A synergistic hydrothermal-deep eutectic solvent (DES) pretreatment for rapid fractionation and targeted valorization of hemicelluloses and cellulose from poplar wood

Polyol-assisted ternary deep eutectic solvent protective lignocellulose pretreatment for high-efficiency xylan utilization and ethanol production

The traditional lignocellulose pretreatment by deep eutectic solvent (DES) was usually conducted under higher acidic, alkaline and high temperature conditions, which leads to the severe degradation of xylan, decreasing the subsequent reducing sugar concentration by enzymatic hydrolysis and further ethanol fermentation. It is essential to develop an effective DES that selectively removes lignin while preventing excessive xylan degradation during lignocellulose pretreatment. An effective ethylene glycol-assisted ternary DES was designed to treat corn straw (CS) at 100 °C for 6 h. 65.51 % lignin removal was achieved, over 93.46 % cellulose and 50.22 % xylan were retained in pretreated CS with excellent enzymatic digestibility (glucan conversion of 77.05 % and xylan conversion of 71.72 %), total sugar conversion could reach 75.93 %, implying the unique capacity to selectively remove lignin while preserving carbohydrate components. Furthermore, the universality of the selective removal of lignin and effective retention of xylan by ternary DES has been successfully proven by other polyols. The enzymatic hydrolysate of ternary DES-pretreated CS fermented over our genetically engineered yeast strain SFA1OE gave a high ethanol yield of 0.488 g/g total reducing sugar, demonstrating the effectiveness of the polyol-assisted ternary DES pretreatment in achieving high-efficiency cellulosic ethanol production.

A cascaded process to upgrade bleached bamboo pulp into dissolving pulp and arabinoxylan

The dissolving pulp preparation from bleached kraft pulp while realizing the high-value application of hemicellulose fraction is of great significance for improving the overall economics of the process. This work proposed a two-step cascaded process of deep eutectic solvent (DES) pretreatment combined with mechanical refining for the co-production of dissolving pulp and arabinoxylan (AX) from bleached bamboo pulp. Results showed that using alkaline DES composed of quaternary ammonium hydroxide and urea prepared high-quality dissolving pulp (α-cellulose content of 97.7 %) while selectively extracting high-quality AX. The mechanical refining rapidly opened up the cellulose structure to increase its Fock reactivity to over 70.0 %. When 100 g bleached bamboo pulp was subjected to this technology route, the high yields of dissolving pulp (63.8 g) and AX (13.0 g) were respectively obtained. It was proposed that the tailored DES with different alkalinity could specifically produce dissolving pulp or AX which were more favorable for downstream application through distinct action pathways. The swelling effects of DES on the cellulose surface facilitated the subsequent mechanical fibrillation, allowing a synergistic enhancement of the reactivity. Thus, the integrated process provided a sustainable alternative for dissolving pulp upgrading while adding attractiveness by co-producing AX product stream.

Unveiling the potential of novel recyclable deep eutectic solvent pretreatment: Effective separation of lignin from poplar hydrolyzed residue

To effectively convert the fermentable sugars present in lignocellulosic biomass into biofuels and additional value-added products, it is crucial to remove lignin from the biomass. With the intention of expeditiously remove lignin from poplar wood and improve cellulose saccharification, an innovative ternary deep eutectic solvent (DES) benzyl triethyl ammonium chloride-ethylene glycol-FeCl3 (T-EG-F) was studied for the pretreatment of poplar hydrolyzed residue (PHR). The results revealed that following T-EG-F DES pretreatment at 130 °C for 4 h, the lignin removal rate reached 91.88 %. The effect of DES on PHR and regenerated lignin was comprehensively investigated using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Thermogravimetric (TG) and other characterization methods, providing valuable insights into the mechanism of this innovative biomass pretreatment. Moreover, there was a significant improvement in the enzyme digestibility of the DES pretreatment residue. At 48 h, the enzyme load of 30 FPU/g cellulose achieved a remarkable enzyme digestibility of 97.31 %, and this value exhibited a notable increase of 6.56 times compared to the untreated poplar sample. In addition, the T-EG-F could be recycled and reused. This study demonstrates that the potential of T-EG-F DES pretreatment as a green and efficient method for lignin dissociation from lignocellulosic biomass, offering a promising approach for biomass component separation.

