Method for preparing sugar from lignocellulose

Abstract

The invention belongs to the field of biomass conversion, and particularly relates to a method for preparing sugar from lignocellulose, which comprises the following steps: preparing modified carbon nitride containing sulfonic acid groups; preparing a copper-doped ferrite; preparing a molecular sieve carrier, adding ferrite after crystallization, and roasting to obtain a magnetic carrier; loading the modified carbon nitride in the magnetic carrier to obtain a magnetic catalyst for hydrolyzing lignocellulose; the method comprises the following steps: putting lignocellulose and a magnetic catalyst into hot water together, carrying out illumination hydrolysis while aerating, and then taking out the catalyst to obtain hydrolysate containing glucose; and continuously carrying out enzymolysis on the hydrolysate by using an enzyme, and purifying to obtain the glucose. The method can catalytically oxidize degradation of lignin and cellulose under the condition of illumination and hydrolyze cellulose to prepare glucose, and is low in equipment requirement and free of pollution.

Description

Technical Field

[0001] The present invention belongs to the field of biomass conversion, and particularly relates to a method for preparing sugar from lignocellulose. Background Art

[0002] Lignocellulose is the main component of plant cell walls, mainly composed of cellulose, hemicellulose, and lignin. Cellulose, which constitutes the basic framework, is formed by glucose linked by β-1,4 glycosidic bonds; hemicellulose, which is intertwined with cellulose, is mainly composed of xylose and sometimes contains a small amount of mannose, galactose, arabinose, etc.; lignin, which tightly wraps cellulose and hemicellulose and is also covalently bonded to part of hemicellulose, is composed of phenylpropane structural units. The complex structure among the components makes the entire lignocellulose structure tight, stable, and not easily damaged. Currently, pretreatment methods such as acid treatment, alkali treatment, and microbial enzymatic hydrolysis treatment are mainly used to destroy the basic structure of lignocellulose. Cellulase is a general term for a class of complex enzyme systems that can degrade cellulose. Cellulase is essentially a protein, and its activity is greatly affected by temperature, pH value, enzyme concentration, substrate concentration, and ionic strength. Natural cellulose is formed by the interlaced arrangement of crystalline region cellulose and non-crystalline region cellulose. Cellulase mainly degrades the non-crystalline region of cellulose and is severely hindered when acting on crystalline cellulose, and the effect of enzymatic hydrolysis directly determines the sugar concentration in the enzymatic hydrolysate. Defects such as high production cost, low enzyme activity, large consumption of cellulase, and long production cycle limit the enzymatic hydrolysis of cellulose biomass. Developing a method for hydrolyzing lignocellulose with low production cost, good recyclability, high catalytic activity, easy recovery, and environmental friendliness has become a research hotspot in recent years. Summary of the Invention

[0003] To solve the problems of high cost, low efficiency, and difficult recovery in the prior art for preparing sugar by enzymatic hydrolysis of woody cellulose, the present invention mainly provides a method that is easy to recover and can efficiently decompose straw to prepare sugar solution. The technical solution is as follows:

[0004] A method for preparing sugar from lignocellulose, which comprises preparing modified carbon nitride containing sulfonic acid groups; preparing copper-doped ferrite; preparing a molecular sieve support, adding ferrite after crystallization, and obtaining a magnetic support after calcination; loading modified carbon nitride in the magnetic support to obtain a magnetic catalyst for hydrolyzing lignocellulose; placing lignocellulose and the magnetic catalyst together in hot water, hydrolyzing while aerating and irradiating with light, then taking out the catalyst to obtain a hydrolyzate containing glucose; and using an enzyme to continue enzymatic hydrolysis of the hydrolyzate and purifying to obtain glucose.

[0005] Further, the lignocellulose and the magnetic catalyst are placed together in hot water at a temperature above 80°C, and hydrolyzed by aeration and light for 6 to 24 hours; the mass ratio of the magnetic carrier to the modified carbon nitride is 1:0.1 to 0.6; the mass ratio of the straw to the magnetic catalyst is 1:0.5 to 4.

