Lignin Condensation Research Articles

Microwave-Assisted Urea-Based-Hydrotropic Pretreatment of Rice Straw: Experimental Data and Mechanistic Kinetic Models.

The three major lignocellulose components can be transformed into various biomass-derived platform fuels, chemicals, and materials upon pretreatment and chemical upgrading. Lignocellulose pretreatment is an important step to obtain an eco-friendly, economical, and effective biomass utilization process. The combination of microwave heating and hydrotropic pretreatment is considered as a green method of lignocellulose pretreatment. Experimental data and two mechanistic kinetic models of microwave-assisted pretreatment of rice straw are presented. Here, the use of urea solution as the hydrotropic agent was examined to facilitate the degradation of three major lignocellulose components. The first kinetic model assumes that the soluble lignin does not undergo condensation, while the second one assumes that part of the soluble lignin condenses to a solid product. The mechanistic models were validated with a series of experimental data obtained from microwave-assisted hydrotropic pretreatment of rice straw. The results show that both models could generally describe the experimental data well. However, based on the evaluation of the results of the kinetic models, it turned out that the rate of lignin condensation was relatively slow compared to the rate of lignin degradation to soluble lignin (the value of kc is relatively small compared to the value of kl1). Hence, the kinetic model with exclusion of lignin condensation is suggested more since it is mathematically simpler. The proposed mechanistic model can also predict the cellulose and hemicellulose dissolution and thereby can be used as a process optimization tool. The microwave-assisted urea-based hydrotropic pretreatment conducted at a solid–liquid ratio of 1:35, a urea concentration of 36.8%, a reaction temperature of 90 °C, and a pretreatment duration of 73.6 min is predicted to give a solid residue with low lignin content and high cellulose content which resulted in a cellulose to lignin ratio of 5.53. Cellulosic biomass characterization revealed that microwave-assisted hydrotropic pretreatment was able to produce higher crystallinity and thermally stable cellulosic biomass.

Revealing the topochemical and structural changes of poplar lignin during a two-step hydrothermal pretreatment combined with alkali extraction

Lignin is an underutilized renewable resource in nature because of its complex structure and special distribution in plant cell walls. The proposal of an efficient treatment and the reveal of the structural characteristics of the isolated lignin are considerably important for the sustainable valorization of lignin. In this work, a two-step of hydrothermal pretreatment combined with alkali extraction was assembled into an integrated treatment and performed to extract lignin from poplar. The yield, purity, and structural changes of the lignin isolated from different treatment conditions were comparatively investigated. Results showed that 71.8 % of lignin with ultra-high purity was isolated during the integrated treatment at 180 °C. Confocal Raman microscopy demonstrated that the delignification occurred preferentially in the secondary wall (SW) and compound middle lamella (CML), and then in the whole morphological regions of the cell wall during the integrated treatment. NMR results revealed that the cleavage of β-O-4 linkages was dominant among the various reactions, which resulted in the increase of phenolic hydroxyl groups, the decrease of molecular weight, and the heterogeneity of the isolated lignin. However, the condensation of lignin became more serious with the increase of hydrothermal pretreatment temperature. These findings provide new insights for the separation and sustainable utilization of lignin for industries.

QUICK NON-DESTRUCTIVE ANALYSIS OF CONDENSED LIGNIN BY FTIR. PART 2. PULP SAMPLES FROM ACID SULFITE COOKING

"In our previous work, we demonstrated how lignin condensation and precipitation taking place in kraft pulping can be detected and even quantified by Fourier Transform Infrared (FTIR) spectroscopy. Because lignin reactions in acid sulfite pulping are very different from those occurring during kraft cooking, a new analysis method is proposed to rapidly analyze the condensed lignin in acid sulfite pulp. This kind of analysis is useful for sulfite pulp mills to detect the elevated risk of black cook. This paper presents and discusses the novel method using FTIR spectroscopy to rapidly analyze lignin condensation in softwood pulp samples from acid sulfite processes. Several softwood pulp samples from acid sulfite pulping at varying levels of condensation were included in this research. According to the results, FTIR spectroscopy allows indirect quantification of lignin condensation in a difficult matrix of wood constituents, such as in incompletely delignified acid sulfite pulp."