Structural elucidation and targeted valorization of untractable lignin from pre-hydrolysis liquor of xylose production via a simple and robust separation approach

Effective separation of lignin macromolecules from the xylose pre-hydrolysates (XPH) during the xylose production, thus optimizing the separation and purification process of xylose, is of great significance for reducing the production costs, achieving the high value-added utilization of lignin and increasing the industrial revenue. In this study, a simple and robust method (pH adjustment) for the separation of lignin from XPH was proposed and systematically compared with the conventional acid-promoted lignin precipitation method. The results showed that the lignin removal ratio (up to 60.34 %) of this simple method was higher than that of the conventional method, and the proposed method eliminated the necessity of heating and specialized equipment, which greatly reduced the separation cost. Meanwhile, this simple method does not destroy the components in XPH (especially xylose), ensuring the yield of the target product. On the other hand, the obtained lignin was nano-scale with less condensed structures, which also possessed small molecular weights with narrow distribution, excellent antioxidant activity (8-14 times higher than commercial antioxidants) and UV protection properties. In conclusion, the proposed simple separation method could effectively separate lignin from XPH at low cost, and the obtained lignin had potential commercial applications, which would further enhance the overall profitability of industrial production.

Sustainable ultrasound-assisted extraction of Polygonatum sibiricum saponins using ionic strength-responsive natural deep eutectic solvents

The sustainable extraction of saponins was investigated using natural deep eutectic solvents (NADESs) combined with ultrasound-assisted extraction. A novel NADES (butyric acid-urea) that was responsive to ionic strength was designed and used as the extractant. Ultrasound treatment and a catalyst ferric chloride with plant cell wall breaking function were applied to improve the extraction efficiency.Since the solubility of the NADES varied significantly with ionic strength, 95% of NADES was readily separated from the water phase after the addition of sodium chloride, while saponins remained in the water phase for easy collection. The reuse capacity of NADES, the eco-friendliness of the extraction method, and the antioxidant activity of the extract were further evaluated.NADES was continuously recovered and used to extract Polygonatum sibiricum powder: the yield of saponins did not decrease after five cycles of recovery and re-extraction. The penalty point on the "Eco-scale" suggested that the extraction method was "green" (i.e. eco-friendly).Compared with ethanol extracts, the NADES extracts showed a higher saponin concentration and antioxidant activity.The study can contribute to the sustainable and green extraction of hydrophilic active substances in the food and pharmaceutical industries.

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

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

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl₃·6H₂O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl₃·6H₂O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55-1.73) and molecular weight (1380-2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

Deep eutectic solvents for improved biomass pretreatment: Current status and future prospective towards sustainable processes

Pretreatment processes - recognized as critical steps for efficient biomass refining - have received much attention over the last two decades. In this context, deep eutectic solvents (DES) have emerged as a novel alternative to conventional solvents representing a step forward in achieving more sustainable processes with both environmental and economic benefits. This paper presents an updated review of the state-of-the-art of DES-based applications in biorefinery schemes. Besides describing the fundamentals of DES composition, synthesis, and recycling, this study presents a comprehensive review of existing techno-economic and life cycle assessment studies. Challenges, barriers, and perspectives for the scale-up of DES-based processes are also discussed.

Advances in physicochemical pretreatment strategies for lignocellulose biomass and their effectiveness in bioconversion for biofuel production

The inherent recalcitrance of lignocellulosic biomass is a significant barrier to efficient lignocellulosic biorefinery owing to its complex structure and the presence of inhibitory components, primarily lignin. Efficient biomass pretreatment strategies are crucial for fragmentation of lignocellulosic biocomponents, increasing the surface area and solubility of cellulose fibers, and removing or extracting lignin. Conventional pretreatment methods have several disadvantages, such as high operational costs, equipment corrosion, and the generation of toxic byproducts and effluents. In recent years, many emerging single-step, multi-step, and/or combined physicochemical pretreatment regimes have been developed, which are simpler in operation, more economical, and environmentally friendly. Furthermore, many of these combined physicochemical methods improve biomass bioaccessibility and effectively fractionate ∼96 % of lignocellulosic biocomponents into cellulose, hemicellulose, and lignin, thereby allowing for highly efficient lignocellulose bioconversion. This review critically discusses the emerging physicochemical pretreatment methods for efficient lignocellulose bioconversion for biofuel production to address the global energy crisis.

