Method for treating castor straw cellulase to hydrolyze associated xylooligosaccharide and micro-nano lignin through subcritical hydrolysis alkaline DES

Abstract

The invention belongs to the field of separation of biomass components in agriculture and forestry, and provides a method for hydrolyzing associated xylooligosaccharide and micro-nano lignin by treating castor straw cellulase through subcritical hydrolysis alkaline DES. The method comprises the following steps: firstly, treating a castor straw raw material by using a subcritical hydrolysis method to obtain a large amount of xylooligosaccharide, a small amount of micro-nano low-molecular-weight lignin and hydrolysis residues rich in cellulose and lignin; and treating the hydrolysis residue by using an alkaline deep eutectic solvent (DES) to obtain a slurry rich in cellulose and micro-nano high aryl ether bond lignin. And finally, carrying out enzymolysis on the cellulose-rich pulp by adopting a biotechnology to obtain a high-yield glucose product. According to the method, the subcritical hydrolysis reaction and the alkaline DES treatment technology are integrated, various castor straw biomass high-added-value products can be obtained under mild reaction conditions, and technical support is provided for increasing the output value of the castor industry and utilizing castor straw resources.

Description

Technical Field

[0001] The present invention belongs to the field of separation of components of agricultural and forestry biomass, and relates to a method for hydrolyzing ricinus straw fibers by subcritical hydrolysis and alkaline DES treatment to accompany xylooligosaccharides and micro-nano lignin. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] The ecological environment deterioration caused by the excessive dependence of human society on fossil fuels such as petroleum and the continuous depletion of fossil fuel reserves are increasingly severe challenges facing. Against this background, biomass, as a renewable resource with rich reserves, has gradually become a powerful alternative to fossil energy. Effectively developing and utilizing these natural renewable resources is of great significance for promoting the sustainable development of human society. In the field of biomass utilization, ricinus, as an important cash crop, its seeds can extract castor oil, and its stalks are mainly composed of cellulose, hemicellulose and lignin, and the cell wall structure and composition are similar to those of broad-leaved poplar wood. As a rich non-grain crop straw resource, it has high potential utilization value and can be converted into a variety of valuable chemicals, bio-based materials and biofuels. However, the utilization of ricinus straw resources has not been emphasized and developed.

[0004] Previously, it was reported that artificial boards were prepared using ricinus straw. In addition, there has been no report on the utilization of this rich straw resource. Currently, the biomass refining industry is severely restricted by factors such as single product and low process efficiency, which seriously limits the development of this green industry. Therefore, it is very urgent to develop a green and efficient biorefining method that can simultaneously produce a variety of biomass-based conversion products, and it is expected to further promote the vigorous development of the ricinus industry.

[0005] As a green and low-energy hydrolysis technology, subcritical hydrolysis technology does not use harmful chemical solvents during the extraction process, reducing environmental pollution and the generation of chemical waste. Compared with traditional acid hydrolysis and supercritical hydrolysis extraction methods, subcritical water extraction can be carried out at lower temperatures and pressures, and does not require corrosion-resistant equipment and high-pressure equipment, thus saving energy and equipment costs, and maintaining the biological activity of hemicellulose.

[0006] Patent CN118725357A discloses a biomass lignin micro-nano sphere based on a deep eutectic solvent, its preparation method and application. However, this method cannot achieve the full utilization of biomass components. At the same time, the original structure of lignin in this method is completely destroyed, and the retention rate of aryl ether bonds is low. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a method for subcritical hydrolysis coupled with alkaline DES treatment of castor straw fiber enzymatic hydrolysis to accompany xylo-oligosaccharides and micro-nano lignin. This technology promotes the reaction of castor straw through a combined pretreatment technology, realizing the multi-product development of xylo-oligosaccharides, glucose, and two kinds of micro-nano lignin.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In the first aspect of the present invention, there is provided a method for subcritical hydrolysis of alkaline DES treatment of castor straw fiber enzymatic hydrolysis to accompany xylo-oligosaccharides and micro-nano lignin, including:

[0010] Mix castor straw with water and carry out subcritical hydrolysis reaction. After the reaction is completed, filter and collect the hydrolysis residue; wash the hydrolysis residue with water and collect the washing liquid, which is the liquid rich in xylo-oligosaccharides; wash with an organic solvent and collect the washing liquid, which is the low-molecular-weight micro-nano lignin; dry the hydrolysis residue to obtain a solid hydrolysis residue;

[0011] Mix alkaline DES with the solid hydrolysis residue and carry out a dissociation reaction. After the reaction is completed, separate the solid and the slurry. Wash the solid with an organic solvent. The washing liquid is rotary evaporated and concentrated and then dialyzed to obtain micro-nano lignin with high aryl ether bonds; carry out biocatalytic hydrolysis on the slurry to obtain glucose.

