A method for preparing sugar from crop straw based on enzyme

Abstract

The application discloses an enzyme-based method for preparing sugar from crop straw, and relates to the technical field of straw enzymatic saccharification. The method comprises the following steps: removing impurities, crushing and drying the crop straw to obtain straw microparticles; soaking the straw microparticles in a magnesium sulfate solution and etching the straw microparticles in a mixed gas of ammonia and air by using plasma; performing ammonia steam steam explosion treatment to obtain straw fibers; soaking the straw fibers in a modified surfactant; and finally, using a composite enzyme preparation to enzymatically hydrolyze the straw fibers to obtain a sugar solution and straw residues. The method significantly improves the lignin removal rate and enzymatic hydrolysis efficiency, increases the sugar solution leaching rate, and reduces the production cost by means of loading magnesium ions on the surface of the straw microparticles to assist in degrading lignin, etching the straw microparticles by using plasma, and occupying the lignin enzyme adsorption sites by using a modified surfactant.

Description

Technical Field

[0001] This application belongs to the field of straw enzymatic hydrolysis and saccharification technology, specifically relating to a method for preparing sugar from crop straw based on enzymes. Background Technology

[0002] As a major agricultural country, my country produces nearly 1 billion tons of crop straw annually, accounting for about one-third of the global total, making it one of the richest renewable biomass resources. For a long time, straw has been primarily disposed of through burning and piling, causing not only severe air pollution and resource waste but also a series of environmental and safety problems such as soil degradation and fire hazards. Straw is rich in lignocellulose, and cellulose and hemicellulose can be converted into sugars, with a sugar content reaching 85% of that in grains, while the cost is only 10% of that of grains, providing a core material basis for the high-value utilization of straw. The core challenge of enzymatic hydrolysis for sugar production from straw lies in the natural resistance barrier formed by the complex structure of lignocellulose in straw—a double barrier formed by the tight cross-linking of lignin, cellulose, and hemicellulose through chemical bonds. This barrier greatly hinders the contact between enzymes and substrates, reducing enzymatic hydrolysis efficiency. Lignin acts as an armor layer on the surface of cellulose and hemicellulose, directly blocking the attack path of cellulase. The binding products of hemicellulose and lignin further reinforce this dense network structure, making it difficult for enzymes to penetrate into the cellulose and exert their effects. Furthermore, lignin can non-productively adsorb cellulase, preventing the enzyme from focusing on breaking down cellulose. To address these issues, current technologies require pretreatment of straw to refine straw particles and remove lignin, thereby improving the conversion rate of enzymatic hydrolysis for sugar production. Common pretreatment methods include mechanical crushing, microwave treatment, steam explosion treatment, and acid-alkali treatment. Among them, Chinese invention patent with publication number CN119061092A discloses a method for enzymatic hydrolysis of crop straw fiber to produce sugar. The method obtains pretreated fiber material by crushing, soaking, cooking and kneading the straw fiber, and then converts the straw fiber into mixed sugar through the combined action of enzyme preparation and stirring tank. The method does not require the addition of acid or alkali during the pretreatment process, and the straw fiber is further filamentized by twin-screw kneading. It can improve the efficiency of enzymatic hydrolysis to produce sugar at a relatively low processing cost, while being environmentally friendly.

[0003] However, existing technologies for pre-treating straw have low lignin removal rates, resulting in low enzymatic hydrolysis efficiency. Therefore, there is an urgent need to develop a more efficient method for enzymatic hydrolysis of straw to produce sugar. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the primary objective of this application is to provide a method for preparing sugar from crop straw based on enzymes. By soaking straw microparticles with a magnesium sulfate adjuvant, magnesium ions are loaded onto the straw microparticles. During subsequent ammonia steam explosion, this helps the ammonia steam break the ester bonds of lignin, degrading lignin into small molecule phenolic compounds. This reduces the lignin content in the straw fiber, thereby reducing enzyme adsorption by lignin and improving enzymatic hydrolysis efficiency. Furthermore, plasma treatment is used to etch the straw microparticles, making them easier to pulverize during steam explosion. Finally, before enzymatic hydrolysis, carboxymethylated fatty alcohol polyoxyethylene ether is added to soak the straw fiber, adsorbing magnesium ions and preventing them from affecting the enzymatic hydrolysis process. Simultaneously, it occupies the enzyme adsorption sites of lignin, reducing the non-productive adsorption of cellulase by lignin. This method effectively reduces the impact of lignin on enzymatic hydrolysis efficiency and increases the sugar extraction rate.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] This application provides a method for preparing sugar from crop straw based on enzymes, comprising the following steps:

[0007] The recycled crop straw is cleaned, crushed, and dried to obtain straw microparticles;

[0008] Pretreated straw particles were obtained by soaking straw particles in magnesium sulfate solution.

