Method for recovering acidic deep-eutectic solvent by combining anti-solvent precipitation with activated carbon adsorption

Abstract

The invention belongs to the technical field of green chemistry and sustainable chemical engineering, and discloses a method for recovering an acidic eutectic solvent by combining anti-solvent precipitation with activated carbon adsorption. Water-insoluble high-molecular-weight lignin in the deep eutectic solvent black liquor is removed by an anti-solvent precipitation technology, and then residual low-molecular-weight water-soluble lignin and polysaccharide in the solution are further adsorbed and removed by using activated carbon with high specific surface area and rich pore structure; and the eutectic solvent with high purity and unobviously changed structure is recovered. The method is suitable for various acidic deep-eutectic solvents, the operation is simple, water and activated carbon in the recovery process can be repeatedly used, and the obtained water-insoluble lignin, water-soluble lignin and polysaccharide have high application value.

Description

Technical Field

[0001] The present invention relates to the technical field of green chemistry and sustainable chemical engineering, and in particular to a method for recovering an acidic deep eutectic solvent by combining anti-solvent precipitation with activated carbon adsorption. Background Art

[0002] Deep eutectic solvents are a new class of green solvent systems composed of hydrogen bond donors and hydrogen bond acceptors. They offer numerous advantages, including low toxicity, biodegradability, low cost, and simple preparation. In recent years, deep eutectic solvents have demonstrated significant potential for separating lignocellulosic biomass components and their subsequent high-value utilization. These solvents selectively cleave ester, ether, and carbon-carbon bonds within lignin molecules while minimizing damage to cellulose. This allows for the effective separation of lignocellulosic components, promoting their efficient resource development and utilization. Acidic deep eutectic solvents are particularly effective for lignin removal. For example, a deep eutectic solvent system composed of benzyltriethylammonium chloride and formic acid can remove over 90% of lignin after treatment at 130°C for two hours at ambient pressure (Green Chem., 2023, 25, 3256). However, the large-scale application of deep eutectic solvents still faces key bottlenecks, one of the most prominent being their efficient recovery and recycling after use. Compared to the commercially viable alkali recovery systems used in traditional kraft pulping processes, the current application of deep eutectic solvents lacks a mature, systematic solvent recovery solution. Existing recovery methods still leave significant room for improvement in terms of solvent purity, cost-effectiveness, and environmental friendliness. Therefore, exploring low-energy, high-efficiency deep eutectic solvent recovery technologies is crucial for promoting their industrial application.

[0003] Research on the recovery of deep eutectic solvents is still in the exploratory stage. Due to their diverse composition and significant differences in properties, the recovery process presents significant challenges. Currently reported recovery strategies include antisolvent precipitation, extraction, electrodialysis, and membrane separation. Antisolvent precipitation is widely adopted due to its ease of operation and excellent results. This method primarily introduces an antisolvent (such as water, alcohols, or ketones) into the spent deep eutectic solvent solution, significantly reducing the solubility of lignin in the solution and causing it to precipitate, thereby achieving a preliminary separation of lignin from the solvent components. The antisolvent can then be removed by methods such as vacuum distillation to recover the deep eutectic solvent at a higher purity. However, this method still has certain limitations. For example, some lignin remains soluble in the solvent phase, making complete precipitation difficult. Furthermore, the hemicellulose fraction and the small amount of dissolved cellulose cannot be effectively separated by this process. With increasing recycling cycles, the amount of residual lignin and carbohydrates in the solvent gradually accumulates, affecting the solvent purity, and in turn, its physical and chemical properties and subsequent delignification. Therefore, developing auxiliary methods to further remove impurities from the solution has become a research priority for improving the reusability of recovered deep eutectic solvents. Activated carbon, due to its high surface area, rich pore structure, and excellent adsorption capacity, is widely used in wastewater purification, material separation, catalyst support, and energy storage. China's annual activated carbon production has reached 210,000 tons, with a mature industrial system and a wide range of products, providing a good foundation for its promotion and application in deep eutectic solvent recovery. Activated carbon is expected to play a significant role in the regeneration of deep eutectic solvents, especially in further removing residual lignin and carbohydrates in the solution, improving the purity of the recovered solvent, and enhancing its reuse efficiency. Summary of the Invention

