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This study shows a functional deep eutectic solvent (DES) employing choline chloride (ChCl) and glyoxylic acid (GA) for lignocellulose fractionation. This DES exhibited a higher pretreatment efficiency (92.15%) than that composed of ChCl and lactic acid (10.36%). Molecular dynamic (MD) simulations indicated that the ChCl : GA DES showed a higher total binding energy (ΔE) with lignin than the ChCl : LA DES, resulting in a higher dissolution of lignin. GA prevented lignin condensation during pretreatment. The stabilized lignin containing 69.39% β-O-4 linkages can be used for phenolic monomer production with a bio-oil yield of 59.60% and lignin-based sunscreen preparation with a SPF of 58.46. The cellulose residues with a mild pretreatment severity exhibited a high enzymatic saccharification yield of 91.99%. Meanwhile, an esterification reaction occurred between cellulose and GA during pretreatment. The inhibition of enzymatic hydrolysis and microbial growth enables the use of functional cellulose to produce antibacterial paper. Furthermore, 96.80% of the DES could be easily recycled and reused for biorefinery purposes. [ABSTRACT FROM AUTHOR]

Derived from lignocellulosic biomass, sustainable hard carbon has emerged as a promising low-cost anode material for sodium-ion batteries (SIBs). However, the intricate formation process of the hard carbon microstructure remains unclear. This study investigates the structural differences and pyrolysis behaviors of pine lignin and its graded variants obtained through a lignin molecular sieving engineering strategy. Moreover, it delves into the relationship between the microstructure of lignin-derived hard carbon and its sodium-ion storage characteristics. Pristine pine lignin, along with ethanol-isolated lignin, acetone-isolated lignin, and residual lignin, serves as a precursor for synthesizing hard carbon materials. Quantitative analysis via31P NMR spectroscopy reveals the highest content of polar functional groups in ethanol-isolated lignin. Interestingly, hard carbon derived from ethanol-isolated lignin exhibits the smallest closed pore volume, leading to the lowest plateau capacity of sodium-ion storage. Conversely, hard carbon derived from acetone-dissolved lignin displays the highest plateau capacity owing to its largest closed pore volume formed in the carbonization process. The origin of open and closed pore structures of hard carbons is thoroughly analyzed. [ABSTRACT FROM AUTHOR]

Lignin, a crucial component of lignocellulosic biomass, holds immense promise for advancing biorefineries and producing sustainable energy alternatives. This study engineered a CN/rGO/BMO (2 : 1) heterojunction photocatalyst with varying Pd NP loading to selectively target the hydrogenolysis of challenging C–O ether bonds in lignin model compounds. Specific focus was on β-O-4, α-O-4, and the formidable 4-O-5 linkages. The 4-O-5 linkage, due to its high dissociation energy, poses a significant challenge. Electrochemical and spectral analyses unveiled improvements in charge separation, leading to delayed recombination of charge carriers in the heterojunction photocatalyst. Decorating the heterojunction with Pd NPs exhibited an elevated work function and a low Fermi energy level, facilitating the accommodation of photogenerated electrons and enabling efficient H2 dissociation. Such enhancement facilitated the cleavage of all three linkages, including the resistant 4-O-5 bonds under ambient conditions. The photocatalyst exhibited effective cleavage, yielding aromatic (toluene, phenol, ethylbenzene) and aliphatic (cyclohexane, ethylcyclohexane) products. Selectivity modulation was achieved by adjusting the time, hydrogen pressure, and Pd loading. Furthermore, this photocatalytic approach successfully transformed simulated lignin bio-oil containing all three linkages into valuable monomers. The alcoholic solvents efficiently harnessed photogenerated holes and prevented electron–hole recombination. The photocatalyst also demonstrated the capability to produce monomers from the native lignin extracted from teak wood sawdust. Emphasizing the focus on the reaction pathway and mechanism, scavenging studies and analyses were conducted, including UPS and VBXPS, to establish the Z-scheme charge transfer mechanism within the heterojunction. These findings provide a sustainable and efficient pathway for lignin valorisation in biorefineries, significantly contributing to the advancement of green fuels and aligning with the principles of green chemistry. [ABSTRACT FROM AUTHOR]

