Eutectic solvent for enzymolysis saccharification of Alkaline wheat straw and application of eutectic solvent

Abstract

The invention discloses a co-melting solvent for enzymolysis saccharification of Alkaline wheat straw and application of the co-melting solvent. Comprising the following components in parts by weight: 5-10 parts of choline chloride, 4-8 parts of N-(2-ethoxyl) ethylenediamine and 12-30 parts of ethylene glycol. The DES system is green and recoverable, secondary pollution is avoided, the selective dissolving capacity of DES to lignin is remarkably improved through introduction of the weak base additive, the contradiction between lignin removal and carbohydrate retention in traditional DES pretreatment is broken through, the straw enzymolysis saccharification rate after pretreatment is extremely high, and the quality of the straw is improved. The method provides a key technical support for high-valued conversion (such as yeast protein, biofuel, bio-based materials and the like) of the drought alkali wheat straw, and has remarkable economic value and environmental benefit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of agricultural waste resource utilization, and particularly relates to a eutectic solvent for enzymatic saccharification of dry alkali wheat straw and application thereof. BACKGROUND

[0002] As a characteristic agricultural waste in saline-alkali land in northern China, dry alkali wheat straw has rich resource reserves, represents a huge biomass resource reserve, and reflects its potential application value in the fields of energy and materials. However, the cell wall of the dry alkali wheat straw is tightly cross-linked by cellulose, hemicellulose and lignin through covalent bonds and hydrogen bonds to form a dense structure, which leads to great difficulty in resource utilization and limits the conversion efficiency in the process of bio-refining. Therefore, developing an efficient pretreatment technology to optimize the component structure of the biomass raw material and improve the efficiency of subsequent enzymatic saccharification and catalytic conversion has become the core task of current biomass chemical conversion research.

[0003] At present, the existing pretreatment technologies mainly include physical methods (high energy consumption and limited effect), chemical methods (serious pollution by strong acid and strong base and high loss rate of carbohydrates), traditional low eutectic solvent methods (low lignin removal rate when used alone, and easy degradation and loss of hemicellulose), and biological methods (long processing period and low efficiency). Under the continuous exploration of researchers, various new pretreatment technologies have been initially formed. Among them, the deep eutectic solvent (DES) pretreatment technology has attracted widespread attention in the field of biomass pretreatment. The deep eutectic solvent is composed of a fixed molar ratio of hydrogen bond donor and hydrogen bond acceptor, has the advantages of low toxicity, easy preparation, easy biodegradation, good biocompatibility and high extraction efficiency, is a recognized green solvent, has good delignification ability, and can be recycled, which provides a new solution for the pretreatment of biomass raw materials.

[0004] When choline chloride-glycol DES is used to pretreat wheat straw, the lignin removal rate is generally not high, the hemicellulose retention rate is insufficient, and the subsequent enzymatic saccharification rate is low. When strong acid and strong base (such as sodium hydroxide and concentrated sulfuric acid) are introduced as additives, the lignin removal rate can be improved, but cellulose degradation occurs, and the strong alkaline corrosion is strong and has high environmental risk. Therefore, developing a dry alkali wheat straw pretreatment technology that can balance “high lignin removal rate, high carbohydrate retention rate and green environmental protection” has become a key bottleneck restricting its high-value utilization. SUMMARY

[0005] The purpose of the present application is to provide a eutectic solvent for enzymatic saccharification of dry alkali wheat straw and application thereof.

[0006] A kind of eutectic solvent for enzymatic saccharification of straw of Aeluropus littoralis, comprising the following components by weight: 5-10 parts of choline chloride, 4-8 parts of N-(2-hydroxyethyl)ethylenediamine and 12-30 parts of ethylene glycol.

[0007] The preparation method of the eutectic solvent for enzymatic saccharification of straw of Aeluropus littoralis, choline chloride and N-(2-hydroxyethyl)ethylenediamine are mixed with ethylene glycol, heated to liquid clarity at 70-90℃ and 100-300rpm.

[0008] The application of the eutectic solvent in pretreatment of straw of Aeluropus littoralis.