[0006] Further, the preparation of the magnetic catalyst includes the following steps: dispersing the magnetic carrier and the modified carbon nitride in water, adding liquid polyethylene glycol and dispersing evenly, drying at a temperature below 50°C, and then performing heat treatment at 80 to 100°C for 2 to 6 hours to obtain the magnetic catalyst.

[0007] Further, the mass ratio of the magnetic carrier to the polyethylene glycol is 1:0.2 to 0.8.

[0008] Further, the preparation method of the magnetic carrier includes the following steps:

[0009] a. Taking melamine and sulfamic acid and calcining at 500 to 600°C for 3 to 5 hours, cooling and then taking out to obtain carbon nitride;

[0010] b. Then immersing the carbon nitride, sulfamic acid and 1,3 - propane sultone in ethanol, grinding and mixing for 0.5 to 1 hour, adding dilute ammonia water to the system, mixing evenly and reacting at 60 to 75°C for 6 to 10 hours, and then evaporating the solvent at 30 to 60°C, and washing thoroughly to obtain the modified carbon nitride;

[0011] c. Preparing copper - doped ferrite; taking aluminum isopropoxide, dissolving it in tetrapropylammonium hydroxide, diluting with water and stirring at 50 to 70°C until aluminum isopropoxide is fully hydrolyzed to obtain a precursor solution; adding an organic amine to the precursor solution and dispersing evenly; then adding silica sol according to a silicon - aluminum ratio of 150 to 200 and continuing to stir and mix until fully hydrolyzed; aging at 100 to 130°C for 12 to 16 hours after sealing, and crystallizing at 150 to 180°C for 10 to 18 hours;

[0012] d. Then adding ferrite to the system and dispersing evenly; after dispersing evenly, evaporating the solvent, and then calcining at 500 to 600°C for 4 to 8 hours to obtain the magnetic carrier.

[0013] Further, in step a, the mass ratio of the melamine to the sulfamic acid is 1:0.1 to 0.5; in step b, the mass ratio of the carbon nitride to the 1,3 - propane sultone is 1:0.2 to 0.8; in step b, the mass ratio of the sulfamic acid to the 1,3 - propane sultone is 1:1 to 3; in step b, the volume ratio of the ethanol to the dilute ammonia water is 1:2 to 5.

[0014] Furthermore, the mass ratio of the aluminum isopropoxide in step c to tetrapropylammonium hydroxide is 1:20-30; the molar ratio of the organic amine in step c to the aluminum isopropoxide is 150-250:1; and the mass ratio of the aluminum isopropoxide in step c to the ferrite in step d is 1-2:1.

[0015] Furthermore, the organic amine includes one or more of ethanolamine, isopropanolamine, diethanolamine or cyclohexylamine.

[0016] Furthermore, the preparation of the ferrite includes the following steps: taking ferrous sulfate and copper sulfate and placing them in a polyvinyl pyrrolidone solution, using sodium hydroxide solution to adjust the pH of the system to 10-13.5, and mixing them thoroughly to obtain a mixed solution; reacting the mixed solution at 150-180°C for 8-12h, collecting the precipitate, and washing it thoroughly and then drying it to obtain ferrite.

[0017] Furthermore, the molar ratio of the ferrous sulfate to the copper sulfate is 2:1.

[0018] By adopting the above scheme, the method of the present invention has the following advantages:

[0019] 1. The carbon nitride and ferrite on the magnetic catalyst of the present invention can catalyze the degradation of lignin and cellulose under light. Compared with steam explosion pretreatment and enzymatic hydrolysis, and concentrated sulfuric acid one-step hydrolysis, it has the advantages of short cycle, high efficiency, low equipment investment cost, easy magnetic separation and reuse, and environmental protection and pollution-free, making it suitable for industrial promotion.

[0020] 2. The magnetic catalyst of the present invention combines with carbon nitride, which catalyzes hydrogen peroxide production, through a Fenton-like effect, promoting mutual promotion and high catalytic activity. Furthermore, the oxidative free radicals and hydroxyl radicals generated during the catalytic process not only decompose cellulose but also depolymerize lignin, disrupting the tight connection between the three elements. This solves the problem that cellulase is unable to degrade lignin and crystalline cellulose, requiring pretreatment to disrupt the structure of lignocellulose.

