability, and higher lignin content). Therefore, higher hemicellulose separation selectivity and rich hemicellulose-derived sugars were obtained using TA pretreatment. The work would bring up a new method for biomass refining.

Application and prospect of organic acid pretreatment in lignocellulosic biomass separation: A review

As a clean and efficient method of lignocellulosic biomass separation, organic acid pretreatment has attracted extensive research. Hemicellulose or lignin is selectively isolated and the cellulose structure is preserved. Effective fractionation of lignocellulosic biomass is achieved. The separation characteristics of hemicellulose or lignin by different organic acids were summarized. The organic acids of hemicellulose were separated into hydrogen ionized, autocatalytic and α-hydroxy acids according to the separation mechanism. The separation of lignin depends on the dissolution mechanism and spatial effect of organic acids. In addition, the challenges and prospects of organic acid pretreatment were analyzed. The separation of hemicellulose and enzymatic hydrolysis of cellulose were significantly affected by the polycondensation of lignin, which is effectively inhibited by the addition of green additives such as ketones or alcohols. Lignin separation was improved by developing a deep eutectic solvent treatment based on organic acid pretreatment. This work provides support for efficient cleaning of carbohydrate polymers and lignin to promote global carbon neutrality.

Mechanistic insights into morphological and chemical changes during benzenesulfonic acid pretreatment and simultaneous saccharification and fermentation process for ethanol production

The anatomical and histochemical characterization of pretreated substrates is essential for the further valorization of biomass during the biorefinery process. In this work, the benzenesulfonic acid (BA)-treated substrates were employed for simultaneous saccharification and fermentation (SSF) of ethanol for the first time. An ethanol yield of 50.36% was attained at 10% solids loading and 47.45 g/L of ethanol accumulated at 30 % solids loading. The dramatic improvements could result from the deconstruction of cell walls, which were evidenced by fluorescence microscope and confocal Raman microscopy spectra. Additionally, for a thorough comprehension of the inherent chemistry of lignin during the BA pretreatment, the changes in lignin structure features were identified for the first time by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). In summary, this study tried to probe the possibility of BA-treated Miscanthus for the SSF process and unveiled the mechanism of the efficient BA pretreatment.

Chemocatalytic Conversion of Lignocellulosic Biomass to Ethanol: A Mini-Review

Ethanol has been widely used as a clean fuel, solvent, and hydrogen carrier. Currently, ethanol is generally produced through fermentation of starch- and sugarcane-derived sugars (e.g., glucose and sucrose) or ethylene hydration. Its production from abundant and inexpensive lignocellulosic biomass would facilitate the development of green and sustainable society. Biomass-derived carbohydrates and syngas can serve as important feedstocks for ethanol synthesis via biological and chemical pathways. Nevertheless, the biological pathway for producing ethanol through biomass-derived glucose fermentation has the disadvantages of long production period and carbon loss. These issues can be effectively mitigated by chemocatalytic methods, which can readily convert biomass to ethanol in high yields and high atomic efficiency. In this article, we review the recent advances in chemocatalytic conversion of lignocellulosic biomass to ethanol, with a focus on analyzing the mechanism of chemocatalytic pathways and discussing the issues related to these methods. We hope this mini-review can provide new insights into the development of direct ethanol synthesis from renewable lignocellulosic biomass.