[0009] A method for pretreating straw of Aeluropus littoralis with weak base assisted eutectic solvent, comprising the following steps:

[0010] (1) mixing straw of Aeluropus littoralis with eutectic solvent at a solid-liquid ratio of (0.5-2):20 in a container, adding 4-8wt% of sodium carbonate based on the total mass of choline chloride and N-(2-hydroxyethyl)ethylenediamine, and pretreating in an oil bath at 115-135℃ and 100-300rpm for 2-4h;

[0011] (2) cooling the pretreated solid-liquid mixture to room temperature, and separating the obtained pretreatment liquid and solid material by vacuum filtration;

[0012] (3) washing the solid material with 40-60% volume concentration of ethanol aqueous solution for 2-4 times, and continuously washing with hot deionized water at 70-90℃ until the washing liquid becomes colorless;

[0013] (4) drying the solid material in an oven at 70-90℃ to constant weight;

[0014] (5) adding pH=4.0-5.5 citric acid-sodium citrate buffer solution to the pretreated straw of Aeluropus littoralis obtained in step (4), and adding mixed cellulase and mixed hemicellulase, and enzymatically saccharifying at 40-60℃ and 1000-1400rpm for 48-96h to obtain an enzymatic hydrolysate.

[0015] The straw of Aeluropus littoralis in step (1) is crushed, passed through a 40-80 mesh sieve, and dried at 50-70℃ for standby use.

[0016] Collecting the pretreatment liquid obtained in step (2) and the washing liquid in step (3), and removing water and ethanol by vacuum evaporation concentration; adding 8-12 times volume of acidified water to the concentrated liquid, the acidified water is adjusted to pH=1.5-2.5 with HCl, and the lignin is precipitated after standing for 10-14h; after centrifugation at 6000-10000rpm for 3-8min, the precipitated lignin is separated and washed with deionized water for 3-10 times; the recovered lignin is freeze-dried and stored at 4℃.

[0017] The amount of citric acid-sodium citrate buffer added in step (5) is 3-20 times the mass of the dry alkali wheat straw after pretreatment in step (4).

[0018] The mixed cellulase in step (5) is CTec3, added in an amount of 20-30 FPU / g; and the mixed hemicellulase is Aladdin, added in an amount of 20-30 IU / g.

[0019] The beneficial effects of the present application are:

[0020] (1) Synergistic improvement of lignin removal rate and carbohydrate retention rate: the lignin removal rate reaches 72.6%, which is 15-25% higher than that of traditional DES pretreatment; the cellulose retention rate is 96.5%, and the hemicellulose retention rate is 93.8%;

[0021] (2) Breakthrough in enzymatic saccharification efficiency: the cellulose enzymatic saccharification rate reaches 99.7%, and the hemicellulose enzymatic saccharification rate reaches 93.8%;

[0022] (3) Green and environmentally friendly: DES is composed of choline chloride (good biocompatibility) and ethylene glycol (low toxicity), which can be recovered by reduced pressure distillation; sodium carbonate is a weak base and has no strong corrosive property; the entire process has no harmful gas emission and heavy metal pollution;

[0023] (4) Simple and controllable process: the pretreatment temperature is lower than that of traditional high-temperature pretreatment, and the energy consumption is lower; the process parameters are clear and easy to scale up industrially;

[0024] (5) The technology of the present application is not only suitable for dry alkali wheat straw, but also has potential to be extended to the treatment of other crop straws, and has wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A eutectic solvent configured by choline chloride and ethylene glycol.

[0026] Figure 2 Lignin removal rate of dry alkali wheat straw pretreated by different weak base assisted DES.

[0027] Figure 3 Comparison of the effects of dry alkali wheat straw pretreated by different weak base assisted DES.

[0028] Figure 4 Changes in the composition of dry alkali wheat straw before and after pretreatment.

[0029] Figure 5 SEM images of dry alkali wheat straw before and after pretreatment.

[0030] Figure 6 FT-IR images of dry alkali wheat straw before and after pretreatment.

[0031] Figure 7 X-ray diffraction spectra of dry alkali wheat straw before and after pretreatment.

[0032] Figure 8 Evaluation of cellulase and hemicellulase synergistic enzymatic hydrolysis efficiency.