Evaluation of chemical additives in hydrothermal pre-treatment of wood for the integrated production of monosugars and hydrolysis lignins for PLA-based biocomposites

The use of chemical additives (1- and 2-naphthol, formaldehyde) in hydrothermal pre-treatments of pine, birch, and willow wood was evaluated to minimize lignin condensation reactions and consequently improve the saccharification of the pre-treated materials. The residual hydrolysis lignins were then tested in the preparation of polylactic acid (PLA)-based composites. The results showed that addition of 2-naphthol to the hydrothermal pre-treatment increased the saccharification of pine wood by twofold compared to water-only experiments, but the sugar yield was only 50% of the carbohydrate content in the pre-treated pine. The use of 2-naphthol and formaldehyde also improved somewhat the saccharification of bark-containing willow wood, while the use of 1-naphthol had no effect on the saccharification of any of the pre-treated materials. In birch and willow (without bark), almost complete saccharification could be achieved even without additives. Analyses of hydrolysis lignins from birch revealed structural changes caused by the additives, which were consistent with a reduction of condensation reactions. Selected lignins were successfully used at 20% loading in PLA/lignin composites; however, variation in mechanical properties among composites prepared with different lignins was only minor. In general, the use of lignin decreased the strength and ductility of PLA but increased the stiffness. Based on these results, the use of additives may only be beneficial in the pre-treatment of pine or other softwoods to improve the sugar yields.

Staged organosolv pretreatment to increase net energy and reactive lignin yield in whole oil palm tree biorefinery

Pretreatment is the most crucial and energy-intensive unit process affecting the feasibility of biorefinery, especially when lignin valorization is of concern. This study investigated and quantified the potential benefits of an innovative staged organosolv (OS)-dilute acid (DA) pretreatment process for whole oil palm tree residues conversion. The staged OS-DA pretreatment resulted in approximately five times higher net energy (1.50 GJ/tonne) over the single-step OSDA process (0.30GJ/tonne) due to potential energy saving on solvent recovery and less water consumption. For sugar, OS-DA pretreated substrate achieved more than 90% of cellulose digestibility which was more than 40% higher than DA-OS substrate. For mono-lignin, significant reduction in crude lignin condensation (21.7%) was confirmed by two-dimensional NMR analysis. The overall mass balance showed that approximately 142.45 tonnes of bioethanol, or a net energy yield of 969.5 GJ, can be produced by OS-DA process from palm tree residues per hectare of oil palm farm.

Visualizing plant cell wall changes proves the superiority of hydrochloric acid over sulfuric acid catalyzed γ-valerolactone pretreatment

Thermochemical pretreatment is one of the key steps to process lignocellulosic biomass for production of biofuels and biomaterials. γ-valerolactone (GVL) has been used as a green and renewable solvent to efficiently dissolve lignin under acidic conditions and enhance subsequent enzyme digestibility. Further improvement is still required to lower the pretreatment temperature in order to reduce sugar degradation and irreversible lignin condensation, as well as the capital cost. In this study, we compared the use of HCl and H2SO4 as catalysts during GVL pretreatment, and found the performance of GVL-HCl at 100 °C was comparable to that of GVL-H2SO4 at 120 °C in terms of xylan and lignin removal and enzyme digestibility. We further monitored the lignin removal and cellulose accessibility in the cell walls at different pretreatment time points by imaging the changes in lignin auto-fluorescence and in CtCBM3-GFP binding with confocal laser scanning microscopy (CLSM), respectively. We found GVL-HCl pretreatment at a relative low temperature (100 °C) could rapidly remove lignin in the compound middle lamella and cell corner areas, which concurred with the increase of CtCBM3-GFP binding in these areas. Real-time imaging of cell wall degradation by cellulases further revealed that the secondary cell walls could be digested from both cell lumen and CML sides, and eventually fully deconstructed within 24 h. Our results provide new insight into the effects of chloride anions on plant cell wall structure during GVL pretreatment, and offer potential routes to further optimize and enhance the efficiency of GVL-based pretreatment.

Thermal decomposition behavior of thin Makino bamboo (Phyllostachys makinoi) slivers under nitrogen atmosphere

The present study investigated the effects of heat treatment on the thermal decomposition behavior (changes in the chemical composition and color, strain variation, and tensile properties) of a thin Makino bamboo (Phyllostachys makinoi) sliver. The performances, reactions, and formations in heat treated bamboo slivers were measured by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The results indicated that a high thermal stability, cross-linking of lignin condensation, hemicellulose deacetylation, and an increase in cellulose crystallinity were observed. In addition, the bamboo slivers after heat treatment had a higher Poisson’s ratio due to a decrease in the ductility in the loading direction and an increase in the transverse shrinkage. Furthermore, using isothermal dynamic mechanical analysis (DMA), the normalized storage modulus of the bamboo slivers rapidly decreased when the treatment temperature exceeded 220 °C. According to first-order thermal decomposition kinetics by Arrhenius activation theory, the activation energy for thermal decomposition of the bamboo slivers was calculated to be 142.2 kJ/mol.

