Method for co-producing dissolving pulp and xylooligosaccharide by using bagasse

Abstract

The invention belongs to the technical field of xylooligosaccharide preparation, and discloses a method for co-producing dissolving pulp and xylooligosaccharide by using bagasse. Comprising the following steps: (1) mixing a hydrogen bond acceptor, an alkaline hydrogen bond donor and a protective agent, and heating and stirring to prepare an alkaline eutectic solvent; (2) adding the bagasse into an alkaline eutectic solvent, and heating and stirring for reaction to obtain a reaction mixture; (3) carrying out solid-liquid separation on the reaction mixture, washing a solid component to be neutral to obtain holocellulose, and collecting a washing solution; mixing the washing solution and the liquid component, adding into absolute ethyl alcohol, standing and precipitating, then carrying out solid-liquid separation, and washing and freeze-drying the solid precipitate to obtain hemicellulose; (4) respectively performing enzymolysis on holocellulose and hemicellulose by adopting xylanase, collecting enzymatic hydrolysate and enzymolysis residues, merging the enzymatic hydrolysate, and treating to obtain xylooligosaccharide; washing and freeze-drying holocellulose enzymolysis residues to obtain the dissolving pulp. The alkaline eutectic solvent is used for assisting enzymolysis to obtain the dissolving pulp and the xylooligosaccharide.

Description

Technical Field

[0001] This invention belongs to the field of xylooligosaccharide preparation technology, specifically relating to a method for co-producing dissolving pulp and xylooligosaccharides using sugarcane bagasse. Background Technology

[0002] Sugarcane bagasse, a major byproduct of the sugarcane industry, is rich in cellulose, hemicellulose, and lignin, making it an important renewable biomass resource. Currently, sugarcane bagasse is widely used in the papermaking industry, but in this process, the hemicellulose fraction is dissolved and discarded, resulting in significant resource waste. Therefore, the efficient and environmentally friendly utilization of sugarcane bagasse, achieving the separation and conversion of its various components, has become a research hotspot in the field of biomass refining.

[0003] Traditional biomass refining methods mainly include acid methods, alkali methods, and organic solvent methods. While these methods are effective in separating cellulose, hemicellulose, and lignin, they still have many problems. For example, the use of strong acids and alkalis leads to equipment corrosion and serious environmental pollution; organic solvents are costly and difficult to recycle; and harsh reaction conditions can easily lead to hemicellulose degradation and low yield of xylooligosaccharides.

[0004] Deep eutectic solvents (DES), as a novel green solvent, possess advantages such as simple preparation, high designability, good biocompatibility, and recyclability, showing promising application prospects in the field of biomass pretreatment. In particular, alkaline DES, due to their alkalinity, can effectively disrupt the lignin structure and promote hemicellulose dissolution while maintaining the integrity of cellulose, providing a new approach for the efficient fractionation and value-added utilization of bagasse. However, current research on the use of alkaline DES for the co-production of dissolving pulp and xylooligosaccharides from bagasse remains limited, especially in areas such as solvent formulation, process condition optimization, solvent recovery, and product performance control, which lack systematic and in-depth research. Therefore, developing an efficient, green, and economical alkaline DES-assisted enzymatic hydrolysis process to achieve efficient separation of cellulose, hemicellulose, and lignin from bagasse, and simultaneously produce high-purity dissolving pulp and high-yield xylooligosaccharides, has significant scientific research value and practical application potential. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for co-producing dissolving pulp and xylooligosaccharides from sugarcane bagasse, using an alkaline eutectic solvent to assist enzymatic hydrolysis in converting sugarcane bagasse into xylooligosaccharides and dissolving pulp.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of this invention provides a method for preparing an alkaline eutectic solvent, comprising mixing a hydrogen bond acceptor, an alkaline hydrogen bond donor, and a protective agent, and heating and stirring the mixture to obtain an alkaline eutectic solvent; wherein the hydrogen bond acceptor is choline chloride, and the alkaline hydrogen bond donor is a short-chain amino alcohol or aliphatic amine organic compound.

