Method for subcritical hydrolysis of alkaline des treatment of castor straw fibers for enzymatic hydrolysis associated with low oligomeric xylose and micro-nano lignin

Abstract

The present application belongs to the field of separation of agroforestry biomass components, and provides a method for subcritical hydrolysis and alkaline DES treatment of castor straw fiber to hydrolyze associated oligomeric xylose and micro-nano lignin. The subcritical hydrolysis method is used to treat castor straw raw materials to obtain a large amount of oligomeric xylose, a small amount of micro-nano low molecular weight lignin and a hydrolysis residue rich in cellulose and lignin; then the hydrolysis residue is treated with alkaline deep eutectic solvent (DES) to obtain a slurry rich in cellulose and micro-nano high aryl ether bond lignin. Finally, the slurry rich in cellulose is enzymatically hydrolyzed by biotechnology to obtain high-yield glucose products. The present application integrates subcritical hydrolysis reaction and alkaline DES treatment technology, and can obtain various high-value-added products of castor straw biomass under mild reaction conditions, thereby providing technical support for the value-added of castor industry and the utilization of castor straw resources.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of separation of agroforestry biomass components, and relates to a method for subcritical hydrolysis and alkaline DES treatment of castor stalk fibers to hydrolyze associated oligomeric xylose and micro-nano lignin. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing an understanding of the general context of the present application and is not necessarily recognized as prior art.

[0003] The ecological environment deterioration caused by the over-reliance of human society on fossil energy such as petroleum and the continuous depletion of fossil fuel reserves are increasingly severe challenges. Under this background, biomass, as a renewable resource with abundant reserves, has gradually become a powerful substitute for 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, castor is an important economic crop, and its seeds can be used to extract castor oil. Its stalks are mainly composed of cellulose, hemicellulose and lignin, and the cell wall structure and composition are similar to those of broad-leaved wood. As a rich non-food crop stalk resource, it has high potential value and can be converted into various valuable chemicals, bio-based materials and biofuels. However, the utilization of castor stalk resources has not been valued and developed.

[0004] Previously, there have been reports of using castor stalks to prepare artificial boards. In addition to this, there have been no reports of using this rich stalk resource. The current biomass refining industry is severely limited in its development due to factors such as single product and low process efficiency. Therefore, it is very urgent to develop a green and efficient bio-refining method that can produce multiple biomass-based conversion products at the same time, and it is expected to further promote the vigorous development of the castor industry.

[0005] Subcritical hydrolysis technology is a green and low-energy hydrolysis technology that does not use harmful chemical solvents in the extraction process, reducing environmental pollution and the generation of chemical waste. Compared with traditional acid hydrolysis and supercritical water 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, thereby 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 and a preparation method and application thereof. However, this method cannot realize the full component utilization of biomass, and the original structure of lignin is completely destroyed in this method, with low retention rate of aryl ether bonds. SUMMARY

[0007] To solve the above problems, the application proposes a method for subcritical hydrolysis coupled with alkaline DES treatment of castor straw fiber enzymatic hydrolysis associated with xylo-oligosaccharides and micro-nano lignin, which promotes the reaction of castor straw by combining pretreatment technology, and realizes the multi-product development of xylo-oligosaccharides, glucose and two kinds of micro-nano lignin.

[0008] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0009] In a first aspect of the application, a method for subcritical hydrolysis coupled with alkaline DES treatment of castor straw fiber enzymatic hydrolysis associated with xylo-oligosaccharides and micro-nano lignin is provided, comprising:

[0010] Mixing castor straw with water to carry out subcritical hydrolysis reaction, after the reaction is completed, filtering and collecting the hydrolysis residue; washing the hydrolysis residue with water and collecting the washing liquid, which is a liquid rich in xylo-oligosaccharides; washing with an organic solvent and collecting the washing liquid, which is low molecular weight micro-nano lignin; drying the hydrolysis residue to obtain solid hydrolysis residue;

[0011] Mixing alkaline DES with the solid hydrolysis residue to carry out dissociation reaction, after the reaction is completed, solid-liquid separation is carried out, 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 aryl ether bonds; the slurry is subjected to biological enzyme hydrolysis 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 lignin supermolecule and obtaining micro-nano morphology. This combined technology not only improves the yield of sugars, but also realizes the simultaneous production of various 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 associated with xylo-oligosaccharides and micro-nano lignin proposed by the application aims to optimize the treatment conditions, improve the yield and purity of target products, and reduce 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 the form of powder, and the particle size is 20-80 mesh.

