A method for treating lignocellulosic feedstock

Abstract

The application belongs to the technical field of bio-chemical industry, and particularly relates to a treatment method of lignocellulose raw material, which utilizes a new ternary deep eutectic solvent to treat sorghum straw to realize three-component utilization. The method uses octadecyl trimethyl ammonium chloride, propionic acid and p-toluene sulfonic acid as raw materials to synthesize a new ternary deep eutectic solvent for promoting enzymatic saccharification of sorghum straw. The new pretreatment strategy can effectively remove hemicellulose in the sorghum straw, and simultaneously coproduce xylo-oligosaccharides (X2~X3) in the pretreatment process. The reaction liquid after pretreatment can be used for extracting lignin and then used for antioxidant application in life. The method can realize separation and full utilization of three components of biomass, and has the advantages of high efficiency, high selectivity, simple process, environmental friendliness and the like, the potential added value of the obtained product is high, and the method has a strong industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of biochemical technology, specifically relating to a method for processing lignocellulose raw materials, and particularly to a method for utilizing sorghum straw in a novel ternary deep eutectic solvent to achieve its three-component utilization. Background Technology

[0002] With the increasing global demand for sustainable energy, the efficient utilization of biomass resources has become a research hotspot. Sorghum straw, as one of the abundant agricultural wastes, contains a large amount of lignocellulose (cellulose, hemicellulose, and lignin), possessing enormous potential value. Hemicellulose mainly includes xylan and its derivatives, especially xylo-oligosaccharides (XOS), which play important roles in various applications, such as regulating gut microbiota, acting as antioxidants, and enhancing human immunity. Xylan is used in the feed industry, health and medical products, food, and beverages. Cellulose, a component of biomass, is easily broken down by cellulase, producing reducing sugars. The resulting glucose plays a crucial role in multiple fields such as chemical engineering, healthcare, and the food industry. Furthermore, these glucose molecules can serve as a raw material for subsequent fermentation to produce biofuels, thus solidifying its status as a high-quality renewable energy source. However, due to its dense structure and the large amounts of cellulose and lignin, sorghum straw has low biomass conversion efficiency. Currently, a large amount of biomass resources are discarded or even incinerated without effective utilization, leading to environmental pollution. Traditional biomass pretreatment methods can only utilize one or two components, failing to achieve full utilization of all three components. Therefore, exploring effective biomass pretreatment methods is crucial.

[0003] Hydrothermal pretreatment has attracted significant interest in biomass treatment due to its simplicity, relatively short operating time, environmental friendliness, cost-effectiveness, and low risk of equipment corrosion. Hydrothermal pretreatment is one of the simplest treatment methods. It only requires adding purified water to the reactor and pretreating the biomass through heating. Compared to other types of thermal pretreatment, hydrothermal pretreatment uses only water as the treatment medium, eliminating the need for other chemical reagents and thus avoiding potential corrosion, high performance costs, and severe environmental pollution. Furthermore, this pretreatment avoids the need for precious metal catalysts, expensive additives, and corrosion-resistant designs. Unlike other treatment technologies, hydrothermal pretreatment uses liquid water, allowing for high moisture content in lignocellulose without costly drying steps. During hydrothermal pretreatment, water molecules can act as a reaction solvent at high temperatures (>100°C), increasing the solubility of substances during pretreatment. Besides acting as a solvent, water molecules can also act as reactants or chemical catalysts in hydrothermal methods. During hydrolysis, water ionization produces H₂... +Polysaccharide depolymerization occurs through selective disruption of acetyl groups and hydrolysis of heterocyclic ether bonds. Therefore, a simple hydrothermal pretreatment method can be used to obtain an aqueous solution rich in xylooligosaccharides.