[0009] Pretreated straw microparticles were plasma-treated under a mixture of ammonia and air to obtain etched straw microparticles.

[0010] Ammonia vapor was used to perform steam explosion treatment on the etched straw microparticles to obtain straw fibers and condensate;

[0011] The straw fiber was washed with water until neutral, then a surfactant was added and the mixture was stirred. The straw fiber was then removed and placed in an enzymatic hydrolysis reactor. Buffer solution and compound enzyme preparation were added, and the mixture was enzymatically hydrolyzed and filtered to obtain sugar solution and straw residue.

[0012] It should be noted that the condensate recovered after steam explosion treatment and the washing liquid obtained from washing straw fibers can be recycled together. Magnesium sulfate is recovered by evaporation and crystallization, and then mixed with steam condensate to prepare a magnesium sulfate auxiliary solution, thereby reducing the consumption of magnesium sulfate and saving production costs.

[0013] Preferably, the crop straw includes any one of corn straw, cotton straw, and wheat straw.

[0014] Preferably, the straw microparticles have a particle size of 20-40 mesh and a moisture content of ≤10%.

[0015] It should be noted that by reducing the straw particle size and increasing the specific surface area, more contact sites can be provided for subsequent magnesium ion loading and plasma etching. At the same time, controlling the moisture content of the straw microparticles can avoid the dilution of the magnesium sulfate solution and the plasma reaction system by water, thus ensuring stable magnesium ion adsorption efficiency.

[0016] Preferably, the specific preparation steps of the pretreated straw microparticles are as follows:

[0017] The straw microparticles are immersed in a 0.1-0.3 wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:(10-15) and stirred at a constant temperature of 25-35℃ and 10-20 rpm for 2-3 hours. Then the straw microparticles are removed and dried at 40-50℃ until the moisture content is 15-20% to obtain pretreated straw microparticles.

[0018] It should be noted that magnesium ions in the magnesium sulfate aqueous solution adhere to active sites such as lignin phenolic hydroxyl groups and cellulose hydroxyl groups on the surface of straw through electrostatic adsorption. By moderately drying, a trace amount of magnesium ion solution is retained in the pores of the straw to form an ionic liquid film, which provides in-situ catalytic sites for subsequent plasma etching and steam explosion.

[0019] Preferably, the specific steps of the plasma treatment are as follows:

[0020] The pretreated straw microparticles were placed in the reaction chamber, and an ammonia / air mixture with an ammonia content of 8% was introduced. The pressure inside the reaction chamber was adjusted to 40~60Pa, the reaction power was set to 120~160W, the frequency was 13.56MHz, and the etching process was continued for 10~20min to obtain etched straw microparticles.

[0021] It should be noted that the high-energy electrons and ions generated by the plasma bombard the surface of the straw, forming micron-sized micropores, destroying the dense structure of the lignin epidermis, weakening the binding force between cellulose and hemicellulose, and making the straw easier to crush in the subsequent steam explosion; the doped ammonia decomposes into active nitrogen species under the action of plasma, and undergoes an addition reaction with the aromatic ring of lignin, introducing amino groups; the polarity of the aminated lignin is enhanced, and it can tightly bind with magnesium ions and ammonia molecules through hydrogen bonds, improving the affinity of subsequent reactions.

[0022] Preferably, the specific steps for handling the steam explosion are as follows:

[0023] The etched straw microparticles are fed into a steam explosion reactor, and saturated steam generated from ammonia water with a mass fraction of 5-7% is introduced. The temperature is raised to 160-180℃, the pressure is raised to 1.3-1.5MPa, and the pressure is maintained for 5 minutes. Then the pressure is released to complete the steam explosion, and straw fibers and condensate are obtained.