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

[0016] The hydrothermal reaction conditions can greatly affect the production of oligosaccharides. When the hydrothermal reaction conditions are too mild, hemicellulose cannot be efficiently dissolved; when the reaction conditions are too severe, hemicellulose is largely hydrolyzed into monosaccharides, 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] In the basic DES treatment reaction, the hydrated DES has a water content of 10-50%. When the water content exceeds 50%, excessive water changes the properties of the DES solution, thereby affecting the solubility of lignin in the solvent and the reaction mechanism. Therefore, in some embodiments, the hydrated basic DES is obtained by mixing a basic DES with water, and has a water content of 10%-50%.

[0022] In the basic DES treatment reaction, when the mass ratio of the subcritical hydrolysis residue to the DES is less than 1:8, the low density of the castor straw residue causes the DES to be unable to completely infiltrate the raw material, affecting the mass transfer and making it difficult to achieve effective separation of components; when the mass ratio of the hydrolysis residue to the DES is higher than 1:30, excessive DES leads to waste of reagents and increased cost. Therefore, in some embodiments, the mass ratio of the solid hydrolysis residue to the 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 dialysis bag has a specification of 200-2000 Da.

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

[0026] More specifically, comprising the following steps:

[0027] The first step reaction is: castor straw is mixed with deionized water according to a certain solid-liquid ratio and added into a stainless steel reaction kettle, and subcritical hydrolysis reaction is carried out at a set temperature. After the hydrolysis reaction is completed, a filtering operation is carried out, and the hydrolysis residue is washed with deionized water to obtain a liquid rich in xylo-oligosaccharides. Then, the organic solvent is washed to obtain a low molecular weight micro-nano lignin product. At the same time, the solid hydrolysis residue is dried. The second step reaction is: the first step subcritical hydrolysis castor straw residue is treated by using an alkaline DES, and component separation is carried out according to a certain solid-liquid ratio, reaction temperature and time. After the reaction is completed, a filtering separation is carried out, and the washing liquid is concentrated by rotary evaporation and then dialyzed to obtain a high-aryl ether bond micro-nano lignin product. The slurry obtained after the two-step treatment is subjected to biological enzyme hydrolysis to obtain a glucose product.

[0028] In a second aspect of the present application, a product prepared by the above method is provided, and the product comprises at least one of the following: a liquid rich in xylo-oligosaccharides, a low molecular weight micro-nano lignin, a high-aryl ether bond micro-nano lignin and glucose. The high-aryl ether bond lignin can retain its natural structure and chemical activity, and provides a real model and functional basis for accurate research on biomass conversion mechanism and development of high-value materials.

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

[0030] Advantages of the present application

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

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

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

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

[0035] (4) The reaction condition of traditional acid hydrolysis is severe, the structure of hemicellulose in biomass has been completely destroyed, and the product yield is very low. Therefore, in view of the high retention of subsequent cellulose, the present application selects a non-acid subcritical hydrolysis system, and a common material reaction kettle can obtain high value xylooligosaccharides.

[0036] (5) The lignin product separated by patent CN118725357A is single, and the original structure of lignin is completely destroyed. In the two treatment processes of the present application, lignin is micronized, and two lignin products can be obtained. In addition, the molecular structure of the lignin separated after two-step reaction is very complete, and about 80% or more of the aryl ether bond is retained. The high aryl ether bond lignin separated can retain its natural structure and chemical activity, providing a real model and functional basis for precise research on biomass conversion mechanism and development of high-value materials. At the same time, the lignin of the present application has high purity, greatly retains the essential characteristics of lignin, and can fully exert the advantages of lignin itself.

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

[0038] The present application realizes efficient separation of components of castor straw by a high-efficiency and green biomass component separation technology. The process is simple, easy to operate, and low in economic cost, which meets the multi-product development strategy and is expected to realize industrialization. DETAILED DESCRIPTION

[0039] It should be pointed out that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0040] The present application will be further described in detail below in conjunction with specific examples, it should be pointed out that the specific examples are an explanation of the present application rather than a limitation.

