Treatment method of lignocellulose raw material

Abstract

The invention belongs to the technical field of biochemical engineering, and particularly relates to a treatment method of a lignocellulose raw material, which utilizes a novel ternary deep eutectic solvent to treat sorghum straws so as to realize three-component utilization of the sorghum straws. According to the method, octadecyl trimethyl ammonium chloride, propionic acid and p-toluenesulfonic acid serve as raw materials, and a novel ternary deep eutectic solvent is synthesized and used for promoting enzymolysis saccharification of sorghum straw. The novel pretreatment strategy can effectively remove hemicelluloses in the sorghum straws, meanwhile, xylooligosaccharide (X2-X3) is co-produced in the pretreatment process, and the pretreated reaction liquid can be used for extracting lignin and further used for anti-oxidation application in life. The method can realize separation and full utilization of three components of biomass, has the advantages of high efficiency, high selectivity, simple process, environmental friendliness and the like, and the obtained product is high in potential additional value and has a very strong industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of biochemical engineering, and specifically relates to a method for processing lignocellulose raw materials, and in particular to a method for utilizing sorghum straw by processing sorghum straw with a novel ternary deep eutectic solvent to realize utilization of three components thereof. Background Art

[0002] With the growing 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) and has great potential value. Hemicellulose mainly includes xylan and its derivatives, especially xylo-oligosaccharides (XOS), which play an important role in various applications, such as regulating intestinal flora, acting as antioxidants and enhancing human immunity. Xylan is used in feed industry, health and medical products, food and beverages, etc. Cellulose is a component of biomass and is easily decomposed by cellulase to produce reducing sugars. The subsequent glucose plays a vital role in many fields such as chemical engineering, health care and food industry. In addition, these glucose molecules can be used as raw materials for subsequent fermentation to produce biofuels, thus consolidating its position as a high-quality renewable energy source. However, sorghum straw has a low biomass conversion efficiency due to its dense structural strength and large amounts of cellulose and lignin. At present, a large amount of biomass resources are discarded or even burned without being effectively utilized, resulting in environmental pollution. Traditional biomass pretreatment methods can only utilize one or two of the components, and cannot achieve full utilization of the three components. Therefore, it is crucial to explore effective biomass pretreatment methods.

[0003] Hydrothermal pretreatment has attracted great interest in biomass treatment due to its ease of operation, relatively short operating time, environmental friendliness, high cost-effectiveness, and low risk of equipment corrosion. Hydrothermal pretreatment is one of the simplest treatment methods. It only requires the addition of pure water to the reactor and pretreatment of the biomass by heating. Compared with other types of thermal pretreatment, hydrothermal pretreatment uses only water as the treatment medium and does not require other chemical reagents, thus avoiding potential corrosion, high performance costs, and serious environmental pollution. In addition, 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 high moisture content of lignocellulose without the need for expensive drying steps. During hydrothermal pretreatment, water molecules can act as a reaction solvent at high temperatures (>100°C), thereby increasing the solubility of substances in the pretreatment process. In addition to being a solvent, water molecules can also act as reactants or chemical catalysts in the hydrothermal method. During the hydrolysis process, H produced by water ionization +The polysaccharide depolymerization was caused by selective destruction of acetyl groups and hydrolysis of heterocyclic ether bonds. Therefore, an aqueous solution rich in xylo-oligosaccharides could be obtained using a simple hydrothermal pretreatment.

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

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to propose a method for treating lignocellulosic raw materials, using a new ternary deep eutectic solvent to treat the straw to achieve the utilization of its three components. Taking sorghum straw as an example, the ternary deep eutectic solvent is used to catalyze the waste sorghum straw to improve its enzymatic saccharification efficiency while producing xylooligosaccharides, and the filtrate is used to extract lignin. The structure of bio-based lignin is well preserved, containing a large number of phenolic hydroxyl groups and methoxy groups, and has antioxidant activity, biocompatibility and safety, and can be used for daily antioxidants. The present invention not only solves the problem of sorghum straw waste treatment, but also realizes the full utilization of the three components of biomass. The process is simple, easy to control, and the efficiency of enzymatic saccharification is improved.