[0007] Preferably, the basic hydrogen bond donor is one of 1-amino-2-propanol, 1,3-propanediamine, and diethylenetriamine; the protecting agent is ethylene glycol or glycerol.

[0008] Preferably, the molar ratio of hydrogen bond acceptor to basic hydrogen bond donor is 1:5 to 1:8, and the molar ratio of protectant to hydrogen bond acceptor is 1:1 to 1:3; the heating and stirring temperature is 90 to 130°C.

[0009] A second aspect of the present invention provides an alkaline eutectic solvent prepared using the preparation method described in the first aspect.

[0010] The third aspect of the present invention provides the application of the alkaline eutectic solvent described in the second aspect in biomass processing and / or hemicellulose extraction.

[0011] A fourth aspect of the present invention provides a method for co-producing dissolving pulp and xylooligosaccharides from sugarcane bagasse, comprising the following steps: (1) Add sugarcane bagasse to the alkaline eutectic solvent described in the third aspect, and stir the reaction at 70-130°C for 6-10 h to obtain the reaction mixture; (2) The reaction mixture obtained in step (1) is subjected to solid-liquid separation, and the solid component and liquid component are collected separately. The solid component is washed with water until neutral, and freeze-dried to obtain holocellulose. The washing liquid during the water washing process is collected. The washing liquid and liquid component are mixed and then added to anhydrous ethanol for static precipitation. After static precipitation, solid-liquid separation is performed, and the solid precipitate and filtrate are collected separately. The solid precipitate is washed and freeze-dried to obtain hemicellulose. (3) Xylanase was used to enzymatically hydrolyze the holocellulose and hemicellulose obtained in step (2). After the enzymatic hydrolysis was completed, the enzymatic hydrolysate and the enzymatic hydrolysis residue were collected respectively. The enzymatic hydrolysate of holocellulose and the enzymatic hydrolysate of hemicellulose were combined and purified to obtain xylooligosaccharide products. The enzymatic hydrolysis residue of holocellulose was washed and freeze-dried to obtain dissolving pulp.

[0012] Preferably, in step (1), the mass ratio of bagasse to alkaline eutectic solvent is 1:20 to 1:30.

[0013] Preferably, the specific operation of step (3) enzymatic hydrolysis is as follows: add holocellulose or hemicellulose to water, then add xylanase, mix well and carry out enzymatic hydrolysis reaction, after the enzymatic hydrolysis reaction is completed, carry out solid-liquid separation, and collect the enzymatic hydrolysate and enzymatic hydrolysis residue.

[0014] More preferably, the solid-liquid ratio of holocellulose or hemicellulose to water is 1:50.

[0015] Preferably, in step (3), the amount of xylanase added is 1% to 6% of the mass of holocellulose or hemicellulose, the enzymatic hydrolysis temperature is 50 to 60°C, and the enzymatic hydrolysis time is 6 to 24 h.

[0016] Preferably, the settling time in step (2) is 12 to 16 hours.

[0017] In step (2), the filtrate is treated with ethanol to remove the alkaline eutectic solvent.

[0018] More preferably, rotary evaporation is used for ethanol removal, with the rotary evaporation temperature being 50–60°C and the time being 2–3 h.

[0019] Preferably, the freeze-drying temperature in steps (2) and (3) is -30 to -60°C, and the vacuum degree is 0.5 to 1 MPa.

[0020] More preferably, the freeze-drying time for the solid component in step (2) is 12-24 h, the freeze-drying time for the solid precipitate is 6-12 h, and the freeze-drying time for the enzymatic hydrolysis residue of cellulose in step (3) is 12-24 h.

[0021] Preferably, in step (2), the bagasse is pretreated with distilled water and anhydrous ethanol before being added to remove the extract.

[0022] Preferably, water is added to the reaction mixture to dilute it before solid-liquid separation in step (2).

[0023] Preferably, in step (2), after the washing liquid is mixed with the liquid component, the water is first removed by rotary evaporation, and then anhydrous ethanol is added for static precipitation.

[0024] More preferably, the rotary evaporation temperature is 70–80°C and the time is 2–5 h.

