Lignin Fragments Research Articles

Comparison on thermally modified beech wood in different mediums: Morphology, chemical change and water-related properties

Thermal modification has been proved to be an effective approach to improve the dimensional stability of wood, while different processes of thermal modification often resulted in various efficacy. In this study, the morphology, chemical structure, crystallinity, pore size distribution, and some water-related properties were investigated in order to explore the effect of different mediums (vacuum, nitrogen, steam and air) on thermally modified wood (TMW). It was found that heating medium plays an important role in thermal modification of wood. At both 180 and 210 ℃, the general severity of thermal modification is in the following order: air > steam > nitrogen > vacuum. Accordingly, the highest dimensional stability appeared in air TMW, and then steam, nitrogen, and vacuum. It seemed that the water-related properties were primarily affected by the extent of decomposition of the amorphous polysaccharides, but showed no direct relationship with the pore structure. Lignin changed greatly for TMW treated in steam at 180 ℃ and all TMW treated at 210 ℃, by showing more uniform distribution in all cell wall layers. It might be resulted from the migration of lignin fragments after depolymerization, the formation of pseudo lignin from holocellulose, and the increased relative lignin content in secondary wall. The changes on pore structure and lignin structure might have significant effect on other wood properties.

The etherase system of Novosphingobium sp. MBES04 functions as a sensor of lignin fragments through phenylpropanone production to induce specific transcriptional responses.

The MBES04 strain of Novosphingobium accumulates phenylpropanone monomers as end-products of the etherase system, which specifically and reductively cleaves the β-O-4 ether bond (a major bond in lignin molecules). However, it does not utilise phenylpropanone monomers as an energy source. Here, we studied the response to the lignin-related perturbation to clarify the physiological significance of its etherase system. Transcriptome analysis revealed two gene clusters, each consisting of four tandemly linked genes, specifically induced by a lignin preparation extracted from hardwood (Eucalyptus globulus) and a β-O-4-type lignin model biaryl compound, but not by vanillin. The most strongly induced gene was a 2,4'-dihydroxyacetophenone dioxygenase-like protein, which leads to energy production through oxidative degradation. The other cluster was related to multidrug resistance. The former cluster was transcriptionally regulated by a common promoter, where a phenylpropanone monomer acted as one of the effectors responsible for gene induction. These results indicate that the physiological significance of the etherase system of the strain lies in its function as a sensor for lignin fragments. This may be a survival strategy to detect nutrients and gain tolerance to recalcitrant toxic compounds, while the strain preferentially utilises easily degradable aromatic compounds with lower energy demands for catabolism.

Efficient production of low molecular weight lignin from eucalyptus wood through methanol-alkali system

With the high phenolic hydroxyl content and excellent bioactivity, low molecular weight lignin (LMW-Lignin) holds tremendous potential for various applications in energy storage and antibacterial materials. However, conventional sources of lignin currently available are characterized by large molecular weights, and many of their active functional groups remain unreleased, limiting their exploitation for potential applications. In this study, we investigated the inhibition effect of methanol on the recondensation of lignin fragments under a hydrothermal system of methanol/sodium hydroxide, using eucalyptus wood flour as the raw material. Our findings revealed that, in the hydrothermal alkaline system,·OCH3 free radicals formed from methanol can effectively target and react with the active sites (Cα and Cβ) on the dissolved lignin side chains, resulting in the formation of stable methoxyl structures and preventing the formation of C-C bonds and polycondensation of dissolved lignin. Optimized conditions, including 20% CH3OH (methanol content), 14% NaOH (sodium hydroxide content), and a reaction temperature of 160 ℃, led to a weight-average molecular weight of 1478 for the lignin product, with a yield of 62.90%.