[0006] The present invention provides a method for processing a lignocellulose raw material. The lignocellulose raw material described in the present invention is a biomass material containing lignocellulose, such as wood, bamboo, straw, etc. Among them, the straw includes sorghum straw, corn straw, wheat straw, etc. In the specific embodiment of the present invention, sorghum straw is taken as an example.

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

[0008] (1) Hydrothermal pretreatment to produce xylooligosaccharides, the specific method is: crush the sorghum straw waste and sieve 20-80 mesh, add sorghum straw powder and water into the reaction container, and hydrothermally react at a temperature of 150-200°C for 10-50 minutes. After the reaction is completed, cool and separate the solid and liquid, the solid phase is sorghum straw waste residue I, and the liquid phase is an aqueous solution containing xylooligosaccharides; heat the xylooligosaccharide aqueous solution to a certain temperature to allow the water to evaporate gradually, control the temperature to avoid the decomposition of xylooligosaccharides, and after the solution reaches a certain concentration, cool and collect the concentrated liquid, dry and grind at low temperature to obtain xylooligosaccharides; dry the sorghum straw waste residue I to constant weight for use;

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

[0010] The evaporation concentration condition of the xylo-oligosaccharide aqueous solution is evaporation concentration at 100° C. to a colloidal state, and the low-temperature drying condition is low-temperature drying at 60° C.

[0011] (2) Using a novel organic acid deep eutectic solvent to treat sorghum straw waste residue, the specific method is: octadecyl trimethyl ammonium chloride, propionic acid and p-toluenesulfonic acid are mixed and stirred at different molar ratios (1-2:1-3:0.05-0.15) at 80°C for 1-3 hours to obtain a clear and transparent deep eutectic solvent as a pretreatment reagent. Sorghum straw waste residue I and the pretreatment reagent are added to a reaction vessel, heated at a temperature of 50-90°C for 10-50 minutes, solid-liquid separation, and the solid phase is dried to constant weight to obtain cellulose-rich sorghum straw waste residue II and pretreated filtrate.

[0012] An equal volume of water and an equal volume of anhydrous ethanol were added to the pretreated filtrate and the mixture was stirred thoroughly. Lignin was easily precipitated under acidic conditions. The pH was adjusted to 2-3 with a 1M HCl solution. After the lignin was precipitated, it was filtered, washed, and dried to obtain lignin powder. The filtrate obtained by filtration was fractionated and recovered according to different boiling points. p-Toluenesulfonic acid, propionic acid, and octadecyltrimethylammonium chloride were collected respectively, and a low eutectic solvent was re-prepared according to the required molar ratio.

[0013] Preferably, anhydrous ethanol is added to the pretreated filtrate, which is fully washed and concentrated to obtain a concentrated solution, and an appropriate amount of pure water is added to allow the solution to stand to obtain a precipitate containing lignin, which is then washed and dried to obtain lignin.

[0014] Among them, 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 saccharification: The sorghum straw waste residue II obtained by the previous pretreatment is enzymatically saccharified with cellulase in a buffer solution to obtain a cellulosic hydrolysate.

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

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

[0018] Among them, the mass of the pretreated waste residue accounts for 5% of the entire pretreatment mixed system.

[0019] The present invention is based on the development of an innovative ternary deep eutectic solvent (TDES), using OTAC as the HBA, PA as the HBD, and p-TsOH as the auxiliary for sorghum straw pretreatment. OTAC is used to change the physical structure of biomass and promote the deeper penetration of the pretreatment solvent into the sorghum straw. Propionic acid and p-TsOH act as acidic catalysts to catalyze the sulfonation of lignin and the degradation of part of hemicellulose, weaken the binding of lignin to cellulose and hemicellulose, thereby relaxing the biomass structure and successfully separating and utilizing the three components of biomass. The present invention demonstrates the ability of a green and efficient TDES system to produce valuable xylooligosaccharides (XOS) and extract lignin, thereby broadening the application range of OTAC and providing an environmentally friendly biomass conversion method.