[0025] Preferably, the solid precipitate in step (2) should be washed before it dries to prevent hemicellulose from forming a coprecipitate with the eutectic solvent.

[0026] Preferably, in step (3), the enzymatic hydrolysate and enzymatic hydrolysate are separated by centrifugation at a speed of 4000-8000 rpm for 10-20 min.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, sugarcane bagasse is converted into xylooligosaccharides and dissolving pulp by alkaline eutectic solvent-assisted enzymatic hydrolysis. The alkaline eutectic solvent preparation method is simple and stable, and can efficiently separate cellulose, hemicellulose and lignin in biomass. Xylanase has a good effect on enzymatic hydrolysis of hemicellulose and holocellulose, and the yield of xylooligosaccharides is high (38.88%~48.20%). The dissolving pulp has high purity (79.57%~90.09%), low hemicellulose content and good reactivity (42.89%~60.78%).

[0028] (2) The present invention does not require the use of any other chemical solvents, and the eutectic solvent can be recycled, which reduces production costs and waste liquid discharge. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the invention. Any person skilled in the art will understand that these embodiments do not limit the invention in any way, and appropriate modifications can be made without departing from the spirit and scope of the invention.

[0030] In the following examples, the concentrations of glucose, xylose, arabinose, 5-hydroxymethylfurfural, furfural, and xylooligosaccharides (a collective term for xylose disaccharides, xylose trisaccharides, xylose tetrasaccharides, and xylose pentasaccharides) were determined by high-performance liquid chromatography (HPLC). The concentrations of glucose, xylose, arabinose, 5-hydroxymethylfurfural, and furfural were used to correct for the content of cellulose and hemicellulose in the samples; while the determination of xylooligosaccharide concentrations was primarily used to calculate the yield of xylooligosaccharides.

[0031] The chromatographic conditions for glucose, xylose, arabinose, and xylooligosaccharides were as follows: Chromatograph: Agilent 1260 high-performance liquid chromatograph; Column: Agilent Hi-Plex-H; Mobile phase: 5 mmol / L sulfuric acid; Flow rate: 0.6 mL / min; Column temperature: 65℃; Detector: Differential refractive index detector; Injection volume: 10 μL. External standard method was used for determination. The chromatographic conditions for 5-hydroxymethylfurfural and furfural were as follows: Chromatograph: Agilent 1260 high-performance liquid chromatograph; Column: Agilent TC-C18; Mobile phase: methanol and water (6:4); Flow rate: 0.6 mL / min; Column temperature: 35℃; Detector: Diode array detector; Injection volume: 2 μL.

[0032] The specific methods for determining the content of each component in sugarcane bagasse and hemicellulose samples are as follows: Take 0.15–0.16 g of sample, add 1.5 mL of 72% sulfuric acid, react at 30℃ for 60 min, add 42 mL of distilled water to dilute the sulfuric acid concentration to 4%, react at 121℃ for 60 min, and separate the hydrolysate and hydrolysis residue by vacuum filtration. Take 5 mL of hydrolysate and add 0.5–0.505 g of barium hydroxide for neutralization, and take the supernatant for HPLC analysis. HPLC is used to analyze the concentrations of glucose, xylose, arabinose, 5-hydroxymethylfurfural, and furfural. The hydrolysis residue mainly contains lignin and residual ash. The lignin content is obtained by calcining in a muffle furnace at 575℃ for 4 h and measuring the mass difference before and after calcination.

