Method for extracting light lignin by using ternary eutectic solvent

Abstract

The application provides a method for extracting light-colored lignin by using a ternary eutectic solvent, and belongs to the technical field of lignin separation and high-value utilization. A hydrogen bond donor (ethylene glycol and maleic acid) and a hydrogen bond acceptor are mixed and heated to form a transparent and uniform liquid, thereby obtaining a ternary eutectic solvent. After lignin raw materials are mixed with the obtained ternary eutectic solvent and reacted, light-colored lignin is extracted, and the lignin extraction rate is improved. In the method, the molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid is 1:0.5-9:0.2-8. The extracted lignin is light-colored, which effectively expands the application potential of lignin in the fields of cosmetics, ultraviolet absorbers and the like. Moreover, the method is simple to operate and friendly to the environment.

Description

TECHNICAL FIELD

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

[0002] With the rapid advancement of industrialization and globalization, the overuse of fossil fuels not only triggers energy shortage problems, but also causes significant damage to the ecological system. In the face of dual pressures of resource depletion and ecological deterioration, it is particularly urgent to develop sustainable renewable resources. Lignin is the second largest natural polymer material in nature after cellulose, and widely exists in plant cells. China is rich in forestry resources. Due to the rapid development of forestry industry and the continuous progress of wood processing technology, the utilization rate of wood has been significantly improved, but there is still a phenomenon of randomly piling up of pine, poplar and eucalyptus in rural areas during the logging season. Not only occupies valuable land resources, but also may cause safety hazards such as pests and fires. In addition, it will also cause a series of environmental problems such as environmental damage, reduction of biodiversity and loss of soil nutrients. The random piling up of pine, poplar and eucalyptus also leads to the waste of biological resources and destroys the microbial ecology in the forest, affecting 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 of 35% to 45%, hemicellulose content of 20% to 40%, and lignin content of 15% to 30%. In order to improve the economic value of pine, poplar and eucalyptus lignocellulose, cellulose can be enzymatically hydrolyzed and fermented to produce a variety of bio-based materials and chemicals; hemicellulose can be converted into furfural, furfuryl alcohol and other bio-chemicals; 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 wide application prospects in the fields of food industry, cosmetics, health care products and the like. In addition, the reasonable processing and conversion of lignin can obtain many types of fuels, chemicals and materials, which is the premise for realizing its high-value utilization.

[0003] Lignin from pine, poplar and eucalyptus is mainly extracted by traditional solvents such as dilute acid, alkali solvent and organic solvent. Although these solvents can effectively dissolve lignin, the extraction process is complex, and there are disadvantages such as equipment corrosion, easy evaporation and high toxicity, which may reduce commercial profitability. Deep eutectic solvent as a green and efficient pretreatment method has attracted widespread attention. Deep eutectic solvent has the characteristics of biocompatibility, biodegradability, low cost and environmental protection, which greatly promotes its application in biomass pretreatment. Deep eutectic solvent is a eutectic mixture composed of at least one hydrogen bond donor and one hydrogen bond acceptor, usually transparent liquid, and its feature is low freezing point under mild conditions. According to different hydrogen bond donors, deep eutectic solvent can be divided into acid-based deep eutectic solvent and alcohol-based deep eutectic solvent. Acid-based deep eutectic solvent catalyzes the cleavage of β-O-4 bond in lignin model compounds through its acidic component, resulting in depolymerization of lignin. However, this type of deep eutectic solvent may cause condensation reaction of lignin during the treatment process, forming C-C bond, thereby affecting the further utilization of lignin. In contrast, alcohol-based deep eutectic solvent stabilizes the reaction intermediates by capturing unstable C2-aldehyde produced by acid-catalyzed cleavage to form C2-acetals, thereby inhibiting the condensation reaction of lignin. This type of deep eutectic solvent usually does not change the chemical structure of lignin, maintaining the original characteristics of lignin. The prior art discloses a method for clean separation of main components of lignocellulose, which uses acid, alcohol and hydrogen bond acceptor to prepare ternary deep eutectic solvent, and the extraction rate of lignin is 50-65%, which is low, and the color of lignin and its expanded application are not further studied.