[0012] Research has found that the subcritical hydrolysis coupled with alkaline DES treatment technology can further separate cellulose and lignin in the cell wall of castor straw under relatively mild conditions, while retaining the original structure of the lignin supramolecule and obtaining a micro-nano morphology. This combined technology can not only improve the yield of sugars, but also realize the simultaneous production of multiple biomass-based products, providing a new technology for the resource utilization of castor straw.

[0013] The method for subcritical hydrolysis coupled with alkaline DES treatment of castor straw fiber enzymatic hydrolysis to accompany xylo-oligosaccharides and micro-nano lignin proposed by the present invention aims to optimize the treatment conditions, improve the yield and purity of target products, while reducing energy consumption and environmental impact, providing an efficient and environmentally friendly solution for the comprehensive utilization of castor straw.

[0014] In some embodiments, the castor straw is in powder form with a particle size of 20 - 80 mesh.

[0015] In some embodiments, the mass ratio of the castor straw to water is 1:5 - 1:20;

[0016] In the subcritical hydrothermal reaction, the hydrothermal reaction conditions can greatly affect the production effect of oligosaccharides. When the hydrothermal reaction conditions are too mild, hemicellulose cannot be efficiently dissolved; when the reaction conditions are relatively severe, hemicellulose is hydrolyzed into monosaccharides in large quantities, thereby reducing the recovery rate and purity of xylooligosaccharides. Therefore, in some embodiments, the subcritical hydrolysis temperature is 150-200 °C, and the reaction time is 10-180 minutes.

[0017] In some embodiments, the organic solvent is selected from one or a mixture of two of ethanol, acetone, tetrahydrofuran, and butyrolactone.

[0018] In some embodiments, the hydrogen bond acceptor of the basic DES is selected from one of choline chloride, betaine, ethylamine hydrochloride, and guanidine hydrochloride;

[0019] In some embodiments, the hydrogen bond donor is selected from one of ethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, and diethanolamine;

[0020] In some embodiments, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:2-10, or 1:5-10;

[0021] During the treatment reaction with basic DES, the water content in the hydrated DES is 10-50%. When the water content exceeds 50%, too much water will change the properties of the DES solution, thereby affecting the solubility and reaction mechanism of lignin in the solvent. Therefore, in some embodiments, the hydrated basic DES is obtained by mixing basic DES with water, and the water content is 10%-50%.

[0022] During the treatment reaction with basic DES, when the mass ratio of the subcritical hydrolysis residue to DES is lower than 1:8, the low density of castor straw results in incomplete wetting of the raw material by DES, affecting mass transfer in the process and making it difficult to achieve effective separation of components; while when the mass ratio of the hydrolysis residue to DES is higher than 1:30, excessive DES leads to waste of reagents and increases the cost. Therefore, in some embodiments, the mass ratio of the solid hydrolysis residue to basic DES is 1:8-20.

[0023] In some embodiments, the temperature of the dissociation reaction is 100-150 °C, the reaction time is 1-6 hours, and the stirring speed is 200-500 rpm.

[0024] In some embodiments, the specification of the dialysis bag is 200-2000 Da;

[0025] In some embodiments, the biological enzyme is cellulase, the dosage of cellulase is 10-20 FPU / g, the enzyme hydrolysis temperature is 45-55 °C, and enzymatic hydrolysis is carried out for more than 3 days under the condition that the pH of the buffer solution is 4.0-6.0.