[0004] Pretreatment of lignocellulose mainly includes steam explosion and pretreatment using ionic liquids, organic solvents, dilute acids, and dilute alkalis. Traditional pretreatment methods have disadvantages such as high energy consumption, high performance costs, and significant environmental impact. In recent years, deep eutectic solvents (DESs) have attracted widespread attention due to their unique solubility, lower cost, and environmental friendliness. DESs are mainly composed of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) in a specific molar ratio. Choline chloride (ChCl) is commonly used as the HBA in the pretreatment of DESs. When poplar is pretreated with acidic DESs (such as ChCl:formic acid, ChCl:acetic acid, or ChCl:lactic acid), higher acidity levels are associated with increased lignin fragmentation and condensation. The ChCl:OA (2:1, mol:mol) system exhibits excellent pretreatment capabilities, achieving an enzymatic saccharification efficiency of 83.7% under optimized conditions (110℃, 5h) (Yu et al. Industrial Crops and Products, 2022). The complex polymer matrix of lignin consists of phenylpropane monomers interconnected by multiple chemical bonds. The solubility of these phenylpropane groups in lignin may improve cellulose accessibility and enhance enzymatic digestibility. Nitrogen-containing organic amines from cationic surfactants can enhance biomass solubility and pretreatment by interacting with lignin and eliminating hydrophobic substances. A deligation solvent (DES) composed of hexadecyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) was used to treat rapeseed straw, achieving a delignification rate of 62.2% and a xylan removal rate of 53.2% (Tang et al., Bioresource Technology, 2023). DES synthesized using CTAB and lactic acid (LA) for pretreatment of rice husks effectively removed xylan (79.9%) (Tang et al., Bioresource Technology, 2023), while the delignification rate was only 51.5%. Ternary deep eutectic solvents exhibit better solubility and selectivity compared to traditional binary systems, but their application in sorghum straw treatment requires further investigation. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to propose a method for processing lignocellulose raw materials, utilizing a novel ternary deep eutectic solvent to treat straw and achieve the utilization of its three components. Taking sorghum straw as an example, the ternary deep eutectic solvent is used to catalyze the enzymatic hydrolysis and saccharification of waste sorghum straw, improving its efficiency while producing xylooligosaccharides, and the filtrate is used to extract lignin. The bio-based lignin retains its structure intact, contains a large number of phenolic hydroxyl and methoxy groups, and possesses antioxidant activity, biocompatibility, and safety, making it suitable for everyday antioxidant applications. This invention solves the problem of sorghum straw waste treatment while achieving full utilization of the three components of biomass. The process is simple, easy to control, and improves enzymatic hydrolysis and saccharification efficiency.

[0006] This invention provides a method for processing lignocellulose raw materials. The lignocellulose raw materials mentioned in this invention are biomass materials containing lignocellulose, such as wood, bamboo, and straw. Straw includes sorghum straw, corn straw, wheat straw, etc., and sorghum straw is used as an example in this specific embodiment.

[0007] Specifically, the present invention provides a method for processing lignocellulose raw materials, comprising the following specific steps:

[0008] (1) Hydrothermal pretreatment to produce xylooligosaccharides: The specific method is as follows: Sorghum straw waste is crushed and sieved through a 20-80 mesh screen. Sorghum straw powder and water are added to a reaction vessel, and the reaction is carried out hydrothermally at a temperature of 150-200℃ for 10-50 minutes. After the reaction, the solid and liquid phases are separated. The solid phase is sorghum straw waste residue I, and the liquid phase is an aqueous solution containing xylooligosaccharides. The xylooligosaccharide aqueous solution is heated to a certain temperature to allow the water to evaporate gradually. The temperature is controlled to avoid decomposition of xylooligosaccharides. After the solution reaches a certain concentration, it is cooled and the concentrated liquid is collected. The solution is dried and ground at a low temperature to obtain xylooligosaccharides. Sorghum straw waste residue I is dried to constant weight for later use.

[0009] Preferably, the hydrothermal reaction temperature is 120–180°C, and more preferably 170°C.

[0010] The evaporation and concentration conditions for the xylooligosaccharide aqueous solution are 100℃ evaporation and concentration to a colloidal state, and low-temperature drying conditions are 60℃ low-temperature drying.

[0011] (2) A novel organic acid deep eutectic solvent was used to treat sorghum straw waste residue. The specific method was as follows: Octadecyltrimethylammonium chloride, propionic acid, and p-toluenesulfonic acid were mixed and stirred at 80°C for 1-3 hours in different molar ratios (1-2:1-3:0.05-0.15) to obtain a clear and transparent deep eutectic solvent as a pretreatment reagent. Sorghum straw waste residue I and the pretreatment reagent were added to a reaction vessel and heated at 50-90°C for 10-50 minutes. The solid and liquid phases were separated, and the solid phase was dried to constant weight to obtain cellulose-rich sorghum straw waste residue II and the pretreated filtrate.