[0020] The lignin extracted by the present invention has antioxidant activity and can be used for antioxidant in daily life. It can be applied to antioxidants and food packaging in the food industry, skin care and anti-aging products in the cosmetics industry, drug ingredients and health products in the pharmaceutical industry, modified materials and composite materials in polymer materials, etc. It can effectively inhibit the oxidation of products during transportation, storage and sales, and ensure quality and stability.

[0021] Beneficial effects of the present invention:

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

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

[0024] (3) Sustainable development: The present invention uses waste sorghum straw as biomass raw material, which is rich in raw material sources and renewable, with simple processes and easy large-scale production, thus reducing energy consumption and pollution in production. Using crop waste as raw material not only solves the problem of straw disposal, but also realizes the recycling of resources, which is in line with the principle of sustainable development.

[0025] (4) Environmentally friendly: Compared with the traditional acid-base hydrolysis method, the new deep eutectic solvent is more environmentally friendly, reducing the use of harmful chemicals and the risk of environmental pollution. The wastewater generated during the extraction process is less and easier to handle, reducing the processing cost.

[0026] (5) Economic benefits: Due to the improved 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, fully utilizes the three components of biomass, and increases the added value of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram showing the effect of TDES on the changes of the three components before and after the pretreatment of sorghum straw;

[0028] Figure 2 This is a diagram showing the effects of pretreating sorghum straw using different pretreatment reagents in a method for pretreating lignocellulose raw materials of the present invention;

[0029] Figure 3 This is a diagram showing the effects of pretreating sorghum straw at different pretreatment temperatures adopted in a method for pretreating lignocellulose raw materials of the present invention;

[0030] Figure 4 This is a diagram showing the effects of pretreating sorghum straw at different pretreatment times in a method for pretreating lignocellulose raw materials according to the present invention;

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

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

[0033] For the convenience of understanding the present invention, the present invention lists specific embodiments for further description. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention. In the field, different forms of changes and modifications can be made on the basis of the following description, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention. The cellulase used in the present invention is produced by Aladdin (≥1000unit / g50mL).

[0034] The following specific embodiments of the present invention take sorghum straw as an example. It should be noted that the straw described in the present invention can also be wheat straw or corn straw. Compared with wheat and corn straw, sorghum straw is often harder and denser, which increases the difficulty of physical crushing, thereby affecting the subsequent processing efficiency. And the cellulose and lignin content of sorghum straw is usually higher than that of wheat straw and corn straw, which makes it more difficult to decompose. The higher lignin content means that more energy and chemicals are needed to pretreat the material, further increasing the difficulty in its biomass conversion process.

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

[0036] Example 1

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

[0038] (1) Dry the sorghum straw at 80°C to constant weight and crush it into 20-80 mesh.

[0039] (2) Add sorghum straw powder and deionized water (solid-liquid ratio of 1:10-20) to the reaction vessel, stir at 150-200°C for 10-50 min, and obtain a reaction solution containing oligoxylose and biomass residue. The analysis results of the reaction solution are shown in Table 1. It can be seen that rich oligoxylose can be obtained when sorghum straw is treated at 170°C for 40 min with a solid-liquid ratio of 1:20. The reaction solution was evaporated to a colloidal state at 100°C and then dried in an oven at 60°C to obtain oligoxylose powder; the biomass residue was dried for later use.

