Method for extracting light-color lignin by using ternary eutectic solvent

Abstract

The invention provides a method for extracting light-color lignin with a ternary eutectic solvent, and belongs to the technical field of lignin separation and high-valued utilization thereof.The method comprises the steps that hydrogen bond donors (ethylene glycol and maleic acid) and hydrogen bond acceptors are mixed and heated to form transparent and uniform liquid, and the ternary eutectic solvent is obtained; lignin raw materials and the prepared ternary eutectic solvent are mixed and react, then light-color lignin is extracted, and meanwhile the lignin extraction rate is increased. According to the method, the molar ratio of the hydrogen bond acceptor to the ethylene glycol to the maleic acid is 1: (0.5-9): (0.2-8), the extracted lignin is light in color, the application potential of the lignin in the fields of cosmetics, ultraviolet light absorbers and the like is effectively expanded, and the method is easy to operate and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of lignin separation and high-value utilization thereof, and more specifically, the present invention relates to a method for extracting light-colored lignin using a ternary low eutectic solvent. Background Art

[0002] With the rapid advancement of industrialization and globalization, the excessive use of fossil fuels has not only caused energy shortages, but also caused significant damage to the ecosystem. Faced with the dual pressures of resource depletion and ecological deterioration, the development of sustainable renewable resources has become particularly urgent. Lignin is the second largest natural polymer material in nature after cellulose and is widely present in plant cells. my country is rich in forestry resources. Due to the rapid development of the forestry industry and the continuous advancement of wood processing technology, the utilization rate of wood has been significantly improved. However, most pine, poplar and eucalyptus trees in rural areas are still randomly piled up during the felling season. Not only does it occupy precious land resources, it may also cause safety hazards such as pests and diseases and fires. In addition, it will also cause a series of environmental problems such as environmental damage, reduced biodiversity and loss of soil nutrients. The random stacking of pine, poplar and eucalyptus also leads to the waste of biological resources, destroys the microbial ecology in the forest, and affects the circulation of soil nutrients and the physical and chemical properties of the soil. The lignocellulose of pine, poplar and eucalyptus is mainly composed of three parts: cellulose content is between 35% and 45%, hemicellulose content is between 20% and 40%, and lignin content is between 15% and 30%. In order to improve the economic value of pine, poplar and eucalyptus lignocellulose, a variety of bio-based materials and chemicals can be produced by enzymatic hydrolysis and fermentation of cellulose; hemicellulose can be converted into biochemicals such as furfural and furfuryl alcohol; lignin can be converted into aromatic compounds and lignin-based materials. In order to maximize the economic value of these components, the key is to find an efficient method to separate lignin. As a natural antioxidant active substance, lignin has broad application prospects in the fields of food industry, cosmetics, health care products, etc. In addition, the rational processing and conversion of lignin can obtain many types of fuels, chemicals and materials, which is the prerequisite for its high-value utilization.

[0003] The extraction of pine, poplar and eucalyptus lignin is mainly carried out through traditional solvents such as dilute acid, alkaline solvents and organic solvents. Although these solvents can effectively dissolve lignin, their extraction process is complicated and has disadvantages such as equipment corrosion, volatility and high toxicity, all of which may reduce commercial profitability. As a green and efficient pretreatment method, deep eutectic solvents have attracted widespread attention. Deep eutectic solvents have the characteristics of biocompatibility, biodegradability, low cost and environmental protection, which greatly promote their application in biomass pretreatment. Deep eutectic solvents are eutectic mixtures composed of at least one hydrogen bond donor and one hydrogen bond acceptor, usually transparent liquids, characterized by a low freezing point under mild conditions. According to different hydrogen bond donors, deep eutectic solvents can be divided into acid-based deep eutectic solvents and alcohol-based deep eutectic solvents. Acid-based deep eutectic solvents catalyze the cleavage of β-O-4 bonds in lignin model compounds through their acidic components, resulting in the depolymerization of lignin. However, this type of deep eutectic solvent may cause condensation reaction of lignin to form CC bonds during treatment, thus affecting the further utilization of lignin. In contrast, alcohol-based low eutectic solvents stabilize the reaction intermediates by capturing unstable C2-aldehydes produced by acid-catalyzed cracking to form C2-acetals, thereby inhibiting the condensation reaction of lignin. This type of low eutectic solvent usually does not change the chemical structure of lignin and maintains the original properties of lignin. The prior art discloses a method for clean separation of the main components of wood fiber, using acid, alcohol and hydrogen bond acceptors to prepare a ternary low eutectic solvent. The extraction rate of lignin is 50-65%, which is relatively low, and no further research has been conducted on the color of lignin and its expanded applications.