Recently, the ambient drying method for the preparation of xerogels has attracted great attention due to its low cost and high drying efficiency. However, the strong capillary forces existing during ambient drying cause severe shrinkage or even collapse of the aerogels (called xerogels). Although chemical crosslinking or displacement of water by organic solvents have been tried to solve the problem, extensive usage of chemicals and time-consuming displacement processes seem to be environmentally unfriendly and complex. Herein, we reported a green and efficient method for the preparation of a lignocellulosic xerogel. The xerogel was fabricated by alkali freezing of unbleached eucalyptus fibers followed by water washing and ambient drying. The alkali freezing promoted fiber swelling and enhanced the hydrogen bonds among the fibers, resulting in the gelation of lignocellulosic fibers. In particular, the residual lignin in the fibers reduced the capillary force during the drying process. The resulting lignocellulosic xerogel achieved a low shrinkage rate (27.50%), low density (0.039 g cm−3 ), high porosity (97.57%), and excellent mechanical strength (782.23 kPa) as well as environmental stability, and low thermal conductivity (44.76 mW m−1 K−1 ). Similarly structured xerogels could be generated using recycled NaOH solution. This technique was suitable for production using various kinds of plant fibers, which shows its great scalable production prospects. [ABSTRACT FROM AUTHOR]

Lignocellulose biorefining has great potential to replace the use of petrochemical resources in the production of fuels and chemicals. However, the full use of lignocellulose, which is depolymerized to yield mainly glucose, xylose, and lignin-derived phenolics, remains challenging. Here, we developed a glucose–xylose–phenolics (GXP) system to fully use lignocellulose for the production of L-tyrosine and its analogues in minimal medium. First, we engineered an Escherichia coli–Escherichia coli consortium carrying a CRISPR/dCas9 interference system to simultaneously use glucose and xylose to support cell growth and produce pyruvate, obtaining 34.3 g L−1 pyruvate with a yield of 0.68 g g−1 sugar. Then, we introduced tyrosine phenol lyase and other biocatalytic enzymes into this consortium to generate the GXP system, which could convert pyruvate and lignin-derived phenolics to L-tyrosine and its analogues. Using this GXP system, 20.8 g L−1L-tyrosine was produced from 12.5 g L−1 phenol with a yield of 86.4%. Using the hydrolysate of the raw material sorghum pith, 0.94 g L−1L-tyrosine was produced from 0.96 g L−1p-coumaric acid with a yield of 88.7%, and 8.1 g L−1 pyruvate remained, corresponding to an overall yield of 0.163 g product g−1 sorghum pith. The development of this GXP system illustrates a strategy for fully utilizing lignocellulosic biomass for the synthesis of value-added chemicals. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) and ionic liquids (ILs) are potential solvents for lignocellulosic biomass fractionation. In this study, the rice straw pretreatment efficiency of four cholinium-based solvents (DESs and ILs) prepared from the same sources (lactic acid and lysine) were comparatively investigated at 110 °C for 4 h. The lignin removal rate correlated well with the saccharification efficiency of the pulps. Quantum chemical (QC) calculations and molecular dynamics (MD) simulations focused on the microscopic structure and non-covalent interactions of the solvents and lignin model molecules (guaiacylglycerol-β-guaiacyl ether, GG) were carried out, and the results indicate that anions of the solvent systems play a leading role (through strong hydrogen bonds or electrostatic interactions) in establishing interactions with GG, supported by cations (via van der Waals interactions). There were clear positive relationships between the total interaction energies (IEs) and lignin removal, cellulose digestibility and glucose yields. In particular, [Ch][Lys] with a low self-interaction energy is able to free some active sites to form strong hydrogen bonds and electrostatic interactions with lignin, thus resulting in lignin dissolution and excellent delignification. For cholinium cations, an ideal partner system provides low self-IEs for solvent molecules and strong IEs between solvents and lignin, which are determined by the type and number of functional groups and the alkyl chain length of the partner components. This work provides ideas about tailoring suitable partner systems for cholinium cations to build solvents for efficient biomass deconstruction. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) are widely used as recyclable green solvents for the separation of lignin from lignocellulosic biomass. However, the poor permeability of DES solution limits the green advancement of separation systems. In addition, lignin fragment molecules are susceptible to repolymerization reactions during separation, resulting in reduced lignin reactivity. In this study, a DES consisting of choline chloride (ChCl) as a hydrogen acceptor, 5-sulfosalicylic acid (5Saa) as a hydrogen donor, and a certain amount of γ-valerolactone (GVL) as an additive was designed. The system not only efficiently fractionated lignin from poplar (71.35%), but also selectively retained almost complete cellulose (retention 92.87%) under the optimal fractionation (ChCl/5Saa/GVL molar ratio 1/4/15, temperature 120 °C, time 3.0 h). Pre-crushing processing of raw materials was avoided as the new DES solution has stronger permeability compared to the previous DES solution. Selective deconstruction of lignocellulose was achieved due to a strong hydrogen network structure. The lignin fragments were effectively dissolved. The results showed that the stability of the carbo-positive active intermediates was enhanced by ChCl–5Saa/GVL. Lignin with a low molecular weight (2305 g mol−1), high purity (98.77%) and high total phenolic hydroxyl content (6.92 mmol g−1) was obtained. Homogeneous lignin nanoparticles (LNPs) were prepared with an average particle size of 23 nm. LNPs had high dispersion stability and excellent UV shielding properties. The green advancement of the new DES has been significantly improved and the efficient fractionation of high-value lignin was realized. [ABSTRACT FROM AUTHOR]