High-efficiency recovery and regeneration of choline-polyol deep eutectic solvent for biorefinery via bipolar membrane electrodialysis and ultrafiltration

Deep eutectic solvents (DES) have been widely studied for interesting solvent properties in resources utilization and green conversion of energy. Complex composition of DES and lack of recovery techniques restricts their further scale-up application. Exploring efficient recovery and regeneration methodology of DES in biorefinery could be beneficial for low-carbon circular bioeconomy. Recovery and regeneration of choline-polyol DES (choline chloride-ethylene glycol, ChCl-EG) after biomass pretreatment was studied using bipolar membrane electrodialysis (BMED) with ultrafiltration (UF). UF-BMED treatment worked based on the interception of macromolecular degradation products in pretreatment liquor and regional recovery of Ch⁺, Cl^- with EG. Influence of major parameters on DES recovery performance was studied with emphasis. Maximum recovery ratio of DES reached 97.4% and minimum specific energy consumption of DES recovery approached 6.0 kW·h/kg. Cognition gained from this research revealed an efficient technique for DES recycling after biorefinery.

Valorization of bamboo shoot shell waste for the coproduction of fermentable sugars and xylooligosaccharides

In this work, hydrothermal pretreatment (autohydrolysis) was coupled with endo-xylanase enzymatic hydrolysis for bamboo shoot shell (BSS) to produce glucose and valuable xylooligosaccharides (XOS) rich in xylobiose (X2) and xylotriose (X3). Results showed that the enzymatic hydrolysis efficiency of pretreated BSS residue reached 88.4% with addition of PEG during the hydrolysis process. To enrich the portions of X2–X3 in XOS, endo-xylanase was used to hydrolyze the XOS in the prehydrolysate, which was obtained at the optimum condition (170°C, 50 min). After enzymatic hydrolysis, the yield of XOS reached 25.6%, which contained 76.7% of X2–X3. Moreover, the prehydrolysate contained a low concentration of fermentation inhibitors (formic acid 0.7 g/L, acetic acid 2.6 g/L, furfural 0.7 g/L). Based on mass balance, 32.1 g of glucose and 6.6 g of XOS (containing 5.1 g of X2-X3) could be produced from 100.0 g of BSS by the coupled technology. These results indicate that BSS could be an economical feedstock for the production of glucose and XOS.

New Poplar-Derived Biocomposites via Single-Step Thermoforming Assisted by Phosphoric Acid Pretreatment

One-step thermoforming represents an effective approach to preparing glue-free biocomposites. This study aimed to produce glue-free biocomposites with high-temperature resistance and mechanical properties using phosphoric acid pretreatments combined with thermoforming. Due to the hot-moulding process, the cell wall was destroyed, which allowed the fibres to adhere closely together. Most hemicelluloses were hydrolysed through pretreatment with phosphoric acid, and the contact area between the cellulose and lignin was significantly increased. The biocomposites prepared by ball milling demonstrated remarkable flexural strength (49.03 MPa) and tensile strength (148.23 MPa). Moreover, they had excellent thermal stability, with the maximum temperature for pyrolysis rate at 374 °C, which was much higher than that of poplar (337 °C). In addition, the material released no formaldehyde during the preparation process, which is in line with the concept of green production.