[0004] To address these issues, the present invention proposes a green, simple, and efficient method for recovering deep eutectic solvents, aiming to improve their purity and reusability, providing strong support for the development of low-energy, biomass-friendly deep eutectic solvent delignification technologies. The present invention aims to provide a method for recovering acidic deep eutectic solvents by combining antisolvent precipitation with activated carbon adsorption, addressing the current issues of low recovered purity and poor reusability of deep eutectic solvents.

[0005] The technical solutions adopted in the present invention are as follows:

[0006] A method for recovering an acidic deep eutectic solvent by combining anti-solvent precipitation with activated carbon adsorption, characterized in that the acidic deep eutectic solvent is a deep eutectic solvent obtained by treating lignocellulose;

[0007] The method comprises the following steps:

[0008] (1) mixing the acidic deep eutectic solvent with water, separating the precipitate, and obtaining a deep eutectic solvent aqueous solution;

[0009] (2) mixing the activated carbon with the deep eutectic solvent aqueous solution obtained in step (1) for adsorption, separating the activated carbon, and obtaining a treated deep eutectic solvent aqueous solution;

[0010] (3) mixing the activated carbon separated in step (2) with an alkaline solution for desorption, separating the solid and liquid, and obtaining regenerated activated carbon and water-soluble lignin and polysaccharides;

[0011] (4) dehydrating the treated low eutectic solvent aqueous solution obtained in step (2), determining the composition of hydrogen bond acceptors and hydrogen bond donors, and replenishing the corresponding chemical components to the initial ratio to obtain a recovered low eutectic solvent.

[0012] Preferably, the hydrogen bond acceptor of the acidic deep eutectic solvent is one or more of benzyltrimethylammonium chloride, benzyltriethylammonium chloride or choline chloride, and the hydrogen bond donor is one or more of formic acid, acetic acid or lactic acid.

[0013] Preferably, in step (1), the mass of the water is 5 to 15 times the mass of the acidic deep eutectic solvent; when the hydrogen bond donor is formic acid, free formic acid is extracted by vacuum rotary evaporation before step (1); and the separated precipitate is water-insoluble lignin.

[0014] Preferably, in step (2), the mass of the activated carbon is 0.01 to 0.04 times the mass of the deep eutectic solvent aqueous solution.

[0015] Preferably, in step (2), the adsorption temperature is 20-60° C., and the adsorption time is 0.1-1 h.

[0016] Preferably, in step (3), the alkaline solution is an aqueous solution of ethylenediamine, wherein the volume concentration of ethylenediamine is 5 to 40%.

[0017] Preferably, in step (3), the mass of the activated carbon is 0.01 to 0.1 times that of the alkaline solution.

[0018] Preferably, in step (3), the desorption temperature is 20-60° C., and the desorption time is 0.1-1 h; and the polysaccharide is one or more of glucose and xylose.

[0019] Preferably, in step (4), the dehydration treatment method is vacuum rotary evaporation at a temperature of 40 to 90° C. for 1 to 5 hours.

[0020] Preferably, in step (4), the method for determining the composition of the hydrogen bond acceptor and the hydrogen bond donor is precipitation titration and acid-base titration.

[0021] The present invention uses antisolvent precipitation to remove water-insoluble, high-molecular-weight lignin from the deep eutectic solvent black liquor. Subsequently, activated carbon with a high specific surface area and rich pore structure is used to further adsorb and remove the remaining low-molecular-weight, water-soluble lignin and polysaccharides in the solution, recovering a high-purity, structurally unchanged deep eutectic solvent. Compared to existing methods for recovering deep eutectic solvents, the present invention has the following advantages and effects:

[0022] (1) In the method for recovering the deep eutectic solvent provided by the present invention, the activated carbon has low selectivity for hydrogen bond acceptors and hydrogen bond donors in the deep eutectic solvent, and the loss of the deep eutectic solvent is small.