[0004] The dark color of lignin limits its application in high-value fields, so the extraction of light-colored lignin from wood cellulose has important research and application value. Due to its good optical properties and low molecular weight, light-colored lignin shows potential for application in cosmetics, ultraviolet absorbers and other fields. The light-colored lignin extracted by ternary low eutectic solvents not only expands the application range of lignin, but also helps to improve the market competitiveness of related products.

[0005] The prior art discloses a method for reducing the color of lignin by combining an acidic low eutectic solvent with a monohydric alcohol, wherein an acidic low eutectic solvent and a monohydric alcohol are mixed, wherein the hydrogen bond acceptor is at least one of benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and choline chloride, and the hydrogen bond donor is at least one of formic acid, acetic acid, and lactic acid. Although the extraction of light-colored lignin is achieved, the type of hydrogen bond donor used will cause a condensation reaction of the lignin, and the extraction rate is significantly reduced.

[0006] Therefore, developing a method for extracting light-colored lignin with a ternary low eutectic solvent can not only improve the extraction rate of lignin, but also extract lignin as light-colored, thereby expanding the application of lignin in high value-added fields, which is of great significance for promoting the sustainable utilization of lignin resources and the development of biorefining technology. Summary of the invention

[0007] The present invention aims to overcome the deficiencies of the prior art and provide a method for extracting light-colored lignin using a ternary low eutectic solvent, thereby improving the extraction efficiency of lignin and making the extracted lignin light-colored.

[0008] Therefore, the object of the present invention is to provide a method for extracting light-colored lignin using a ternary deep eutectic solvent.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention protects a method for extracting light-colored lignin with a ternary deep eutectic solvent, comprising the following steps:

[0011] S1. mixing two hydrogen bond donors and a hydrogen bond acceptor, heating and mixing to form a transparent uniform liquid, and obtaining a ternary deep eutectic solvent;

[0012] S2. mixing the lignin raw material with the ternary deep eutectic solvent prepared in S1 for reaction;

[0013] S3. adding anhydrous ethanol to the solid-liquid mixture obtained in S2, stirring, filtering to obtain a filtrate, and precipitating and separating to obtain lignin;

[0014] Wherein, the two hydrogen bond donors are ethylene glycol and maleic acid;

[0015] The molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid is 1:0.5-9:0.2-8;

[0016] The reaction temperature in step S2 is 80-150°C;

[0017] The reaction time in step S2 is 0.5 to 6 hours.

[0018] The present invention provides a method for extracting light-colored lignin using a ternary low eutectic solvent. On the one hand, the extracted lignin is light-colored, effectively expanding the application of lignin in high value-added fields. On the other hand, compared with traditional dibasic acid-based low eutectic solvents, the condensation of lignin during the reaction is effectively avoided, and the extraction rate of lignin is improved. The method is simple to operate, and the entire extraction process is environmentally friendly.

[0019] Improving the extraction efficiency of lignin is closely related to the selected low eutectic solvent. Different low eutectic solvents show different abilities in dissolving lignin, resulting in significant differences in extraction rates. Maleic acid not only has good solubility and biodegradability, but also provides good solubility performance when used as a component of the low eutectic solvent, which has positive significance for environmental protection and sustainable development. It also has good acidity and reactivity, and can undergo a variety of chemical reactions with other components to form specific energy-supplying derivatives. At the same time, the addition of maleic acid is conducive to promoting the dissolution of lignin and protecting the structure of lignin. Maleic acid with weaker acidity can extract lignin with a lower degree of polymerization and a higher degree of carboxylation. At the same time, ethylene glycol is added as another hydrogen bond donor to avoid lignin condensation during the reaction and improve the extraction rate of lignin.