[0033] Figure 9 Determination of glucose concentration and xylose concentration under different solid loadings. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present application, the present application will be described more fully below. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0035] Preparation of the eutectic solvent

[0036] According to the weight fraction, take 8 parts of choline chloride, 6 parts of N-(2-hydroxyethyl)ethylenediamine, and 25 parts of ethylene glycol. After mixing uniformly, continuously stir at 200 rpm in an 80℃ oil bath until a clear and uniform liquid is formed (avoiding light and drying under the condition), and store. Figure 1

[0037] Pretreatment of dry alkali wheat straw

[0038] The dry alkali wheat straw is crushed to 60 mesh and dried in a 40℃ oven. The dry alkali wheat straw is mixed with the eutectic solvent at a solid-liquid ratio of 1:20. Under the condition of adding 6wt% Na2CO3, the mixture is heated in a 120℃ oil bath for 3h with stirring at 200rpm to promote the full contact and reaction of the dry alkali wheat straw and the eutectic solvent. After the pretreatment is completed, the pretreated solid-liquid mixture is cooled to room temperature, and the pretreatment solution and solid residue are separated by vacuum filtration.

[0039] After washing 3 times with 50% ethanol aqueous solution, the solid residue is repeatedly washed with hot deionized water (80℃) until the filtrate is colorless, ensuring the removal of residual solvent and catalyst. The washed solid residue is dried to constant weight in an 80℃ oven for standby.

[0040] Screening of the optimal pretreatment method for dry alkali wheat straw

[0041] The cellulose and lignin content of the pretreated dry alkali wheat straw is determined according to NY / T3494-2019. The cellulose retention rate and lignin removal rate of the eutectic solvent with different auxiliary agents are compared and comprehensively evaluated. Figure 2 ​, 3, 4). Based on the above indicators, the best pretreatment method was screened out: the mass ratio of choline chloride: N-(2-hydroxyethyl) ethylenediamine: ethylene glycol was 8:6:25, and the cellulose retention rate and lignin removal rate reached the highest under the condition of adding 6wt% Na2CO3. The results showed that the pretreatment method of dry alkali wheat with sodium carbonate had the highest cellulose retention rate, hemicellulose retention rate and lignin removal rate.

[0042] SEM showed the structure characterization surface of raw material and pretreated straw ( Figure 5 ). The untreated straw surface was smooth and complete, in the form of dense blocks, which hindered the entry of cellulase into the interior of the straw and was not conducive to further saccharification. The outer surface of the DES pretreated straw became rough, the originally dense and complete structure gradually loosened, promoting the preliminary separation of fiber bundles and the peeling of layers, and improving the looseness of the structure. The addition of weak alkali additive sodium carbonate during pretreatment further strengthened the destruction of the structure of the straw, and significant layer dissociation occurred, better dissolving the lignin, hemicellulose and other binding components between the fibers, so that the fiber bundles were dissociated into single or small bundle fibers, significantly improving the looseness of the structure and the exposure of the fibers.

[0043] FT-IR analyzed the chemical structure changes of dry alkali wheat straw before and after pretreatment ( Figure 6 ). As can be seen from the figure, the content of the functional groups of dry alkali wheat straw before and after DES pretreatment changed compared with the untreated straw. The absorption peak of β-glycosidic bond at 890cm -1 still existed, which indicated that DES pretreatment had no significant effect on the cellulose structure of dry alkali wheat straw. The hydrogen bond interaction formed during the dissolution of lignocellulose in DES pretreatment can stabilize the cellulose structure, and the stretching vibration peak of cellulose (-OH) at 3425cm -1 exists. The absorption peak of xylan and lignin (C=O) of dry alkali wheat straw is 1731cm -1 , which is significantly reduced, thus confirming that DES pretreatment removes xylan and lignin in biomass.

[0044] XRD analyzed the crystallinity changes of dry alkali wheat straw before and after pretreatment ( Figure 7 ). The crystallinity (CrI) after pretreatment is much larger than that of the raw material, and the increase of CrI proves the removal of amorphous lignin. It is shown that Na2CO3 pretreatment can selectively degrade and remove amorphous lignin (and part of hemicellulose), so that the cellulose crystal structure originally wrapped or interfered by amorphous substances is exposed, thus significantly improving the crystallinity.