Flow-through solvolysis enables production of native-like lignin from biomass

Flow-through solvolysis offers an opportunity to limit lignin condensation reactions that prevent isolation of native lignin in biomass processing, thus allowing for the study of intrinsic lignin properties and steady-state lignin depolymerization.

반응 시간 및 에피클로로하이드린 투입량에 따른 리그닌의 중합 반응 분석

본 연구에서는 반응 시간 및 에피클로로하이드린(ECH) 투입량에 따른 크라프트 리그닌의 중합 반응 양상을 분석하였다. 반응 온도 40 ℃에서 ECH의 투입량을 리그닌 대비 60wt%로 고정하여 반응 시간(1, 3, 5, 7시간)에 따라 반응 양상을 평가하였고, 동일 반응 온도에서 ECH 투입량 (리그닌 대비 6, 12, 30, 60wt%)에 따라 24시간 반응 후 반응 양상을 평가하였다. 반응 시간 7시간 이내의 반응 시간에서 분자량 증가 양상을 고려하였을 때, 저분자량의 리그닌이 먼저 중합되면서 평균분자량이 증가하고, 7시간 이후에는 리그닌이 입자 형태로 중합되었다고 사료된다. 또한 ECH 투입량이 리그닌 대비30wt% 이상일 때 리그닌이 입자 형태로 중합이 되었으며, ECH 투입량이 리그닌 대비 6wt%였을 때 ECH의 연쇄 반응에 의하여 –CH<SUB>2-</SUB>와 에테르 결합으로 이루어진 사슬 구조가 리그닌 구조 내에 도입되면서 수용성으로 개질되었다고 판단된다. ECH와 리그닌의 중합 반응은 반응이 진행됨에 따라 리그닌 구조 내 사슬 구조가 생성된 후 입체 장애가 줄어들면서 진행된다고 사료된다.

Solid state NMR investigation of the roman Acqualadroni rostrum: tenth year assessment of the consolidation treatment of the wooden part

This work follows a previous one dealing with the state of conservation study of the wooden part of the roman Acqualadroni rostrum soon after its finding in the seabed of Acqualadroni (Messina, Italy). The archaeological survey and recovery were particularly relevant since this artefact is one of the two rostrums, nowadays known, found together with its wooden part. Following the recovery, it was consolidated by immersion in a melamine-formaldehyde resin (Kauramin) aqueous solution for eight months at the “Centro di Restauro del Legno Bagnato” (Pisa, Italy). The present investigation is aimed to determine at microscopic scale the wood state of conservation and to highlight interactions of the consolidant with wood components, by using solid-state NMR spectroscopy ten years after the consolidation treatment. Sampling by coring was exceptionally authorized, and the wood core was divided into seven aliquots as a function of depth. 13C cross-polarization magic angle spinning (13C{1H} CP-MAS NMR) spectra and variable contact time (VCT) experiments have been carried out to determine the cellulose crystallinity index, the lignin condensation degree and the holocellulose-lignin ratio. The interactions between the resin and the wood components were highlighted by T1ρH relaxation times determination and two-dimensional 13C–1H correlation (FSLG CP HETCOR) NMR experiments. Findings revealed specific interactions between the aromatic part of the resin and the lignin, as well as a network of hydrogen bonds involving all components of the system.

In-situ real-time monitoring of hydroxyethyl modification in obtaining uniform lignin derivatives