Biomass-derived solvents have been proposed as a novel pathway in biorefining for the realization of biofuels and bioproducts derived from lignocellulosic biomass. Cyrene derived from cellulose has recently been shown to have a high potential as a green organic solvent for pretreating poplar biomass. However, due to its high dynamic viscosity nature, high Cyrene concentration could cause negative effects on the sugar release of the pretreated biomass as well as driving up the operational cost of the lignin recovery. In this study, we combine experimental and computational approaches to examine the impact of Cyrene pretreatment with reduced Cyrene concentration under mild conditions on switchgrass lignin. Our experimental studies indicated correlation between pretreatment condition and recovery and structure modification of lignin. Switchgrass lignin extracted by Cyrene pretreatment possessed high preservation of β-O-4 ether inter-unit linkage, which could provide versatility in the integration of downstream lignin valorization into the modern biorefinery industries. Molecular modeling examining the solvation of switchgrass lignin polymer and the disaggregation of low-molecular weight lignin aggregates under pretreatment conditions indicated that a preferential interaction exists between Cyrene and lignin, which likely drives lignin release, and that the disruption of inter-lignin contacts can be modulated as a non-monotonic function of Cyrene : water ratio. Further, while Cyrene–lignin interactions permit the solubilization of lignin, simulations with proxy reactive-species reveal that changes to the diffusion of these reactive proxies and their localization near linkage sites under Cyrene conditions may inhibit chemical processes. The results indicated that loss of pretreatment efficacy caused by low Cyrene concentration could be compensated by prolonged pretreatment time and high catalyst dosage. [ABSTRACT FROM AUTHOR]

Condensation, dark color and low extraction yield of lignin have hindered the full valorization of biomass during lignocellulosic fractionation. Herein, we introduce a novel biomass fractionation concept that addresses the issue of lignin's spatial confinement. Building upon this concept, we have devised an environmentally friendly and straightforward strategy. This approach involves a combination of selective carboxylation at the Cγ-OH position using citric acid and etherification at the Cα-OH position using butanol. The objective is to mitigate the spatial confinement of lignin and stabilize its active intermediates for lignin extraction. Consequently, up to 91.4 ± 0.2% lignin with a light color can be separated from the recalcitrant softwoods, as a UV blocker to improve the performance of sunscreen cream. The cellulosic residue can be enzymatically digested to glucose with a yield of 80%. The initiated biomass fractionation theory and strategy in this study provide a new concept for the isolation of lignin and full valorization of lignocellulose, promoting the development of a sustainable economy. [ABSTRACT FROM AUTHOR]

The conventional fractionation of lignocellulose into cellulose, hemicellulose, and lignin was generally carried out at high temperatures and under highly acidic conditions owing to the rigid matrix of lignocellulose and crystallinity of cellulose, causing the degradation of carbohydrates and condensation of lignin, thus hindering their value-added utilization. In this study, a stepwise fractionation method was proposed in which microwave-assisted fractionation of hemicellulose under mild conditions contributed to 81.9% of xylose yield; then, the cellulose part solid was rapidly dissolved in LiBr molten salt hydrate (LiBr-MSH) solution, followed by a filtration process to isolate lignin solid. It was found that the removal of hemicellulose provided more pores for the next dissolution of cellulose, and LiBr-MSH caused the cleavage of the hydrogen bonds of cellulose. Consequently, the cellulose part solid was rapidly dissolved in LiBr-MSH. The results showed that under the optimal fractionation conditions, 78.0% yield of glucan oligomers and 89.7% purity of noncondensed lignin were obtained from cellulose fractionation and filtration, respectively. A high β-O-4 bond content close to 87.3% of the theoretical maximum yield was detected in the obtained lignin, indicating that most β-O-4 bond structure of lignin was well preserved. Additionally, the isolated lignin can be selectively depolymerized into aromatic monomers with a high yield of 20.4%, which is 74.2% of the theoretical maximum yield. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) are intriguing for biomass fractionation, but high DES dosage and low biomass loading make them challenging to be used in industry. In this study, a DES was integrated into a novel pretreatment technology, namely "Densifying Lignocellulosic biomass with Chemicals followed by Autoclave (DLCA)", to realize lignocellulose fractionation and valorization with low DES dosage and high fractionation efficiency. Remarkably, a total DES dosage of 2 g g−1 biomass, which is substantially low compared to traditional DES pretreatments, achieved a high delignification ratio of 75% with over 95% cellulose preserved at 50% solid loading. Moreover, DLCA(DES)-CS exhibited superior bioconversion efficiency even at high solid loadings, with the maximum total fermentable sugar concentration exceeding 300 g L−1 and the ethanol concentration as high as 110 g L−1. Comprehensive characterization methods such as SEM, XRD, FTIR and Simons' staining were used to disclose the properties of cellulose-rich solids, and the chemical structure of the extracted lignin was characterized by GPC and 2D-HSQC NMR spectroscopy, revealing that DLCA(DES) pretreatment not only ensured complete exposure of cellulose, but also remarkably protected the native structures of lignin. Without recondensation, lignin extracted by DLCA(DES) preserved more than 98% of native β-O-4 linkages. In brief, this study demonstrates great potential for lignocellulose valorization initiated by DLCA(DES) pretreatment, including polysaccharide conversion to bioethanol and selective lignin depolymerization to aromatic monomers. [ABSTRACT FROM AUTHOR]