[0045] The enzymatic saccharification rate of cellulose and hemicellulose showed a gradual upward trend with the extension of enzymatic time ( Figure 8). In the initial stage of enzymatic hydrolysis (0-24h), the sugarization rate of both cellulose and hemicellulose increased rapidly, with the cellulose sugarization rate rising to 74.18% and the hemicellulose sugarization rate rising to 76.47%; in the subsequent enzymatic hydrolysis stage (24-72h), the sugarization rate increased gradually, and finally at 72h, the cellulose sugarization rate reached nearly 100% and the hemicellulose sugarization rate reached about 88%. This shows that the synergistic effect of cellulase and hemicellulase can effectively promote the enzymatic hydrolysis and sugarization of carbohydrates in straw, and the enzymatic hydrolysis rate and final sugarization degree of cellulose are slightly higher than those of hemicellulose, which may be related to the differences in crystal structure and enzymatic hydrolysis kinetics between the two.

[0046] From Figure 9 From the changes in glucose and xylose concentrations, with the increase of solid loading from 5% to 35%, the glucose concentration increased significantly from 34.64g / L to 250.18g / L, and the xylose concentration increased from 18.74g / L to 141.05g / L, and both showed a trend of continuous increase with the increase of solid loading. This shows that in this enzymatic hydrolysis system, the increase of solid loading can effectively improve the yield of glucose and xylose, which may be because higher substrate concentration provides more active sites for enzymatic reaction, thereby promoting the release of sugars. The synergistic enzymatic hydrolysis of cellulase and hemicellulase can efficiently degrade carbohydrates in straw, and by optimizing the enzymatic hydrolysis time and solid loading, the yield of glucose and xylose can be significantly improved, providing key process parameters and theoretical basis for the bioconversion and resource utilization of straw.

[0047] The co-solvent used can be stored at room temperature, is easy to prepare, can effectively destroy the structural barriers of cellulose, hemicellulose and lignin in dry alkali wheat straw, and improve the enzymatic hydrolysis of cellulose, thereby creating favorable conditions for subsequent enzymatic hydrolysis and catalytic conversion.

[0048] Example 4 Recovery of Lignin

[0049] The pretreatment liquid and washing liquid were concentrated by vacuum evaporation to remove water and ethanol. The concentrated solution was added to 10 times the volume of acidified water (pH = 2.0) and left to stand for 12h to promote the precipitation of lignin. The precipitated lignin was recovered by centrifugal separation at 8000rpm. The recovered lignin needs to be washed with deionized water at least three times to remove residual acid and impurities. The washed lignin was freeze-dried and stored at 4°C.

[0050] Example 5 Comparison of Lignin Removal Rate

[0051] Group 1: Take 8 parts of choline chloride, 6 parts of N-(2-hydroxyethyl)ethylenediamine, and 25 parts of ethylene glycol. Mix them evenly, then continuously stir at a speed of 200 rpm in an oil bath at 80°C until a clear and uniform liquid is formed to make a eutectic solvent. Crush the dryland alkali wheat straw to 60 mesh, dry it in an oven at 40°C, mix the dryland alkali wheat straw with the eutectic solvent at a solid-liquid ratio of 1:20, add 6wt% Na2CO3 as an auxiliary, heat in an oil bath at 120°C for 3h, and stir at a speed of 200 rpm. After the pretreatment is completed, cool the pretreated solid-liquid mixture to room temperature, separate the pretreatment solution and the solid residue by vacuum filtration, wash the solid residue with 50% ethanol aqueous solution for 3 times, then repeatedly wash the solid residue with hot deionized water (80°C) until the filtrate is colorless, dry the washed solid residue in an oven at 80°C to constant weight, and reserve it for use.

[0052] Group 2: Take 14 parts of choline chloride and 25 parts of ethylene glycol. Mix them evenly, then continuously stir at a speed of 200 rpm in an oil bath at 80°C until a clear and uniform liquid is formed to make a eutectic solvent. Crush the dryland alkali wheat straw to 60 mesh, dry it in an oven at 40°C, mix the dryland alkali wheat straw with the eutectic solvent at a solid-liquid ratio of 1:20, add 6wt% Na2CO3 as an auxiliary, heat in an oil bath at 120°C for 3h, and stir at a speed of 200 rpm. After the pretreatment is completed, cool the pretreated solid-liquid mixture to room temperature, separate the pretreatment solution and the solid residue by vacuum filtration, wash the solid residue with 50% ethanol aqueous solution for 3 times, then repeatedly wash the solid residue with hot deionized water (80°C) until the filtrate is colorless, dry the washed solid residue in an oven at 80°C to constant weight, and reserve it for use.