[0004] The dark color of lignin limits its application in high-value fields, so it is of important research and application value to extract light-colored lignin from lignocellulose. Light-colored lignin has application potential in the fields of cosmetics, ultraviolet absorbers and the like due to its good optical performance and low molecular weight. The light-colored lignin extracted by the ternary deep eutectic solvent not only improves 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 deep eutectic solvent with a monohydric alcohol, 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 use of hydrogen bond donors of different types may cause condensation reaction of lignin, resulting in a significant decrease in extraction rate.

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

[0007] The present application aims to overcome the deficiencies of the prior art, and provides a method for extracting light-colored lignin by using a ternary deep eutectic solvent, thereby improving the extraction efficiency of lignin and extracting light-colored lignin.

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

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] The present application protects a method for extracting light-colored lignin by using a ternary deep eutectic solvent, which comprises the following steps:

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

[0012] S2. Mixing lignin raw material with the ternary deep eutectic solvent prepared in S1 to react;

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

[0014] Among them, 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 temperature of the reaction in step S2 is 80-150 DEG C;

[0017] The reaction time in step S2 is 0.5-6h.

[0018] The present application provides a method for extracting light-colored lignin by using a ternary deep eutectic solvent, which can extract light-colored lignin, effectively expand the application of lignin in high-value-added fields, and effectively avoid the condensation of lignin during the reaction compared with traditional binary acid-based deep eutectic solvents, thereby improving the extraction rate of lignin, and the method is simple to operate and environmentally friendly during the entire extraction process.

[0019] The extraction efficiency of lignin is closely related to the selected deep eutectic solvent. Different deep eutectic solvents have different abilities to dissolve lignin, resulting in significant differences in extraction rates. Maleic acid not only has good solubility and biodegradability, but also provides good solubility when used as a component of a deep eutectic solvent, which is of positive significance to environmental protection and sustainable development. In addition, maleic acid has good acidity and reactivity, and can react with other components to form specific energy-providing derivatives. At the same time, the addition of maleic acid is beneficial to promote the dissolution of lignin and protect the structure of lignin. Maleic acid with weaker acidity can extract lignin with lower polymerization degree and higher carboxylation degree. At the same time, the addition of ethylene glycol as another hydrogen bond donor can avoid lignin condensation during the reaction and improve the extraction rate of lignin.

[0020] During the extraction of lignin by deep eutectic solvents, ethylene glycol and maleic acid can help extract light lignin and improve the yield of lignin through mechanisms such as enhancing solubility, synergistic effect, and protecting benzyl groups and preventing lignin condensation. For example, Chen et al. (Science Advances, 2017.) found that the Hydrotrope polyacid of maleic acid not only has acid catalytic ability, but also can assist in dissolving lignin; Cai et al. (Green Chemistry, 2020.) proposed that by converting the hydroxyl group at the cγ position of the lignin molecule into a carboxylic acid group, the light color characteristics of lignin can be effectively maintained.

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

[0022] The inventors found that the extraction rate of lignin can be further improved by carrying out the reaction 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 reaction time is too long, not only the energy consumption will be increased, but also other components in the lignin raw material will be excessively lost, the extraction efficiency of lignin will be limitedly improved, and the whiteness of the extracted lignin will be decreased, making it difficult to extract light 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, the molar ratio of the hydrogen bond acceptor, ethylene glycol and maleic acid in step S1 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 temperature of the heating in step S1 is 120-130°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 temperature of the reaction in step S2 is 100-130°C.

[0030] Preferably, the time of the reaction in step S2 is 1-3h.

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

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

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

[0034] Preferably, the precipitation in step S3 comprises adding deionized water to the solid-liquid mixture.

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

[0036] In particular, the specific steps of step S3 comprise:

[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 to precipitate, and the lignin is obtained after centrifugal drying.

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

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

[0040] Figure 1 It is a lignin extraction process flowchart.