[0021] 3. The magnetic catalyst of the present invention carries a highly electronegative sulfonic acid group, which can hydrolyze the glycosidic bonds in the cellulose chain. It can also work together with the residual amino groups in the catalyst and a carrier with strong adsorption properties to adsorb cellulose, allowing the catalyst to fully contact the substrate, which is beneficial for free radicals to act directly on the hydrolysis site and improve the catalytic efficiency.

[0022] 4. In the preparation process of the carbon nitride of the present invention, aminosulfonic acid is introduced. The aminosulfonic acid decomposes and vaporizes at high temperature to make the obtained carbon nitride have fine particle size, and the sulfonic acid substances remaining in the carbon nitride are also beneficial to improving the wetting performance of aminosulfonic acid, 1,3 - propane sultone and carbon nitride in the subsequent steps; the system of aminosulfonic acid, 1,3 - propane sultone and carbon nitride can ensure good dispersibility.

[0023] 5. The amine substances remaining in the system after the zeolite crystallization of the present invention can produce electrostatic interaction with copper in the ferrite, promoting the dispersion of the ferrite and its combination with the crystal, and can also promote the dispersion of the crystal through the presence of ferrite particles to prevent secondary crystallization.

[0024] 6. The remaining amino groups in the modified carbon nitride of the present invention can produce electrostatic interaction with copper in the ferrite, which is beneficial to the tight combination of the modified carbon nitride and the ferrite and promotes the stable loading of the modified carbon nitride on the magnetic carrier.

[0025] 7. The present invention uses polyethylene glycol to bond the modified carbon nitride and the magnetic carrier, promoting the modified carbon nitride to enter the pores inside the carrier. Then, through the oxidation of hydrophilic sulfonic acid groups, the carbon nitride is combined. Under the action of heat treatment, the polyethylene glycol decomposes, so that the modified carbon nitride enters the deep pores of the carrier and is not easy to escape. Description of the Drawings

[0026] Figure 1 : Physical picture of glucose obtained by purifying the hydrolysis solution hydrolyzed from the magnetic catalyst in Example 1. Detailed Embodiments

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1: (1) Take 2 g of melamine and 1 g of aminosulfonic acid and calcine them at 550 °C for 4 h. After cooling, take them out to obtain carbon nitride; then take 1 g of carbon nitride, 0.5 g of aminosulfonic acid and 0.5 g of 1,3 - propane sultone, immerse them in ethanol, grind and mix for 0.5 h, then add 10% dilute ammonia water with a volume 4 times that of ethanol to the system, mix evenly and react at 65 °C for 8 h, and then evaporate the solvent at 40 °C to dryness. After sufficient washing, modified carbon nitride is obtained;

[0029] (2) 2.78 g of ferrous sulfate heptahydrate and 1.25 g of copper sulfate pentahydrate were placed in a 3-6 g / L polyvinyl pyrrolidone solution, and the pH of the system was adjusted to 12.5 using a sodium hydroxide solution. After thorough mixing, a mixed solution was obtained; the mixed solution was reacted at 160° C. for 10 h, and the precipitate was collected, thoroughly washed, and then dried to obtain ferrite;

[0030] (3) Take 2g of aluminum isopropoxide, dissolve it in 50mL of tetrapropylammonium hydroxide, dilute it with water, and stir it at 60°C until the aluminum isopropoxide is fully hydrolyzed to obtain a precursor liquid; take 120mL of ethanolamine and add it to the precursor liquid to fully disperse it; then add silica sol at a silicon-aluminum ratio of 180 and continue stirring and mixing until it is fully hydrolyzed; after sealing, age it at 120°C for 14h and crystallize it at 160°C for 12h;

[0031] (4) Then, 2 g of ferrite is added to the system and fully dispersed; after uniform dispersion, the solvent is evaporated, and then calcined at 550°C for 5 h to obtain a magnetic carrier; the magnetic carrier and 0.3 times the mass of the magnetic carrier of modified carbon nitride are dispersed in water, and 0.5 times the mass of the magnetic carrier of liquid polyethylene glycol is added to disperse evenly, dried below 50°C, and then heat treated at 90°C for 4 h to obtain a magnetic catalyst.