Integrated biorefinery approaches for the industrialization of cellulosic ethanol fuel

Lignocellulosic biomass is an abundant and sustainable raw material, but its conversion into ethanol fuel has not yet achieved large-scale industrialization and economic benefits. Integrated biorefineries have been widely identified as the key to achieving this goal. Here, four promising routes were summarized to assemble the new industrial plants for cellulose-based fuels and chemicals, including 1) integration of cellulase production systems into current cellulosic ethanol processes; 2) combination of processes and facilities between cellulosic ethanol and first-generation ethanol; 3) application of enzyme-free saccharification processes and computational approaches to increase the bioethanol yield and optimize the integration process; 4) production of multiple products to maximize the value derived from the lignocellulosic biomass. Finally, the remaining challenges and perspectives of this field are also discussed.

Syntrophic bacteria- and Methanosarcina-rich acclimatized microbiota with better carbohydrate metabolism enhances biomethanation of fractionated lignocellulosic biocomponents

An inadequate lignocellulolytic capacity of a conventional anaerobic digester sludge (ADS) microbiota is the bottleneck for the maximal utilization of lignocellulose in anaerobic digestion. A well-constructed microbial consortium acclimatized to lignocellulose outperformed the ADS in terms of biogas productivity when fractionated biocomponents of rice straw were used to achieve a high methane bioconversion rate. A 33.3 % higher methane yield was obtained with the acclimatized consortium (AC) compared to that of ADS control. The dominant pair-wise link between Firmicutes (18.99-40.03 %), Bacteroidota (10.94-28.75 %), and archaeal Halobacteriota (3.59-20.57 %) phyla in the AC seed digesters indicated that the keystone members of these phyla were responsible for higher methane yield. A high abundance of syntrophic bacteria such as Proteiniphilum (1.22-5.19 %), Fermentimonas (0.71-5.31 %), Syntrophomonas (0.87-3.59 %), and their syntrophic partner Methanosarcina (4.26-18.80 %) maintained the digester stability and facilitated higher substrate-to-methane conversion in the AC seed digesters. The present combined strategy will help in boosting the 'biomass-to-methane" conversion.

Deep eutectic solvents as promising pretreatment agents for sustainable lignocellulosic biorefineries: A review

Increasing reliance on non-renewable fuels has shifted research attention to environmentally friendly and sustainable energy sources.The inherently recalcitrant nature of lignocellulosic biomass (LCB) makes downstream processing of the bioprocess challenging. Deep eutectic solvents (DESs) are popular and inexpensive green liquids found effective for LCB valorisation. DESs have negligible vapor-pressure and are non-flammable, recyclable, cost-economic, and thermochemically stable. This review provides a detailed overview on the DESs types, properties and their role in effective delignification and enzymatic digestibility of polysaccharides for cost-effective conversion of LCB into biofuels and bioproducts. The conglomeration of DESs with assistive pretreatment techniques can augment the process of biomass deconstruction. The current challenges in upscaling the DESs-based pretreatment technology up to commercial scale is summarized, with possible solutions and future directions. These insights would fill the knowledge-gaps to towards development of lignocellulosic biorefineries and to address the global energy crisis and environment issues.

Comparison of alkali and ionic liquid pretreatment methods on the biochemical methane potential of date palm waste biomass

Date palm waste biomass is a readily accessible agricultural waste biomass that may be used to produce biogas. Because the complex structure of date palm waste biomass prevents the embedded holo-cellulosic sugars from biodegrading, pretreatment is required to increase methane (CH₄) yield. The present investigation aimed to comparatively determine the impact of alkali and ionic liquid pretreatment on the biochemical methane potential (BMP) of different types of date palm waste biomass. The findings revealed that ionic liquid pretreated Palm and Fruit bunch showed the highest BMP (321.67 mL CH₄/g-TS) and substrate conversion efficiency (68.01%), respectively, over other biomass samples. In alkali pretreatment, the highest BMP and substrate conversion efficiency were detected with Palm (309.76 mL CH₄/g-TS) and Spathe (62.09%). The high BMP and substrate conversion efficiency of date palm waste biomass may be harnessed for bioenergy production when this ionic liquid pretreatment technology is used.