[0012] Add an equal volume of water and anhydrous ethanol to the pretreated filtrate and stir thoroughly. Lignin is easily precipitated under acidic conditions. Adjust the pH to 2-3 with 1M HCl solution. After the lignin precipitates, filter, wash and dry to obtain lignin powder. The filtrate obtained from filtration is fractionated and recovered according to different boiling points. Collect p-toluenesulfonic acid, propionic acid and octadecyltrimethylammonium chloride respectively, and re-prepare the eutectic solvent according to the required molar ratio.

[0013] Preferably, anhydrous ethanol is added to the pretreated filtrate, and the solution is thoroughly washed and concentrated to obtain a concentrated solution. An appropriate amount of pure water is added and the solution is allowed to stand to obtain a precipitate containing lignin. The precipitate is then washed, dried, and lignin is obtained.

[0014] In the reaction system, sorghum straw waste residue I and pretreatment reagent are mixed at a mass ratio of 1:10 to 20, with the optimal ratio being 1:20.

[0015] (3) Enzymatic hydrolysis and saccharification: The sorghum straw waste residue II obtained from the previous pretreatment is hydrolyzed and saccharified with cellulase in a buffer solution to obtain cellulase hydrolysate.

[0016] Furthermore, cellulase is added according to the cellulose content in sorghum straw waste residue II, and the amount of cellulase used is 20-50 FPU / g cellulose, with the optimum being 20 FPU / g cellulose.

[0017] Furthermore, the buffer solution is a 50mM citrate buffer solution with pH=4.8 and contains tetracycline at a final concentration of 4mg / L. The buffer solution is added to the pretreated waste residue at a mass ratio of 20:1.

[0018] The mass of the pretreated waste residue accounts for 5% of the total mass of the pretreated mixing system.

[0019] This invention is based on the development of an innovative ternary eutectic solvent (TDES), using OTAC as the HBA, PA as the HBD, and p-TsOH as a supplement for sorghum straw pretreatment. OTAC is used to alter the physical structure of biomass, promoting deeper penetration of the pretreatment solvent into the sorghum straw. Propionic acid and p-TsOH act as acidic catalysts, catalyzing lignin sulfonation and partial hemicellulose degradation, weakening the bond between lignin and cellulose and hemicellulose, thereby relaxing the biomass structure and successfully separating and utilizing the three components of the biomass. This invention demonstrates the ability of a green and efficient TDES system to produce valuable xylooligosaccharides (XOS) and extract lignin, thus broadening the application range of OTAC and providing an environmentally friendly biomass conversion method.

[0020] The lignin extracted in this invention possesses antioxidant activity and can be used for anti-oxidation in daily life. It can be applied as an antioxidant and in food packaging in the food industry, in skin care and anti-aging products in the cosmetics industry, in pharmaceutical ingredients and health products in the pharmaceutical industry, and as a modifier and composite material in polymer materials. It can effectively inhibit oxidation of products during transportation, storage, and sales, ensuring quality and stability.

[0021] The beneficial effects of this invention are:

[0022] (1) The novel ternary deep eutectic solvent can effectively degrade the hemicellulose component in sorghum straw, thereby increasing the yield of xylooligosaccharides. By controlling the reaction conditions, further decomposition of xylooligosaccharides can be minimized, ensuring the purity and quality of the product.

[0023] (2) High-efficiency lignin extraction: Through an optimized deep eutectic solvent system, lignin can be effectively separated from sorghum straw, improving the extraction efficiency and purity. The deep eutectic solvent used has good solubility and selectivity, allowing lignin to maintain its natural structure during extraction, which is very beneficial for subsequent applications.

[0024] (3) Sustainable Development: This invention uses waste sorghum straw as a biomass raw material, which is abundant, renewable, and has a simple process that is easy to scale up, reducing energy consumption and pollution. Utilizing agricultural waste as a raw material solves the problem of straw disposal and realizes resource recycling, which is in line with the principle of sustainable development.

[0025] (4) Environmentally friendly: The new deep eutectic solvent is more environmentally friendly than the traditional acid-base hydrolysis method, reducing the use of harmful chemicals and lowering the risk of environmental pollution. Less wastewater is generated during the extraction process, which is easier to treat and reduces treatment costs.