The chemical modification of kraft lignin is critical in developing value-added opportunities for the valorization of this biobased polymer. Hydroxyethyl modification is capable of improving both the chemical uniformity and thermal stability of lignin by substitution of phenolic and carboxylic acid groups. However, the main drawback of this reaction involving the cyclic carbonate as a derivatizing reagent was the occurrence of crosslinking arising from excess reaction time or temperature. Based on the 13C and 2D 1H–13C heteronucleaer single quantum correlation (HSQC) nuclear magnetic resonance (NMR) spectroscopy analysis, the potential condensation and side reactions were found to accompany the modification at longer reaction times, including the formation of carbonate linkage and intermolecular lignin condensation. These reactions caused a dramatic enhancement of molar mass, decreased solubility, and lowered the quality of modified lignin. Addressing this problem, we developed an in-situ, real-time monitoring method to control the quality of the derivatized lignin. This was achieved by identifying a high correlation between the volume of produced CO2 and the degree of hydroxyethylation of the lignin, as determined with NMR spectroscopy. Longer times led to evidence of carbonate linkage co-polymerization and increased molecular weight of the lignin. A predictive model was developed to reduce the workload on the optimization of the modification of different types of lignin resources and avoid side-product formation, based on the knowledge of the starting phenolic and carboxylic acid content of the materials and CO2 measurement. Finally, as ethylene carbonate can be treated as carbon storage chemical, the hydroxyethyl reaction can be readily integrated with the lignin recovery process, helping to reduce the carbon footprint and overall cost for pulping companies. In so doing, it provides a green route to develop functionalized aromatic renewable polymers for the polymer industry.

Glycerol-assisted one-step instant catapult steam explosion enhances enzymatic digestibility of corn stover

Glycerol-assisted one-step instant catapult steam explosion (ICSE) was studied for corn stover pretreatment. Glycerol addition reduced lignin content from ∼32 % to ∼24 % in pretreated solid residues with a stover/glycerol ratio from 1:0.0 to 1:2.0. Glycerol addition might help to reduce the formation of pseudo-lignin with the reduction of the total lignin recovered in pretreated solid residue from 114 % (possibly because of pseudo-lignin contribution) to 81 %. Furthermore, atomic forced microscopy analysis showed that glycerol addition improved surface roughness of pretreated corn stover. Moreover, it was proposed that glycerol-assisted ICSE likely led to the reactions of glycerol with lignin and lignin-derivatives through α-etherification and γ-esterification, preserving lignin internal β-O-4 linkages and preventing lignin condensation. Finally, enzymatic hydrolysis of corn stover pretreated by glycerol-assisted ICSE at a stover/glycerol ratio of 1:1 led to a glucan digestibility in solid residues of 98.4 % and a glucose yield of 79.3 %, which were 27.9 % and 44.7 % higher than those without glycerol addition, respectively.

Mild fractionation of sugarcane bagasse into fermentable sugars and β-O-4 linkage-rich lignin based on acid-catalysed crude glycerol pretreatment

Acid-catalysed crude glycerol (ACG) pretreatment was carried out at 110 °C and 130 °C for mild fractionation of sugarcane bagasse into fermentable sugars and high-quality lignin. ACG pretreatment at 110 °C led to sugar yields of 71%–74%, comparable to those with acid-catalysed reagent-grade glycerol (AG). ACG pretreatment removed more lignin (53%–75%) than AG pretreatment (38%–49%), likely due to the presence of organic impurities in ACG. Hence, 28% more lignin was recovered from ACG pretreatment hydrolysate than with the AG pretreatment. NMR analysis revealed that recovered lignin was modified by glycerol through etherification of β-aryl ethers and esterification of hydroxycinnamic acids, which prevented lignin condensation and led to the generation of β-O-4 linkage-rich lignin at mild conditions (110 °C for 3 h and 5 h). This study suggests that crude glycerol is a suitable low-cost solvent for mild fractionation of lignocellulosic biomass into fermentable sugars and high-quality lignin for value-adding applications.

Using analytical pyrolysis and scanning electron microscopy to evaluate charcoal formation of four wood taxa from the caatinga of north-east Brazil