[0020] In the process of extracting lignin with a low eutectic solvent, ethylene glycol and maleic acid help to extract light-colored lignin and improve the yield of lignin by enhancing solubility, synergistic effects, protecting lignin benzyl groups, and preventing lignin polycondensation. For example, Chen et al. (Science Advances, 2017.) found that maleic acid-based hydrotrope polyacids not only have acid catalysis capabilities, but also assist in dissolving lignin; Cai et al. (Green Chemistry, 2020.) proposed that the light-colored characteristics of lignin can be effectively maintained by converting the hydroxyl group at the cγ position in the lignin molecule into a carboxylic acid group.

[0021] If the content of maleic acid in the molar ratio of hydrogen bond acceptor, ethylene glycol and maleic acid is much greater than that of ethylene glycol, the viscosity of the synthesized ternary deep eutectic solvent will be too high and the color of the extracted lignin will be too dark. On the contrary, if the content of maleic acid is much less than that of ethylene glycol, the extraction rate of lignin will be too low.

[0022] The inventors found that the extraction rate of lignin can be further improved by performing the reaction of extracting lignin at a certain temperature and time. Because if the reaction temperature is too low or the reaction time is too short, the extraction efficiency of lignin will be unsatisfactory. On the contrary, if the reaction temperature is too high or the time is too long, it will not only increase energy consumption, but also may cause excessive loss of other components in the lignin raw material, while the extraction efficiency of lignin will be limited, and the whiteness of the extracted lignin will decrease, making it difficult to extract light-colored lignin.

[0023] Preferably, the hydrogen bond acceptor is one of choline chloride, betaine or menthol.

[0024] More preferably, the hydrogen bond acceptor is choline chloride.

[0025] Preferably, in step S1, the molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid is 1:2-5:2-6.

[0026] More preferably, the molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid in step S1 is 1:3:0.2-4.

[0027] Preferably, the heating temperature in step S1 is 120°C to 130°C.

[0028] Preferably, the lignin raw material in step S2 is at least one of poplar wood powder, pine wood powder or eucalyptus wood powder.

[0029] Preferably, the reaction temperature in step S2 is 100-130°C.

[0030] Preferably, the reaction time in step S2 is 1 to 3 hours.

[0031] Preferably, in step S2, the mass ratio of the lignin raw material to the ternary deep eutectic solvent is 1:5 to 1:20.

[0032] More preferably, the mass ratio of the lignin raw material to the ternary deep eutectic solvent in step S2 is 1:10 to 1:15.

[0033] The inventors have observed that if the mass ratio of solid to liquid is too high, the solid will not be completely dissolved in the deep eutectic solvent, which will reduce the extraction efficiency of lignin. On the contrary, if the mass ratio of solid to liquid is too low, the solubility of the deep eutectic solvent for lignin will become a limiting factor. Once the solubility of the deep eutectic solvent for lignin reaches the upper limit, further increasing the amount of the deep eutectic solvent will not only fail to improve the extraction rate of lignin, but also lead to unnecessary consumption of deep eutectic solvent resources.

[0034] Preferably, the specific steps of the precipitation in step S3 are: adding deionized water to the solid-liquid mixture for precipitation.

[0035] Preferably, the amount of deionized water added is 5 to 15 times the volume of the filtrate.

[0036] Specifically, the specific steps of step S3 include:

[0037] Anhydrous ethanol is added to the solid-liquid mixture of S2 and stirred, and then filtered to obtain a filtrate containing lignin. Water is added to the filtrate for precipitation, and lignin is obtained after centrifugal drying.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The invention provides a method for extracting light-colored lignin by using a ternary deep eutectic solvent. The ternary deep eutectic solvent is synthesized by using ethylene glycol, maleic acid and a hydrogen bond acceptor. The extracted lignin is light-colored and has a whiteness value of more than 53. The application of lignin in high value-added fields can be expanded and the extraction efficiency of lignin can be improved. The lignin extraction rate reaches more than 50%, which is of great significance for promoting the sustainable utilization of lignin resources and the development of biorefining technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the process flow chart of lignin extraction.

[0041] Figure 2 This is the infrared spectrum of the lignin extracted in Example 1.

[0042] Figure 3 The actual pictures of the extracted lignin are, from left to right, the lignin extracted in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 respectively. DETAILED DESCRIPTION

[0043] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0044] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0045] Test indicators and methods of embodiments and comparative examples:

[0046] (1) Lignin extraction rate: This method follows the standards of the National Renewable Energy Laboratory (NREL) of the United States and uses a two-step acid hydrolysis technique to estimate the weight of lignin. The specific steps are as follows:

[0047] Lignin extraction rate = 100% × (m1-m2) / m1;

[0048] Where: m1 is the mass of lignin in the original samples of pine, poplar and eucalyptus (g);

[0049] m2 is the mass (g) of lignin remaining in the residue obtained after pretreatment with the deep eutectic solvent.