[0026] More specifically, it includes the following steps:

[0027] The first-step reaction is as follows: Mix castor straw and deionized water in a certain solid-liquid ratio and add them to a stainless-steel reactor, and carry out subcritical hydrolysis reaction at a set temperature. After the hydrolysis reaction is completed, carry out a filtration operation, wash the hydrolysis residue with deionized water to obtain a liquid rich in xylo-oligosaccharides. Then wash it with an organic solvent to obtain a low-molecular-weight micro-nano lignin product. At the same time, dry to obtain a solid hydrolysis residue. The second-step reaction is as follows: Use alkaline DES to treat the residue of the first-step subcritical hydrolysis of castor straw, carry out component separation according to a certain solid-liquid ratio, reaction temperature and time. After the reaction is completed, carry out filtration separation, wash with an organic solvent, and dialyze after rotary evaporation and concentration of the washing solution to obtain a micro-nano lignin product with high aryl ether bonds. After two-step treatment, the obtained slurry is subjected to biocatalytic hydrolysis to obtain a glucose product.

[0028] In the second aspect of the present invention, there is provided a product prepared by the above method, and the product includes at least one of a liquid rich in xylo-oligosaccharides, low-molecular-weight micro-nano lignin, micro-nano lignin with high aryl ether bonds, and glucose. Among them, the lignin with high aryl ether bonds can retain its natural structure and chemical activity, providing a real model and functional basis for accurately studying the biomass conversion mechanism and developing high-value materials.

[0029] In the third aspect of the present invention, there is provided the application of the above product in the fields of medicine, chemical industry, and environment.

[0030] Advantages of the present invention

[0031] The present invention proposes a combination of subcritical hydrolysis and alkaline DES biomass component dissociation technology, which can effectively separate xylo-oligosaccharides and lignin in hemicellulose while maintaining the accessibility of cellulose. The combined component dissociation method provided by the present invention opens up a new technical path for separating lignocellulose components and high-value conversion from biomass, which has important economic impacts and social significance for the extraction and application of natural renewable resources. Specifically:

[0032] (1) Compared with the prior art, in the present invention, the subcritical hydrothermal process converts the xylan in the hemicellulose of castor straw into xylo-oligosaccharides, and a low-molecular-weight micro-nano lignin product is concomitantly produced in this process.

[0033] (2) After the second-step alkaline DES treatment, the biologic accessibility of cellulose is significantly improved, and the yield of the glucose product is greatly increased. At the same time, a micro-nano lignin product with high aryl ether bonds is obtained.

[0034] (3) Based on the combined technology of subcritical hydrolysis and alkaline DES, the components of castor straw are efficiently converted into glucose, xylooligosaccharides, micro-nano lignin with high aryl ether bonds, and low molecular weight micro-nano lignin products, providing technical support for the utilization of castor straw resources.

[0035] (4) The reaction conditions of traditional acid hydrolysis are severe, and the hemicellulose structure in biomass has been completely destroyed, resulting in very low product yields. Therefore, in this invention, considering the high retention of subsequent cellulose, a non-acid subcritical hydrolysis system is selected, and high-value xylooligosaccharides can be obtained using a reaction kettle made of ordinary materials.

[0036] (5) The lignin products separated in Patent CN118725357A are single, and the original structure of lignin has been completely destroyed. In the two treatment processes of this invention, lignin is micronized and nanoized, and two lignin products can be obtained. In addition, the molecular structure of lignin separated after two-step reactions remains very complete, and more than about 80% of aryl ether bonds are retained. The separated lignin with high aryl ether bonds can retain its natural structure and chemical activity, providing a real model and functional basis for accurately studying the biomass conversion mechanism and developing high-value materials. At the same time, the lignin of this invention has high purity, greatly retaining the essential characteristics of lignin and giving full play to the advantages of lignin itself.

[0037] (6) In addition to hemicellulose and lignin products, this invention also converts cellulose in the raw materials into glucose with a high yield.

[0038] This invention realizes the efficient separation of castor straw components through an efficient and green biomass component separation technology. The process flow is simple and easy to implement, with low economic costs, in line with the multi-product development strategy, and is expected to be industrialized. Detailed implementation mode

[0039] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0040] The following will further elaborate on the present invention in combination with specific embodiments. It should be noted that the specific embodiments are interpretations rather than limitations of the present invention.

[0041] In the following examples, the enzyme is Novozymes cellulase, a commercially available product.

