Method for high-value utilization of agricultural residues by ternary deep eutectic solvent system

Abstract

A method for high-value utilization of agricultural residues by ternary deep eutectic solvent system, two hydrogen bond donors are mixed with hydrogen bond acceptors, heated and stirred to prepare ternary deep eutectic solvent; agricultural waste powder, ternary deep eutectic solvent, water and organic solvent are mixed and heated to react; after the reaction is completed, the reactor is cooled to room temperature, the reaction phase and the extraction phase are collected, and furfural is prepared; acetone and water are added to the solid-liquid mixture for washing, and the filtrate is collected; the filtrate is placed in an oil bath pot, and after the acetone is evaporated, deionized water is added for washing, and the filtrate is dried by suction filtration to obtain lignin; the solid obtained after suction filtration is washed with deionized water and dried to obtain cellulose; the extracted lignin is mixed with iron salt and stirred, and after the water is evaporated, high-temperature calcination is carried out to obtain a lignin-based graphitized carbon-based catalyst. The method can effectively separate the three main elements, at the same time, hemicellulose is converted into high-value platform chemical furfural, the enzymatic hydrolysis efficiency of cellulose is enhanced, and the high-value utilization of agricultural waste is realized.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of biomass resources, specifically involving a method for high-value utilization of straw raw materials using ternary deep eutectic solvent. Background Technology

[0002] With the shortage of non-renewable energy sources such as oil and coal and the worsening of global environmental problems, the development and utilization of renewable energy has become a research hotspot. Compared with first-generation biofuels, second-generation biofuels are receiving increasing attention. First-generation biofuels use edible starch as a raw material, while second-generation biofuels have a wider range of raw materials, especially pesticide residues from lignocellulosic biomass. Straw is one of the main agricultural residues, with low cost and large availability. It is estimated that China produces 6.5 × 10⁶ wheat, rice, and corn straw as agricultural residues annually. 8 Tons of wheat straw are produced, but not effectively utilized. Wheat straw is mainly composed of cellulose (30-35%), hemicellulose (15-25%), and lignin (10-25%). Cellulose and hemicellulose fractions can be hydrolyzed and dehydrated into furan compounds, such as furfural and 5-HMF, which can then be used to synthesize fuels and chemicals. Lignin is used for combustion power generation, conversion into phenolic compounds, or lignin-based materials. To resist microbial and enzymatic degradation, lignocellulose has a stubborn structure, namely a lignin-carbohydrate complex, limiting the separation of the three components and the production of subsequent value-added products. To achieve efficient utilization of agricultural waste, green and environmentally friendly methods are needed to separate these three components. Biomass pretreatment is one of the most commonly used technologies for removing and modifying lignin in biorefining, disrupting the lignin-carbohydrate structure by altering the interactions between its components, cellulose, hemicellulose, and lignin. Pretreatment can improve the enzymatic hydrolysis efficiency of carbohydrates and effectively recover cellulose, hemicellulose, and lignin to achieve biomass value-added.

[0003] Various pretreatment methods have been developed to overcome the stubbornness of lignocellulose in decomposition, such as dilute acid, alkali treatment, sulfite treatment, and organic solvent methods. However, these methods have drawbacks, including environmental damage, high cost, and equipment damage. In 2004, Abboot et al. discovered a novel solvent with physical and chemical properties similar to ionic liquids, named deep eutectic solvents (DES). Deep eutectic solvents have advantages such as low cost, non-toxicity, ease of preparation, biodegradability, and easy recycling. They are composed of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD), forming complexes through hydrogen bonds, and have been widely used in catalysis, organic synthesis, electrochemistry, and biomass treatment. Deep eutectic solvents exhibit high selectivity for dissolved lignin, which is beneficial for regenerating lignin and preserving the high-value utilization of cellulose. p-Toluenesulfonic acid (p-TSA) is an aromatic acid and a water-soluble growth promoter with excellent delignification properties at low temperatures below the boiling point of water, and can be used as an acidic hydrogen bond donor for DES. Acidic hydrogen bond donors in eutectic solvents can effectively separate cellulose, hemicellulose, and lignin from lignocellulose. p-Toluenesulfonic acid can depolymerize lignin via ether bond cleavage, allowing the separation of carbohydrate-free lignin from lignocellulose. Ethylene glycol, with its inferior performance, is used as a neutral HBD. DES containing one HBA and two HBD components has proven to be more effective in biomass deconstruction.