Advances and Challenges in Biocatalysts Application for High Solid-Loading of Biomass for 2nd Generation Bio-Ethanol Production

Growth in population and thereby increased industrialization to meet its requirement, has elevated significantly the demand for energy resources. Depletion of fossil fuel and environmental sustainability issues encouraged the exploration of alternative renewable eco-friendly fuel resources. Among major alternative fuels, bio-ethanol produced from lignocellulosic biomass is the most popular one. Lignocellulosic biomass is the most abundant renewable resource which is ubiquitous on our planet. All the plant biomass is lignocellulosic which is composed of cellulose, hemicellulose and lignin, intricately linked to each other. Filamentous fungi are known to secrete a plethora of biomass hydrolyzing enzymes. Mostly these enzymes are inducible, hence the fungi secrete them economically which causes challenges in their hyperproduction. Biomass’s complicated structure also throws challenges for which pre-treatments of biomass are necessary to make the biomass amorphous to be accessible for the enzymes to act on it. The enzymatic hydrolysis of biomass is the most sustainable way for fermentable sugar generation to convert into ethanol. To have sufficient ethanol concentration in the broth for efficient distillation, high solid loading ~<20% of biomass is desirable and is the crux of the whole technology. High solid loading offers several benefits including a high concentration of sugars in broth, low equipment sizing, saving cost on infrastructure, etc. Along with the benefits, several challenges also emerged simultaneously, like issues of mass transfer, low reaction rate due to water constrains in, high inhibitor concentration, non-productive binding of enzyme lignin, etc. This article will give an insight into the challenges for cellulase action on cellulosic biomass at a high solid loading of biomass and its probable solutions.

Structural elucidation and targeted valorization of poplar lignin from the synergistic hydrothermal-deep eutectic solvent pretreatment

Elucidating the structural variations of lignin during the pretreatment is very important for lignin valorization. Herein, poplar wood was pretreated with an integrated process, which was composed of AlCl₃-catalyzed hydrothermal pretreatment (HTP, 130-150 °C, 1.0 h) and mild deep-eutectic solvents (DES, 100 °C, 10 min) delignification for recycling lignin fractions. Confocal Raman Microscopy (CRM) was developed to visually monitor the delignification process during the HTP-DES pretreatment. NMR characterizations (2D-HSQC and ³¹P NMR) and elemental analysis demonstrated that the lignin fractions had undergone the following structural changes, such as dehydration, depolymerization, condensation. Molecular weights (GPC), microstructure (SEM and TEM), and antioxidant activity (DPPH analysis) of the lignins revealed that the DES delignification resulted in homogeneous lignin fragments (1.32 < PDI < 1.58) and facilitated the rapid assemblage of lignin nanoparticles (LNPs) with controllable nanoscale sizes (30-210 nm) and excellent antioxidant activity. These findings will enhance the understanding of structural transformations of the lignin during the integrated process and maximize the lignin valorization in a current biorefinery process.

Ultrafast alkaline deep eutectic solvent pretreatment for enhancing enzymatic saccharification and lignin fractionation from industrial xylose residue

An aspirational pretreatment method for efficient fractionation and tailored valorization of large industrial biomass can ensure the realizability of sustainable biorefinery strategies. In this study, an ultrafast alkaline deep eutectic solvents (DES) pretreatment strategy was developed to efficiently extract the lignin nanoparticles and retain cellulose residues that could be readily enzymatic saccharified to obtain fermentative glucose for the bioenergy production from industrial xylose residue. Results showed that the DES pretreatment had excellent delignification performance and the regenerated DES lignin nanoparticles exhibited well-preserved structures and excellent antioxidant activity, as well as low molecular weights and relatively uniform size distribution, which could facilitate downstream catalytic degradation for production of chemicals and preparation of lignin-based materials. Under the optimal condition (DES pretreatment: 80 °C, 10 min; saccharification: 10 FPU/g, 5 wt%, 100 mg/g Tween 80), the glucose yield of 90.12% could be achieved, which was dramatically increased compared to raw materials.