[0042] Example 1:

[0043] A method for subcritical hydrolysis and alkaline DES treatment of castor straw fibers followed by enzymatic hydrolysis to produce associated xylooligosaccharides and micro-nano lignin, the specific steps are as follows:

[0044] (1) Subcritical hydrolysis reaction: Take 5 g of castor straw powder with a particle size of 40 - 60 mesh and mix it with 75 mL of deionized water, then add it to a stainless-steel reactor for subcritical hydrolysis reaction. Hydrolyze at 180 °C for 30 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue with 75 ml of deionized water twice to collect the solution containing xylooligosaccharides. Then, wash the hydrolysis residue with 75 ml of ethanol twice, and concentrate the lignin ethanol solution under reduced pressure to a concentration of 2 mg / ml. Stir at a speed of 600 rpm at room temperature, and add three times the volume of deionized water to the lignin ethanol solution at a dropping rate of 1 mL / min, and centrifuge at 3000 rpm to obtain micro-nano low-molecular-weight lignin. Freeze-dry the hydrolysis residue.

[0045] (2) Alkaline DES reaction: Mix choline chloride and monoethanolamine in a molar ratio of 1:8, and heat at 60 °C until a homogeneous transparent solution is formed, i.e., alkaline DES. Mix and react the freeze-dried hydrolysis residue in step (1) with alkaline DES at a mass ratio of 1:20 under magnetic stirring at 300 rpm, and react at 140 °C for 3 hours. After the reaction is completed, add acetone and filter through a G3 crucible until the filtrate is colorless. The filtrate is the solution containing lignin, and the cellulose slurry collected by the G3 crucible is dried in an oven at 105 °C until constant weight. The solution is first concentrated by rotary evaporation, then three times the volume of deionized water is added dropwise to the above-mentioned concentrated lignin solution, dialyze for three days, and freeze-dry to obtain micro-nano lignin with high aryl ether bonds. Add the castor straw pulp treated by subcritical hydrolysis coupled with alkaline DES to a citric acid buffer solution with pH = 4.8 according to a solid content ratio of 2% for enzymatic hydrolysis reaction. The dosage of cellulase is 10 FPU / g biomass, and the reaction is carried out in a constant-temperature shaker at 50 °C; after enzymatic hydrolysis for 72 hours, glucose is obtained. The yield of xylooligosaccharides can reach 64%; the yield of micro-nano low-molecular-weight lignin is about 32%, and the weight-average molecular weight is 1194 Da; after treatment with alkaline DES, the yield of micro-nano lignin (hereinafter referred to as: DES lignin) is 66%, and the β-O-4 content is 81.47%; the yield of glucose is 98%.

[0046] Example 2:

[0047] Method for co-producing xylooligosaccharides and micro-nano lignin by subcritical hydrolysis and alkaline DES treatment of castor straw fibers and enzymatic hydrolysis, the specific steps are as follows:

[0048] (1) Subcritical hydrolysis reaction: Take 5 g of castor straw powder with a particle size of 40 - 60 mesh and mix it with 75 mL of deionized water, then add it to a stainless-steel reactor for subcritical hydrolysis reaction. Hydrolyze at 175 °C for 35 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue with 75 ml of deionized water twice to collect the solution containing xylo-oligosaccharides. Then wash the hydrolysis residue with 75 ml of ethanol twice, and concentrate the lignin ethanol solution under reduced pressure to a concentration of 2 mg / ml. Stir at a speed of 600 rpm at room temperature, and add three times the volume of deionized water to the lignin ethanol solution at a dropping rate of 1 mL / min, and centrifuge at 3000 rpm to obtain micro-nano low-molecular-weight lignin. Freeze-dry the hydrolysis residue.

[0049] (2) Alkaline DES reaction: Mix choline chloride and monoethanolamine in a molar ratio of 1:8, and heat at 60 °C until a homogeneous transparent solution is formed, namely: alkaline DES. Mix the freeze-dried hydrolysis residue in step (1) with hydrated alkaline DES in a mass ratio of 1:15, where DES is alkaline DES containing 20% water. Then react under magnetic stirring conditions at 130 °C and 300 rpm for 5 hours. After the reaction is completed, add acetone and filter through a G3 crucible until the filtrate is colorless. The filtrate is the solution containing lignin, and the cellulose slurry collected by the G3 crucible is dried in an oven at 105 °C until a constant weight is obtained. The solution is first concentrated by rotary evaporation, add three times the volume of deionized water dropwise to the above-mentioned lignin concentrate, dialyze for three days, and freeze-dry to obtain micro-nano lignin with high aryl ether bonds. Add the castor straw pulp treated by subcritical hydrolysis coupled with alkaline DES to a citric acid buffer solution with pH = 4.8 according to a solid content ratio of 2% for enzymatic hydrolysis reaction. The dosage of cellulase is 10 FPU / g of biomass, and the reaction is carried out in a constant-temperature shaker at 50 °C; enzymatically hydrolyze for 72 hours to obtain glucose. The yield of xylo-oligosaccharides that can be obtained is 67%; the yield of micro-nano low-molecular-weight lignin is about 30%, and the weight-average molecular weight is 1250 Da; the yield of DES lignin is 65%; the content of β-O-4 is 82.5%; the yield of glucose is 95%.