[0023] (2) In the low eutectic solvent recovery method provided by the present invention, the activated carbon exhibits strong adsorption selectivity for the residual lignin and carbohydrates in the low eutectic solvent aqueous solution, and can remove most of the impurities.

[0024] (3) In the low eutectic solvent recovery method provided by the present invention, the graded recovery of lignin and polysaccharide resources in black liquor is achieved, and the obtained water-insoluble lignin, water-soluble lignin and polysaccharides have high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 From left to right are unused deep eutectic solvent, deep eutectic solvent recovered in Example 1 and Comparative Example 1.

[0026] Figure 2 IR spectra of unused deep eutectic solvent and the deep eutectic solvent recovered in Example 1.

[0027] Figure 3 The slurrying effects of unused deep eutectic solvent and deep eutectic solvent recovered according to the steps of Example 1 are shown. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited to the specific embodiments. Other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the technical essence of the present invention should be considered as equivalent replacement methods and fall within the scope of protection of the technical solution of the present invention.

[0029] The activated carbon used in the examples of the present invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a mesh size of 200. The chemical composition of the deep eutectic solvent solution before treating lignocellulose in the examples and comparative examples was: formic acid content 50.26 wt % and benzyltriethylammonium chloride content 49.74 wt %.

[0030] Example 1

[0031] A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption comprises the following steps:

[0032] Eucalyptus wood was treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor, producing a deep eutectic solvent black liquor. Free formic acid was extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor was then mixed with water at a mass ratio of 5 times the mass of the deep eutectic solvent black liquor. Solid-liquid separation was performed to yield water-insoluble lignin and a deep eutectic solvent aqueous solution. Unused activated carbon was mixed with the deep eutectic solvent aqueous solution at a mass ratio of 0.025 times the mass of the deep eutectic solvent aqueous solution and adsorbed at 25°C for 10 minutes. The activated carbon was then separated from the deep eutectic solvent aqueous solution. The adsorbed activated carbon was then mixed with an ethylenediamine aqueous solution and desorbed at 50°C for 10 minutes. The ethylenediamine volume ratio was 10% and the mass of the activated carbon was 0.1 times the mass of the ethylenediamine aqueous solution. The activated carbon and ethylenediamine aqueous solution were then separated. The ethylenediamine aqueous solution was recovered and reused by vacuum rotary evaporation. The remaining solids consisted of water-soluble lignin and polysaccharides. The adsorbed deep eutectic solvent aqueous solution was dehydrated by vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution were measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals were supplemented to align the composition with that of the unused deep eutectic solvent solution, thereby obtaining a recovered deep eutectic solvent.

[0033] Attachment Figure 1 The figure is a physical picture of the deep eutectic solvent. The deep eutectic solvent in Example 1 is clear and transparent, indicating that its purity is relatively high. Figure 2 These are infrared spectra of the unused and recovered deep eutectic solvents in Example 1. The relevant characteristic peaks of the deep eutectic solvent all appear in the spectra, indicating that the structure of the recovered deep eutectic solvent is not destroyed; no new characteristic peaks appear in the spectra, indicating that the impurity content in the recovered deep eutectic solvent is low.