[0033] Cellulose content (%) = 100 × 0.9 × hydrolysate volume (mL) × (glucose concentration in hydrolysate mg / mL + 25.18 × 5-hydroxymethylfurfural concentration in hydrolysate) ÷ (sample mass g × 1000); Hemicellulose content (%) = 100 × 0.88 × hydrolysate volume (mL) × (arabinose concentration in hydrolysate mg / mL + xylose concentration in hydrolysate mg / mL + 5.55 × furfural concentration in hydrolysate mg / mL) ÷ (sample mass g × 1000); Lignin content (%) = 100 × (dry weight of crucible before ignition g - dry weight of crucible after ignition g) / sample mass g; Hemicellulose dissolution rate (%) = 100 × (hemicellulose content in bagasse - hemicellulose content in holocellulose) / hemicellulose content in bagasse. Lignin dissolution rate (%) = 100 × (Lignin content in sugarcane bagasse - Lignin content in holocellulose) / Lignin content in sugarcane bagasse; The yield of xylooligosaccharides (%) = 100 × (concentration of xylose disaccharide in the combined enzymatic hydrolysate (mg / mL) + concentration of xylose triaccharide in the combined enzymatic hydrolysate (mg / mL) + concentration of xylose tetraaccharide in the combined enzymatic hydrolysate (mg / mL) + concentration of xylose pentase in the combined enzymatic hydrolysate (mg / mL) × volume of the combined enzymatic hydrolysate (mL) / (mass of the original sugarcane bagasse (mg) × hemicellulose content in the sugarcane bagasse (%)). The reactivity of the dissolving pulp was assessed using a modified Fock reaction test method. The specific procedure was as follows: a 0.5 g dry weight dissolving pulp sample was mixed with 50 mL of sodium hydroxide solution and shaken. Carbon disulfide was then added for xanthation, followed by centrifugation at 5000 rpm for 15 min. 10 mL of the supernatant was collected, and 20% sulfuric acid was added to remove the carbon disulfide. Potassium dichromate and potassium iodide solutions were then added, and the mixture was titrated with Na₂S₂O₃ for analysis.

[0034] (I) Effects of different alkaline eutectic solvents on the purity of the dissolved slurry and the yield of xylooligosaccharides Example 1 A method for co-producing dissolving pulp and xylooligosaccharides using sugarcane bagasse, the specific steps of which are as follows: (1) The sugarcane bagasse was air-dried and crushed, and sieved to obtain sugarcane bagasse of 20-80 mesh. Then, it was extracted twice with distilled water at 80°C and twice with 95% ethanol at 60°C to obtain sugarcane bagasse with the extract removed. (2) Choline chloride, 1-amino-2-propanol and glycerol were mixed in a molar ratio of 1:5:2 and heated and stirred at 130°C for 6 hours to obtain a homogeneous and stable basic eutectic solvent of choline chloride / 1-amino-2-propanol / glycerol. (3) Add the sugarcane bagasse from which the extract was removed in step (1) to the alkaline eutectic solvent prepared in step (2) at a mass ratio of 1:25, and stir the reaction at 130°C for 8 h to obtain the reaction mixture. (4) Add 20% water by mass of the reaction mixture to the reaction mixture obtained in step (3) and stir to dilute the high viscosity slurry mixture. Separate the solid and liquid by vacuum filtration to obtain filtrate and holocellulose filter cake. Wash the holocellulose filter cake until neutral and freeze dry at -50℃ and 0.9MPa for 24 h to obtain holocellulose. (5) Mix the washing liquid of the holocellulose filter cake with the filtrate, evaporate at 80°C for 5 hours to remove water, then add it to 3 times the volume of anhydrous ethanol and let it stand for 12 hours to precipitate. After the sedimentation is complete, separate the solid and liquid by vacuum filtration to obtain the filtrate and hemicellulose filter cake. Wash the hemicellulose filter cake with anhydrous ethanol until neutral, freeze dry at -50°C and 0.9 MPa for 16 hours to obtain hemicellulose. Evaporate the obtained filtrate at 60°C for 3 hours to remove ethanol and recover the alkaline eutectic solvent. (6) Add distilled water to the holocellulose obtained in step (4) and the hemicellulose obtained in step (5) at a solid-liquid ratio of 1:50, add xylanase at 1% of the mass of holocellulose or hemicellulose, and perform enzymatic hydrolysis at 55℃ for 8 hours. After the enzymatic hydrolysis is completed, centrifuge at 6000 rpm for 20 minutes to separate the enzymatic hydrolysate and the enzymatic hydrolysis residue. Combine the enzymatic hydrolysate of holocellulose and the enzymatic hydrolysate of hemicellulose and purify them to obtain xylooligosaccharide product. Collect the enzymatic hydrolysis residue after holocellulose enzymatic hydrolysis, wash it, and freeze dry it at -50℃ and 0.9MPa for 24 hours to obtain cellulose dissolving slurry.