The development of novel catalysts to regulate product selectivity and insight into the mechanism of lignin hydrogenolysis are important for the comprehensive utilization of lignocellulose. Herein, we present a non-precious bimetallic catalyst Ni5Fe5/Al2O3 with improved catalytic performance relative to commercial Pd/C and Ni10/Al2O3 for hydrogenolysis of woody sawdust. In particular, the selectivity of propylguaiacol and propylsyringol is 79.1%. We developed kinetic experimental studies on β-O-4 model compounds and directly monitored the coniferyl alcohol or sinapyl alcohol intermediates in the reaction system for the first time. This directly demonstrates the lignin hydrolysis reaction pathway with simultaneous breakage of Cα-OH and Cβ-O. In the catalytic system, the reason for the difference in selectivity between Ni5Fe5/Al2O3 and other catalysts is their different hydrogenation pathways for intermediates coniferyl alcohol or sinapyl alcohol. Our work provides both an efficient catalyst and insight into understanding and regulating the mechanism of lignin hydrogenolysis. [ABSTRACT FROM AUTHOR]

DLC pretreatment is a novel and efficient pretreatment method for lignocellulosic biomass, but its mechanism of action has not been illustrated yet. In this study, a systematic investigation was conducted to find that the synergy of acidic chemical and mechanical actions during DLC pretreatment played an important role to ensure excellent performance. Mechanical actions likely exposed the internal polysaccharides of biomass by disrupting the cell wall structure, and the exposed polysaccharides reacted with concentrated acid until they were partially deconstructed, thereby significantly reducing the severity of subsequent dilute acid treatment. This synergism increased the accessible breakpoints of crystalline cellulose to cellulase by reducing the cellulose crystallinity and polymerization degree, as well as by digesting amorphous cellulose. Additionally, the large removal (about 60%) of hemicellulose increased biomass porosity. The native lignin structure was well preserved without the generation of pseudo-lignin and large amounts of toxic degradation products. These properties contribute to the high sugar recovery (97.2%), great digestibility (83.4% total yield of monosaccharides), and outstanding fermentability of DLC biomass; these results are not achievable for traditional dilute acid pretreatment. Simultaneous saccharification and co-fermentation of DLC-pretreated rice straw resulted in an ethanol titer as high as 82.9 g L−1 without detoxification. Detailed structural analysis revealed that the well-preserved inter-unit linkages (>80%) and non-condensed subunits remained in the DLC lignin. This study revealed the mechanism of DLC technology in promoting biomass conversion, and thus, provides guidance to potentially realize efficient and economical biorefinery. [ABSTRACT FROM AUTHOR]

Rapid population growth and industrialization have pressed the search for alternative sources to synthesize biomaterials. In this venture, this manuscript deals with process development for the synthesis of a lignin hydrogel (LH) which has biomedical applications viz., wound healing, etc. Two different synthesis strategies have been studied: single and two-step processes and likely categorized as grade A and B LHs, respectively. These strategies have been considered to study the role of the raw material (native vs. methacrylated lignin) on the overall technoeconomic analysis (TEA) and life-cycle assessment (LCA) of the process. The minimum selling price (MSP) of LH grades A and B has been estimated to be 2774 US$ per ton and 4489 US$ per ton, respectively, and have been observed to corroborate with the market price range of wound dressing gels. A "hydrogel production" sub-system has been observed to be the major contributor towards the MSP of LH due to the use of costly monomers in polymerization. Sensitivity analysis was conducted to find out parameters having a significant influence on MSP. Uncertainty analysis was also carried out to study the influence of market uncertainties on the MSP of LH. From the LCA study, it was estimated that the grade A hydrogel production process is comparatively cleaner than that of grade B. Overall, the proposed strategy of lignin upgradation can be integrated within the lignocellulosic biorefinery in future studies for the development of eco-friendly processes. [ABSTRACT FROM AUTHOR]