[0026] (5) Economic benefits: By improving the extraction efficiency of xylooligosaccharides and lignin, production costs can be reduced and overall economic benefits can be improved. The co-production of xylooligosaccharides and lignin maximizes the utilization of resources, realizes the full utilization of the three components of biomass, and increases the added value of the product. Attached image description:

[0027] Figure 1 This is a diagram showing the changes in the three components of sorghum straw before and after pretreatment using TDES in this invention.

[0028] Figure 2 These are diagrams illustrating the effects of different pretreatment reagents used in the pretreatment of sorghum straw in a lignocellulose raw material pretreatment method of the present invention.

[0029] Figure 3 These are diagrams illustrating the effects of different pretreatment temperatures on sorghum straw in a lignocellulose raw material pretreatment method according to the present invention.

[0030] Figure 4 These are diagrams illustrating the effects of different pretreatment times on sorghum straw in a lignocellulose raw material pretreatment method according to the present invention.

[0031] Figure 5 This is an image showing the effect of reusing the pretreatment reagent to treat sorghum straw in a lignocellulose raw material pretreatment method of the present invention.

[0032] Figure 6 This is a diagram showing the scavenging effect of lignin on ABTS+ free radicals in Example 7. Detailed Implementation

[0033] To facilitate understanding of the present invention, specific embodiments are provided for further description. Those skilled in the art should understand that these embodiments are merely illustrative and should not be considered as specific limitations of the invention. Within the scope of this art, various variations and modifications can be made based on the following description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims. The cellulase used in this invention is produced by Aladdin (≥1000 units / g 50 mL).

[0034] In the following specific embodiments of the present invention, sorghum stalks are used as an example. It should be noted that the stalks mentioned in the present invention can also be wheat stalks or corn stalks, etc. Compared with wheat and corn stalks, sorghum stalks are often harder and denser, which increases the difficulty of physical crushing, thus affecting subsequent processing efficiency. Furthermore, the cellulose and lignin content of sorghum stalks is generally higher than that of wheat and corn stalks, making it more difficult to decompose. The higher lignin content means that more energy and chemicals are needed to pre-treat the material, further increasing the difficulty of its biomass conversion process.

[0035] In the following specific embodiments of the present invention, an Aminex hx-87h column and high-performance liquid chromatography (Agilent Technologies Co., Ltd., USA) were used to analyze sugars and other byproducts in the hydrolysis products. The flow rate was 0.6 mL / min, and the mobile phase was 5 mM H2SO4. Lignin determination was divided into acid-insoluble lignin determination and acid-soluble lignin determination. Acid-insoluble lignin was separated from the biomass by hydrolysis with 72% sulfuric acid, followed by filtration and calcination at 550°C for 4 hours, after which the ash weight was measured. For acid-soluble lignin determination, the filtrate from the above acid hydrolysis step was collected, and the absorbance was measured at 205 nm using a UV spectrophotometer. The content of acid-soluble lignin was calculated using a standard curve.

[0036] Example 1

[0037] Analysis of xylooligosaccharide content under different treatment conditions:

[0038] (1) Dry the sorghum stalks at 80°C to constant weight and then crush them to 20-80 mesh.

[0039] (2) Add sorghum straw powder and deionized water (solid-liquid ratio of 1:10-20) to the reaction vessel and stir at 150-200℃ for 10-50 min to obtain a reaction solution containing xylooligosaccharides and biomass residue. The analysis results of the reaction solution are shown in Table 1. It can be seen that under the condition of treating sorghum straw at 170℃ for 40 min with a solid-liquid ratio of 1:20, abundant xylooligosaccharides can be obtained. Evaporate the reaction solution to a colloidal state at 100℃ and then dry it in an oven at 60℃ to obtain xylooligosaccharide powder; dry the biomass residue for later use.

[0040] Table 1. Analysis of xylooligosaccharide content under different treatment conditions.

[0041]

[0042] Example 2

[0043] Using octadecyltrimethylammonium chloride, propionic acid, and p-toluenesulfonic acid as HBA and HBD, an acidic deep eutectic solvent was prepared as an acidic catalyst.