[0024] It should be noted that the steam explosion process involves both physical and chemical effects on the straw microparticles. The physical effects are primarily due to the impact force generated by the release of high-pressure, high-temperature steam, which tears apart the loose structure of the straw microparticles after etching, pulverizing them into straw fibers, increasing their specific surface area, and promoting subsequent enzymatic hydrolysis. The chemical effects are manifested in the degradation of lignin by magnesium ions and ammonia molecules. Magnesium ions can coordinate with oxygen atoms in the lignin ester bonds, weakening the CO bond strength and lowering the activation energy for ester bond breakage. Then, the OH groups released by the ionization of ammonia molecules... - Attacking the carbonyl carbon of the lignin ester bond breaks the ester bond, degrading lignin and thus reducing the lignin content in straw fiber.

[0025] Preferably, the surfactant is a carboxymethylated modified fatty alcohol polyoxyethylene ether, and the modification method is as follows:

[0026] Fatty alcohol polyoxyethylene ether was mixed with sodium chloroacetate, and 3 wt.% sodium hydroxide solution was added. The mixture was stirred at 55-65℃ for 3-5 hours. Then, 10 wt.% hydrochloric acid was added to neutralize the pH to 7. The mixture was filtered and dried to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether. The mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution was 10:(2-3):(12-14).

[0027] It should be noted that the carboxyl groups in the modified fatty alcohol polyoxyethylene ether molecules can form chelates with the magnesium ions remaining in the straw fiber, preventing the magnesium ions from being free in the enzymatic hydrolysis system. At the same time, the hydrophobic ends in the fatty alcohol polyoxyethylene ether molecules can target and adsorb lignin aromatic fragments through intermolecular forces, occupying enzyme adsorption sites on the lignin surface and reducing the adsorption rate of lignin for enzymes.

[0028] Preferably, the buffer solution comprises either an acetic acid / sodium acetate mixture or a citric acid / sodium citrate mixture.

[0029] It should be noted that the concentrations of acetic acid, sodium acetate, citric acid, and sodium citrate are all 0.1 mol / L, and the mass ratio of acetic acid / sodium acetate or citric acid / sodium citrate in the buffer system is (3~4):(6~7).

[0030] Preferably, the compound enzyme preparation is obtained by combining cellulase and hemicellulase.

[0031] Preferably, the parameters for soaking and stirring the surfactant are: temperature 35~40℃, time 1~1.5h, surfactant solution concentration 0.4wt.%, and straw fiber to surfactant solution mass ratio 1:10; the addition of buffer solution adjusts the pH of the system to 4.5~5; the mass ratio of straw fiber to compound enzyme preparation is 100:(0.8~1.5); the enzymatic hydrolysis temperature is 45~55℃, time is 45~50h, and stirring rate is 130~160rpm.

[0032] The beneficial effects of this application are:

[0033] This scheme uses magnesium sulfate as a pretreatment aid to load magnesium ions onto the surface of straw. During steam explosion, these magnesium ions act as coordination atoms in the ester bonds between Lewis acids and lignin, weakening the CO bond strength and allowing the OH groups generated by the ionization of ammonia vapor to... - This process facilitates the cleavage of ester bonds via nucleophilic addition reactions, leading to the degradation of lignin into small-molecule phenolic compounds, thereby reducing the lignin content in straw and improving enzymatic saccharification efficiency. Furthermore, this method utilizes plasma treatment to etch micropores onto the straw surface, disrupting the dense structure of lignin and weakening the binding force between cellulose and hemicellulose, making the straw easier to pulverize via steam explosion. Simultaneously, the microporous structure provides permeation channels for magnesium ions and subsequent ammonia vapor, increasing the contact area for the reaction. Under the influence of plasma, the doped ammonia decomposes into active nitrogen-containing substances, which can react with lignin... The aromatic ring of lignin undergoes an addition reaction, introducing an amino group. The amination of lignin enhances its polarity, allowing it to bind tightly to magnesium ions and ammonia molecules via hydrogen bonds, thus improving the affinity for subsequent ester bond cleavage reactions. Finally, this method uses carboxymethylated modified fatty alcohol polyoxyethylene ether surfactant to treat straw fibers. The modified surfactant adsorbs residual magnesium ions, preventing magnesium ions from inhibiting cellulase activity. At the same time, the surfactant can also adsorb onto the enzyme adsorption sites of lignin, reducing the non-specific adsorption of cellulase by lignin, thereby improving the efficiency of enzymatic hydrolysis for sugar production. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart of a method for preparing sugar from crop straw based on enzymes, provided in this application. Detailed Implementation