[0032] Example 2: The difference from Example 1 is that:

[0033] (1) 2 g of melamine and 0.2 g of aminosulfonic acid were calcined at 550 ° C for 4 h, and then taken out after cooling to obtain carbon nitride; then 1 g of carbon nitride was taken, 0.5 g of aminosulfonic acid and 0.5 g of 1,3-propane sultone were immersed in ethanol, ground and mixed for 0.5 h, and then 10% dilute ammonia water 4 times the volume of ethanol was added to the system, mixed evenly, and reacted at 65 ° C for 8 h, and then the solvent was evaporated at 40 ° C. After thorough washing, the modified carbon nitride was obtained.

[0034] Example 3: The difference from Example 1 is that:

[0035] (1) 2 g of melamine and 1 g of aminosulfonic acid were calcined at 550 ° C for 4 h, and then taken out after cooling to obtain carbon nitride; then 1 g of carbon nitride was taken, 0.2 g of aminosulfonic acid and 0.5 g of 1,3-propane sultone were immersed in ethanol, ground and mixed for 0.5 h, and then 10% dilute ammonia water 3 times the volume of ethanol was added to the system, mixed evenly, and reacted at 65 ° C for 8 h, and then the solvent was evaporated at 40 ° C. After thorough washing, modified carbon nitride was obtained.

[0036] Example 4: The difference from Example 1 is that:

[0037] (1) Take 2 g of melamine and 1 g of sulfamic acid, calcine them at 550 °C for 4 h, take them out after cooling to obtain carbon nitride; then take 1 g of carbon nitride, immerse it with 0.5 g of sulfamic acid and 0.5 g of 1,3 - propane sultone in ethanol, grind and mix for 0.5 h, then add 10% dilute ammonia water with a volume twice that of ethanol to the system, mix evenly, react at 65 °C for 8 h, then evaporate the solvent at 40 °C, and obtain modified carbon nitride after thorough washing.

[0038] Example 5: The difference from Example 1 is that:

[0039] (4) Then add 1 g of ferrite to the system and disperse it thoroughly; after uniform dispersion, evaporate the solvent, and then calcine at 550 °C for 5 h to obtain a magnetic carrier; disperse the magnetic carrier and 0.3 times the mass of the magnetic carrier of modified carbon nitride in water, add 0.5 times the mass of the magnetic carrier of liquid polyethylene glycol and disperse evenly, dry at below 50 °C, and then heat - treat at 90 °C for 4 h to obtain a magnetic catalyst.

[0040] Example 6: The difference from Example 1 is that:

[0041] (4) Then add 2 g of ferrite to the system and disperse it thoroughly; after uniform dispersion, evaporate the solvent, and then calcine at 550 °C for 5 h to obtain a magnetic carrier; disperse the magnetic carrier and 0.1 times the mass of the magnetic carrier of modified carbon nitride in water, add 0.5 times the mass of the magnetic carrier of liquid polyethylene glycol and disperse evenly, dry at below 50 °C, and then heat - treat at 90 °C for 4 h to obtain a magnetic catalyst.

[0042] Example 7: The difference from Example 1 is that:

[0043] (4) Then add 2 g of ferrite to the system and disperse it thoroughly; after uniform dispersion, evaporate the solvent, and then calcine at 550 °C for 5 h to obtain a magnetic carrier; disperse the magnetic carrier and 0.6 times the mass of the magnetic carrier of modified carbon nitride in water, add 0.5 times the mass of the magnetic carrier of liquid polyethylene glycol and disperse evenly, dry at below 50 °C, and then heat - treat at 90 °C for 4 h to obtain a magnetic catalyst.