[0053] Group 3: Take 14 parts of N-(2-hydroxyethyl)ethylenediamine and 25 parts of ethylene glycol. Mix them evenly, then continuously stir at a speed of 200 rpm in an oil bath at 80°C until a clear and uniform liquid is formed to make a eutectic solvent. Crush the dryland alkali wheat straw to 60 mesh, dry it in an oven at 40°C, mix the dryland alkali wheat straw with the eutectic solvent at a solid-liquid ratio of 1:20, add 6wt% Na2CO3 as an auxiliary, heat in an oil bath at 120°C for 3h, and stir at a speed of 200 rpm. After the pretreatment is completed, cool the pretreated solid-liquid mixture to room temperature, separate the pretreatment solution and the solid residue by vacuum filtration, wash the solid residue with 50% ethanol aqueous solution for 3 times, then repeatedly wash the solid residue with hot deionized water (80°C) until the filtrate is colorless, dry the washed solid residue in an oven at 80°C to constant weight, and reserve it for use.

[0054] Determination of lignin removal rate: The lignin content of the straw of Group 1-Group 3 before and after pretreatment was determined according to the national standard NY / T 3494-2019.

[0055] (1) Concentrated acid hydrolysis: 300 mg (exact value 0.1 mg) of dried straw sample was taken in a pressure-resistant test tube, 3 mL of 72% sulfuric acid solution was added immediately after mixing evenly, and stirred in a water bath at 30°C. After constant temperature for 60 min, 84 mL of water was added to the pressure-resistant test tube and mixed evenly.

[0056] (2) Dilute acid hydrolysis: The above test tube was placed in a high-pressure steam sterilization pot, hydrolyzed at 121°C for 1 h, and after the hydrolysis product was cooled to room temperature, it was filtered through a glass sand core crucible, and the filtrate was collected for determination of acid-soluble lignin within 6 h.

[0057] (3) Determination of acid-soluble lignin: The above filtrate was used. The absorbance of the liquid sample was measured at 320 nm by ultraviolet-visible spectrophotometer. Water was used as blank control.

[0058] (4) Determination of acid-insoluble lignin: The acid-insoluble residue in the flat-bottomed test tube was washed with hot water, so that the residue was completely retained in the glass sand core crucible, and was dried with a vacuum filter. The glass sand core crucible and acid-insoluble residue were dried at 105°C to constant weight, and the mass of the glass sand core crucible and acid-insoluble residue was recorded, accurate to 0.1 mg.

[0059] (5) The glass sand core crucible and acid-insoluble residue were placed in a muffle furnace at 600°C for at least 3 h until all organic matter was ashed. After ashing, the temperature was lowered to 105°C, and the crucible and ash were removed and cooled in a desiccator. The mass of the crucible and ash was measured to an accuracy of 0.1 mg.

[0060] (6) Acid-soluble lignin content

[0061] The acid-soluble lignin content ASL in the sample, expressed as a percentage (%), was calculated as follows:

[0062]

[0063] In the formula:

[0064] ASL—acid-soluble lignin content in the sample, expressed as a percentage (%);

[0065] A—average value of ultraviolet-visible absorbance of the filtrate at 320 nm;

[0066] V—volume of the filtrate, with a value of 87 mL;

[0067] N—dilution multiple of the filtrate;

[0068] L—cuvette thickness, expressed in centimeters (cm);

[0069] —Absorbance of acid-soluble lignin at 320 nm, 25 L / (g-cm) for dry wheat straw;

[0070] w0—Mass of the sample before extraction, in grams (g);

[0071] w1—Mass of the sample after extraction, in grams (g);

[0072] w ef —Mass of the sample without extractives, in grams (g).

[0073] (7) Acid-insoluble lignin content

[0074] The acid-insoluble lignin content AIL in the sample, expressed as a percentage (%), is calculated according to the following formula:

[0075]

[0076] In the formula:

[0077] AIL—Acid-insoluble lignin content in the sample, in percentage (%);

[0078] m1—Mass of the glass-sand core crucible (G4), in grams (g);

[0079] m2—Mass of the glass-sand core crucible (G4) and acid-insoluble residue, in grams (g);

[0080] m3—Mass of the glass-sand core crucible (G4) and ash, in grams (g).