[0050] Example 3:

[0051] Method for subcritical hydrolysis and alkaline DES treatment of castor stalk fibers for enzymatic hydrolysis to produce associated xylo-oligosaccharides and micro-nano lignin, the specific steps are as follows:

[0052] (1) Subcritical hydrolysis reaction: Take 5 g of castor straw powder with a particle size of 40 - 60 mesh and mix it with 75 mL of deionized water, then add it to a stainless-steel reactor for subcritical hydrolysis reaction. Hydrolyze at 180 °C for 30 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue with 75 ml of deionized water twice to collect the solution containing xylo-oligosaccharides. Then wash the hydrolysis residue with 75 ml of acetone twice, and concentrate the lignin ethanol solution under reduced pressure to a concentration of 2 mg / ml. Stir at a speed of 600 rpm at room temperature, and add three times the volume of deionized water to the lignin ethanol solution at a dropping rate of 1 mL / min, then centrifuge at 3000 rpm to obtain micro-nano low-molecular-weight lignin. Freeze-dry the hydrolysis residue.

[0053] (2) Alkaline DES reaction: Mix choline chloride and monoethanolamine in a molar ratio of 1:8, and heat at 60 °C until a homogeneous transparent solution is formed, i.e., alkaline DES. Mix the freeze-dried hydrolysis residue in step (1) with hydrated alkaline DES in a mass ratio of 1:15, where DES is alkaline DES containing 40% water. Then react at 140 °C and under magnetic stirring at 300 rpm for 3 hours. After the reaction is completed, add acetone and filter through a G3 crucible until the filtrate is colorless. The filtrate is the solution containing lignin, and the cellulose slurry collected by the G3 crucible is dried in an oven at 105 °C until constant weight. The solution is first concentrated by rotary evaporation, add three times the volume of deionized water dropwise to the above-mentioned lignin concentrate, dialyze for three days, and then freeze-dry to obtain micro-nano lignin with high aryl ether bonds. Add the castor straw slurry treated by subcritical hydrolysis coupling with alkaline DES to the citric acid buffer solution with pH = 4.8 according to a solid content ratio of 2% for enzymatic hydrolysis reaction. The dosage of cellulase is 10 FPU / g of biomass, and the reaction is carried out in a constant-temperature shaker at 50 °C; after enzymatic hydrolysis for 72 hours, glucose is obtained. The yield of xylo-oligosaccharides can reach 64%; the yield of micro-nano low-molecular-weight lignin is about 34%, and the weight-average molecular weight is 1194 Da; the yield of DES lignin is 57.25%, and the β-O-4 content is 81.94%; the yield of glucose is 93%.

[0054] It can be seen from the results of the above examples that under the same conditions, compared with the simple use of DES, by using the subcritical hydrothermal method and DES of the present application to separate the components in lignocellulose, the yields and purities of lignin and cellulose can be improved to varying degrees.

[0055] Comparative Example 1

[0056] The difference from Example 1 is that the subcritical hydrolysis reaction is not carried out.

[0057] The yield of xylo-oligosaccharides is 0%; the yield of micro-nano low-molecular-weight lignin is about 0%; the yield of DES lignin is 45%, and the β-O-4 content is 70%; the yield of glucose is 80%.

[0058] Comparative Example 2

[0059] It is different from Example 1 in that hydrolysis is carried out under the conditions of step (1) in Example 1 of Patent CN118725357A: 5 g of castor straw powder is taken, 75 mL of 3 M sulfuric acid solution is added, and the reaction is carried out at 180 °C for 30 min. After the reaction is completed, solid-liquid separation is carried out, and the obtained residue is dried and pulverized for later use.