[0036] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0037] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0038] The following specific embodiments further illustrate this point:

[0039] Example 1

[0040] like Figure 1 As shown, this embodiment provides a method for preparing sugar from crop straw based on enzymes, including the following steps:

[0041] 1. Remove impurities from the recycled corn stalks, then crush them to a particle size of 20-40 mesh, and dry them until the moisture content is ≤10% to obtain straw microparticles;

[0042] 2. Immerse the straw microparticles in a 0.2 wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:13. Stir at 30℃ and 15 rpm for 2.5 h. Then remove the straw microparticles and dry them at 45℃ until the moisture content is 18% to obtain pretreated straw microparticles.

[0043] 3. Place the pretreated straw microparticles in the reaction chamber, introduce an ammonia / air mixture with an ammonia content of 8%, adjust the pressure inside the reaction chamber to 50Pa, set the reaction power to 150W and the frequency to 13.56MHz, and continue etching for 15min to obtain etched straw microparticles.

[0044] 4. The etched straw microparticles are fed into the steam explosion reactor, and saturated steam generated by 6% ammonia water is introduced. The temperature is raised to 170℃ and the pressure is raised to 1.4MPa. The pressure is maintained for 5 minutes, and then the pressure is released to complete the steam explosion, and straw fiber and condensate are obtained.

[0045] 5. Mix fatty alcohol polyoxyethylene ether with sodium chloroacetate, add 3 wt.% sodium hydroxide solution, stir and react at 60℃ for 4 h, then add 10 wt.% hydrochloric acid to neutralize to pH 7, filter and dry to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether, then prepare a 0.4 wt.% aqueous solution of carboxymethylated modified fatty alcohol polyoxyethylene ether for later use; the mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution is 10:2.3:13;

[0046] 6. Wash the straw fiber with water until neutral, add 0.4 wt.% of carboxymethylated modified fatty alcohol polyoxyethylene ether solution (material-to-liquid mass ratio 1:10), soak and stir at 36℃ for 1.2 h, then remove the straw fiber, add acetic acid / sodium acetate buffer solution (mass ratio 3:7, acetic acid and sodium acetate solution concentrations 0.1 mol / L), adjust the pH of the system to 4.8, add cellulase and hemicellulase at 1% of the straw fiber mass, and enzymatically hydrolyze at 50℃ and 150 rpm for 48 h, filter to obtain the sugar solution and straw residue of the method described in Example 1.

[0047] Example 2

[0048] like Figure 1 As shown, this embodiment provides a method for preparing sugar from crop straw based on enzymes, including the following steps:

[0049] 1. Remove impurities from the recycled cotton stalks, then crush them to a particle size of 20-40 mesh, and dry them until the moisture content is ≤10% to obtain straw microparticles;

[0050] 2. Immerse the straw microparticles in a 0.1 wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:10. Stir at 25℃ and 10 rpm for 2 hours. Then, remove the straw microparticles and dry them at 40℃ until the moisture content is 15% to obtain pretreated straw microparticles.

[0051] 3. Place the pretreated straw microparticles in the reaction chamber, introduce an ammonia / air mixture with an ammonia content of 8%, adjust the pressure in the reaction chamber to 40Pa, set the reaction power to 120W and the frequency to 13.56MHz, and continue etching for 10min to obtain etched straw microparticles.

[0052] 4. The etched straw microparticles are fed into the steam explosion reactor, and saturated steam generated by 5% ammonia water is introduced. The temperature is raised to 160℃, the pressure is raised to 1.3MPa, and the pressure is maintained for 5 minutes. Then the pressure is released to complete the steam explosion and obtain straw fiber and condensate.