Lewis acid/base mediated deep eutectic solvents intensify lignocellulose fractionation to facilitate enzymatic hydrolysis and lignin nanosphere preparation

In this work, Lewis acids (FeCl3, AlCl3) and bases (Na2CO3, Na2SO3) were incorporated into a neutral deep eutectic solvent (DES, choline chloride/glycerin) to intensify the lignocellulose fractionation. The efficiency of fractionation in terms of the maximum delignification rate (89.7 %) and well-pleasing cellulose saccharification (100 %) could be achieved by the Lewis acid-mediated DES. An in-depth insight of the evolution of lignin structure revealed that Lewis acid-mediated DES could cleave the β-O-4 linkages efficiently to achieve a high yield lignin fragments. Meanwhile, the lignin fragments with the enhanced amphiphilic properties facilitate the preparation of lignin nanospheres (LNSs) via the self-assembly process. The resultant LNSs extracted by Lewis acid-mediated DES exhibited an excellent thermal stability, and enhanced antibacterial capacity, which were associated with the phenolic OH content. However, the extracted lignin by Lewis base-mediated DES was mainly attributed to the cleavage of lignin-carbohydrate complexes bond, especially the lignin-carbohydrate ester bond, which retained more ether bonds and a relatively complete structure. This study illuminated the different mechanisms of lignin extraction and the structural evolution of lignin from Lewis acid/base-mediated DES, and provided guidance to select suitable fractionation techniques for upgrading the downstream products.

Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression

Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation.

Green bio-based aprotic solvents for efficient fractionation of hemicellulose and targeted value addition of lignin

It is of great significance to inhibit the repolymerization of lignin when removing hemicellulose by acid pretreatment. Adding a lignin fragment scavenger is an effective method to inhibit its repolymerization. Here, the effect of a bio-based polar aprotic solvent, levulinic acid (Lev), and γ-valerolactone (GVL) coupled pretreatment system on the separation yield of poplar biomass components was investigated. The optimum pretreatment conditions were a Lev concentration was 7.0%, reaction temperature was 170 °C, pretreatment time was 60 min, and GVL concentration was 9.0%. The separation yield of hemicellulose was 84.54%, which was a 4.53% increase over that with Lev pretreatment. The retention yield of cellulose was 89.68%. In addition, the separation efficiency was significantly improved when the pretreatment time was reduced by 40 min. The reaggregation of lignin was suppressed under the condition of maximum hemicellulose separation. In the lignin samples the content of β-O-4 was as high as 47.81%. Simultaneously, the content of phenolic and aliphatic hydroxyl increased. The results revealed that Lev/GVL pretreatment had good hemicellulose separation selectivity and excellent lignin fragment removal efficiency. This provides a new strategy for suppressing adverse effects on the lignin structure in the efficient separation of hemicellulose in pretreatment.

Unraveling Electrochemical Lignin Degradation in Organic Solvent for Production of Valuable Fuels and Chemicals

Lignin is the second most abundant biopolymer in nature after cellulose. Due to its distinctive aromatic backbone, it is also one of the most unique biopolymers. The aromatic components in lignin provide structural support to plants and comprises about 30% of the plant material. These aromatic groups can be used to produce renewable aromatic compounds. Also, these aromatic compounds can be used to produce biofuels which can be promising alternative to fossil-based fuels and chemicals. Besides, from previous studies it is found that about 40 to 60 million tons of lignin are generated from pulp and paper industry, mostly as wastes. So, developing novel and attractive strategies for fragmentation of lignin is gaining increased interest among scientific community for valorizing this underexploited material. Also, by valorizing lignin the sustainability of biorefinery and paper industry can be enhanced. However, the present technologies used for degradation of lignin generally requires the use of metallic catalysts at high temperatures and harsh reaction conditions. As a result, catalyst recovery and decomposition often become difficult under such harsh conditions and the process becomes impractical. Also, these technologies suffer from poor selectivity and usually produce the desired fragmentation products in low yields. Compared to the thermocatalytic transformation of lignin, electrocatalytic approaches have several advantages like it is environmentally friendly, have mild reaction conditions and the cost is low. Besides, there is a lack of studies incorporating electrocatalytic oxidation and reduction of lignin in organic solvent. In this project, the main goal was to overcome the challenge of using isolated lignin from various industrial processes by electrochemical depolymerization of lignin in organic solvent like tetrahydrofuran. Tetrahydrofuran is mainly used in Co-solvent Enhanced Lignocellulosic Fractionation (CELF) process. So, electrocatalytic degradation of lignin in this solvent is beneficial because the product from CELF process can be directly used here and thus it can work as a secondary treatment process for CELF process. Cyclic voltammetry (CV) and Chronoamperometry (CA) which are important tools for identifying redox reactions happening in the system is used here. In this presentation, for varying concentrations of Lignin, Tetrahydrofuran and sulfuric acid the results found from CV and CA will be discussed with practical significance.Keywords: Recalcitrant biopolymer, Lignin in organic solvent, controlled electrocatalysis, secondary treatment for CELF process, Cyclic Voltammetry

Exoproteomic Study and Transcriptional Responses of Laccase and Ligninolytic Peroxidase Genes of White-Rot Fungus Trametes hirsuta LE-BIN 072 Grown in the Presence of Monolignol-Related Phenolic Compounds.