[0004] Chinese invention (CN110218335A) discloses a method for extracting lignin using a ternary eutectic solvent. The method includes the following steps: mixing the raw material with a ternary eutectic solvent and reacting; cooling to room temperature after the reaction is complete to obtain the reaction product; adding anhydrous ethanol to the reaction product and stirring; washing with ethanol; filtering; concentrating; adding water; allowing to stand to obtain a precipitate containing lignin; filtering; and drying to obtain lignin. This method does not mention the subsequent utilization of the three lignins and does not meet the expectations of the art.

[0005] Chinese invention (CN113956299A) discloses a method for pretreating graded lignin from eucalyptus wood and co-producing furfural using a two-phase system based on DES. The method involves mixing raw materials, DES, an organic solvent, and a catalyst in a reactor for reaction. After the reaction, the mixture is cooled to obtain a solvent and extract containing furfural. The eutectic reaction mixture is then washed and dried with acetone / water solution to obtain lignin. While this invention achieves the co-production of furfural and lignin, it requires the addition of a catalyst during the reaction process, and the separation steps are cumbersome and do not conform to economic and environmental principles.

[0006] Chinese invention (CN106495132A) discloses a method for preparing graphene from lignin. First, lignin raw materials are purified using a special enzyme treatment to obtain high-purity lignin. Then, high-quality graphene is obtained through processes such as oxidation, carbonization, and graphitization. However, this method involves cumbersome steps in lignin purification and is prone to side reactions such as decomposition, dehydration, and esterification during the purification process. Summary of the Invention

[0007] Technical Problems Solved: Given that existing technologies fail to achieve full utilization of agricultural residues, produce relatively simple products, have low added value, and are environmentally unfriendly, and that the stubbornness of lignin-carbohydrate complex (LCC) bonds during biomass decomposition makes the separation of the three major lignins difficult, this invention provides a method for high-value utilization of agricultural residues using a ternary deep eutectic solvent system. This method effectively separates the three major lignins, while simultaneously converting hemicellulose into furfural, a high-value platform chemical, enhancing the enzymatic hydrolysis efficiency of cellulose. The extracted lignin is then mixed with iron salts and pyrolyzed to prepare a lignin-based graphitized carbon catalyst, thus achieving high-value utilization of agricultural waste.

[0008] Technical solution: A method for high-value utilization of agricultural waste using a ternary deep eutectic solvent system, comprising the following steps: (1) mixing two hydrogen bond donors and hydrogen bond acceptors, heating and stirring to obtain a ternary deep eutectic solvent; the hydrogen bond acceptor is choline chloride, and the two hydrogen bond donors are p-toluenesulfonic acid and ethylene glycol, respectively, wherein the molar ratio of choline chloride, p-toluenesulfonic acid, and ethylene glycol is 1:1:0.2-0.5; (2) mixing agricultural waste powder, ternary deep eutectic solvent, water, and organic solvent, wherein the mass ratio of agricultural waste powder to ternary deep eutectic solvent is 1:(10-100), reacting at 80℃-120℃ for 0.5h-2h; 3) After the reaction is completed, the reactor is cooled to room temperature, the reaction phase and the extraction phase are collected, and furfural is prepared; (4) Acetone and water are added to the solid-liquid mixture in step (3) for washing, the ratio of acetone to water is (1-4):1, and the filtrate is collected; (5) The filtrate is placed in an oil bath, the acetone is evaporated, deionized water is added for washing, and the mixture is filtered and dried to obtain lignin; (6) The solid obtained after filtration in step (4) is washed with deionized water and dried to obtain cellulose; (7) The extracted lignin is mixed and stirred with iron salt, the mass ratio of lignin to iron salt is 1:(0.2-2), the water is evaporated and then calcined at high temperature to obtain lignin-based graphitized carbon-based catalyst.

[0009] Preferably, in step (1): p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.3.

[0010] Preferably, in step (2): the agricultural waste is wheat straw or corn straw with a particle size of 40-400 mesh.