[0053] 5. Mix fatty alcohol polyoxyethylene ether with sodium chloroacetate, add 3 wt.% sodium hydroxide solution, stir and react at 55℃ for 3 h, then add 10 wt.% hydrochloric acid to neutralize to pH 7, filter and dry to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether, then prepare a 0.4 wt.% aqueous solution of carboxymethylated modified fatty alcohol polyoxyethylene ether for later use; the mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution is 10:2:12;

[0054] 6. Wash the straw fiber with water until neutral, add 0.4 wt.% of carboxymethylated modified fatty alcohol polyoxyethylene ether solution (material-to-liquid mass ratio 1:10), soak and stir at 35℃ for 1 hour, then remove the straw fiber, add acetic acid / sodium acetate buffer solution (mass ratio 4:6, acetic acid and sodium acetate solution concentrations 0.1 mol / L), adjust the pH of the system to 4.5, add cellulase and hemicellulase at 0.8% of the straw fiber mass, and enzymatically hydrolyze at 45℃ and 130 rpm for 45 hours. Filter to obtain the sugar solution and straw residue of the method described in Example 2.

[0055] Example 3

[0056] like Figure 1 As shown, this embodiment provides a method for preparing sugar from crop straw based on enzymes, including the following steps:

[0057] 1. Remove impurities from the recycled wheat straw, then crush it to a particle size of 20-40 mesh, and dry it to a moisture content of ≤10% to obtain straw microparticles;

[0058] 2. Immerse the straw microparticles in a 0.3 wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:15. Stir at 35℃ and 20 rpm for 3 hours. Then remove the straw microparticles and dry them at 50℃ until the moisture content is 20% to obtain pretreated straw microparticles.

[0059] 3. Place the pretreated straw microparticles in the reaction chamber, introduce an ammonia / air mixture with an ammonia content of 8%, adjust the pressure inside the reaction chamber to 60Pa, set the reaction power to 160W and the frequency to 13.56MHz, and continue etching for 20min to obtain etched straw microparticles.

[0060] 4. The etched straw microparticles are fed into the steam explosion reactor, and saturated steam generated by 7% ammonia water is introduced. The temperature is raised to 180℃, the pressure is raised to 1.5MPa, and the pressure is maintained for 5 minutes. Then the pressure is released to complete the steam explosion and obtain straw fiber and condensate.

[0061] 5. Mix fatty alcohol polyoxyethylene ether with sodium chloroacetate, add 3 wt.% sodium hydroxide solution, stir and react at 65℃ for 5 h, then add 10 wt.% hydrochloric acid to neutralize to pH 7, filter and dry to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether, then prepare a 0.4 wt.% aqueous solution of carboxymethylated modified fatty alcohol polyoxyethylene ether for later use; the mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution is 10:3:14;

[0062] 6. Wash the straw fiber with water until neutral, add 0.4 wt.% of carboxymethylated modified fatty alcohol polyoxyethylene ether solution (material-to-liquid mass ratio 1:10), soak and stir at 40℃ for 1.5 h, then remove the straw fiber, add citric acid / sodium citrate buffer solution (mass ratio 3.5:6.5, concentration of citric acid and sodium citrate solution both 0.1 mol / L), adjust the pH of the system to 5, add cellulase and hemicellulase at 1.5% of the straw fiber mass, and enzymatically hydrolyze at 55℃ and stirring speed 160 rpm for 50 h, filter to obtain the sugar solution and straw residue of the method described in Example 3.

[0063] Example 4

[0064] like Figure 1 As shown, this embodiment provides a method for preparing sugar from crop straw based on enzymes, including the following steps:

[0065] 1. Remove impurities from the recycled corn stalks, then crush them to a particle size of 20-40 mesh, and dry them until the moisture content is ≤10% to obtain straw microparticles;

[0066] 2. Immerse the straw microparticles in a 0.25wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:14. Stir at 30℃ and 15rpm for 2.5h. Then remove the straw microparticles and dry them at 45℃ until the moisture content is 17% to obtain pretreated straw microparticles.

[0067] 3. Place the pretreated straw microparticles in the reaction chamber, introduce an ammonia / air mixture with an ammonia content of 8%, adjust the pressure in the reaction chamber to 50Pa, set the reaction power to 140W and the frequency to 13.56MHz, and continue etching for 18min to obtain etched straw microparticles.