Being an abundant renewable source of aromatic compounds, lignin is an important component of future bio-based economy. Currently, biotechnological processing of lignin through low molecular weight compounds is one of the conceptually promising ways for its valorization. To obtain lignin fragments suitable for further inclusion into microbial metabolism, it is proposed to use a ligninolytic system of white-rot fungi, which mainly comprises laccases and peroxidases. However, laccase and peroxidase genes are almost always represented by many non-allelic copies that form multigene families within the genome of white-rot fungi, and the contributions of exact family members to the overall process of lignin degradation has not yet been determined. In this article, the response of the Trametes hirsuta LE-BIN 072 ligninolytic system to the presence of various monolignol-related phenolic compounds (veratryl alcohol, p-coumaric acid, vanillic acid, and syringic acid) in culture media was monitored at the level of gene transcription and protein secretion. By showing which isozymes contribute to the overall functioning of the ligninolytic system of the T. hirsuta LE-BIN 072, the data obtained in this study will greatly contribute to the possible application of this fungus and its ligninolytic enzymes in lignin depolymerization processes.

Lignin extraction and fractionation from rice straw biorefinery residues

Crops straw contains many valuable natural compounds. Cellulose and hemicellulose in agricultural wastes have been widely used in biofuel production. However, the large-scale application of residue lignin from biorefinery is still an unsolved problem. Various impurities and heterogeneous lignin with a very complicated molecular weight distribution were generally found in the recovered raw solid products. In this study, brown solid residue from rice straw biorefinery was processed using membrane separation in combination with the soda-ethylene glycol (Soda-EG) process to extract high-purity lignin. At first, wet brown solid was mixed into an aqueous solution of sodium hydroxide and ethylene glycol for lignin fragmentation, depolymerization, and solubilization at elevated temperatures. Afterwards, microfiltration (MF) was applied to recover the dissolved lignin in the filtrate from the extracts. As high as 90% of the lignin in the brown solid could be recovered after acid precipitation of the filtrate. The highest lignin content in the precipitate product could be 90% (dry basis). The precipitate was re-dissolved at high pH aqueous solutions for further molecular weight fractionation by ultrafiltration (UF). The best rejection of high-molecular-weight (>1 × 105 g/mol) lignin was 77%, while low-molecular-weight (<3 × 103 g/mol) lignin was <13% with a MWCO of 10 kDa polysulfone UF membrane in a dead-end filtration system. The cross-flow operation with the same UF membrane showed that >80% lignin could be recovered from the retentate and the flux of permeate could be maintained after three operation-cleaning cycles. Overall, the combined MF-UF operation could be a viable method for obtaining high-value-added lignin products with a specific molecular weight range.

Insights into co-solvent roles in oxidative depolymerization of lignin to vanillin and lactic acid

Efficient low-boiling-point co-solvent systems were developed for the oxidative depolymerization of lignin to high-value platform chemicals, mainly vanillin and lactic acid, using molybdenum (Mo)-based solid oxide catalysts and hydrogen peroxide (H2O2) oxidant. The co-solvent, designed with the matching Hansen solubility parameter (HSP) values to lignin, facilitated efficient solvation of lignin. Various factors, including co-solvents, catalyst supports, H2O2 concentrations, and active metals, were detailly investigated. Optimal yields of total liquid products (EA oils: 19.8 %) were obtained in water-tetrahydrofuran (H2O-THF) co-solvent systems, increased by 61.0 % compared to that of the sole aqueous solution, employing a MoO3/Al2O3 catalyst. Additionally, the oxidized lignin (O-lignin) or EA oils was analyzed using UV–vis, CHN, GPC, and FT-IR techniques. Results indicated that the co-solvent system remarkably inhibited the repolymerization of lignin fragments, and enhanced the oxidative cleavage of lignin side chains. Lastly, a hypothetical mechanism explained the reaction pathway of lignin depolymerization in co-solvent systems.