[0060] The yield of xylooligosaccharides is 0%; the yield of large-size acid lignin is about 36%, and the weight-average molecular weight is 1526 Da; the yield of DES lignin is 51%, and the β-O-4 content is 25%; the yield of glucose is 83%.

[0061] Comparative Example 3

[0062] It is different from Example 1 in that during the alkaline DES reaction process, an equal amount of pure water is used to replace the alkaline DES.

[0063] The yield of xylooligosaccharides is 64%; the yield of micro-nano low-molecular-weight lignin is about 32%, and the weight-average molecular weight is 1194 Da; the yield of lignin separated in the second step is 1%, and the β-O-4 content is 18%; the yield of glucose is 53%.

[0064] It can be seen from the comparison between Example 1 and Comparative Example 1 that the hydrolysis intensity has a great influence on the subsequent coupling effect. Using subcritical hydrolysis with moderate intensity coupled with alkaline DES treatment can obtain xylooligosaccharides and micro-nano low-molecular-weight lignin. At the same time, the β-O-4 content and the glucose yield are also significantly improved.

[0065] It can be seen from the comparison between Example 1 and Comparative Example 2 that if acidic hydrolysis is coupled with alkaline DES treatment, xylooligosaccharides and micro-nano low-molecular-weight lignin cannot be obtained, and the β-O-4 content and the glucose yield are also relatively low.

[0066] It can be seen from the comparison between Example 1 and Comparative Example 3 that if alkaline DES treatment is not used, micro-nano lignin cannot be obtained, and at the same time, the β-O-4 content and the glucose yield are also relatively low.

[0067] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for treating castor straw fiber with alkaline DES by subcritical hydrolysis to hydrolyze associated xylo-oligosaccharides and micro-nano lignin, characterized in that: include: The castor straw is mixed with water to carry out a subcritical hydrolysis reaction, and after the reaction is completed, the hydrolysis residue is filtered and collected; Washing the hydrolysis residue with water, collecting the washing liquid, which is a liquid rich in xylooligosaccharides; washing with an organic solvent, collecting the washing liquid, which is low molecular weight micro-nano lignin; drying the hydrolysis residue to obtain a solid hydrolysis residue; The alkaline DES is mixed with the solid hydrolysis residue to carry out a dissociation reaction. After the reaction is completed, the solid and the liquid are separated, and the solid and the slurry are collected respectively. The solid is washed with an organic solvent, and the washing liquid is concentrated by rotary evaporation and then dialyzed to obtain micro-nano lignin with high aromatic ether bonds; the slurry is hydrolyzed by biological enzymes to obtain glucose.

2. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The castor straw is powder, and its particle size is 20-80 meshes.

3. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The mass ratio of castor straw to water is 1:5-1:20; Alternatively, the subcritical hydrolysis temperature is 150-200° C., and the reaction time is 10 to 180 minutes.

4. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The organic solvent is selected from one of ethanol, acetone, tetrahydrofuran, and butyrolactone, or a mixture of two of them.

5. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The hydrogen bond acceptor of the alkaline DES is selected from one of choline chloride, betaine, ethylamine hydrochloride and guanidine hydrochloride; the hydrogen bond donor is selected from one of ethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine and diethanolamine; the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:2-10, or 1:5-10; Alternatively, the hydrated alkaline DES is obtained by mixing alkaline DES with water, and the water content is 10%-50%.

6. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The mass ratio of the solid hydrolysis residue to the alkaline DES is 1:8-20.

7. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The temperature of the dissociation reaction is 100-150° C., the reaction time is 1-6 hours, and the stirring speed is 200-500 rpm.

8. The method for treating castor straw fiber with subcritical hydrolysis alkaline DES to hydrolyze associated xylo-oligosaccharides and micro-nano lignin as claimed in claim 1, characterized in that: The specification of the dialysis bag is 200-2000Da; Alternatively, the biological enzyme is cellulase, the amount of cellulase used is 10-20 FPU / g, the enzymatic hydrolysis temperature is 45-55° C., and the enzymatic hydrolysis is carried out for more than 3 days under the conditions of a buffer solution pH of 4.0-6.

0.

9. The product prepared by the method according to any one of claims 1 to 8, comprising: At least one of liquid rich in xylooligosaccharides, low molecular weight micro-nano lignin, micro-nano lignin with high aromatic ether bonds, and glucose.

10. Use of the product according to any one of claims 1 to 9 in the fields of medicine, chemical industry and environment.