The integration of nanotechnology into lignocellulose biorefineries with multi-product outcomes is appealing but technically challenging due to lignin's random chemical structure. In this work, FeCl3- mediated deep eutectic solvents (DESs) were proposed to integrate microcapsulated pesticide production into current lignocellulose biorefineries to overcome this technical barrier. The addition of FeCl3 to choline chloride/lactic acid DES significantly enhanced hemicellulose removal (by nearly 100%) and lignin yield (62.1%). A high delignification ratio (70.8%) was obtained by FeCl3-mediated neutral DES (choline chloride/glycerol) pretreatment, which also significantly contributed to cellulose saccharification (81.6%). Moreover, an acid-catalyzed condensation reaction and the cleavage of β-O-4 linkages of lignin occurred during the FeCl3-mediated DES pretreatment. The condensation structure and abundant phenolic-OH content produced its special aromatic structure and enhanced the amphiphilic properties for the preparation of lignin nanospheres (LNSs), and further improved the anti-photolysis performance of LNS-encapsulated avermectin (AVM@LNS) pesticide. A strong positive correlation (R² = 0.86) between the phenolic- OH content and the half-life was also found. The tailored chemical structure of lignin also provided for its strong π-π stacking to promote nonradiative migration and trigger photothermal conversion. Unlike the bare AVM solution, AVM@LNS presented controlled release performance and temperature response behaviors for sustained pest control. This study achieved technical integration using the tailored lignin to realize the targeted downstream products, and also improved the high-value utilization of lignin by-products for green agriculture. [ABSTRACT FROM AUTHOR]

Lignin is the largest natural source of functionalized aromatics on the planet, therefore exploiting its inherent structural features for the synthesis of aromatic products is a timely and ambitious goal. While the recently developed lignin depolymerization strategies gave rise to well-defined aromatic platform chemicals, the diversification of these structures, especially toward high-end applications is still poorly addressed. Molecular motors and switches have found widespread application in many important areas such as targeted drug delivery systems, responsive coatings for self-healing surfaces, paints and resins or muscles for soft robotics. They typically comprise a functionalized aromatic backbone, yet their synthesis from lignin has not been considered before. In this contribution, we showcase the synthesis of a novel light-driven unidirectional molecular motor from the specific aromatic platform chemical 4-(3-hydroxypropyl)-2,6-dimethoxyphenol (dihydrosynapyl alcohol) that can be directly obtained from lignocellulose via a reductive catalytic fractionation strategy. The synthetic path takes into account the principles of green chemistry and aims to maintain the intrinsic functionality of the lignin-derived platform molecule. [ABSTRACT FROM AUTHOR]

Efficient fractionation of lignocellulose and refinery of all its components remain challenging. Here we describe the use of diol-tailored deep eutectic solvents for superior lignocellulose fractionation and maximizing the refinery efficiency. Near-quantitative cellulose extraction from lignocellulose was achieved after a one-pot treatment, while excellent solubilization of lignin (92%-96%) and hemicellulose (85%- 89%) was achieved simultaneously. For downstream valorization, up to 99% glucose yield was obtained after enzymatic hydrolysis or quantitative cellulose nanofibers were obtained by ultrasonication of the cellulose fractions. Hemicellulose was selectively converted to furfural and xylose with up to 67% yield. The lignin fractions were easily recovered with yields up to 70% and showed diol-alkoxylated and arylether- retained substructures suitable for the production of alkylphenol monomers or direct use as natural polyols for printing ink synthesis. This work demonstrated that tailored deep eutectic solvent fractionation allows 85% refinery of lignocellulose, which represents a breakthrough toward holistic and highly efficient biorefinery. [ABSTRACT FROM AUTHOR]