The structure and properties of lignin isolated from various lignocellulosic biomass by different treatment processes

The structure and properties of lignin can vary depending on the type of lignocellulosic biomass it comes from and the separation techniques used, and also affects its suitability for different applications. In this work, the structure and properties of lignin isolated from moso bamboo, wheat straw, and poplar wood by different treatment processes were compared. Results show that deep eutectic solvent (DES) extracted lignin exhibits well-preserved structures (including β-O-4, β–β, and β-5 linkages), a low molecular weight (Mn = 2300–3200 g/mol), and relatively homogeneous lignin fragments (1.93 < PDI < 2.33) compared to dealkaline lignin (DL) and milled wood lignin (MWL). Besides, lignin samples extracted by DES have a regular nanostructure, higher carbon residue content (>40 %), and excellent antioxidant properties (the free radical scavenging index >20). Among the three types of biomass, the structural destruction of lignin in straw is the most obvious, which is due to the degradation of β-O-4 and β-β linkages during DES treatment. These findings can contribute to a better understanding of the structural changes that occur in various treatment processes from different lignocellulosic biomass, and help maximize the targeted development of their applications based on the characteristics of lignin.

Formation and Identification of Lignin-Carbohydrate Complexes in Pre-hydrolysis Liquors.

The lignin-carbohydrate complexes (LCCs) typically present in the liquors produced in the pre-hydrolysis of biomass cause severe difficulties in downstream fractionation. To address this issue, a series of LCC samples were accessed from solutions obtained from the pre-hydrolysis of extractive-free pine wood meal (H-LCC) and compared with LCC obtained from the corresponding residues (B-LCC). Chromatographic and spectroscopic techniques revealed that 8.2% of the lignins were degraded at 160 °C, resulting from the breakage of β-O-4' linkages during pre-hydrolysis. Meanwhile, (reactive) hemicelluloses were mainly removed from the fibers' cell walls. Some hemicelluloses in the pre-hydrolysis liquor, such as glucomannans, were associated with degraded lignin fragments via ether and ester bonds. However, the newly formed LCCs were pH-labile and underwent rapid hydrolysis. Overall, we reveal details about LCC formation and degradation during pre-hydrolysis at given temperatures, critically important in efforts to improve biomass processing and valorization.

Surfactants facilitated glycerol organosolv pretreatment of lignocellulosic biomass by structural modification for co-production of fermentable sugars and highly reactive lignin

This study reported that surfactants could facilitate the organosolv pretreatment of lignocellulosic biomass (LCB) to produce fermentable sugars and highly active lignin. Under the optimized conditions, the surfactant-assisted glycerol organosolv (saGO) pretreatment achieved 80.7% delignification with a retention of 93.4% cellulose and 83.0% hemicellulose. The saGO pretreated substrate exhibited an excellent enzymatic hydrolyzability, achieving 93% of glucose yield from the enzymatic hydrolysis at 48 h. Structural analysis showed that the saGO lignin contained rich β–O–4 bondings with less repolymerization and lower phenolic hydroxyl groups, thus forming highly reactive lignin fragments. The analysis evidenced that the surfactant graft the lignin by structural modification, which was responsible for the excellent substrate hydrolyzability. The co-production of fermentable sugars and organosolv lignin almost recovered a gross energy (87.2%) from LCB. Overall, the saGO pretreatment holds a lot of promise for launching a novel pathway towards lignocellulosic fractionation and lignin valorization.

Insight into the Enzymatic Mechanism of Straw Carbon Source and Its Denitrification Availability

The application of an enzymatic straw carbon source (SCS) to a denitrifying system was a promising method for recycling straw waste. However, the total components of an enzymatic SCS, and their effectiveness for denitrification, are still controversial, which hinders its application to denitrifying. In this study, we combined silylation derivatization and GC-MS technology to conduct a comprehensive analysis of the enzymatic SCS components, and further identified the availability of the components in nitrogen removal. The addition of cellulase could improve both the carbon release amount (increase by 300%) and its effectiveness (66% to 83.7%). The components in both the SCS and enzymatic SCS could be divided into three categories: saccharides, VFAs and aromatic structures. Both saccharides and VFAs were effective for denitrifying and accounted for 86.8% of the enzymatic SCS. Most of the invalid components (aromatic structure) belonged to benzoic acid derivatives which originated from the fragments of straw lignin. In summary, the parameters regarding the components, manufacture and availability of the enzymatic SCS were figured out in this study, laying the foundation for straw waste application to the denitrifying process.