[0011] Preferably, in step (2): the organic solvent is methyl isobutyl ketone, the target reaction temperature is 100°C, and the reaction time is 1 hour.

[0012] Preferably, in step (4), the ratio of acetone to water is 1:1.

[0013] Preferably, in step (7): the iron salt is ferric acetate.

[0014] Preferably, in step (7): the high-temperature calcination is carried out at a temperature of 600 to 1000°C.

[0015] Preferably, in step (7), the mass ratio of lignin to iron salt is 1:0.2.

[0016] Beneficial effects: (1) Compared with other traditional pretreatment methods or binary eutectic solvents, this invention can improve the utilization and extraction rate of the three major elements when treating straw, and at the same time, it can convert hemicellulose into high-value platform chemicals. (2) The lignin obtained by the extraction method of this invention can be combined with iron salts to obtain lignin-based graphitized carbon-based catalysts through carbonization, graphitization and other processes, exhibiting advanced oxidation technology. (3) Existing binary eutectic solvent treatment technology has only one hydrogen bond donor, which is insufficient to occupy all sites of hydrogen bond acceptors, resulting in weak hydrogen bond formation and low solubility of lignin and hemicellulose when separating and utilizing the three major elements. After treating straw with ternary eutectic solvent, this invention can not only enhance the solubility and utilization rate of lignin and hemicellulose, but also retain relatively intact cellulose and enhance the enzymatic hydrolysis efficiency of cellulose. (4) Compared with traditional organic solvent and inorganic acid and alkali treatment methods, the extraction method used in this invention has less environmental damage, lower cost and higher economic benefits, which is in line with the green and environmentally friendly development concept. Attached Figure Description

[0017] Figure 1 The XRD pattern of the lignin-based graphitized carbon catalyst prepared in this invention;

[0018] Figure 2 The reaction results of the lignin-based graphitized carbon catalyst prepared in this invention degrading tetracycline in wastewater via the Fenton reaction;

[0019] Figure 3 This invention illustrates the effect of the extraction method used on the crystallinity of cellulose. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0021] Example 1

[0022] (1) Preparation of deep eutectic solvent

[0023] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.3 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0024] (2) Lignocellulose pretreatment and furfural testing

[0025] Straw was sieved through a 40-mesh sieve and then dried in an oven at 60°C to constant weight. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:10 and heated at 100°C for 1 hour. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 69.43%.

[0026] (3) Extraction and purification of lignin and cellulose

[0027] Add 80 mL of a mixture of acetone and water (1:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water, then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0028] (4) Preparation of lignin-based graphitized carbon catalysts

[0029] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80 °C, and the mixture was then dried in an oven. The mass ratio of ferric acetate to lignin was 1:0.2. The mixture was calcined at 1000 °C for 1 hour at a rate of 2 °C / min to obtain a lignin-based catalyst.

[0030] Example 2

[0031] (1) Preparation of deep eutectic solvent

[0032] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.6 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0033] (2) Lignocellulose pretreatment

[0034] Straw was sieved through an 80-mesh sieve and then dried in an oven at 60°C to constant weight. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:20, and heated at 100°C for 1 hour. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 57.45%.

[0035] (3) Extraction and purification of lignin and cellulose

[0036] Add 80 mL of a mixture of acetone and water (2:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water, then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0037] (4) Preparation of lignin-based graphitized carbon catalysts

[0038] Ferric oxalate was dissolved in 50 mL of water and stirred until dissolved. Extractive lignin was added, and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80°C, and the mixture was then dried in an oven. The mass ratio of ferric oxalate to lignin was 1:0.5. The mixture was calcined at 900°C for 2 hours at a rate of 2°C / min to obtain a lignin-based catalyst.

[0039] Example 3

[0040] (1) Preparation of deep eutectic solvent

[0041] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:1 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0042] (2) Lignocellulose pretreatment

[0043] Straw was sieved through a 120-mesh sieve and then dried in an oven at 60°C to constant weight. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor and mixed at a solid-liquid ratio of 1:40. The mixture was heated at 100°C for 1 hour. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 58.79%.