Highly-efficient pretreatment using alkaline enhanced aqueous deep eutectic solvent to unlock poplar for high yield of fermentable sugars: Synergistic removal of lignin and mannan

Herein, a short-time alkaline enhanced aqueous DES (AaDES) pretreatment using choline chloride/ethylene glycol was reported, aiming at enhancing cellulose and xylan enzymatic digestibility. Simultaneously, saccharification efficiency of cellulose and xylan was reached to 91.2% and 99.0%, respectively, ∼4 and ∼ 24 times that of raw poplar. Pretreatment time was substantially shortened from 15-24 h to 4 h. Notably, 43.00 kg fermentable sugars (73% of the theoretical maximum) and 12.98 kg lignin with rich β-O-4' linkages were obtained based on 100 kg poplar. The complete removal of acetyl and partial removal of lignin and mannan contributed to excellent pretreatment performance. It was found that enzymatic digestibility of xylan/cellulose was positively correlated with removal of mannan (R² = 0.9719; R² = 0.9010) and delignification (R² = 0.6888; R² = 0.8293). Drastic reduction in pretreatment time along with high-yield sugars in AaDES system will provide strength towards industrial level biorefinery.

Integrated hydrothermal and deep eutectic solvent-mediated fractionation of lignocellulosic biocomponents for enhanced accessibility and efficient conversion in anaerobic digestion

Effective fractionation of lignocellulosic biocomponents of lignocellulosic biomass can increase its utilization in anaerobic digestion for high yield biomethane production. A hydrothermal process was optimized and integrated with a deep eutectic solvent (DES) pretreatment to preferentially fractionate hemicellulose, cellulose, and lignin in rice straw. The optimized hydrothermal process resulted in 96% hemicellulose solubilization at moderately low combined pretreatment severity (log S = 2.26), allowing increased hemicellulosic sugar recovery with minimal formation of inhibitory byproducts. Subsequent DES pretreatment resulted in highly bioaccessible cellulosic pulp, removing 81.3% of lignin that can be recovered and converted into value-added products. Anaerobic digestion of hemicellulosic fraction and cellulosic pulp using a microbial methanogenic consortium seed acclimatized to the lignocellulosic inhibitors resulted in a 33.4% higher yield of methane (467.84 mL g^-1 VS_initial) than with anaerobic digester sludge seed. This integrated approach can facilitate and maximize the targeted utilization of different biocomponents through sustainable biorefining.

Deep eutectic solvent with bifunctional Brønsted-Lewis acids for highly efficient lignocellulose fractionation

Green and low cost deep eutectic solvents (DESs) are promising to replace the solid acids and ionic liquids in biomass fractionation process. To enhance the lignocellulose pretreatment efficiency, an acidic DES that composed of Brønsted acid (ZnCl₂) as hydrogen bond acceptor and Lewis acid (lactic acid) as hydrogen bond donator was designed. This bifunctional DES was used for the extraction of lignin from poplar sawdust. Under the optimal pretreatment condition, the ZnCl₂-lactic acid DES could recover 95.2 wt% of lignin with a purity of 92.1%. The recovered lignin demonstrated a low polydispersity of 1.67 and small amount of β-aryl-ethers. Moreover, the acidic DES had a good recyclability and reusability. Such performance was attributed to the presence of bifunctional acid sites, which help selectively cleave lignin-carbohydrate complex linkages. The acidity and polarity of Brønsted acid can be modulated by the Lewis acid, thus synergistically promote the lignin extraction and production.

An effective strategy for improving the specific activity and saccharification efficiency of cellulase by pre-incubation with phenolic acids

This short communication analyzed the effects of lignin-derived phenolic acid compounds on cellulase. Vanillic acid, syringic acid, ferulic acid, and isovanillic acid improved cellulase specific activity and saccharification efficiency. In the enzymatic hydrolysis process, the promotion effect of phenolic acid was concentration-dependent. The effect of low concentration of phenolic acids (less than 5 mM) was negligible. After pre-incubating 1 g cellulase with 5 mmol phenolic acid, FPase-specific activity, CMCase-specific activity, and pNPGase-specific activity increased by 57.06%, 136.79%, and 110.61%, respectively. After digestion with pre-incubated cellulase, the saccharification efficiency of phosphoric acid-swollen cellulose increased by 45.13%. Pre-incubation with phenolic acid improved the saccharification efficiency of cellulase. It might be helpful to enhance the comprehensive utilization capacity of lignin-derived compounds.