Pretreatment of lignocellulosic biomass is essential for efficient conversion into biofuels and bioproducts. The present study develops a predictive toolset to computationally identify solvents that can efficiently dissolve lignin and therefore can be used to extract it from lignocellulose during pretreatment, a process known to reduce recalcitrance to enzymatic deconstruction and increase conversion efficiency. Two approaches were taken to examine the potential of eleven organic solvents to solubilize lignin, Hansen solubility parameters (HSP) and activity coefficients and excess enthalpies of solvent/lignin mixtures predicted by COSMO-RS (COnductor like Screening MOdel for Real Solvents). The screening revealed that diethylenetriamine was the most effective solvent, promoting the highest lignin removal (79.2%) and fermentable sugar yields (>72%). Therefore, a COSMO-RS-based predictive model for the lignin removal as a function of number and type of amines was developed. Among the fitted models, the non-linear regression model predicts the lignin solubility more accurately than the linear model. Experimental results demonstrated a >65% lignin removal and >70% of sugar yield from several amine-based solvents tested, which aligned very well with the model's prediction. Finally, to help understand the dissolution mechanism of lignin by these solvents, quantum theory of atoms in molecules (QTAIM) and quantum chemical calculations (interaction energies and natural bond orbital (NBO) analysis) was performed and suggest that amines exhibit strong electrostatic interactions and hydrogen bonding strengths with lignin leading to higher lignin removal. Together, these computational tools provide an effective approach for rapidly identifying solvents that are tailored for effective biomass pretreatment. [ABSTRACT FROM AUTHOR]

Pretreatment of renewable lignocellulosic biomass is essential to produce fermentable sugars and biofuels in a sustainable biorefinery. However, lignin repolymerization during pretreatment was reported to intensify lignin inhibition in the enzymatic hydrolysis of cellulose. Seeking green additives to mitigate lignin inhibition is of great significance for sustainable lignocellulosic biorefinery. In this work, green additives, mannitol and syringic acid, were thoroughly evaluated for improving the dilute acid pretreatment efficacy of hardwood. The results showed that these additives used in dilute acid pretreatment altered the structure and physicochemical properties of lignin, thus mitigating lignin inhibition on cellulose hydrolysis. In detail, 31P NMR results showed evidently higher aliphatic OH groups of lignin after mannitol addition. The 2D HSQC NMR analysis exhibited more β-O-4 and fewer β–β structures, while GPC analysis showed a lower molecular weight of lignin. Results indicated that mannitol was incorporated into the lignin structure to form etherified lignin with plenty of hydroxyl tails, which suppressed lignin repolymerization. As a result, the surface barrier effect of lignin was largely diminished by mannitol addition, leading to improved ease of cellulose hydrolysis by up to 53%. As far as we know, mannitol as an additive in biomass pretreatment has not been reported. This work presented novel green additives to suppress lignin repolymerization for boosting enzymatic saccharification of cellulose in a sustainable lignocellulosic biorefinery. [ABSTRACT FROM AUTHOR]

This tutorial review aims to describe the status of the scaling up of organosolv treatment. It is a process where various lignocellulosic materials are fractionated, selective depolymerization mechanisms are catalyzed, and their main components (polysaccharides, lignin and extractives) can be extracted, separated and isolated using liquid organic solvents such as alcohols, ketones and proton-donating acid molecules. Organosolv fractionation can be applied to several renewable biomasses, allows the production of pure species systems to prepare valuable chemicals, polymers and biomaterial compositions with a related environmental impact, lower than that of classical industrial plants, and optimizes the resource carbon efficiency. However, the high energy consumption for the recovery after dissolution, input costs and feedstock flexibility robustness are slowing down the piloting of commercial operations. As a critical indicator evaluation, a summary of reasons why engineering organosolv is still extremely interesting, together with an overview of the most important organosolv technologies, describing current equipment scale range economics, limitations and market research opportunities, is presented in detail. A variety of sources (wood, straw, bagasse, wastes...), media (water, methanol, ethanol, formates, acetates...) and products (biogas, bioethanol, (nano)cellulose, glucose, furans...) are comparatively benchmarked. Existing (model) validated, demonstrational or patented configurations are collected, listing strengths as well as challenges. [ABSTRACT FROM AUTHOR]

Lignin, a renewable polymer derived from the lignocellulosic biomass represents more than 20% of the total mass of the Earth's biosphere. However, 98% of lignin is burned as a source of energy in the pulp and paper industry, essentially due to its complex structure. Today, the valorization of lignin into the production of value-added chemicals represents a real challenge in terms of both sustainability and environmental protection. The present contribution aims to provide a critical discussion on the crucial choice of the starting material to study lignin valorization. Next, a comparison between the different oxidation routes investigated by chemists over the past several years is presented, with emphasis on the major difficulties encountered. The main current challenges regarding the heterogeneous catalytic oxidation of lignin and its derivatives are also highlighted. Particular focus is given to innovative strategies favoring mild reaction conditions. Finally, we provide some recommendations and routes worthy of interest in this studied area of research in order to generate value-added chemicals from lignin oxidation through the use of heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