[0081] (8) Lignin content

[0082] The acid-soluble lignin content Lig in the sample, expressed as a percentage (%), is calculated according to the following formula:

[0083] Lig = ASL + AIL

[0084] In the formula:

[0085] Lig—Lignin content, in percentage (%);

[0086] ASL—Mass of the glass-sand core crucible (G4) and acid-insoluble residue, in grams (g);

[0087] AIL—Mass of the glass-sand core crucible (G4) and ash, in grams (g).

[0088] (9) Lignin removal rate

[0089]

[0090] The experimental results were statistically analyzed by SPSS 24.0 software, and the measurement data results were expressed by It is indicated that the data normality test was performed by Kolmogorov-Smirnov test method, for the data conforming to normal distribution, the mean difference comparison between two groups was performed by t test, and P<0.05 was considered to have statistical significance. The determination results are shown in Table 1:

[0091] Table 1

[0092]

[0093] Note: * represents P<0.05 compared with group 1.

[0094] The above-described examples only express several embodiments of the present application, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A eutectic solvent for enzymatic hydrolysis and saccharification of drought-tolerant wheat straw, characterized in that, It includes the following components in parts by weight: 5-10 parts of choline chloride, 4-8 parts of N-(2-hydroxyethyl)ethylenediamine, and 12-30 parts of ethylene glycol.

2. The method for preparing the eutectic solvent for enzymatic hydrolysis and saccharification of drought-resistant wheat straw according to claim 1, characterized in that, Choline chloride and N-(2-hydroxyethyl)ethylenediamine were mixed with ethylene glycol and heated at 70-90°C and 100-300 rpm until the liquid became clear.

3. The application of the eutectic solvent of claim 1 in the pretreatment of drought-resistant wheat straw.

4. A method for pretreating drought-tolerant wheat straw with a weak base-assisted eutectic solvent, characterized in that, Includes the following steps: (1) Mix drought-alkali wheat straw with eutectic solvent in a container at a solid-liquid ratio of (0.5-2):20, add sodium carbonate accounting for 4-8 wt% of the total mass of choline chloride and N-(2-hydroxyethyl)ethylenediamine, and pretreat in an oil bath at 115-135℃ and 100-300 rpm for 2-4 hours. (2) Cool the pretreated solid-liquid mixture to room temperature and separate the pretreated liquid and solid substances by vacuum filtration; (3) Wash the solid substance 2-4 times with an ethanol aqueous solution with a volume concentration of 40-60%, and wash continuously with hot deionized water at 70-90℃ until the washing solution becomes colorless. (4) Dry the solid material in an oven at 70-90℃ until constant weight; (5) Add citrate-sodium citrate buffer solution with pH = 4.0-5.5 to the pretreated drought-alkali wheat straw obtained in step (4), and add mixed cellulase and mixed hemicellulase. Enzymatically hydrolyze for 48-96 hours at 40-60℃ and 1000-1400rpm to obtain the hydrolysate.

5. The method for pretreating drought-resistant and alkaline wheat straw with a weak base-assisted eutectic solvent according to claim 4, characterized in that, The drought-resistant wheat straw mentioned in step (1) is crushed, passed through a 40-80 mesh sieve, and dried at 50-70℃ for later use.

6. The method for pretreating drought-resistant and alkaline wheat straw with a weak base-assisted eutectic solvent according to claim 4, characterized in that, Collect the pretreatment liquid obtained in step (2) and the washing liquid in step (3), and remove water and ethanol by vacuum evaporation concentration; add 8-12 times its volume of acidified water to the concentrate, the pH of which is adjusted to 1.5-2.5 with HCl, and let stand for 10-14 hours to precipitate lignin; after centrifugation at 6000-10000 rpm for 3-8 minutes, separate the precipitated lignin and wash it with deionized water 3-10 times; freeze-dry the recovered lignin and store it at 4°C.

7. The method for pretreating drought-resistant and alkaline wheat straw with a weak base-assisted eutectic solvent according to claim 4, characterized in that, The amount of citric acid-sodium citrate buffer added in step (5) is 3-20 times the mass of drought-resistant wheat straw after pretreatment in step (4).

8. The method for pretreating drought-resistant and alkaline wheat straw with a weak base-assisted eutectic solvent according to claim 4, characterized in that, The mixed cellulase mentioned in step (5) is CTec3, added at a rate of 20-30 FPU / g; the mixed hemicellulase is Aladdin, added at a rate of 20-30 IU / g.

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