[0034] Example 2

[0035] A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption comprises the following steps:

[0036] Eucalyptus wood was treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor, producing a deep eutectic solvent black liquor. Free formic acid was extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor was then mixed with water at a mass ratio of 5 times the mass of the deep eutectic solvent black liquor. Solid-liquid separation was performed to yield water-insoluble lignin and a deep eutectic solvent aqueous solution. Unused activated carbon was mixed with the deep eutectic solvent aqueous solution at a mass ratio of 0.02 times the mass of the deep eutectic solvent aqueous solution and adsorbed at 25°C for 10 minutes. The activated carbon was then separated from the deep eutectic solvent aqueous solution. The adsorbed activated carbon was then mixed with an ethylenediamine aqueous solution and desorbed at 50°C for 10 minutes. The ethylenediamine volume ratio was 10% and the mass of the activated carbon was 0.1 times the mass of the ethylenediamine aqueous solution. The activated carbon and ethylenediamine aqueous solution were then separated. The ethylenediamine aqueous solution was recovered and reused by vacuum rotary evaporation. The remaining solids consisted of water-soluble lignin and polysaccharides. The adsorbed deep eutectic solvent aqueous solution was dehydrated by vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution were measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals were supplemented to align the composition with that of the unused deep eutectic solvent solution, thereby obtaining a recovered deep eutectic solvent.

[0037] Example 3

[0038] A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption comprises the following steps:

[0039] Eucalyptus wood was treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor, producing a deep eutectic solvent black liquor. Free formic acid was extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor was then mixed with water at a mass ratio of 5 times the mass of the deep eutectic solvent black liquor. Solid-liquid separation was performed to yield water-insoluble lignin and a deep eutectic solvent aqueous solution. Unused activated carbon was mixed with the deep eutectic solvent aqueous solution at a mass ratio of 0.017 times the mass of the deep eutectic solvent aqueous solution and adsorbed at 25°C for 10 minutes. The activated carbon was then separated from the deep eutectic solvent aqueous solution. The adsorbed activated carbon was then mixed with an ethylenediamine aqueous solution and desorbed at 50°C for 10 minutes. The ethylenediamine volume ratio was 10% and the mass of the activated carbon was 0.1 times the mass of the ethylenediamine aqueous solution. The activated carbon and ethylenediamine aqueous solution were then separated. The ethylenediamine aqueous solution was recovered and reused by vacuum rotary evaporation. The remaining solids consisted of water-soluble lignin and polysaccharides. The adsorbed deep eutectic solvent aqueous solution was dehydrated by vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution were measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals were supplemented to align the composition with that of the unused deep eutectic solvent solution, thereby obtaining a recovered deep eutectic solvent.

[0040] Example 4

[0041] A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption comprises the following steps:

[0042] Eucalyptus wood was treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor, producing a deep eutectic solvent black liquor. Free formic acid was extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor was then mixed with water at a mass ratio of 5 times the mass of the deep eutectic solvent black liquor. Solid-liquid separation was performed to yield water-insoluble lignin and a deep eutectic solvent aqueous solution. Unused activated carbon was mixed with the deep eutectic solvent aqueous solution at a mass ratio of 0.014 times the mass of the deep eutectic solvent aqueous solution and adsorbed at 25°C for 10 minutes. The activated carbon was then separated from the deep eutectic solvent aqueous solution. The adsorbed activated carbon was then mixed with an ethylenediamine aqueous solution and desorbed at 50°C for 10 minutes. The ethylenediamine volume ratio was 10% and the mass of the activated carbon was 0.1 times the mass of the ethylenediamine aqueous solution. The activated carbon and ethylenediamine aqueous solution were then separated. The ethylenediamine aqueous solution was recovered and reused by vacuum rotary evaporation. The remaining solids consisted of water-soluble lignin and polysaccharides. The adsorbed deep eutectic solvent aqueous solution was dehydrated by vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution were measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals were supplemented to align the composition with that of the unused deep eutectic solvent solution, thereby obtaining a recovered deep eutectic solvent.