[0044] Octadecyltrimethylammonium chloride / benzyltrimethylammonium chloride (BTAC), propionic acid / oxalic acid / lactic acid and p-toluenesulfonic acid were mixed and stirred at 80°C for 1 to 3 hours in different molar ratios (1 to 2: 1 to 3: 0.05 to 0.15) to obtain a clear and transparent ternary deep eutectic solvent as a pretreatment reagent for lignin raw materials.

[0045] Alternatively, octadecyltrimethylammonium chloride, propionic acid / oxalic acid / lactic acid / p-toluenesulfonic acid are mixed and stirred at 80°C for 1-3 hours in different molar ratios (1:0.5-2) to obtain a clear and transparent binary deep eutectic solvent as a pretreatment reagent for lignin raw materials.

[0046] The parameters of 48 prepared ternary deep eutectic solvents were measured, and the results are shown in Table 2. The Kamlet-Taft (KT) solvent colorimetric parameter π* (i.e., polarizability) is commonly used to evaluate the polarity of DES. α represents the solvent's energy conducive to proton and solute formation, and β represents its hydrogen bond acceptor capacity. Table 2 shows that when the molar ratio of OTAC to p-TsOH is fixed, increasing the PA content can reduce the solvent viscosity. Increasing the OTAC content in TDES can promote solvent penetration into biomass, effectively removing or modifying lignin, making cellulose and hemicellulose easier to degrade by subsequent enzymes or chemical reagents. Tables 3-5 show that the α and β values ​​of the ternary deep eutectic solvents synthesized from oxalic acid (OA) and lactic acid (LA) are higher than those of the ternary deep eutectic solvents synthesized from PA, and their viscosity is also higher, which is not conducive to sufficient contact reaction between biomass and pretreatment reagents. As can be seen from Table 6, among the KT parameters of binary deep eutectic solvents, α is relatively higher, β is relatively lower, and viscosity is relatively reduced compared to ternary deep eutectic solvents.

[0047] Table 2. Parameter determination of ternary deep eutectic solvents synthesized with different OTAC:PA:p-TsOH molar ratios.

[0048]

[0049] Table 3. Parameter determination of ternary deep eutectic solvents synthesized with different OTAC:LA:p-TsOH molar ratios.

[0050]

[0051] Table 4. Parameter determination of ternary deep eutectic solvents synthesized with different OTAC:OA:p-TsOH molar ratios.

[0052]

[0053] Table 5. Parameter determination of ternary deep eutectic solvents synthesized with different BTAC:PA:p-TsOH molar ratios.

[0054]

[0055] Table 6. Parameter determination of eutectic solvents with different binary depths

[0056]

[0057] Example 3

[0058] Comparison of glucose production from sorghum straw treated with different pretreatment reagents

[0059] 3.0 g of the biomass residue from Example 1 was weighed and placed in a round-bottom flask. 60 mL of the prepared ternary deep eutectic solvent acidic catalyst was added, and the mixture was stirred at 80 °C for 30 min to obtain a pretreated mixture. The pretreated mixture was then regenerated, filtered, washed, and dried to obtain pretreated dry raw material. The obtained dry raw material was cellulose-rich biomass, and the liquid was the reaction solution. The obtained dry raw material was subjected to component analysis to calculate the cellulose content. Based on the cellulose content, the required amount of cellulase was calculated. The amount of cellulase used was 20 FPU / g cellulose for subsequent enzymatic hydrolysis and saccharification.

[0060] Citrate buffer (pH = 4.8, 50 mM) containing tetracycline at a final concentration of 4 mg / L was added to a 100 mL Erlenmeyer flask. The dry raw material was added at 5 wt%, and the reaction was carried out at 50 °C and 150 rpm for 72 h. The changes in the three components of TDES pretreatment of sorghum straw are as follows: Figure 1 As shown in the figure, after pretreatment with TDES (OTAC:PA:p-TsOH), the dextran recovery rate was 78.3%, the delignification rate was 71.15%, and the xylan removal rate was 75.67%. The results of glucose production from sorghum straw under different pretreatment reagent conditions are shown in the figure. Figure 2 As shown in the figure, the highest glucose yield, reaching 69.29%, is achieved when the molar ratio of octadecyltrimethylammonium chloride, propionic acid, and p-toluenesulfonic acid is 1:2:0.1.