Enhanced lignin-first valorization of biomass for producing monophenols over Ru/C cooperated with H2WO4

Herein, using Ru/C and H2WO4 as the catalysts, native lignin in biomass was efficiently depolymerized into monophenols following the lignin-first strategy at mild conditions. Upon the co-presence of Ru/C and H2WO4, birch lignin afforded monophenols in 40.4 wt% yield at 200 °C, which was 2.5 times that upon Ru/C and 7.5 times that upon H2WO4. 4-Propylsyringol and 4-propylguaiacol were two major products with a combined selectivity of 73%. 2D HSQC NMR of liquid product reveals that β-O-4 bonds in the soluble lignin fragments had been thoroughly disrupted. H2WO4 dissolving at high temperatures promoted the solvolysis of lignin from the biomass matrix, and Ru/C enhanced the following reductive depolymerization. The solid catalysts can be readily recovered for reuse at room temperature after the hydrolysis of carbohydrates, and the catalysts exhibited high activity after four recycles.

Using citric acid to suppress lignin repolymerization in the organosolv pretreatment of corn stalk

The esterification reactions that occur between citric acid (CA) and lignin on hydroxyl groups of side chains can inhibit the formation of reactive intermediates in acid-catalyzed pretreatments. The effects of CA on dilute hydrochloric acid (1.0%) pretreatments of corn stalk in hydrated 1,4–dioxane were investigated with sodium hypophosphite (0.5%) as the catalyst at 95 °C for 3.5 h. The resulting cellulose recovery (62.5–80.9%) and lignin removal (72.5–85.0%) after adding CA were significantly higher than those in the pretreatment without CA. Water content influenced pretreatment and delignification when CA was added into the treatment systems. The highest yield of total reducing sugar (97.1%) was achieved during the enzymatic hydrolysis of cellulose-rich materials obtained from the pretreatment with 11.4% water content. Meanwhile, β–O–4′ in the extracted lignin increased from 22.4/100Ar to 41.2/100Ar with increasing water content from 11.4% to 25.9%. These findings implied that CA as a stabilization agent could inhibit the repolymerization of degraded lignin fragments due to the esterification between CA and lignin and then improved the enzymatic saccharification of cellulose.

Fully upgrade lignocellulose to three nanomaterials by combinational pretreatment: Refining straw waste to pesticide nanocarrier

To achieve the maximum value from lignocellulosic biomass, an integrated biorefinery based on molecule-level design is required. In this study, a combination of hydrothermal pretreatment (HTP) coupling deep eutectic solvent (DES) pretreatment was proposed to produce three upgraded products, namely hemicellulose-derived activated nanocarbon (ANC), lignin nanosphere (LNS), and lignin-containing cellulose nanofiber (LCNF) pesticide nanocarrier, from rice straw. The hydrothermal filtrate, which consists of 100% hemicellulose, was converted into value-added nanocarbon by in-situ carbon sequestration. The upgraded nanocarbon exhibited an excellent specific surface area (2692.3 m2 g−1) and a high degree of graphitization, which value-added attributes could increase revenue to integrated biorefinery. The subsequent DES extraction increased the phenolic –OH content and further aggregated the lignin condensed structure, which facilitated lignin nanosphere preparation by the self-assembly process. Meanwhile, the DES swelling of cellulose facilitated the nanofibrillation of LCNF, which was used as a pesticide carrier to improve pesticide utilization efficiency by simple cationic modification. The residual lignin with functional groups facilitated the crosslinking between the lignin fragments and cellulose fibers by hydrogen bonding interactions, which endowed LNCF highly entangled network and unique lignin properties. The functionalized LCNF exhibited enhanced adhesion and unique anti-UV ability for pesticide deposition and retention. This work realized the all-components upgrading of lignocellulose and inspired the development of sustainable and viable biorefineries.