[0041] Figure 2 It is an infrared spectrum of lignin extracted in Example 1.

[0042] Figure 3 It is a real object diagram of the extracted lignin, and from left to right, the lignin extracted in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 is respectively. DETAILED DESCRIPTION

[0043] In order to more clearly and completely describe the technical scheme of the application, the application will be further described in detail through specific examples below, and it should be understood that the specific examples described herein are only used to explain the application and are not used to limit the application, and various changes can be made within the scope of the application.

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

[0045] Test indexes and methods of examples and comparative examples:

[0046] (1) Lignin extraction rate: this method follows the standard of the United States National Renewable Energy Laboratory (NREL), and adopts a two-step acid hydrolysis technology to estimate the weight of lignin, and the specific steps are as follows:

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

[0048] Wherein: m1 is the mass (g) of lignin in the pine wood, poplar wood and eucalyptus wood as received;

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

[0050] (2) Whiteness of lignin

[0051] The value of lignin is tested by using a spectrophotometer (data color 200 SCI mode).

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

[0053] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:3:4, mix and heat stir at 130°C until a homogeneous, transparent and clear eutectic solvent is formed.

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

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

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

[0057] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:0.5:0.2, mix and heat stir at 130°C until a homogeneous, transparent and clear eutectic solvent is formed.

[0058] S2. Add pine powder and the eutectic solvent in S1 to the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, and the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

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

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

[0061] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:2:6, mix and heat stir at 130°C until a homogeneous, transparent and clear eutectic solvent is formed.

[0062] S2. Add pine powder and the eutectic solvent in S1 to the reactor in a mass ratio of 1:15, set the reaction temperature to 130°C, and the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

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

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

[0065] S1. Choline chloride, ethylene glycol, maleic acid were mixed in a molar ratio of 1:5:2, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

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

[0067] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

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

[0069] S1. Choline chloride, ethylene glycol, maleic acid were mixed in a molar ratio of 1:5:8, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

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

[0071] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

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

[0073] S1. Choline chloride, ethylene glycol, maleic acid were mixed in a molar ratio of 1:9:7, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

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

[0075] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

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

[0077] S1. Choline chloride, ethylene glycol, maleic acid were mixed in a molar ratio of 1:3:4, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

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

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

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

[0081] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:3:4, mix and heat stir at 130°C until a uniform, transparent and clear deep eutectic solvent is formed.

[0082] S2. Add pine powder and the deep eutectic solvent in S1 in a mass ratio of 1:5 into a reactor, set the reaction temperature to 130°C, and the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

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

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

[0085] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:3:4, mix and heat stir at 130°C until a uniform, transparent and clear deep eutectic solvent is formed.

[0086] S2. Add pine powder and the deep eutectic solvent in S1 in a mass ratio of 1:5 into a reactor, set the reaction temperature to 130°C, and the reaction time to 2h, and obtain a solid-liquid mixture after the reaction is completed.

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

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

[0089] S1. Mix choline chloride, ethylene glycol, and maleic acid in a molar ratio of 1:3:4, mix and heat stir at 130°C until a uniform, transparent and clear deep eutectic solvent is formed.

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

[0091] S3. 45 ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

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

[0093] S1. Choline chloride, ethylene glycol, and maleic acid were mixed at a molar ratio of 1:3:4, and mixed and heated under stirring at 130°C until a uniform, transparent, and clear deep eutectic solvent was formed.

[0094] S2. Poplar powder and the deep eutectic solvent in S1 were added into a reactor at a mass ratio of 1:15, the reaction temperature was set to 130°C, and the reaction time was 0.5 h. After the reaction was completed, a solid-liquid mixture was obtained.

[0095] S3. 45 ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

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

[0097] S1. Choline chloride, ethylene glycol, and maleic acid were mixed at a molar ratio of 1:3:4, and mixed and heated under stirring at 130°C until a uniform, transparent, and clear deep eutectic solvent was formed.

[0098] S2. Poplar powder and the deep eutectic solvent in S1 were added into a reactor at a mass ratio of 1:15, the reaction temperature was set to 130°C, and the reaction time was 6 h. After the reaction was completed, a solid-liquid mixture was obtained.