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

[0042] Example 1:

[0043] The method for subcritical hydrolysis and alkaline DES treatment of castor straw fiber enzymatic hydrolysis associated xylooligosaccharides and micro-nano lignin is as follows:

[0044] (1) Subcritical hydrolysis reaction: 5 g of castor straw powder with a particle size of 40-60 mesh was mixed with 75 mL of deionized water and added to a stainless steel reactor for subcritical hydrolysis reaction. Hydrolysis was carried out at 180°C for 30 minutes. After hydrolysis, the residue was filtered through a glass funnel. The hydrolysis residue was washed twice with 75 mL of deionized water, and the solution containing xylo-oligosaccharides was collected. The hydrolysis residue was washed twice with 75 mL of ethanol, and the lignin ethanol solution was concentrated under reduced pressure to a concentration of 2 mg / mL. Stirring was carried out at room temperature at a speed of 600 rpm, and three times the volume of deionized water was added to the lignin ethanol solution at a dropwise addition rate of 1 mL / min, and 3000 rpm centrifugation was carried out to obtain micro-nano low molecular weight lignin. The hydrolysis residue was freeze-dried.

[0045] (2) Alkaline DES reaction: Choline chloride and monoethanolamine were mixed at a molar ratio of 1:8 and heated at 60°C to form a uniform transparent solution, i.e. alkaline DES. The freeze-dried hydrolysis residue from step (1) was mixed with the alkaline DES at a mass ratio of 1:20 under magnetic stirring at 300 rpm and reacted at 140°C for 3 hours. After the reaction was completed, acetone was added and mixed, and then filtered through a G3 crucible until the filtrate was colorless, wherein the filtrate was a lignin-containing solution, and the cellulose slurry collected in the G3 crucible was dried in an oven at 105°C until the weight was constant. The solution was first concentrated by rotary evaporation, and three times the volume of deionized water was added to the lignin concentrate, dialyzed for three days, and freeze-dried to obtain micro-nano high aryl ether bond lignin. The castor straw slurry treated by subcritical hydrolysis coupled with alkaline DES was added to a citric acid buffer solution at pH = 4.8 for enzymatic hydrolysis reaction, and the cellulase dosage was 10 FPU / g biomass, which was carried out in a constant temperature shaker at 50°C; enzymatic hydrolysis was carried out for 72 hours to obtain glucose. The yield of xylo-oligosaccharides was 64%; the yield of micro-nano low molecular weight lignin was about 32%, and the weight average molecular weight was 1194 Da; the yield of micro-nano lignin (hereinafter referred to as: DES lignin) after alkaline DES treatment was 66%, the β-O-4 content was 81.47%; and the glucose yield was 98%.

[0046] Example 2:

[0047] The method for enzymatic hydrolysis of castor straw fiber treated by subcritical hydrolysis and alkaline DES, and the accompanying xylo-oligosaccharides and micro-nano lignin, is as follows:

[0048] (1) Subcritical hydrolysis reaction: 5 g of castor straw powder with 40-60 mesh was mixed with 75 mL of deionized water and added to a stainless steel reactor for subcritical hydrolysis reaction. Hydrolysis was carried out at 175°C for 35 minutes. After hydrolysis, the residue was filtered through a glass funnel. The hydrolysis residue was washed twice with 75 mL of deionized water, and the solution containing xylooligosaccharides was collected. The hydrolysis residue was washed twice with 75 mL of ethanol, and the lignin ethanol solution was concentrated under reduced pressure to a concentration of 2 mg / mL. At room temperature, with stirring at 600 rpm, three times the volume of deionized water was added to the lignin ethanol solution at a drop rate of 1 mL / min, and 3000 rpm centrifugation was used to obtain micro-nano low molecular weight lignin. The hydrolysis residue was freeze-dried.