[0044] Example 8: The difference from Example 1 is that:

[0045] (4) Then add 2 g of ferrite to the system and disperse it thoroughly; after uniform dispersion, evaporate the solvent, and then calcine at 550 °C for 5 h to obtain a magnetic carrier; disperse the magnetic carrier and 0.3 times the mass of the magnetic carrier of modified carbon nitride in water, add 0.2 times the mass of the magnetic carrier of liquid polyethylene glycol and disperse evenly, dry at below 50 °C, and then heat - treat at 90 °C for 4 h to obtain a magnetic catalyst.

[0046] Example 9: The difference from Example 1 is as follows:

[0047] (4) Then, 2 g of ferrite was added to the system and dispersed thoroughly. After uniform dispersion, the solvent was evaporated, and then it was calcined at 550 °C for 5 h to obtain a magnetic support. The magnetic support and modified carbon nitride with a mass 0.3 times that of the magnetic support were dispersed in water, and liquid polyethylene glycol with a mass 0.8 times that of the magnetic support was added and dispersed evenly. It was dried below 50 °C and then heat-treated at 90 °C for 4 h to obtain a magnetic catalyst.

[0048] Example 10: The difference from Example 1 is as follows:

[0049] (4) Then, 2 g of ferrite was added to the system and dispersed thoroughly. After uniform dispersion, the solvent was evaporated, and then it was calcined at 550 °C for 5 h to obtain a magnetic support. The magnetic support and modified carbon nitride with a mass 0.3 times that of the magnetic support were dispersed in water, and liquid polyethylene glycol with a mass 0.5 times that of the magnetic support was added and dispersed evenly. It was dried below 50 °C and then heat-treated at 90 °C for 2 h to obtain a magnetic catalyst.

[0050] Sugar production example: Take clean corn straw, crush it and pass through a 60-mesh sieve. Then, set the mass ratio of the catalyst to the straw as 1.5 (g / g), place it together with the magnetic catalyst in hot water at 90 °C, and carry out hydrolysis under light while aerating for 12 h. Then, the catalyst was magnetically removed to obtain a hydrolysis solution. The hydrolysis solution was further enzymatically hydrolyzed with cellulase for 16 - 20 h, and glucose was obtained through purification.

[0051] Sugar production comparative example 1: Take clean corn straw, crush it and pass through a 60-mesh sieve. Then, set the mass ratio of the catalyst to the straw as 1.5 (g / g), place it together with the magnetic catalyst in hot water at 90 °C, carry out hydrolysis under light for 12 h, and then the catalyst was magnetically removed to obtain a hydrolysis solution. The hydrolysis solution was further enzymatically hydrolyzed with cellulase for 16 - 20 h, and glucose was obtained through purification.

[0052] Sugar production comparative example 2: Take clean corn straw, crush it and pass through a 60-mesh sieve. Then, set the mass ratio of the catalyst to the straw as 1.5 (g / g), place it together with the magnetic catalyst in hot water at 90 °C, carry out hydrolysis while aerating for 12 h, and then the catalyst was magnetically removed to obtain a hydrolysis solution. The hydrolysis solution was further enzymatically hydrolyzed with cellulase for 16 - 20 h, and glucose was obtained through purification.

[0053] Sugar production comparative example 3: Take clean corn straw, crush it and pass through a 60-mesh sieve. Then, set the mass ratio of the catalyst to the straw as 1.5 (g / g), place it together with the magnetic catalyst in hot water at 70 °C, carry out hydrolysis under light while aerating for 12 h, and then the catalyst was magnetically removed to obtain a hydrolysis solution. The hydrolysis solution was further enzymatically hydrolyzed with cellulase for 16 - 20 h, and glucose was obtained through purification.