[0099] S3. 45 ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained.

[0100] Table 1 Test results of lignin extracted by the methods in Examples 1-10

[0101]

[0102]

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

[0104] S1. Choline chloride, glycerol, maleic acid were mixed in a molar ratio of 1:3:4, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

[0105] S2. Poplar powder and the deep eutectic solvent in S1 were added into a reactor in a mass ratio of 1:15, the reaction temperature was set to 130°C, and the reaction time was 2h. After the reaction was completed, a solid-liquid mixture was obtained.

[0106] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained, and the extraction rate was 35%. The whiteness value was 35.4.

[0107] Example 1 A method for extracting light-colored lignin by a ternary deep eutectic solvent

[0108] S1. Choline chloride, ethylene glycol, p-hydroxybenzenesulfonic acid were mixed in a molar ratio of 1:3:4, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

[0109] S2. Poplar powder and the deep eutectic solvent in S1 were added into a reactor in a mass ratio of 1:15, the reaction temperature was set to 130°C, and the reaction time was 2h. After the reaction was completed, a solid-liquid mixture was obtained.

[0110] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained, and the extraction rate was 31%. The whiteness value was 40.2.

[0111] Example 2 A method for extracting light-colored lignin by a ternary deep eutectic solvent

[0112] S1. Choline chloride, isopropyl alcohol, formic acid were mixed in a molar ratio of 1:3:4, mixed and heated under stirring at 130°C until a homogeneous, transparent and clear deep eutectic solvent was formed.

[0113] S2. Poplar powder and the deep eutectic solvent in S1 were added into a reactor in a mass ratio of 1:15, the reaction temperature was set to 130°C, and the reaction time was 2h. After the reaction was completed, a solid-liquid mixture was obtained.

[0114] S3. 45ml of anhydrous ethanol was added to the solid-liquid mixture in S2 and stirred, then filtered to obtain a filtrate, and water was added to precipitate lignin. After centrifugation and freeze-drying, lignin was obtained, and the extraction rate was 23%. The whiteness value was 32.6.

[0115] Example 3 A method for extracting light-colored lignin by a ternary deep eutectic solvent

[0116] The same as the experimental method of Example 1, the difference is that choline chloride, ethylene glycol, 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] Example 2 A method for extracting light-colored lignin by a ternary eutectic solvent

[0118] The same as the experimental method of Example 1, the difference is that choline chloride, ethylene glycol, 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] Example 3 A method for extracting light-colored lignin by a ternary eutectic solvent

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

[0121] Example 4 A method for extracting light-colored lignin by a ternary eutectic solvent

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

[0123] Example 5 A method for extracting light-colored lignin by a ternary eutectic solvent

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

[0125] Example 6 A method for extracting light-colored lignin by a ternary eutectic solvent

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

[0127] According to Table 1, the whiteness value of the lignin extracted by the method of Examples 1-12 is above 53, and the extraction rate is above 50%, which not only meets the light color requirement of lignin, but also effectively avoids the condensation of lignin during the reaction and improves the extraction rate of lignin.

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

[0129] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. It is not necessary or possible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A method for extracting light-colored lignin using a ternary eutectic solvent, characterized in that, Includes the following steps: S1. Mix two hydrogen bond donors and hydrogen bond acceptors, heat the mixture to form a transparent and homogeneous liquid, and obtain a ternary eutectic solvent; S2. Mix and react the lignin raw material with the ternary eutectic solvent prepared in S1; S3. Add anhydrous ethanol to the solid-liquid mixture obtained in S2, stir, filter to obtain filtrate, and separate the precipitate to obtain lignin; 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 1:3~9:4~8; The reaction temperature in step S2 is 130°C; The reaction time in step S2 is 2 hours; The hydrogen bond acceptor is choline chloride.

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

20.

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

4. The method according to claim 3, characterized in that, The amount of deionized water added is 5 to 15 times the volume of the filtrate.

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