[0043] Example 5

[0044] A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption comprises the following steps:

[0045] Eucalyptus wood was treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor, producing a deep eutectic solvent black liquor. Free formic acid was extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor was then mixed with water at a mass ratio of 5 times the mass of the deep eutectic solvent black liquor. Solid-liquid separation was performed to yield water-insoluble lignin and a deep eutectic solvent aqueous solution. Unused activated carbon was mixed with the deep eutectic solvent aqueous solution at a mass ratio of 0.0125 times the mass of the deep eutectic solvent aqueous solution and adsorbed at 25°C for 10 minutes. The activated carbon was then separated from the deep eutectic solvent aqueous solution. The adsorbed activated carbon was then mixed with an ethylenediamine aqueous solution and desorbed at 50°C for 10 minutes. The volume ratio of ethylenediamine was 10% and the mass of the activated carbon was 0.1 times the mass of the ethylenediamine aqueous solution. The activated carbon and ethylenediamine aqueous solution were then separated. The ethylenediamine aqueous solution was recovered and reused by vacuum rotary evaporation. The remaining solids consisted of water-soluble lignin and polysaccharides. The adsorbed deep eutectic solvent aqueous solution was dehydrated by vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution were measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals were supplemented to align the composition with that of the unused deep eutectic solvent solution, thereby obtaining a recovered deep eutectic solvent.

[0046] Comparative Example 1

[0047] A method for recovering an acidic deep eutectic solvent comprises the following steps:

[0048] Eucalyptus wood is treated with a deep eutectic solvent containing benzyltriethylammonium chloride as a hydrogen bond acceptor and formic acid as a hydrogen bond donor to produce a deep eutectic solvent black liquor. Free formic acid is extracted from the black liquor using vacuum rotary evaporation. The deep eutectic solvent black liquor is then mixed with water (5 times the mass of the deep eutectic solvent black liquor), and solid-liquid separation is performed to obtain water-insoluble lignin and a deep eutectic solvent aqueous solution. The deep eutectic solvent aqueous solution is dehydrated using vacuum rotary evaporation at a heating temperature of 45°C for 3 hours. The formic acid and benzyltriethylammonium chloride contents in the dehydrated solution are measured by acid-base titration and precipitation titration, respectively. The corresponding chemicals are then added to align the composition with that of the unused deep eutectic solvent solution, yielding a recovered deep eutectic solvent.

[0049] Test Case

[0050] 1. The drug retention rate and lignin, glucose and xylose removal rates of Examples 1 to 5 before and after activated carbon adsorption were tested. The test steps are as follows:

[0051] The formic acid content was determined by acid-base titration: 0.3 g of the deep eutectic solvent was diluted with water, phenolphthalein indicator was added dropwise, and the formic acid content was titrated using 1 mol / L NaOH solution.

[0052] The content of benzyltriethylammonium chloride was determined using precipitation titration: 0.2 g of the deep eutectic solvent was diluted with water, neutralized with NaOH solution, and filtered through a 0.22 μm filter to remove any solid impurities that might interfere with the determination of the titration endpoint. A 2 wt% starch solution and 2 mL of fluorescent yellow indicator were then added dropwise to the solution, and the benzyltriethylammonium chloride content was titrated using a 0.1 mol / L AgNO3 solution.

[0053] The ratio of the drug content before and after activated carbon adsorption is the retention rate.

[0054] Lignin was measured using a UV spectrophotometer, measuring the absorbance at 440 nm in the deep eutectic solvent before and after activated carbon adsorption. The lignin removal rate was calculated as 1 minus the ratio of the solvent absorbance before and after adsorption. Glucose and xylose were quantitatively determined using ion chromatography. The glucose and xylose removal rates were calculated as 1 minus the ratio of the corresponding sugar contents in the solvent before and after adsorption.

[0055] The test results are shown in Table 1. Activated carbon has low selectivity for hydrogen bond acceptors and donors in the deep eutectic solvent, resulting in minimal loss of the deep eutectic solvent. Activated carbon exhibits strong adsorption selectivity for lignin, glucose, and xylose, achieving most removal.