Toward a hydrogen-free reductive catalytic fractionation of wheat straw biomass.

The reductive catalytic fractionation (RCF) of lignocellulosic biomass is an attractive method for the conversion of lignin toward valuable low-molecular weight aromatics. A limitation to the upscaling of such technology is represented by the use of pressurized hydrogen gas. Here, the role of hydrogen gas within the RCF of wheat straw biomass is investigated. The use of H2 is shown to enhance lignin depolymerization, by virtue of an improved hydrogenolysis and hydrogenation of lignin fragments, with a yield of phenolic monomers that increased from ~12 wt% of acid-insoluble lignin in the initial biomass under inert atmosphere, up to ~25 wt% under H2 (in methanol, at 250 °C, with Ru/C). The adoption of methanol, ethanol or isopropanol as hydrogen-donor solvents was also investigated in the absence of H2. Ethanol was found to give the highest yield of monophenolics (up to ~20 wt%) owing to a better balance between solvolysis, hydrogenolysis, and hydrogenation of lignin. Nevertheless, a substantial loss of the carbohydrate fraction was observed. The use of a lower temperature (200 °C) in combination with H3PO4 resulted in an improved recovery of cellulose in the pulp and in the solubilization of hemicellulose and lignin, with the formation of monosaccharides (~14 wt% of polysaccharides in the initial biomass) and phenolic monomers (up to 18 wt%, in the absence of H2). Overall, a tradeoff exists between the removal of H2 from the process and the production of low-MW phenolics during RCF.

Changes in chemical structures and molar mass parameters of birch wood powder by ethylene diamine treatment

It is necessary to delignify wood samples and treat them with ethylene diamine (EDA) before they are dissolved in 8% (w/v) lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) prior to size-exclusion chromatography (SEC) analysis. In the present study, the effects of delignifying birch wood powder 0–3 times with NaClO2 and subsequently treating it with EDA on its solubility in 8% (w/v) LiCl/DMAc and its SEC data. The neutral sugar composition of the birch powder was almost unaffected by either delignification or treatment with EDA. Treatment of the birch powder with EDA resulted in 28% solubilities in 8% (w/v) LiCl/DMAc. Approximately 11% of cellulose molecules in the birch wood powder was dissolved, and detected as a high-molar-mass (HMM) fraction in the SEC elution pattern. Each single delignification treatment increased the solubility in 8% (w/v) LiCl/DMAc to 68–74% after EDA treatment. Based on the glucose contents of the delignified samples, almost all cellulose molecules in the delignified samples were dissolved in 8% (w/v) LiCl/DMAc after EDA treatment, and detected as the HMM fractions in the SEC elution patterns. The HMM cellulose molecules in the EDA-treated birch powder had linear random-coil conformations in 1% (w/v) LiCl/DMAc. However, the SEC data suggest that there probably were some chemical linkages between the HMM cellulose molecules and lignin or NaClO2-treated lignin fragments in the HMM fractions.

Enzymatic hydrolysis lignin dissolution and low-temperature solvolysis in ethylene glycol

The dissolution and solvolysis processes of enzymatic hydrolysis lignin (EHL) in ethylene glycol are investigated. Ethylene glycol exhibits high EHL solubility and achieves complete EHL dissolution at room temperature. Gaussian simulation reveals that van de Waals interactions between ethylene glycol and EHL, including C-H⋯O and lone pair⋯π interactions, break the π-π stacking in EHL, achieving complete EHL dissolution. EHL is partly depolymerized in ethylene glycol at 200 °C even without a catalyst due to the strong van de Waals interactions. When NaOH and Ni are used as co-catalysts, EHL is efficiently depolymerized at 200 °C, and the overall monomer yield reaches 18.8 wt%. Fourier transform infrared spectroscopy (FT-IR) and molecular dynamics simulation results indicate that the adsorption of ethylene glycol over Ni surface hinders the adsorption of lignin fragments and monomers. Hence, EHL catalytic solvolysis in ethylene glycol occurs in the liquid phase, where OH− of NaOH promotes the EHL linkage breakage and active hydrogen atoms formed on Ni surface stabilize the active monomers.