[0035] The purification of the combined enzymatic hydrolysate in step (6) follows the method described in patent "CN 201610878650.5", specifically: 2.5% (w / v) 200-mesh wood-based activated carbon powder and 1% (m / v) 5-mesh wood-based activated carbon particles are added to the enzymatic hydrolysate for adsorption, followed by adsorption at 60°C with stirring for 30 minutes. Then, 2% (m / v) diatomaceous earth is added, and the mixture is filtered. During filtration, the volume of the enzymatic hydrolysate is calculated based on the filtration area of ​​the funnel, ensuring the filter cake mass is 0.3 g / cm³. 2 The product was eluted stepwise with equal volume concentrations of 10%, 30%, 50%, and 70% (v / v) ethanol. The eluents were then concentrated under reduced pressure and freeze-dried to obtain xylooligosaccharide products.

[0036] In Example 1, after treatment with a basic eutectic solvent of choline chloride / 1-amino-2-propanol / glycerol, the dissolution rate of hemicellulose in sugarcane bagasse was 39.16%, and the dissolution rate of lignin was 87.92%. After enzymatic hydrolysis, the yield of xylooligosaccharides was 38.88%, the cellulose content in the dissolving pulp reached 86.52%, and the reactivity of the dissolving pulp was 46.77%.

[0037] The alkaline eutectic solvent recovered in step (6) was further recycled for bagasse treatment (i.e., bagasse was treated using the method described in this embodiment of co-producing dissolving pulp and xylooligosaccharides from bagasse). After three cycles, the dissolution rate of hemicellulose in the bagasse was 37.01%, and the dissolution rate of lignin was 65.34%. This indicates that after recycling, the dissolution effect of choline chloride / 1-amino-2-propanol / glycerol on hemicellulose and lignin decreased by 5.49% and 25.68%, respectively.

[0038] Example 2 Example 2 is basically the same as Example 1, except that 1,3-propanediamine is used instead of 1-amino-2-propanol in step (2) to obtain a basic eutectic solvent of choline chloride / 1,3-propanediamine / glycerol.

[0039] In Example 2, after treatment with a basic eutectic solvent of choline chloride / 1,3-propanediamine / glycerol, the dissolution rate of hemicellulose in sugarcane bagasse was 63.94%, and the dissolution rate of lignin was 91.05%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 48.20%, the cellulose content in the dissolving pulp reached 90.09%, and the reactivity was 60.78%.

[0040] The alkaline eutectic solvent recovered in step (3) was further recycled for bagasse treatment (i.e., bagasse was treated using the method described in this embodiment of co-producing dissolving pulp and xylooligosaccharides from bagasse). After three cycles, the dissolution rate of hemicellulose was 53.47%, and the dissolution rate of lignin was 82.67%. This indicates that after recycling, the dissolution effect of choline chloride / 1,3-propanediamine / glycerol on hemicellulose and lignin decreased by 14.97% and 9.20%, respectively, indicating that choline chloride / 1,3-propanediamine / glycerol is a eutectic solvent with both good dissolution effect and recycling performance.

[0041] Example 3 Example 3 is basically the same as Example 1, except that in step (2), diethylenetriamine is used instead of 1-amino-2-propanol to obtain a basic eutectic solvent of choline chloride / diethylenetriamine / glycerol.

[0042] In Example 3, after treatment with an alkaline eutectic solvent of choline chloride / diethylenetriamine / glycerol, the dissolution rate of hemicellulose in sugarcane bagasse was 60.32%, and the dissolution rate of lignin was 74.53%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 41.12%, the cellulose content in the dissolving pulp reached 79.57%, and the reactivity was 42.89%.

[0043] The alkaline eutectic solvent recovered in step (3) was further recycled for bagasse treatment (i.e., bagasse was treated using the method described in this embodiment of co-producing dissolving pulp and xylooligosaccharides from bagasse). After three cycles, the dissolution rate of hemicellulose was 45.94%, and the dissolution rate of lignin was 66.09%. This indicates that after recycling, the dissolution effect of choline chloride / diethylenetriamine / glycerol on hemicellulose and lignin decreased by 23.84% and 10.75%, respectively.