[0056] Table 1 Retention rates of hydrogen bond donors and acceptors, and removal rates of lignin, glucose, and xylose after activated carbon adsorption

[0057]

[0058] 2. Pulping was performed using the deep eutectic solvent of untreated lignocellulose and the deep eutectic solvent recovered four times according to the steps of Example 1, as follows:

[0059] The mass ratio of the deep eutectic solvent to eucalyptus was set at 10:1, the reaction temperature was 130°C, and the reaction time was 1.5 hours. The pulping process was carried out in a round-bottom flask equipped with a reflux device and heated in a constant-temperature oil bath. After the reaction, the coarse pulp was separated from the deep eutectic solvent black liquor using a G3 sand core funnel. The coarse pulp was then washed with formic acid and finally washed with water until neutral. The fine pulp and coarse residue in the coarse pulp were screened using a pulp flat plate sieving instrument with a mesh size of 0.25 mm. The fine pulp yield was the ratio of the fine pulp mass to the raw material mass.

[0060] The test results are as attached Figure 3 As shown, although the fine slurry yield of the low eutectic solvent recovered in Example 1 is slightly lower than that of the fresh low eutectic solvent, it still has a relatively high fine slurry yield, and the fine slurry yield remains at a relatively high level after four times of recycling, which meets the demand for solvent recycling in industrial production and reduces costs and environmental burdens.

[0061] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications arising from the technical solution of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for recovering an acidic deep eutectic solvent by combining antisolvent precipitation with activated carbon adsorption, characterized in that: The acidic deep eutectic solvent is a deep eutectic solvent obtained by treating lignocellulose; The method comprises the following steps: (1) mixing the acidic deep eutectic solvent with water, separating the precipitate, and obtaining a deep eutectic solvent aqueous solution; (2) mixing the activated carbon with the deep eutectic solvent aqueous solution obtained in step (1) for adsorption, separating the activated carbon, and obtaining a treated deep eutectic solvent aqueous solution; (3) mixing the activated carbon separated in step (2) with an alkaline solution for desorption, separating the solid and liquid, and obtaining regenerated activated carbon and water-soluble lignin and polysaccharides; (4) dehydrating the treated low eutectic solvent aqueous solution obtained in step (2), determining the composition of hydrogen bond acceptors and hydrogen bond donors, and replenishing the corresponding chemical components to the initial ratio to obtain a recovered low eutectic solvent.

2. The method according to claim 1, characterized in that The hydrogen bond acceptor of the acidic deep eutectic solvent is one or more of benzyltrimethylammonium chloride, benzyltriethylammonium chloride or choline chloride, and the hydrogen bond donor is one or more of formic acid, acetic acid or lactic acid.

3. The method according to claim 2, characterized in that In step (1), the mass of the water is 5 to 15 times the mass of the acidic low eutectic solvent; when the hydrogen bond donor is formic acid, free formic acid is extracted by vacuum rotary evaporation before step (1); and the separated precipitate is water-insoluble lignin.

4. The method according to claim 1, wherein In step (2), the mass of the activated carbon is 0.01 to 0.04 times the mass of the deep eutectic solvent aqueous solution.

5. The method according to claim 4, characterized in that In step (2), the adsorption temperature is 20-60° C., and the adsorption time is 0.1-1 h.

6. The method according to claim 1, wherein In step (3), the alkaline solution is an aqueous solution of ethylenediamine, wherein the volume concentration of ethylenediamine is 5 to 40%.

7. The method according to claim 6, characterized in that In step (3), the mass of the activated carbon is 0.01 to 0.1 times that of the alkaline solution.

8. The method according to claim 6, characterized in that In step (3), the desorption temperature is 20-60° C., and the desorption time is 0.1-1 h; the polysaccharide is one or more of glucose and xylose.

9. The method according to claim 1, characterized in that In step (4), the dehydration treatment method is vacuum rotary evaporation at a temperature of 40 to 90° C. for 1 to 5 hours.

10. The method according to claim 9, characterized in that In step (4), the method for determining the composition of the hydrogen bond acceptor and the hydrogen bond donor is precipitation titration and acid-base titration.

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