[0049] (2) Alkaline DES reaction: Choline chloride and monoethanolamine were mixed at a molar ratio of 1:8 and heated to form a uniform transparent solution at 60°C, i.e. alkaline DES. The freeze-dried hydrolysis residue from step (1) was mixed with hydrated alkaline DES at a mass ratio of 1:15, and the DES was alkaline DES containing 20% water. Then the reaction was carried out at 130°C and 300 rpm magnetic stirring for 5 hours. After the reaction was completed, acetone was added and mixed, and then filtered through a G3 crucible until the filtrate was colorless, where the filtrate was a lignin-containing solution, and the cellulose slurry collected in the G3 crucible was dried in an oven at 105°C until the weight was constant. The solution was first concentrated by rotary evaporation, and three times the volume of deionized water was added to the lignin concentrate. The dialysis was carried out for three days, and the freeze-drying obtained micro-nano high aryl ether bond lignin. The castor straw slurry treated by subcritical hydrolysis coupled with alkaline DES was added to a citric acid buffer solution at pH = 4.8 for enzymatic hydrolysis reaction, and the cellulase dosage was 10 FPU / g biomass, which was carried out in a constant temperature shaker at 50°C; enzymatic hydrolysis for 72 hours obtained glucose. The yield of xylooligosaccharides was 67%; the yield of micro-nano low molecular weight lignin was about 30%, and the weight average molecular weight was 1250 Da; the yield of DES lignin was 65%; the content of β-O-4 was 82.5%; and the yield of glucose was 95%.

[0050] Example 3:

[0051] The method for subcritical hydrolysis and alkaline DES treatment of castor straw fiber for enzymatic hydrolysis associated with xylooligosaccharides and micro-nano lignin is as follows:

[0052] (1) Subcritical hydrolysis reaction: 5 g of castor straw powder with a particle size of 40-60 mesh was mixed with 75 mL of deionized water and added to a stainless steel reactor for subcritical hydrolysis reaction. The hydrolysis was carried out at 180°C for 30 minutes. After the hydrolysis was completed, it was filtered through a glass funnel. The hydrolysis residue was washed with 75 mL of deionized water twice, and the solution containing xylo-oligosaccharides was collected. The hydrolysis residue was then washed with 75 mL of acetone twice, and the lignin ethanol solution was concentrated under reduced pressure to a concentration of 2 mg / mL. At room temperature, with stirring at 600 rpm, three times the volume of deionized water was added to the lignin ethanol solution at a drop rate of 1 mL / min, and 3000 rpm centrifugation was used to obtain micro-nano low molecular weight lignin. The hydrolysis residue was freeze-dried.

[0053] (2) Alkaline DES reaction: Choline chloride and monoethanolamine were mixed at a molar ratio of 1:8 and heated at 60°C to form a uniform transparent solution, i.e., alkaline DES. The freeze-dried hydrolysis residue from step (1) was mixed with hydrated alkaline DES at a mass ratio of 1:15, and the DES was alkaline DES containing 40% water. Then, under the conditions of 140°C and 300 rpm magnetic stirring, the reaction was carried out for 3 hours. After the reaction was completed, acetone was added and mixed, and then filtered through a G3 crucible until the filtrate was colorless, where the filtrate was a lignin-containing solution, and the cellulose slurry collected in the G3 crucible was dried in an oven at 105°C until the weight was constant. The solution was first concentrated by rotary evaporation, and three times the volume of deionized water was added to the above lignin concentrate. The dialysis was carried out for three days, and the freeze-drying obtained micro-nano high aryl ether bond lignin. The castor straw slurry treated by subcritical hydrolysis coupled with alkaline DES was added to a citric acid buffer solution with pH = 4.8 for enzymatic reaction, and the cellulase dosage was 10 FPU / g biomass, which was carried out in a constant temperature shaker at 50°C; enzymatic hydrolysis for 72 hours obtained glucose. The yield of xylo-oligosaccharides was 64%; the yield of micro-nano low molecular weight lignin was about 34%, and the weight average molecular weight was 1194 Da; the DES lignin was 57.25%, and the β-O-4 content was 81.94%; the glucose yield was 93%.

[0054] From the results of the above examples, it can be seen that, under the same conditions, compared with the use of DES alone, the use of the subcritical hydrothermal method and DES of the present application to separate the components in lignocellulose can improve the yield and purity of lignin and cellulose to varying degrees.

[0055] Comparative Example 1

[0056] The difference from Example 1 is that no subcritical hydrolysis reaction is carried out.

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

[0058] Comparative Example 2

[0059] The difference from Example 1 is that the hydrolysis is carried out using the conditions of step (1) in patent CN118725357A: 5 g of castor straw powder is added to 75 mL of 3M sulfuric acid solution, and reacted at 180°C for 30 min. After the reaction is completed, solid-liquid separation is carried out, the obtained residue is dried and crushed for standby.