[0044] (3) Extraction and purification of lignin and cellulose

[0045] Add 80 mL of a mixture of acetone and water (3:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water, then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0046] (4) Preparation of lignin-based graphitized carbon catalysts

[0047] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80°C, and the mixture was then dried in an oven. The mass ratio of ferric nitrate to lignin was 1:1.5. The mixture was then calcined at 800°C for 2 hours at a rate of 2°C / min to obtain a lignin-based catalyst.

[0048] Example 4

[0049] (1) Preparation of deep eutectic solvent

[0050] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.3 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0051] (2) Lignocellulose pretreatment

[0052] Straw was sieved through a 200-mesh sieve and then dried in an oven at 60°C to constant weight. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:100, and heated at 120°C for 0.5 hours. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 57.47%.

[0053] (3) Extraction and purification of lignin and cellulose

[0054] Add 80 mL of a mixture of acetone and water (4:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water and then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0055] (4) Preparation of lignin-based graphitized carbon catalysts

[0056] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80 °C, and the mixture was then dried in an oven. The mass ratio of ferric nitrate to lignin was 1:1. The mixture was calcined at 1000 °C for 2 hours at a rate of 2 °C / min to obtain a lignin-based catalyst.

[0057] Example 5

[0058] (1) Preparation of deep eutectic solvent

[0059] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.3 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0060] (2) Lignocellulose pretreatment

[0061] Straw was sieved through a 200-mesh sieve and then dried in an oven at 60°C to constant weight. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:80, and heated at 100°C for 1.5 hours. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 47.47%.

[0062] (3) Extraction and purification of lignin and cellulose

[0063] Add 80 mL of a mixture of acetone and water (4:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water and then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0064] (4) Preparation of lignin-based graphitized carbon catalysts

[0065] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80 °C, and the mixture was then dried in an oven. The mass ratio of ferric nitrate to lignin was 1:2. The mixture was calcined at 1000 °C for 3 hours at a rate of 2 °C / min to obtain a lignin-based catalyst.

[0066] Example 6

[0067] (1) Preparation of deep eutectic solvent

[0068] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.3 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0069] (2) Lignocellulose pretreatment

[0070] Straw was sieved through a 200-mesh sieve and then dried to constant weight in an oven at 60°C. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:80, and heated at 100°C for 0.5 h. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 62.93%.

[0071] (3) Extraction and purification of lignin and cellulose

[0072] Add 80 mL of a mixture of acetone and water (4:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water and then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0073] (4) Preparation of lignin-based graphitized carbon catalysts

[0074] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80 °C, and the mixture was then dried in an oven. The mass ratio of ferric nitrate to lignin was 1:1. The mixture was calcined at 1000 °C for 1 hour at a rate of 2 °C / min to obtain a lignin-based catalyst.

[0075] Example 7

[0076] (1) Preparation of deep eutectic solvent

[0077] Dry p-toluenesulfonic acid, choline chloride, and ethylene glycol are mixed in a molar ratio of 1:1:0.1 and heated and stirred at 80°C for 1 hour until all solids dissolve into a clear and transparent solution.

[0078] (2) Lignocellulose pretreatment

[0079] Straw was sieved through a 200-mesh sieve and then dried to constant weight in an oven at 60°C. The dried straw powder, methyl isobutyl ketone, water, and a deep eutectic solvent were added to a reactor at a solid-liquid ratio of 1:60, and heated at 100°C for 1 hour. After the reaction was complete, the reactants were cooled to room temperature and mixed with deionized water. The reactants were then subjected to vacuum filtration to separate the solid residue and the pretreated liquid. The furfural yield was determined to be 65.13%.

[0080] (3) Extraction and purification of lignin and cellulose

[0081] Add 80 mL of a mixture of acetone and water (4:1 volume ratio) to the solid residue, stir well, and filter under reduced pressure. Repeat this process three times. Wash the filtered cellulose solid three times with deionized water and then dry it in an 80°C oven. Combine the filtrates from the three filtrations and place them in an 80°C oil bath to evaporate the acetone. Add 200 mL of deionized water to the filtrate, place it in a magnetic stirrer, stir for 2 hours, and filter under reduced pressure. Repeat this process three times until neutral. Place the extracted lignin in an 80°C oven until constant weight is achieved.