Isolation and Fractionation of the Tobacco Stalk Lignin for Customized Value-Added Utilization

The value-added utilization of tobacco stalk lignin is the key to the development of tobacco stalk resources. However, the serious heterogeneity is the bottleneck for making full use of tobacco stalk lignin. Based on this, lignin was separated from tobacco stalk through hydrothermal assisted dilute alkali pretreatment. Subsequently, the tobacco stalk alkaline lignin was fractionated into five uniform lignin components by sequential solvent fractionation. Advanced spectral technologies (FT-IR, NMR, and GPC) were used to reveal the effects of hydrothermal assisted dilute alkali pretreatment and solvent fractionation on the structural features of tobacco stalk lignin. The lignin fractions extracted with n-butanol and ethanol had low molecular weight and high phenolic hydroxyl content, thus exhibiting superior chemical reactivity and antioxidant capacity. By contrast, the lignin fraction extracted with dioxane had high molecular weight and low reactivity, nevertheless, the high residual carbon rate made it suitable as a precursor for preparing carbon materials. In general, hydrothermal assisted dilute alkali pretreatment was proved to be an efficient method to separate lignin from tobacco stalk, and the application of sequential solvent fractionation to prepare lignin fractions with homogeneous structural features has specific application prospect.

Effects of P-Coumarate 3-Hydroxylase Downregulation on the Compositional and Structural Characteristics of Lignin and Hemicelluloses in Poplar Wood (Populus alba × Populus glandulosa)

Elucidating the chemical and structural characteristics of hemicelluloses and lignin in the p-coumarate 3-hydroxylase (C3H) down-regulated poplar wood will be beneficial to the upstream gene validation and downstream biomass conversion of this kind of transgenic poplar. Herein, the representative hemicelluloses and lignin with unaltered structures were prepared from control (CK) and C3H down-regulated 84K poplars. Modern analytical techniques, such as ¹³C NMR, 2D-HSQC NMR, and gel chromatography (GPC), were performed to better delineate the structural changes of hemicelluloses and lignin caused by transgenesis. Results showed that both the hemicelluloses (H_-CK and H_-C3H) extracted from control and C3H down-regulated poplar wood have a chain backbone of (1→4)-β-D-Xylan with 4-O-Me-α-D-GlcpA as side chain, and the branch degree of the H_-C3H is higher than that of H_-CK. With regarding to the lignin macromolecules, NMR results demonstrated that the syringyl/guaiacyl (S/G) ratio and dominant substructure β-O-4 linkages in C3H down-regulated poplar were lower than those of control poplar wood. By contrast, native lignin from C3H down-regulated poplar wood exhibited higher contents of p-hydroxybenzoate (PB) and p-hydroxyphenyl (H) units. In short, C3H down-regulation resulted in the chemical and structural changes of the hemicelluloses and lignin in these poplar wood. The identified structures will facilitate the downstream utilization and applications of lignocellulosic materials in the biorefinery strategy. Furthermore, this study could provide some illuminating results for genetic breeding on the improvement of wood properties and efficient utilization of poplar wood.

Hydrothermal pretreatment of lignocellulosic biomass for hemicellulose recovery

The hemicellulosic fraction recovery is of interest for integrated processes in biorefineries, considering the possibility of high economic value products produced from their structural compounds of this polysaccharide. However, to perform an efficient recovery, it is necessary to use biomass fractionation techniques, and hydrothermal pretreatment is highlighted as a valuable technique in the hemicellulose recovery by applying high temperatures and pressure, causing dissolution of the structure. Considering the possibility of this pretreatment technique for current approaches to hemicellulose recovery, this article aimed to explore the relevance of hydrothermal pretreatment techniques (sub and supercritical water) as a strategy for recovering the hemicellulosic fraction from lignocellulosic biomass. Discussions about potential products to be generated, current market profile, and perspectives and challenges of applying the technique are also addressed.