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

[0061] Comparative Example 3

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

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

[0064] From the comparison of Example 1 and Comparative Example 1, it can be seen that the hydrolysis intensity has a great influence on the subsequent coupling effect. The use of moderate-intensity subcritical hydrolysis coupled with alkaline DES treatment can obtain xylo-oligosaccharides and micro-nano low molecular weight lignin, and the β-O-4 content and glucose yield are also significantly improved.

[0065] From the comparison of Example 1 and Comparative Example 2, it can be seen that if acid hydrolysis is coupled with alkaline DES treatment, xylo-oligosaccharides and micro-nano low molecular weight lignin cannot be obtained, and the β-O-4 content and glucose yield are also low.

[0066] From the comparison of Example 1 and Comparative Example 3, it can be seen that if no alkaline DES treatment is used, micro-nano lignin cannot be obtained, and the β-O-4 content and glucose yield are also low.

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

Claims

1. A method for subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with low oligomeric xylose and micro-nano lignin, characterized by, The application relates to a method for preparing micro-nano lignin with high aryl ether bond content from castor stalks. The castor stalks are mixed with water to carry out a subcritical hydrolysis reaction, and after the reaction is completed, the hydrolysis residue is collected by filtration; The hydrolysis residue is washed with water, and the washing liquid is collected, which is a liquid rich in xylo-oligosaccharides; the washing liquid is collected by washing with an organic solvent, which is a low-molecular-weight micro-nano lignin; the hydrolysis residue is dried to obtain a solid hydrolysis residue; The solid hydrolysis residue is mixed with an alkaline DES or a hydrated alkaline DES to carry out a dissociation reaction, and after the reaction is completed, solid-liquid separation is carried out, 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 a micro-nano lignin with high aryl ether bond content; the slurry is subjected to biological enzymatic hydrolysis to obtain glucose; The subcritical hydrolysis temperature is 150-200 DEG C, and the reaction time is 10-180 minutes; The organic solvent is selected from one or two of ethanol, acetone, tetrahydrofuran and butyrolactone; The hydrogen bond acceptor of the alkaline DES is selected from one of choline chloride, betaine, ethylamine hydrochloride and guanidine hydrochloride; and the hydrogen bond donor is selected from one of ethanolamine, N, N-dimethylethanolamine, N, N-diethylethanolamine and diethanolamine; The hydrated alkaline DES is obtained by mixing the alkaline DES with water, and the water content is 10%-50%; The biological enzyme is cellulase.

2. The method of subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with oligomeric xylose and micro-nano lignin as claimed in claim 1 wherein, The castor stalks are powders with a particle size of 20-80 meshes.

3. The method of subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with oligomeric xylose and micro-nano lignin as claimed in claim 1, wherein, The mass ratio of the castor stalks to water is 1:5-1:

20.

4. The method of subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with oligomeric xylose and micro-nano lignin as claimed in claim 1, wherein, The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:2-10.

5. The method of subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with xylo-oligosaccharides and micro-nano lignin as claimed in claim 4, wherein, The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:5-10.

6. The method of subcritical hydrolysis of alkaline DES treated castor stalk fiber for enzymatic hydrolysis associated with oligomeric xylose and micro-nano lignin as claimed in claim 1 wherein, The mass ratio of the solid hydrolysis residue to the alkaline DES is 1:8-20.

7. The method of subcritical hydrolytic alkaline DES treatment of castor straw fiber enzymatic hydrolysis associated with low oligomeric xylose and micro-nano lignin according to claim 1, characterized in that, The dissociation reaction temperature is 100-150 DEG C, the reaction time is 1-6 hours, and the stirring speed is 200-500 rpm.

8. The method of subcritical hydrolytic alkaline DES treatment of castor straw fiber enzymatic hydrolysis associated with low oligomeric xylose and micro-nano lignin according to claim 1, characterized in that, The dialysis bag has a specification of 200-2000 Da; Or, the cellulase dosage is 10-20 FPU / g, the enzymatic hydrolysis temperature is 45-55 DEG C, the buffer solution pH is 4.0-6.0, and the enzymolysis time is more than 3 days.