[0054] Example sample test:

[0055] The magnetic catalyst of each embodiment was used to conduct hydrolysis experiments according to the method of the sugar production embodiment. The corn straw powder before hydrolysis was taken and the cellulose content therein was determined by concentrated sulfuric acid acid hydrolysis method. The glucose content in the hydrolyzate was determined by high performance liquid chromatography, and the glucose yield was calculated according to the formula: glucose yield = glucose content / cellulose content × 100%. After the hydrolysis was completed, the magnetic catalyst was taken out and thoroughly washed with water and ethanol, and a new corn straw hydrolysis experiment was carried out again. The glucose yield of the 1st and 10th times was calculated and compared to evaluate the reuse rate of the catalyst. Five parallel experiments were set up for each experiment, and the average value was taken. The results are as follows:

[0056]

[0057] Comparing the glucose yields of the examples in the above table, it can be seen that when calcining to prepare carbon nitride, the yield of Example 2, which has less aminosulfonic acid involved, decreases. This may be because less aminosulfonic acid is not conducive to increasing the porosity of carbon nitride, and there are fewer residual sulfonic acid groups in the carbon nitride, resulting in a decrease in catalytic performance. When modifying carbon nitride, the amount of aminosulfonic acid added in Example 3 is small, and the amount of ammonia water in Example 4 is also small. The catalytic performance of both decreases significantly, and the decrease in catalytic performance increases after 10 cycles. This shows that the treatment of aminosulfonic acid and ammonia water here is beneficial to the modification of carbon nitride, improves catalytic ability, and is also beneficial to the stable combination of modified carbon nitride and magnetic carrier, reducing losses generated during the cycle.

[0058] In Example 5, less ferrite was added, and the initial glucose yield decreased, but the yield after 10 cycles did not decrease much, indicating that less ferrite would affect the catalytic effect, but the stability of the catalyst was stronger. In Example 6, in which less modified carbon nitride was added, the initial glucose yield decreased, and at the same time, the cycle stability was stronger. The effect of Example 7, in which more modified carbon nitride was added, was opposite to that of Example 6. However, comparing Example 7 with Example 1, the yield decrease after 10 cycles in Example 7 was not much different from that in Example 1, and the phenomenon of sudden drop in data that is easy to occur when physical adsorption is saturated did not occur. This shows that the ferrite and modified carbon nitride of the present invention are not just physically adsorbed when combined with the carrier. There is a strong adsorption attraction between the ferrite and modified carbon nitride and the carrier, as well as between the ferrite and the modified carbon nitride. When combining a magnetic carrier with modified carbon nitride, Example 8, with a low amount of polyethylene glycol, showed an increased initial glucose yield, but the yield decreased significantly after 10 cycles. Example 9, with a high amount of polyethylene glycol, showed the opposite effect. This may be because more polyethylene glycol can easily affect the exposure of catalytic sites, but polyethylene glycol can improve catalyst stability. The initial glucose yield decreased in Example 10, indicating that a longer heat treatment time can fully decompose the polyethylene glycol and avoid blocking the catalytic sites.

[0059] The hydrolysis experiments were respectively carried out using the magnetic catalyst of Example 1 according to the methods of Sugar Making Comparative Examples 1, 2, and 3. The glucose yields were calculated according to the above methods and compared with the glucose yields obtained by the experiments using the methods of Sugar Making Examples. The results are as follows.

[0060]

[0061]

[0062] As can be seen from the above table, during the sugar-making process, the conditions of aeration and light have very important effects on the method for preparing sugar in the present invention. The operation of aeration can increase the dissolved oxygen content in the system and continuously provide raw materials for the generation of substances such as oxygen free radicals, hydroxyl free radicals, and hydrogen peroxide, which is a key condition for hydrolyzing cellulose. The condition of light can provide catalytic energy for catalytic substances such as carbon nitride and is the key energy source for catalysis generation and progress. At the same time, the temperature during the sugar-making process also has an obvious influence on the hydrolysis of cellulose, and a higher temperature is beneficial to the swelling of cellulose and the progress of the catalytic reaction.

[0063] For those skilled in the art, various corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing sugar from lignocellulose, characterized in that, Prepare sulfonic acid group-containing modified carbon nitride; prepare copper-doped ferrite; prepare a molecular sieve support, add ferrite after crystallization, and obtain a magnetic support after calcination; load modified carbon nitride in the magnetic support to obtain a magnetic catalyst for hydrolyzing lignocellulose; place lignocellulose and the magnetic catalyst together in hot water, hydrolyze while aerating and irradiating with light, and then take out the catalyst to obtain a hydrolyzate containing glucose; use an enzyme to continue enzymatic hydrolysis of the hydrolyzate and purify to obtain glucose.