[0061] Example 4

[0062] Comparison of glucose production from sorghum straw treated with different pretreatment temperatures

[0063] Weigh 3.0 g of the dry raw material powder from Example 1 and place it in a round-bottom flask. Add 60 mL of a ternary deep eutectic solvent acidic catalyst (octadecyltrimethylammonium chloride: propionic acid: p-toluenesulfonic acid = 1:2:0.1, mol:mol:mol). Stir at 50–90 °C for 30 min to obtain a pretreated mixture. The pretreated mixture is then regenerated, filtered, washed, and dried to obtain the pretreated dry raw material. The obtained dry raw material is cellulose-rich biomass, and the liquid is the reaction solution. The obtained dry raw material is used for subsequent enzymatic hydrolysis and saccharification. Citrate buffer (pH = 4.8, 50 mM) containing tetracycline at a final concentration of 4 mg / L is added to a 100 mL Erlenmeyer flask. The dry raw material is added at 5 wt%, and the reaction is carried out at 50 °C and 150 rpm for 72 h. The results of glucose production from sorghum straw treated at different pretreatment temperatures are shown below. Figure 3 As shown in the figure, the glucose yield is highest when the pretreatment temperature is 80℃.

[0064] Example 5

[0065] Comparison of glucose production from sorghum straw treated with different pretreatment times

[0066] Weigh 3.0 g of the dry raw material powder from Example 1 and place it in a round-bottom flask. Add 60 mL of a ternary deep eutectic solvent acidic catalyst (octadecyltrimethylammonium chloride: propionic acid: p-toluenesulfonic acid = 1:2:0.1, mol:mol:mol). Stir at 80 °C for 10–50 min to obtain a pretreated mixture. The pretreated mixture is then regenerated, filtered, washed, and dried to obtain the pretreated dry raw material. The obtained dry raw material is cellulose-rich biomass, and the liquid is the reaction solution. The obtained dry raw material is used for subsequent enzymatic hydrolysis and saccharification. Citrate buffer (pH = 4.8, 50 mM) containing tetracycline at a final concentration of 4 mg / L is added to a 100 mL Erlenmeyer flask. The dry raw material is added at 5 wt%, and the reaction is carried out at 50 °C and 150 rpm for 72 h. The results of glucose production from sorghum straw treated with different pretreatment times are shown below. Figure 4 As shown in the figure, the glucose yield was highest when the pretreatment time was 30 min.

[0067] Example 6

[0068] Comparison of ternary deep eutectic solvent recycling for sorghum straw treatment

[0069] Weigh 3.0 g of the dry raw material powder from Example 1 and place it in a round-bottom flask. Add 60 mL of the prepared ternary deep eutectic solvent acidic catalyst and stir at 80 °C for 20 min to obtain a pretreated mixture. Filter the mixture and centrifuge to obtain the reaction solvent. Recycle the reaction solvent 5 times; the treatment effect is as follows. Figure 5 As shown. After five cycles of reuse, the delignification rate of the OTAC / PA / p-TsOH solvent remained at 53.2%, and the xylan elimination rate was 57.6%, demonstrating its excellent performance and recyclability in pretreatment. Experimental observations showed that solvent viscosity was positively correlated with the frequency of reuse, which may be due to the decomposition of hemicellulose into soluble sugars during pretreatment, thereby increasing the solute concentration and thus increasing the solvent viscosity. This higher viscosity slowed down the rate of delignification and hemicellulose elimination. This invention investigated the efficiency of enzymatic hydrolysis of sorghum straw using recycled solvent. The results showed that glucose yield decreased with repeated solvent reuse. Even after four cycles, the glucose yield from enzymatic hydrolysis of pretreated sorghum straw was still approximately 1.5 times that of enzymatic hydrolysis of pretreated sorghum straw.

[0070] Example 7

[0071] The antioxidant capacity of lignin samples treated with ternary eutectic solvent (OTAC:PA:p-TsOH = 1:2:0.1) and binary eutectic solvent (OTAC:PA = 1:2) was investigated.