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

[0041]

[0042] Example 2

[0043] Octadecyltrimethylammonium chloride, propionic acid and p-toluenesulfonic acid were used as HBA and HBD to prepare an acidic deep eutectic solvent as an acidic catalyst:

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

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

[0046] The parameters of the 48 prepared ternary deep eutectic solvents were measured, and the results are shown in Table 2. The Kamlet-Taft (KT) solvent color parameter π* (i.e., polarizability) is usually used to evaluate the polarity of DES. α represents the energy of the solvent that is conducive to the formation of protons and solutes, and β represents the hydrogen bond acceptor ability. As shown in Table 2, 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 the penetration of the solvent into the biomass, effectively remove or modify lignin, and make cellulose and hemicellulose easier to be degraded by subsequent enzymes or chemical reagents. As shown in Tables 3 to 5, the α and β values ​​of the ternary deep eutectic solvents synthesized by oxalic acid (OA) and lactic acid (LA) are higher than those of the ternary deep eutectic solvents synthesized by PA, and the viscosity is larger, which is not conducive to the full contact reaction between the biomass and the pretreatment reagent. It can be seen from Table 6 that, in the KT parameters of the binary deep eutectic solvent, compared with the ternary deep eutectic solvent, the α value is relatively higher, the β value is relatively lower, and the viscosity is relatively lower.

[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 different binary deep eutectic solvents

[0056]

[0057] Example 3

[0058] Comparison of glucose production in sorghum straw treated with different pretreatment agents

[0059] Weigh 3.0g of the biomass residue in Example 1 and place it in a round-bottom flask, add 60mL of the prepared ternary deep eutectic solvent acid catalyst, stir at 80°C for 30min to obtain a pretreated mixed solution. The obtained pretreated mixed solution is regenerated, filtered, washed, and dried to obtain a pretreated dry raw material. The obtained dry raw material is a cellulose-rich biomass, and the liquid is a reaction solution. The obtained dry raw material is subjected to component analysis, and the cellulose content in the dry material is calculated. The required amount of cellulase is calculated according to the cellulose content. The amount of cellulase used is 20FPU / g cellulose for subsequent enzymatic saccharification.

[0060] A citric acid buffer solution (pH = 4.8, 50 mM) containing a final concentration of 4 mg / L tetracycline was added to a 100 mL conical flask, and the amount of dry raw material added was 5 wt %. The reaction was carried out in an incubator at 50 ° C and 150 rpm for 72 h. Figure 1 As shown in the figure, after TDES (OTAC:PA:p-TsOH) pretreatment, the glucan 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 reagents are shown in Figure 2 As shown in the figure, when the molar ratio of octadecyltrimethylammonium chloride, propionic acid and p-toluenesulfonic acid is 1:2:0.1, the yield of glucose is the highest, which can reach 69.29%.

[0061] Example 4

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

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

[0064] Example 5

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

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

[0067] Example 6

[0068] Comparison of recycling of ternary deep eutectic solvents for treating sorghum straw

[0069] Weigh 3.0 g of the dry raw material powder in Example 1 and place it in a round-bottom flask, add 60 mL of the prepared ternary deep eutectic solvent acid catalyst, stir at 80 ° C for 20 min to obtain a pretreated mixed solution. The mixed solution was filtered and centrifuged to obtain a reaction solvent. The reaction solvent was recycled 5 times, and the treatment effect was as follows: Figure 5 As shown. After five repeated uses, the delignification rate of OTAC / PA / p-TsOH solvent remained at 53.2% and the xylan elimination rate was 57.6%, showing its excellent performance in pretreatment and excellent recyclability. 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 the pretreatment process, thereby increasing the solute concentration and thus the solvent viscosity. This higher viscosity slows down the rate of delignification and hemicellulose elimination. The present invention investigates the efficiency of enzymatic hydrolysis of sorghum straw treated with recycled solvent. It was found that the glucose yield decreased with the repeated use of the solvent. Even after 4 cycles, the glucose yield of enzymatic hydrolysis of sorghum straw after pretreatment can still reach about 1.5 times the glucose yield of enzymatic hydrolysis of sorghum straw after pretreatment.