The cost of sugar production remains a key challenge in future lignocellulosic biorefineries. We demonstrate that ZnBr2, an inexpensive inorganic salt, provides nearly theoretical yields of glucose and xylose in one-step from poplar wood at 85 °C and short reaction times at molten salt hydrate (MSH) conditions without an acid. Catalytic depolymerization of the isolated MSH lignin, using a CoS2 catalyst, yields 17% phenol-like monomers compared to only 1% produced from the acidified MSH lignin. Reductive catalytic fractionation of MSH lignin over Ru/C resulted in two times higher total monomer yield compared to the AMSH lignin. Both the lignin samples were characterized using 2D HSQC NMR and the thioacidolysis method. Thioacidolysis studies reveal 8.4% and 1.8% of β-O-4 linkages in MSH and acidified MSH lignin, respectively. Thermodynamic modeling and 13C NMR spectroscopy indicate that the effectiveness of this catalyst arises from the strong interaction of the Lewis acidic zinc cation (Zn2+) with the coordinated water molecules resulting in hydrolysis of the metal aquo complex and to the salt-driven increase in the H+ activity coefficient. Techno-economic analysis demonstrates that despite being slower, the ZnBr2 MSH media has cost advantages, compared to conventional hydrolysis and even to the LiBr and ZnBr2 AMSH, due to the higher quality of lignin. [ABSTRACT FROM AUTHOR]

In recent years, there have been many advances toward developing sustainable, micro- and nanoscale materials from biobased resources such as lignin aimed at strengthening the bioeconomy. It is critical to study the factors affecting nucleation and growth mechanisms, as well as the stability of lignin micro-and nanoparticles (LPs), to further enhance the development of such materials. However, there remains a gap in the literature examining the many interactions present during and after LP formation. These interactions vary with the chemical composition and molecular weight distribution of different kraft lignin (KL) fractions. To examine the composition of different lignin fractions, KL can be fractionated using water-miscible organic solvents of different polarities such as tetrahydrofuran (THF), acetone, and ethanol. Herein, we show that the micro- and nanoparticles formed from each lignin fraction exhibit significant differences in their size (50–300 nm), particle aggregation and fusion propensity, and spherical morphology in aqueous suspensions. These differences are proposed to be a result of the solvent–lignin–water interactions related to molecular weight and functional groups of the lignin fractions and solvent/water polarity. Another factor affecting the nucleation and growth of LPs is the lignin concentration. The LPs formed at low lignin concentrations exhibit a larger average particle size compared to the LPs formed at higher lignin concentrations due to the aggregation and fusion of the small particles. These results will allow for a stronger foundation in understanding the nucleation and growth of LPs when attempting to develop value-added applications for kraft lignin. [ABSTRACT FROM AUTHOR]

The methoxyl group is the most abundant functional group of lignin and affects the properties, reactivity, and application of lignin. Efficient demethylation is always of interest in the area of lignin chemistry and application. This study demonstrated a new method for cleaving ether compounds and demethylating lignin in acidic concentrated lithium bromide (ACLB) solution under mild conditions. It was found that the ACLB system could universally cleave ether compounds except for diaryl ethers. The study on lignin model compounds (creosol, syringol, and 1,2,3-trimethoxybenzene) verified that ACLB could demethylate them to corresponding phenols. Four real lignin samples produced from various sources by different methods were also efficiently demethylated by 69–82% in ACLB. The lignin demethylation resulted in more phenolic hydroxyl groups, which benefits some downstream applications of lignin. This study also provided new insights into the cleavage of the ether bonds in lignin. In addition to the methyl–aryl ether bond, ACLB could cleave other ether bonds of lignin in β-O-4, β-5, and β-β structures except for the 4-O-5 bond in the diphenyl structure. The ether bonds were cleaved via the SN2 substitution except for the β-O-4 bond, which was primarily cleaved via the benzyl cation and enol ether intermediates, leading to Hibbert's ketones. Some of the β-O-4 structures were transformed into benzodioxane (BD) structures, which were stable in the ACLB system. [ABSTRACT FROM AUTHOR]

Due to their low cost and excellent solubility, functional ionic liquids (ILs) have been widely used in the pretreatment of lignocellulose. However, the high viscosity and harsh pretreatment conditions of ILs usually bring difficulties in separation and regeneration, hindering the large-scale use of ILs for industrial applications. To solve these problems, four sugar-platform renewable high boiling alcohol solvents (HBS) that can form hydrogen bonds with lignin were chosen as co-solvents. This confirmed that HBS not only have an effect on the interaction of ILs and lignin, but they also participate in the interaction of the co-solvent and lignin. The cation–anion interaction energy in 2-hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium methanesulfonate ([BHEM]mesy) is weakened, but for hydrogen bond interactions, like IL-lignin and co-solvent-lignin, the energy is increased, as shown by a series of characterization and analysis studies. The system has advantages, like mild reaction conditions, low cost, renewability, high biomass pretreatment efficiency, and excellent cycling performance, which can increase the lignin removal ratio to 95.2%. The recycling and reusability were also evaluated and, after seven rounds, there was no significant reduction in activity. This work provides a promising large-scale sustainable biomass pretreatment strategy for biorefinery processes. [ABSTRACT FROM AUTHOR]