[0082] (4) Preparation of lignin-based graphitized carbon catalysts

[0083] Ferric nitrate was dissolved in 50 mL of water and stirred until dissolved. Lignin was added and the mixture was soaked for 12 hours. The water was evaporated in an oil bath at 80°C, and the mixture was then dried in an oven. The mass ratio of ferric nitrate to lignin was 1:1. The mixture was calcined at 900°C for 2 hours at a rate of 2°C / min to obtain a lignin-based catalyst.

[0084] Performance testing

[0085] Furfural prepared under different molar ratios of ternary eutectic solvents and different experimental conditions of temperature and time was tested by HPLC. The test results are shown in Table 1. As can be seen from Table 1, hemicellulose can be converted into furfural with relatively high efficiency, and the highest furfural yield can reach 69.43%.

[0086] Table 1. Furfural yield from wheat straw treated with ternary eutectic solvent

[0087]

[0088] The prepared lignin-based graphitized carbon catalyst was subjected to XRD analysis, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the diffraction peak at 43.74° belongs to Fe3C (JCPDS:35–0772), and the presence of Fe3C also proves that the iron salt is reduced during the carbothermic reduction process; the diffraction peaks at 44.64° and 65° are attributed to α-Fe (JCPDS:06-0696).

[0089] The Fenton reaction performance of the prepared graphitized carbon material was tested. The test method was as follows: 6 mg of tetracycline was dissolved in 100 mL of water, and an appropriate amount of HCl solution was added to adjust the pH to approximately 3. An initial sample was taken. 10 mg of catalyst was added, and the mixture was stirred for 1 h, with samples taken every 30 min. The time of adding 20 μL of H₂O₂ was used as the timer origin, and samples were taken every 5 min using a syringe. The absorbance of TC was then measured at a maximum wavelength of 357 nm using a UV-Vis spectrophotometer. The test results are as follows. Figure 2 As shown, by Figure 2 It can be seen that the degradation rate can reach 88.4% in a relatively short time, which strongly proves that the catalyst has a high oxidation technology.

[0090] XRD tests were performed on the pretreated cellulose, and the results are as follows: Figure 3 As shown, by Figure 3 It can be seen that the crystallinity of cellulose significantly increased after treatment with a ternary deep eutectic solvent, which clearly demonstrates the ability of DES to remove lignin while preserving a fairly complete cellulose structure. Furthermore, the crystallinity of cellulose materials is an important criterion for evaluating the suitability of cellulose for enzymatic hydrolysis; increased crystallinity indicates increased enzymatic hydrolysis efficiency.

[0091] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for high-value utilization of agricultural residues using a ternary deep eutectic solvent system, characterized in that, The process includes the following steps: (1) mixing two hydrogen bond donors with a hydrogen bond acceptor, heating and stirring to obtain a ternary eutectic solvent; the hydrogen bond acceptor is choline chloride, and the two hydrogen bond donors are p-toluenesulfonic acid and ethylene glycol, respectively, with a molar ratio of choline chloride, p-toluenesulfonic acid, and ethylene glycol of 1:1:0.3; (2) mixing agricultural waste powder, the ternary eutectic solvent, water, and an organic solvent, with a mass ratio of agricultural waste powder to the ternary eutectic solvent of 1:(10~100), reacting at 100°C for 1 hour; the agricultural waste is wheat straw or corn straw with a particle size of 40-400 mesh; the organic solvent is methyl isobutyl ketone; (3) after the reaction is completed, cooling the reactor to... At room temperature, add deionized water and mix; filter the reactants under reduced pressure to separate the solid residue and pretreatment liquid to prepare furfural; (4) add acetone and water to the solid residue in step (3) for washing, the ratio of acetone to water is 1:1, and collect the filtrate; (5) put the filtrate into an oil bath, evaporate the acetone, add deionized water for washing, filter and dry to obtain lignin; (6) wash the solid obtained after filtration in step (4) with deionized water and dry to obtain cellulose; (7) mix the extracted lignin with iron salt, the mass ratio of lignin to iron salt is 1:0.2, the iron salt is ferric acetate, evaporate the water and calcine at 600-1000℃ to obtain lignin-based graphitized carbon-based catalyst.

Images