People in north-east Brazil mostly rely on fuelwood and charcoal for domestic energy consumption. Traditionally, four local wood taxa (Mimosa tenuiflora, Mimosa ophthalmocentra, Croton sonderianus and Cenostigma pyramidale) from the caatinga have been selected for this purpose. As the final quality of charcoal is directly related to the charring conditions, as well as the chemical composition of the raw materials and the behaviour of the lignocellulosic matrix during the charring process, the aim of this study was to investigate how far differences in these parameters exert a major control on the charcoal formation, in order to give a molecular insight as to why these particular wood species might be preferred for high-quality charcoal in the perspective of sustainable management and harvesting regimes.Pyrolysis gas chromatography mass spectrometry (Py-GC-MS) and scanning electron microscopy (SEM) were used to study the chemical composition and anatomical changes of the wood samples before and after charring experiments were carried out at 400 and 600 °C. The charring conditions were also reproduced in the controlled environment of the pyrolysis chamber and evolved gas analysis mass spectrometry (EGA-MS) was used for the first time to monitor the evolution of the thermal degradation products.The thermal behaviour of the wood components was different compared to other wood taxa for which comparable data are available. These differences were partially related to the particular nature of the carbohydrate-lignin interactions, to a relatively low level of lignin condensation, and to the substantial presence of gums or resins, which formed charred deposits. These characteristics, often neglected in charcoal analysis, imply that the wood components (especially cellulose) are released more slowly during the charring process, and this translates into the ability of these wood species to retain the main features of their anatomical structure even when exposed to high temperature for a relatively long time. The anatomical alterations observed, such as the loss of the middle lamella, the disappearance of the pit membranes, and the homogenisation of cell walls are ultimately in agreement with the formation of a particularly recalcitrant carbonaceous matrix upon charring at relatively low temperature (400 °C for 2 hours).This study presents the first molecular characterisation of these wood species and some methodological advancement on the use of EGA analysis using isothermal conditions is provided. The role of carbohydrate-lignin interactions and non-lignocellulosic wood components in charcoal production is discussed and the importance of combining chemical data and anatomical observations in wood research is underlined.

Non-productive celluase binding onto deep eutectic solvent (DES) extracted lignin from willow and corn stover with inhibitory effects on enzymatic hydrolysis of cellulose

In this work, deep eutectic solvent (DES) was prepared by mixing choline chloride (ChCl) with lactic acid (LA), and effects of cellulase non-productive binding onto DES-extracted lignin from willow and corn stover on enzymatic hydrolysis of cellulose was investigated. The correlation between hydrolysis yield of cellulose and chemical features of lignin was evaluated, and a potential inhibitory mechanism was proposed. Condensation of lignin was observed during DES treatment, and these condensed aromatic structures had an increased tendency to adsorb enzymes through hydrophobic interactions. As well as hydrophobic interactions mediated by lignin condensation, an increase in phenolic hydroxyl groups resulted in a greater amount of hydrogen bonds between cellulases and lignin that appeared to inhibit enzymatic hydrolysis yields of cellulose (39.96–42.86 % to 31.96–32.68 %). Although large amounts of COOHs were generated, the elevated electrostatic repulsion as a result of ionic groups was insufficient to decrease non-productive adsorption.

Revisiting Alkaline Pretreatment of Lignocellulose: Understanding the Structural Evolution of Three Components

AbstractHerein, sodium hydroxide (NaOH) pretreatment of lignocellulose is performed to investigate the structural evolution of lignin, cellulose, and hemicellulose. It is found that most of hemicellulose and part of cellulose are hydrolyzed/converted to monosaccharide, alcohols, and carboxylic acids. Over half of cellulose is stabilized because the reducing end groups of cellulose convert to stable carboxylic groups. In addition, lignin is converted to aromatic monomers (predominately vanillin and acetovanillone) with a highest yield of 6.1 wt%, along with dimers and oligomers with Mw less than 10 000 Da. According to heteronuclear single quantum coherence analysis, no common interlinkages (β‐O‐4, β‐β, β‐5, etc.) appear in lignin oligomers due to lignin fragments condensed during the alkaline pretreatment. Notably, the acidification process is also the cause of lignin condensation since high aromatic monomers yield of 15 wt% (based on original lignin in pine) is achieved by a postoxidation of alkaline solution, while few no aromatic monomers generated by using the isolated lignin oligomers. The direct oxidation of lignocellulose in alkaline solutions to aromatic monomers demonstrates the potential application of lignocellulose alkaline pretreatment for high‐value chemicals production.

Effect of the autohydrolytic treatment of Miscanthus sacchariflorus Andersson on the yield of the reducing substances during the subsequent fermentolysis