We demonstrate for the first time non-catalytic, oxidative cracking with molecular oxygen (O2) to depolymerize native lignin into oxygenated phenolic monomers. Maximum monomer yield of 10.5 wt% was achieved at 250 °C after only 10 min of reaction and included vanillin, syringaldehyde, vanillic acid, and syringic acid. High rates of oxidation are attributed to the use of perfluorodecalin as solvent. Perfluorodecalin is a perfluorocarbon (PFC), characterized by their chemical stability and exceptionally high solubility for O2. Monomer yields were typically five-fold higher in perfluorodecalin compared to solvents more commonly employed in lignin conversion, such as methanol, butanol, acetonitrile, and ethyl acetate. Phenolic monomer production in perfluorodecalin favors high temperatures and short reaction times to prevent further oxidation of the produced monomers. Lignin oil obtained under oxidative conditions in perfluorodecalin showed lower molecular weight and smaller polydispersity compared to other solvents. Increasing the reaction time further decreased the molecular weight, while increasing reaction time in an inert atmosphere increased the molecular weight of the lignin oil. High concentrations of O2 in perfluorodecalin not only increased lignin depolymerization but suppressed undesirable condensation reactions. Depolymerization is likely initiated by thermally induced homolytic cleavage of ether linkages in lignin to form phenoxy and carbon-based radicals. These radicals bind with O2 as a radical scavenger and further react to form phenolic monomeric products rather than repolymerizing to large oligomers. The PFC process was scaled from 5 mL to 250 mL without any loss of yield. Because most organic compounds are not soluble in perfluorodecalin, recycling is easily achieved via liquid–liquid separation. [ABSTRACT FROM AUTHOR]

Upgrading renewable lignocellulose into bulk chemicals and drop-in-fuels has been identified as a state-of-the-art paradigm to fulfill alternative energy demands. Lignin, as the largest precursor of alkyl aromatics, can be depolymerized effectively to maneuver task-specific phenols. Toward an ecofriendly lignin-first depolymerization, photocatalytic lignocellulose conversion, also termed photobiorefining, is of utmost importance to boost economic and technical feasibility of holistic biomass valorization. It is still an urgent but challenging task to rationally design light-driven lignin deconstruction with decent photocatalytic selectivity and durability for developing scalable photobiorefining. A bottom-up approach, beginning with representative model compounds as lignin intermediates, enables a chance to encompass well-defined photocatalytic mechanism/system for providing insights, feasibility, and guidelines before the technical or proto-lignin conversion. The emphasis of this review is mainly placed on photocatalytic lignin-first strategy that includes versatile photocatalyst types, transformation pathways, photoreactors, and reaction medium. The cleavage mechanisms of C–O (e.g., β-O-4′ and α-O-4′) and C–C (e.g., β-1′ and β-5′) linkages in native lignin and its models to form light aromatic hydrocarbons through homogeneous or heterogeneous photocatalysis are proposed. At the end, the remaining challenges for the selective control and practical spread of photocatalytic lignocellulose fractionation are elaborated, and burgeoning prospects to inspire opportunities on photocatalyst manipulation for efficient and sustainable light-mediated lignin conversion are also discussed. The present work sheds light on the structure–property–performance relationship in photocatalytic lignin valorization and forthcoming knacks to spark the bright pearl of high-performance photobiorefining. [ABSTRACT FROM AUTHOR]

In the past few years, cellulose nanomaterials obtained from lignocellulose have attracted extensive attention as functional nanomaterials with excellent properties and great application potential in a variety of high-tech fields. However, the preparation of cellulose nanomaterials is facing several challenges such as the large amount of energy consumption, chemical recovery issues, and complicated purification and pretreatment processes, which have limited their large-scale application. Fortunately, lignin-containing cellulose nanomaterials have emerged as a new type of cellulose nanomaterial because of the low energy and chemical consumption, easy preparation process, and special properties. This review showcases a comprehensive overview of research status on the preparation and application of lignin-containing cellulose nanomaterials, focusing on recently developed green and low-cost preparation processes. The potential applications of lignin-containing cellulose nanomaterials as building blocks and reinforcing agents for the design of various advanced materials are summarized as well. Finally, the current challenges and future directions for the preparation and application of lignin-containing cellulose nanomaterials are provided. [ABSTRACT FROM AUTHOR]