2. The method for preparing sugar from lignocellulose according to claim 1, characterized in that, Place lignocellulose and the magnetic catalyst together in hot water at 80 °C or above, hydrolyze while aerating and irradiating with light for 6 - 24 h; the mass ratio of the magnetic support to the modified carbon nitride is 1:0.1 - 0.6; the mass ratio of the straw to the magnetic catalyst is 1:0.5 - 4.

3. The method for preparing sugar from lignocellulose according to claim 1 or 2, characterized in that, The preparation of the magnetic catalyst includes the following steps: disperse the magnetic support and the modified carbon nitride in water, add liquid polyethylene glycol and disperse evenly, dry at 50 °C or below, and then perform heat treatment at 80 - 100 °C for 2 - 6 h to obtain the magnetic catalyst.

4. The method for preparing sugar from lignocellulose according to claim 3, characterized in that, The mass ratio of the magnetic support to the polyethylene glycol is 1:0.2 - 0.

8.

5. The method for preparing sugar from lignocellulose according to claim 1, characterized in that, The preparation method of the magnetic support includes the following steps: a. Take melamine and aminosulfonic acid and calcine at 500 - 600 °C for 3 - 5 h, take out after cooling to obtain carbon nitride; b. Then immerse the carbon nitride, aminosulfonic acid and 1,3 - propane sultone in ethanol, grind and mix for 0.5 - 1 h, then add dilute ammonia water to the system, mix evenly and react at 60 - 75 °C for 6 - 10 h, and then evaporate the solvent at 30 - 60 °C, wash thoroughly to obtain modified carbon nitride; c. Prepare copper-doped ferrite; take aluminum isopropoxide, dissolve it in tetrapropylammonium hydroxide, add water and dilute, stir at 50 - 70 °C until aluminum isopropoxide is fully hydrolyzed to obtain a precursor solution; take an organic amine and add it to the precursor solution and disperse fully; then add silica sol according to a silicon-aluminum ratio of 150 - 200 and continue to stir and mix until fully hydrolyzed; seal and age at 100 - 130 °C for 12 - 16 h, crystallize at 150 - 180 °C for 10 - 18 h; d. Then add ferrite to the system and disperse fully; after dispersing evenly, evaporate the solvent, and then calcine at 500 - 600 °C for 4 - 8 h to obtain the magnetic support.

6. The method for preparing sugar from lignocellulose according to claim 5, characterized in that, In step a, the mass ratio of melamine to aminosulfonic acid is 1:0.1 - 0.5; in step b, the mass ratio of carbon nitride to 1,3 - propane sultone is 1:0.2 - 0.8; in step b, the mass ratio of aminosulfonic acid to 1,3 - propane sultone is 1:1 - 3; in step b, the volume ratio of ethanol to dilute ammonia water is 1:2 - 5.

7. The method for preparing sugar from lignocellulose according to claim 5, wherein In step c, the mass ratio of aluminum isopropoxide to tetrapropylammonium hydroxide is 1:20 - 30; in step c, the molar ratio of the organic amine to aluminum isopropoxide is 150 - 250:1; in step c, the mass ratio of aluminum isopropoxide to the ferrite in step d is 1 - 2:

1.

8. The method for preparing sugar from lignocellulose according to claim 5, characterized in that, The organic amine includes one or more of ethanolamine, isopropanolamine, diethanolamine or cyclohexylamine.

9. The method for preparing sugar from lignocellulose according to claim 1, wherein The preparation of the ferrite includes the following steps: Ferrous sulfate and copper sulfate are placed in a polyvinyl pyrrolidone solution, and a sodium hydroxide solution is used to adjust the pH of the system to 10-13.

5. After thorough mixing, a mixed solution is obtained; the mixed solution is reacted at 150-180° C. for 8-12 hours, and the precipitate is collected, thoroughly washed, and then dried to obtain ferrite.

10. The method for preparing sugar from lignocellulose according to claim 9, wherein The molar ratio of the ferrous sulfate to the copper sulfate is 2:1.

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