[0070] Example 7

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

[0072] Prepare 7mM 2,2-azo-di(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt (ABTS) solution and 140mM potassium persulfate (K2S2O8) solution. The 2.45mM ABTS+ solution is obtained by mixing 5mL 7mM ABTS solution and 88μL 140mM potassium persulfate (K2S2O8) solution. The ABTS+ solution is protected from light at room temperature for 12-16h. Finally, the generated ABTS+ solution is diluted 8 times with anhydrous ethanol. Add 20μL of lignin samples of different concentrations to be tested and 180μL ABTS+ solution to a 96-well plate and react at room temperature for 6-8min. The absorbance measured at a wavelength of 734 nm is recorded as A1; 20 μL of anhydrous ethanol and 180 μL of ABTS+ solution are mixed, and the measured absorbance is recorded as A0; 20 μL of sample is mixed with 180 μL of distilled water, and the measured absorbance is recorded as A2, with vitamin C as the positive control.

[0073] The calculation formula is:

[0074] The results are as follows Figure 6 As shown in the figure, the scavenging ability of lignin treated with vitamin C and deep eutectic solvents on ABTS+ radicals is affected by the sample concentration. When the concentration increases to a certain level, the scavenging ability of ABTS+ radicals reaches the highest level and tends to be stable. From the results, it can be seen that lignin treated with ternary deep eutectic solvents has a strong scavenging ability of ABTS+ radicals.

[0075] The above descriptions are merely embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any method made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, is also included in the patent protection scope of the present invention.

Claims

1. A method for treating lignocellulosic raw materials, characterized in that: The following steps are involved: S1. Mixing the lignocellulosic raw material with water, performing hydrothermal pretreatment, cooling after the reaction, and performing solid-liquid separation to obtain filtrate I and residue, and drying the residue to constant weight, which is marked as residue I; S2, evaporating and concentrating the filtrate I, and then drying at low temperature to obtain xylo-oligosaccharides; S3, prepare ternary deep eutectic solvent: octadecyltrimethylammonium chloride, propionic acid and p-toluenesulfonic acid in a molar ratio of 1-2:1-3:0.05-0.15, at 80 o C and stir for 1-3 h until it becomes clear and transparent, which is the pretreatment reagent; S4, add residue I to the pretreatment reagent and mix evenly, the mass ratio of residue I to pretreatment reagent is 1:10~20, at a temperature of 50~90 o C for 10-50 min; after the reaction is completed, cool the mixture and separate the solid and liquid to obtain filtrate II; the obtained residue is washed with deionized water until it is neutral, dried to a constant weight, and marked as residue II; S5. Add an equal volume of distilled water to the filtrate II, adjust the pH to 2-3 with 1 mol / L hydrochloric acid solution, let stand and precipitate, collect the precipitate by filtration, wash, and dry to obtain lignin; fractionate and recycle the filtrate for reuse; S6. Evenly mix the residue II with cellulase and a buffer solution containing tetracycline, perform enzymatic hydrolysis and saccharification, and obtain a cellulosic hydrolysate.

2. The method for processing lignocellulosic raw materials according to claim 1, characterized in that: The lignocellulose raw material is wood, bamboo or straw; the lignocellulose raw material is crushed and sieved through a 20-80 mesh sieve.

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

4. The method for processing lignocellulosic raw materials according to claim 1, characterized in that: The low-temperature drying after evaporation concentration in step S2 is as follows: o C evaporated and concentrated to a colloidal state, 60 o C dry.

5. The method for processing lignocellulosic raw materials according to claim 1, characterized in that: The molar ratio of octadecyltrimethylammonium chloride, propionic acid and p-toluenesulfonic acid in the ternary deep eutectic solvent of step S3 is 1:2:0.05-0.

15.

6. The method for processing lignocellulosic raw materials according to claim 1, characterized in that: The temperature of the heating reaction in step S4 is 70-90° C., and the reaction time is 30-50 min.

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

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

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

1.

10. Use of the lignin prepared by the method of claim 1 as an antioxidant.

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