[0050] (2) Whiteness of lignin

[0051] The lignin value was tested using a spectrophotometer (data color 200 SCI model).

[0052] Example 1 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0053] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0054] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

[0055] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0056] Example 2 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0057] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:0.5:0.2, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0058] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0059] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0060] Example 3 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0061] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:2:6, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0062] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0063] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0064] Example 4 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0065] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:5:2, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0066] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0067] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0068] Example 5 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0069] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:5:8, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0070] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0071] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0072] Example 6 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0073] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:9:7, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0074] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0075] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0076] Example 7 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0077] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0078] S2. Eucalyptus powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:20, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0079] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0080] Example 8 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0081] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0082] S2. Pine wood powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:5, the reaction temperature is set to 130°C, the reaction time is set to 2h, and a solid-liquid mixture is obtained after the reaction is completed.

[0083] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0084] Example 9 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0085] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0086] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 80°C, the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

[0087] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain the filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0088] Example 10 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0089] S1. Choline chloride, butanediol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0090] S2. Eucalyptus powder and the low eutectic solvent in S1 are added into the reactor in a mass ratio of 1:15, the reaction temperature is set to 150°C, the reaction time is set to 0.5h, and a solid-liquid mixture is obtained after the reaction is completed.

[0091] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0092] Example 11 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0093] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0094] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 0.5h, and obtain a solid-liquid mixture after the reaction is completed.

[0095] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0096] Example 12 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0097] S1. Choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0098] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 6 hours, and obtain a solid-liquid mixture after the reaction is completed.

[0099] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain a filtrate, add water to precipitate lignin, and obtain lignin after centrifugation and freeze-drying.

[0100] Table 1 Test results of lignin extraction by the methods of Examples 1 to 10

[0101]

[0102]

[0103] Comparative Example 1 A method for extracting light-colored lignin using a ternary deep eutectic solvent

[0104] S1. Mix choline chloride, glycerol and maleic acid in a molar ratio of 1:3:4, mix at 130° C., and heat and stir until a uniform, transparent and clear low eutectic solvent is formed.

[0105] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

[0106] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain the filtrate, add water to precipitate lignin, centrifuge and freeze-dry to obtain lignin, with an extraction rate of 35% and a whiteness value of 35.4.

[0107] Comparative Example 2 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0108] S1. Choline chloride, ethylene glycol and p-hydroxybenzenesulfonic acid are mixed in a molar ratio of 1:3:4, and the mixture is mixed and heated and stirred at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0109] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

[0110] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain the filtrate, add water to precipitate lignin, centrifuge and freeze-dry to obtain lignin, with an extraction rate of 31% and a whiteness value of 40.2.

[0111] Comparative Example 3 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0112] S1. Mix choline chloride, isopropanol and formic acid in a molar ratio of 1:3:4, mix and heat and stir at 130° C. to form a uniform, transparent and clear low eutectic solvent.

[0113] S2. Add poplar wood powder and the low eutectic solvent in S1 into the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

[0114] S3. Add 45 ml of anhydrous ethanol to the solid-liquid mixture in S2 and stir, then filter to obtain the filtrate, add water to precipitate lignin, centrifuge and freeze-dry to obtain lignin, with an extraction rate of 23% and a whiteness value of 32.6.

[0115] Comparative Example 4 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0116] The experimental method is the same as that of Example 1, except that choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:10:9, the extraction rate is 20%, and the whiteness value is 39.5.

[0117] Comparative Example 5 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0118] The experimental method is the same as that of Example 1, except that choline chloride, ethylene glycol and maleic acid are mixed in a molar ratio of 1:0.1:0.1, the extraction rate is 9%, and the whiteness value is 46.7.

[0119] Comparative Example 6 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0120] The experimental method is the same as that of Example 1, except that in step S2, the reaction temperature is 70° C., the extraction rate is 35%, and the whiteness value is 60.3.