The effect of the autohydrolytic treatment of Miscanthus sacchariflorus Andersson on the yield of the reducing substances during the subsequent fermentolysis has been determined. It was established that a change in the conditions of the auto-hydrolytic treatment of Miscanthus sacchariflorus Andersson induces a formation of solid fractions containing cellulose, lignin, hemicellulose and mineral substances, the ratio of which depends on the severity factor, i.e. temperature and processing time. It was shown that at the severity factor of 5.67, almost complete hydrolysis of hemicellulose occurs, however, there is an increase in the lignin content in the solid fraction (up to 46.0 %) relative to the lignin content in the feedstock (20.8 %), which is due to lignin condensation with a consequent formation of pseudo lignin. The highest content of cellulose in the solid phase is observed as a result of hydrolytic processing of raw materials with a severity factor of 4.17 to 4.39, a temperature of 160 о С and a processing time of 25 min. At an increased temperature, an increase in the acidity of the medium catalyzes the hydrolysis of cellulose and reduces its content in the solid fraction to 60 % at a severity factor of 5.67. During the auto-hydrolytic treatment of Miscanthus sacchariflorus Andersson, an increase in the ash content in the solid fraction is observed. The solid fractions obtained after treatment with Miscanthus sacchariflorus Andersson were used as a substrate and were subjected to enzymatic hydrolysis with the enzyme preparations “Cellolux-A” and “BrewZime BGX” at an initial substrate concentration of 33 g/l. The increase in the yield of reducing substances has shown a steady increase with the removal of hemicelluloses and reached its maximum value (45.1 %) with an increase in the treatment severity factor to 4.48. The availability of the cellulose surface for the action of enzymes has decreased with an increase in the stiffness factor beyond a value of 4.48 due to the accumulation of lignin in the solid phase, as evidenced by a decrease in the yield of reducing substances in the enzyme to 31.8 %.

Efficient separation of functional xylooligosaccharide, cellulose and lignin from poplar via thermal acetic acid/sodium acetate hydrolysis and subsequent kraft pulping

Thermal acetic acid/sodium acetate hydrolysis (ASH) on poplar wood chips were carried out to obtain functional xylooligosaccharide, then the hydrolyzed wood chips were subjected to kraft pulping (KP) to fractionate cellulose and lignin. The separated three fractions were extensively characterized for further utilization in view of the integral biorefinery concept. The extraction efficiency of hemicelluloses by ASH strongly depends on the buffer ratio of the acetic acid/sodium acetate buffer solution. The ASH facilitated producing a high ratio of xylooligosaccharides with high molecular weight, while prevented further degradation of the saccharides, and simultaneously inhibited the condensation of lignin facilitating the subsequent kraft delignification. The obtained cellulose pulps had higher intrinsic viscosities as compared with the traditional autohydrolysis-KP process. Moreover, the ASH-KP process delivered a high purity of lignin with relatively high molecular weight. Therefore, the proposed integrated fractionation strategy is conducive to convert the lignocellulosic components into bio-based functional materials.

In-situ extraction of depolymerization products by membrane filtration against lignin condensation

Catalytic depolymerization of lignin is a challenging process due to competitive repolymerization reactions. In this paper, the oxidative depolymerization of lignin was catalyzed by a commercial laccase both in a batch experiment and in a membrane bioreactor using the same catalytic conditions. The membrane bioreactor was previously optimized to reach high permeation flux (25 L.h−1.m−2) during lignin diafiltration. While the lignin was exclusively condensed in the batch experiment leading to high molecular weight macromolecules (from 9 to 16 kDa), its depolymerization was effective in the bioreactor producing fragments of less than 1 kDa thanks to the in-situ extraction of the reaction products. This paper demonstrates that the reactor configuration is playing an essential role in triggering or preventing lignin condensation. It also reports the first proof-of-concept demonstrating that in-situ membrane extraction of the reactive fragments of lignin from the bulk medium can be useful against detrimental repolymerization reactions.

Fractionation of herbaceous biomass using a recyclable hydrotropic p–toluenesulfonic acid (p–TsOH)/choline chloride (ChCl) solvent system at low temperatures

Lignin valorization is significantly influenced by the degrees of lignin condensation measured by the amount of cleaved βO4 ether linkages and interunit CC linkages formed during biomass fractionation. To minimize the cleavage of aryl ether and formation of CC linkages, a p–toluenesulfonic acid (p–TsOH)/choline chloride (ChCl) solvent system with hydrotropic properties was evaluated. The ChCl was chosen to control the H+ concentration of the p–TsOH/ChCl solvent system. Compared with p–TsOH/H2O, the degradation of βO4 was kept in a similar rate during p–TsOH/ChCl fractionation; however, the formation of CC linkage was slower. Under 75/25 p–TsOH/ChCl mass ratio at 80 °C for 20 min, 76.6 % of miscanthus lignin, with βO4 content of 30.9 %, and 88.9 % of wheat straw lignin, with βO4 content of 33.6 %, can be dissolved. In addition, the low polar and layered structure of hydrotropic p–TsOH/ChCl system has a strong ability to dissolve lignin, which resulted in lignin with larger particle size and lower surface charge. The results also indicated that lignin from p–TsOH/ChCl solvent system has great potential for lignin depolymerization to aromatics for valorization.