[0044] All three eutectic solvents in Examples 1 to 3 can produce xylooligosaccharide and cellulose dissolving pulp. Since the 1,3-propanediamine molecule in the eutectic solvent of Example 2 has a simple molecular structure, it is not easy to form steric hindrance during the pretreatment process. Therefore, compared with the other two eutectic solvents, choline chloride / 1,3-propanediamine / glycerol has a good dissolving effect on hemicellulose and lignin. After three cycles of use, the dissolving ability of hemicellulose and lignin did not decrease significantly, making it a relatively ideal solvent.

[0045] (II) Effects of different reaction temperatures on the purity of the dissolving slurry and the yield of xylooligosaccharides Example 4 Example 4 is basically the same as Example 2, except that the reaction temperature in step (3) is 70°C.

[0046] In Example 4, after treatment with a choline chloride / 1-amino-2-propanol / glycerol eutectic solvent, the dissolution rate of hemicellulose in sugarcane bagasse was 51.35%, and the dissolution rate of lignin was 82.22%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 39.87%, the cellulose content in the dissolving pulp reached 83.01%, and the reactivity was 52.13%. The yield of xylooligosaccharides and the reactivity of the dissolving pulp were lower than those in Example 2.

[0047] Example 5 Example 5 is basically the same as Example 2, except that the reaction temperature in step (3) is 90°C.

[0048] In Example 5, after treatment with a choline chloride / 1,3-propanediamine / glycerol eutectic solvent, the dissolution rate of hemicellulose in sugarcane bagasse was 57.82%, and the dissolution rate of lignin was 87.38%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 44.25%, the cellulose content in the dissolving pulp reached 86.69%, and the reactivity was 57.32%. The yield of xylooligosaccharides and the reactivity of the dissolving pulp were lower than those in Example 2.

[0049] Example 6 Example 6 is basically the same as Example 2, except that the reaction temperature in step (3) is 110°C.

[0050] In Example 6, after treatment with a choline chloride / diethylenetriamine / glycerol eutectic solvent, the dissolution rate of hemicellulose in sugarcane bagasse was 61.06%, and the dissolution rate of lignin was 89.84%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 49.52%, the cellulose content in the dissolving pulp reached 89.44%, and the reactivity was 59.53%. The yield of xylooligosaccharides and the reactivity of the dissolving pulp were lower than those in Example 2.

[0051] The comparison between Examples 4-6 and Example 2 shows that the separation effect of biomass is better under high temperature conditions. Among them, the yield of xylooligosaccharide is the highest at 130℃, and the reaction performance of cellulose dissolving pulp is the best.

[0052] (III) Effect of different amounts of eutectic solvent on the purity of the dissolving slurry and the yield of xylooligosaccharides Example 7 Example 7 is basically the same as Example 2, except that the mass ratio of bagasse and alkaline eutectic solvent in step (3) is 1:20.

[0053] In Example 7, after treatment with a choline chloride / 1,3-propanediamine / glycerol eutectic solvent, the dissolution rate of hemicellulose in sugarcane bagasse was 60.55%, and the dissolution rate of lignin was 85.33%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 45.06%, the cellulose content in the dissolving pulp reached 87.75%, and the reactivity was 57.69%. The yield of xylooligosaccharides and the reactivity of the dissolving pulp were lower than those in Example 2.

[0054] Example 8 Example 8 is basically the same as Example 2, except that the mass ratio of bagasse and alkaline eutectic solvent in step (3) is 1:30.

[0055] In Example 8, after treatment with a choline chloride / 1,3-propanediamine / glycerol eutectic solvent, the dissolution rate of hemicellulose in sugarcane bagasse was 74.65%, and the dissolution rate of lignin was 98.74%. After enzymatic hydrolysis, the total yield of xylooligosaccharides was 47.13%, the cellulose content in the dissolving pulp reached 95.36%, and the reactivity was 68.54%. The reactivity of the dissolving pulp was significantly higher than that of Example 2, but the yield of xylooligosaccharides decreased.