[0121] Comparative Example 7 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0122] The experimental method is the same as that in Example 1, except that the reaction temperature in step S2 is 160° C., the extraction rate is 72%, and the whiteness value is 45.1.

[0123] Comparative Example 8 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0124] The experimental method is the same as that in Example 1, except that the reaction time in step S2 is 20 min, the extraction rate is 10%, and the whiteness value is 53.4.

[0125] Comparative Example 9 A method for extracting light-colored lignin using a ternary low eutectic solvent

[0126] The experimental method is the same as that in Example 1, except that the reaction time in step S2 is 7 hours, the extraction rate is 73%, and the whiteness value is 40.6.

[0127] According to Table 1, the whiteness values ​​of the lignin extracted by the method of extracting light-colored lignin with a ternary low eutectic solvent in Examples 1 to 12 are all above 53, and the extraction rate is above 50%, which not only meets the light color requirements of lignin, effectively expands the application of lignin in high value-added fields, but also effectively avoids the condensation of lignin during the reaction and improves the extraction rate of lignin.

[0128] In Comparative Example 1, glycerol is used instead of ethylene glycol, and the whiteness of the lignin is greatly reduced, showing a dark brown color, and the extraction rate is 45%; in Comparative Example 2, p-hydroxybenzenesulfonic acid is used instead of maleic acid, and the extraction rate of lignin is higher, but the whiteness is poor; in Comparative Example 3, isopropanol and formic acid are used as two hydrogen bond donors, and the extracted lignin is light-colored, but the extraction rate is significantly reduced. The above shows that the use of ethylene glycol and maleic acid in combination in the present invention can simultaneously achieve light-colored lignin and a higher extraction rate. In Comparative Example 4, the molar ratio of choline chloride, ethylene glycol, and maleic acid is set, and the amount of ethylene glycol and maleic acid added exceeds the range, and the extraction rate decreases significantly. In Comparative Example 5, the amount of ethylene glycol and maleic acid is too small, and the extraction rate and whiteness are significantly decreased; in Comparative Example 6, the reaction temperature is less than the set range, and the extraction rate decreases significantly; in Comparative Example 7, the reaction temperature is greater than the set range, and the extraction rate increases to a certain extent, but the whiteness value decreases significantly, and the whiteness is not good while the extraction rate is high; in Comparative Example 8, the reaction time is too short, the ternary low eutectic solvent is not fully extracted, and the extraction rate is too low to meet the needs; in Comparative Example 9, the reaction time is too long, exceeding the range, the extraction rate increases, but the whiteness decreases.

[0129] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions 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.

Claims

1. A method for extracting light-colored lignin using a ternary deep eutectic solvent, characterized in that: The following steps are involved: S1. mixing two hydrogen bond donors and a hydrogen bond acceptor, heating and mixing to form a transparent uniform liquid, and obtaining a ternary deep eutectic solvent; S2. mixing the lignin raw material with the ternary deep eutectic solvent prepared in S1 for reaction; S3. adding anhydrous ethanol to the solid-liquid mixture obtained in S2, stirring, filtering to obtain a filtrate, and precipitating and separating to obtain lignin; Wherein, the two hydrogen bond donors are ethylene glycol and maleic acid; The molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid is 1:0.5-9:0.2-8; The reaction temperature in step S2 is 80-150°C; The reaction time in step S2 is 0.5 to 6 hours.

2. The method according to claim 1, characterized in that The hydrogen bond acceptor is one of choline chloride, betaine or menthol.

3. The method according to claim 1, characterized in that The molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid in step S1 is 1:2-5:2-6.

4. The method according to claim 1, characterized in that: The molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid in step S1 is 1:3:0.2-4.

5. The method according to claim 1, characterized in that The heating temperature in step S1 is 120°C to 130°C.

6. The method according to claim 1, characterized in that The reaction temperature in step S2 is 100-130°C.

7. The method according to claim 1, characterized in that The reaction time in step S2 is 1 to 3 hours.

8. The method according to claim 1, characterized in that The mass ratio of the lignin raw material to the ternary deep eutectic solvent in step S2 is 1:5 to 1:

20.

9. The method according to claim 1, characterized in that: The specific steps of the precipitation in step S3 are: adding deionized water to the solid-liquid mixture for precipitation.

10. The method according to claim 9, characterized in that The amount of deionized water added is 5 to 15 times the volume of the filtrate.

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