[0072] A 7 mM solution of 2,2-azino-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt (ABTS) and a 140 mM potassium persulfate (K₂S₂O₈) solution were prepared. A 2.45 mM ABTS⁺ solution was obtained by mixing 5 mL of the 7 mM ABTS solution and 88 μL of the 140 mM potassium persulfate (K₂S₂O₈) solution. The ABTS⁺ solution was incubated at room temperature in the dark for 12–16 h. Finally, the resulting ABTS⁺ solution was diluted 8-fold with anhydrous ethanol. Different concentrations of the lignin sample to be tested, along with 180 μL of the ABTS⁺ solution, were added sequentially to 96-well plates, and the reaction was carried out at room temperature for 6–8 min. The absorbance measured at 734 nm was recorded as A1; the absorbance measured by mixing 20 μL of anhydrous ethanol and 180 μL of LABTS+ solution was recorded as A0; the absorbance measured by mixing 20 μL of sample with 180 μL of distilled water was recorded as A2, with vitamin C as a positive control.

[0073] The calculation formula is:

[0074] The results are as follows Figure 6 As shown, the scavenging ability of lignin treated with vitamin C and deep eutectic solvent against ABTS+ free radicals is affected by the sample concentration. When the concentration is increased to a certain level, the ABTS+ free radical scavenging ability reaches its peak and then tends to stabilize. The results indicate that lignin treated with a ternary deep eutectic solvent has a strong ABTS+ free radical scavenging ability.

[0075] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any method made using the contents of the present invention specification, or directly or indirectly applied to other related technical fields, is similarly included within the patent protection scope of the present invention.

Claims

1. A method for processing lignocellulose raw materials, characterized in that, Includes the following steps: S1. Mix the lignocellulose raw material with water, perform hydrothermal pretreatment, cool after the reaction, separate the solid and liquid to obtain filtrate I and residue, dry the residue to constant weight and mark it as residue I; the lignocellulose raw material is sorghum straw; S2. After evaporating and concentrating filtrate I, dry it at low temperature to obtain xylooligosaccharide; S3. Preparation of ternary deep eutectic solvent: Octadecyltrimethylammonium chloride, propionic acid and p-toluenesulfonic acid are mixed and stirred at 80 °C for 1 to 3 h until clear and transparent, which is the pretreatment reagent; S4. Add residue I to the pretreatment reagent and mix well. The mass ratio of residue I to pretreatment reagent is 1:10~20. Heat the mixture at 50~90 ℃ for 10~50 min. After the reaction is completed, cool the mixture and separate the solid and liquid to obtain filtrate II. Wash the obtained residue with deionized water until neutral, dry it to constant weight, and label it as residue II. S5. Add an equal volume of distilled water to filtrate II, adjust the pH to 2-3 with 1 mol / L hydrochloric acid solution, let it stand to precipitate, filter and collect the precipitate, wash and dry it to obtain lignin; fractionate the filtrate for recycling. S6. Mix residue II with cellulase and a buffer solution containing tetracycline until homogeneous, then enzymatically hydrolyze and saccharify to obtain cellulase hydrolysate.

2. The method for processing lignocellulose raw materials according to claim 1, characterized in that, The lignocellulose raw material is crushed and passed through a 20-80 mesh sieve.

3. The method for processing lignocellulose raw materials according to claim 1, characterized in that, In step S1, the mass ratio of lignocellulose raw material to water is 1:10~20; and / or, the hydrothermal pretreatment conditions are: reaction at 150~200 ℃ for 10~50 min.

4. The method for processing lignocellulose raw materials according to claim 1, characterized in that, The low-temperature drying after evaporation and concentration in step S2 is as follows: evaporate and concentrate at 100 °C to a colloidal state, and then dry at 60 °C.

5. The method for processing lignocellulose raw materials according to claim 1, characterized in that, The heating reaction in step S4 is carried out at a temperature of 70-90°C for 30-50 minutes.

6. The method for processing lignocellulose raw materials according to claim 1, characterized in that, In step S5, an equal volume of anhydrous ethanol is also added.

7. The method for processing lignocellulose raw materials according to claim 1, characterized in that, In step S6, cellulase is added according to the cellulose content in residue II, and the amount of cellulase used is 20~50 FPU / g cellulose.

8. The method for processing lignocellulose raw materials according to claim 1, characterized in that, In step S6, the buffer solution is a 50 mM citrate buffer solution with pH=4.8 and contains tetracycline at a final concentration of 4 mg / L. The buffer solution and residue II are added at a mass ratio of 20:

1.

9. The use of lignin prepared by the method of claim 1 as an antioxidant.

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