[0056] As can be seen from the comparison between Examples 7-8 and Example 2, the more eutectic solvent is used, the better the separation effect of biomass. However, excessive use of eutectic solvent will make it difficult to recover some hemicellulose, which is not conducive to the production of xylooligosaccharides and will increase production costs. Therefore, the mass ratio of sugarcane bagasse to alkaline eutectic solvent is 1:25, which is the most reasonable.

Claims

1. A method for preparing an alkaline eutectic solvent, characterized in that, A basic eutectic solvent is obtained by mixing a hydrogen bond acceptor, a basic hydrogen bond donor, and a protecting agent, and then heating and stirring the mixture. The hydrogen bond acceptor is choline chloride, and the basic hydrogen bond donor is a short-chain amino alcohol or aliphatic amine.

2. The method according to claim 1, characterized in that, The basic hydrogen bond donor is one of 1-amino-2-propanol, 1,3-propanediamine, or diethylenetriamine; the protecting agent is ethylene glycol or glycerol.

3. The method according to claim 2, characterized in that, The molar ratio of hydrogen bond acceptor to basic hydrogen bond donor is 1:5 to 1:8, and the molar ratio of protectant to hydrogen bond acceptor is 1:1 to 1:3; the heating and stirring temperature is 90 to 130°C.

4. An alkaline eutectic solvent prepared by any one of the preparation methods described in claims 1-3.

5. The use of the alkaline eutectic solvent of claim 4 in biomass processing and / or hemicellulose extraction.

6. A method for co-producing dissolving pulp and xylooligosaccharides from sugarcane bagasse, characterized in that, Includes the following steps: (1) Add sugarcane bagasse to the alkaline eutectic solvent of claim 4 and stir at 70-130°C for 4-8 h to obtain a reaction mixture; (2) The reaction mixture obtained in step (1) is subjected to solid-liquid separation, and the solid components and liquid components are collected separately. The solid components are washed with water until neutral, and freeze-dried to obtain holocellulose. The washing liquid from the water washing process is collected. The washing solution was mixed with the liquid component and then added to anhydrous ethanol for static precipitation. After the static precipitation was completed, solid-liquid separation was performed, and the solid precipitate and filtrate were collected separately. The solid precipitate was washed and freeze-dried to obtain hemicellulose. (3) Xylanase was used to enzymatically hydrolyze the holocellulose and hemicellulose obtained in step (2). After the enzymatic hydrolysis was completed, the enzymatic hydrolysate and the enzymatic hydrolysis residue were collected. The enzymatic hydrolysate of holocellulose and the enzymatic hydrolysate of hemicellulose were combined. The xylooligosaccharide product was purified from the combined enzymatic hydrolysate. The enzymatic hydrolysis residue of holocellulose was washed and freeze-dried to obtain cellulose dissolving pulp.

7. The method according to claim 6, characterized in that, Step (1) The mass ratio of sugarcane bagasse to alkaline eutectic solvent is 1:25 to 1:

30.

8. The method according to claim 6, characterized in that, The specific operation of step (3) enzymatic hydrolysis is as follows: add holocellulose or hemicellulose to water, then add xylanase, mix well and carry out enzymatic hydrolysis reaction. After the enzymatic hydrolysis reaction is completed, perform solid-liquid separation and collect the enzymatic hydrolysate and enzymatic hydrolysis residue.

9. The method according to claim 8, characterized in that, In step (3), the amount of xylanase added is 1% to 6% of the mass of holocellulose or hemicellulose, the enzymatic hydrolysis temperature is 50 to 60℃, and the enzymatic hydrolysis time is 6 to 24 h.

10. The method according to claim 6, characterized in that, The settling time in step (2) is 12 to 16 hours; the freeze-drying temperature in steps (2) and (3) is -30 to -60°C and the vacuum degree is 0.5 to 1 MPa; the filtrate in step (2) is removed by ethanol and the alkaline eutectic solvent is recovered.