[0068] 4. The etched straw microparticles are fed into the steam explosion reactor, and saturated steam generated by 6% ammonia water is introduced. The temperature is raised to 180℃, the pressure is raised to 1.5MPa, the pressure is maintained for 5 minutes, and then the pressure is released to complete the steam explosion, and straw fiber and condensate are obtained.

[0069] 5. Mix fatty alcohol polyoxyethylene ether with sodium chloroacetate, add 3 wt.% sodium hydroxide solution, stir and react at 60℃ for 4 h, then add 10 wt.% hydrochloric acid to neutralize to pH 7, filter and dry to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether, then prepare a 0.4 wt.% aqueous solution of the carboxymethylated modified fatty alcohol polyoxyethylene ether for later use; the mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution is 10:2.5:12.5;

[0070] 6. Wash the straw fiber with water until neutral, add 0.4 wt.% of carboxymethylated modified fatty alcohol polyoxyethylene ether solution (material-to-liquid mass ratio 1:10), soak and stir at 36℃ for 1.2 h, then remove the straw fiber, add citric acid / sodium citrate buffer solution (mass ratio 3:7, citric acid and sodium citrate solutions both 0.1 mol / L), adjust the pH of the system to 4.8, add cellulase and hemicellulase at 1.2% of the straw fiber mass, and enzymatically hydrolyze at 50℃ and 150 rpm for 48 h, filter to obtain the sugar solution and straw residue of the method described in Example 4.

[0071] Comparative Example 1

[0072] Comparative Example 1 provides a method for preparing sugar from crop straw based on enzymes. The difference from Example 1 is that the straw microparticles are not soaked in magnesium sulfate solution during the preparation process. The remaining steps are the same as in Example 1 and will not be repeated here.

[0073] Comparative Example 2

[0074] Comparative Example 2 provides a method for preparing sugar from crop straw based on enzymes. The difference from Example 1 is that the straw microparticles are not subjected to plasma treatment. The remaining steps are the same as in Example 1 and will not be repeated here.

[0075] Comparative Example 3

[0076] Comparative Example 3 provides a method for preparing sugar from crop straw based on enzymes. The difference from Example 1 is that no modified surfactant is added to treat the straw fiber during the preparation process. The remaining steps are the same as in Example 1 and will not be repeated here.

[0077] To demonstrate the advantages of this application in improving enzymatic hydrolysis efficiency, high-performance liquid chromatography (HPLC) was used to test the sugar content in the sugar solutions prepared in Examples 1-4 and Comparative Examples 1-3. Combined with the theoretical maximum sugar content in the sugar solution, the enzymatic conversion rate was calculated using the formula: Enzymatic conversion rate = Measured sugar content in the hydrolysate / Theoretical maximum sugar content in the hydrolysate. The test results are shown in Table 1.

[0078] Table 1. Results of enzymatic hydrolysis conversion rate tests in Examples 1-4 and Comparative Examples 1-3

[0079] Test sample Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Enzymatic conversion rate (%) 92.6 91.5 90.4 91.3 86.2 73.6 80.5

[0080] As can be seen from Table 1, the enzymatic conversion rate in Examples 1-4 is significantly higher than that in Comparative Examples 1-3, proving that the proposed solution can effectively improve the enzymatic conversion rate. In Comparative Example 1, compared to Example 1, no magnesium sulfate solution soaking treatment was used. The lack of magnesium ions weakening the ester bonds in lignin molecules resulted in lower lignin degradation efficiency, leading to more lignin residue and affecting cellulase hydrolysis. In Comparative Example 2, compared to Example 1, no plasma treatment step was performed. This step primarily etches the straw microparticles, weakening the lignin structure and the binding force between cellulose and hemicellulose, facilitating further pulverization during the subsequent steam explosion process. Without this step, the fiber fineness after steam explosion pulverization may be poor, thus reducing enzymatic hydrolysis efficiency. Simultaneously, the straw microparticles lack amino groups, reducing their affinity for lignin degradation during steam explosion, further impairing lignin degradation and reducing enzymatic hydrolysis efficiency. In Comparative Example 3, compared to Example 1, no modified surfactant was used to treat the straw fibers. This prevented the adsorption of residual magnesium ions in the straw fibers, potentially affecting the enzymatic hydrolysis reaction. Furthermore, the lack of modified surfactant occupying the enzyme adsorption sites of lignin led to enzyme adsorption by lignin, reducing enzymatic hydrolysis efficiency. Therefore, in summary, the proposed solution can effectively solve the problem of low lignin removal rate in straw fiber, thereby improving the efficiency of enzymatic hydrolysis of straw for sugar production.

[0081] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A method for preparing sugar from crop straw based on enzymes, characterized in that, Includes the following steps: The recycled crop straw is cleaned, crushed, and dried to obtain straw microparticles; Pretreated straw particles were obtained by soaking straw particles in magnesium sulfate solution. Pretreated straw microparticles were plasma-treated under a mixture of ammonia and air to obtain etched straw microparticles. Ammonia vapor was used to perform steam explosion treatment on the etched straw microparticles to obtain straw fibers and condensate; The straw fiber was washed with water until neutral, then a surfactant was added and the mixture was stirred. The straw fiber was then removed and placed in an enzymatic hydrolysis reactor. Buffer solution and compound enzyme preparation were added, and the mixture was enzymatically hydrolyzed and filtered to obtain sugar solution and straw residue.

2. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The crop straw includes any one of corn straw, cotton straw, and wheat straw.

3. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The straw microparticles have a particle size of 20-40 mesh and a moisture content of ≤10%.

4. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The specific preparation steps for the pretreated straw microparticles are as follows: The straw microparticles are immersed in a 0.1-0.3 wt.% magnesium sulfate solution at a material-to-liquid mass ratio of 1:(10-15) and stirred at a constant temperature of 25-35℃ and 10-20 rpm for 2-3 hours. Then the straw microparticles are removed and dried at 40-50℃ until the moisture content is 15-20% to obtain pretreated straw microparticles.

5. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The specific steps of the plasma treatment are as follows: The pretreated straw microparticles were placed in the reaction chamber, and an ammonia / air mixture with an ammonia content of 8% was introduced. The pressure inside the reaction chamber was adjusted to 40~60Pa, the reaction power was set to 120~160W, the frequency was 13.56MHz, and the etching process was continued for 10~20min to obtain etched straw microparticles.

6. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The specific steps for handling the steam explosion are as follows: The etched straw microparticles are fed into a steam explosion reactor, and saturated steam generated from ammonia water with a mass fraction of 5-7% is introduced. The temperature is raised to 160-180℃, the pressure is raised to 1.3-1.5MPa, and the pressure is maintained for 5 minutes. Then the pressure is released to complete the steam explosion, and straw fibers and condensate are obtained.

7. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The surfactant is a carboxymethylated modified fatty alcohol polyoxyethylene ether, and its modification method is as follows: Fatty alcohol polyoxyethylene ether was mixed with sodium chloroacetate, and 3 wt.% sodium hydroxide solution was added. The mixture was stirred at 55-65℃ for 3-5 hours. Then, 10 wt.% hydrochloric acid was added to neutralize the pH to 7. The mixture was filtered and dried to obtain carboxymethylated modified fatty alcohol polyoxyethylene ether. The mass ratio of fatty alcohol polyoxyethylene ether, sodium chloroacetate and 3 wt.% sodium hydroxide solution was 10:(2-3):(12-14).

8. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The buffer solution includes either an acetic acid / sodium acetate mixture or a citric acid / sodium citrate mixture.

9. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The compound enzyme preparation is obtained by combining cellulase and hemicellulase.

10. The method for preparing sugar from crop straw based on enzymes according to claim 1, characterized in that, The parameters for soaking and stirring the surfactant are as follows: temperature 35~40℃, time 1~1.5h, surfactant solution concentration 0.4wt.%, and straw fiber to surfactant solution mass ratio 1:10; the pH of the system is adjusted to 4.5~5 by adding buffer solution; the mass ratio of straw fiber to compound enzyme preparation is 100:(0.8~1.5); the enzymatic hydrolysis temperature is 45~55℃, time is 45~50h, and stirring speed is 130~160rpm.

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