Method for preparing water-soluble fertilizer by using subcritical hydrolysis technology

Abstract

The invention relates to the technical field of water-soluble fertilizers, and particularly discloses a method for preparing a water-soluble fertilizer by using a subcritical hydrolysis technology, which comprises the following steps: selecting ingredients, selecting animal raw material feather, steaming and crushing to obtain feather powder, selecting plant raw material soybean meal, crushing and deoiling to obtain soybean meal powder, selecting microbial raw material mushroom bran, drying and crushing to obtain the water-soluble fertilizer. Selecting deionized water, sulfuric acid and urea; the feather meal is rich in high-content keratin, the feather meal can be decomposed into amino acid and short-chain peptide in the subcritical hydrolysis process by adding the feather meal, a quick-acting nitrogen source capable of being directly absorbed by plants is provided, meanwhile, the sulfur element is released, and the defect of sulfur in a traditional fertilizer is overcome; the small molecule peptide and the free amino acid are complementary with the amino acid spectrum of the feather meal, so that a more comprehensive plant nitrogen source is formed.

Description

Technical Field

[0001] This invention relates to the field of water-soluble fertilizer technology, and in particular to a method for preparing water-soluble fertilizer using subcritical hydrolysis technology. Background Technology

[0002] Water-soluble fertilizers, as a type of fertilizer that is efficient, environmentally friendly, and allows for precise application, have been widely used in modern agriculture. However, traditional methods for preparing water-soluble fertilizers have many shortcomings.

[0003] For example, water-soluble fertilizers prepared by chemical synthesis have relatively simple nutrient components, and long-term use may damage the soil structure and affect the soil ecological environment; while water-soluble fertilizers prepared by ordinary fermentation have long production cycles, unstable product quality, and the effective nutrient content is difficult to meet the high-yield and high-quality requirements of modern agriculture.

[0004] Therefore, it is particularly important to find a method that can overcome the above-mentioned defects and prepare water-soluble fertilizers efficiently and in an environmentally friendly manner. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing water-soluble fertilizer using subcritical hydrolysis technology. The water-soluble fertilizer prepared by this invention has the characteristics of rich nutrients, high absorption efficiency, and environmental friendliness to the soil, effectively improving the quality and fertilizer efficacy of water-soluble fertilizer.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing water-soluble fertilizers using subcritical hydrolysis technology, comprising the following steps: S1: Ingredient selection: animal raw material feathers are selected, steamed and crushed to obtain feather powder; plant raw material soybean meal is selected, crushed and deoiled to obtain soybean meal powder; microbial raw material mushroom bran is selected, dried and crushed to obtain mushroom bran powder; deionized water, sulfuric acid and urea are selected. S2: Ingredient processing: Deionized water is added to the mixing tank and stirred. Then, feather meal, soybean meal powder, mushroom bran powder, sulfuric acid and urea are added in sequence and stirred. After mixing, high-protein feed ingredients are obtained. S3: Hydrolysis reaction. High-protein feed ingredients are added to the reaction vessel and a subcritical hydrolysis reaction is carried out to obtain a separated hydrolysate. The separated hydrolysate is then filtered through a plate filter and a centrifuge to separate the solid and liquid, and a supernatant is obtained. S4: Neutralization and adjustment. The supernatant is pumped into a neutralization tank and stirred. Sodium hydroxide solution is slowly added while stirring to adjust the pH value to the neutral range. The solution is then concentrated and crystallized to obtain the water-soluble fertilizer product.

[0007] Further, in step S1, the feather powder has a particle size of 1-3 mm and a high protein content of 80%-95%, the soybean meal is powdered to 80-100 mesh and has a sieving rate of 85%-95%, the residual oil rate of the soybean meal after degreasing is 1%-2%, the moisture content of the dried mushroom residue is 1%-15%, and the particle size of the powdered mushroom residue is 1-3 mm.

[0008] Furthermore, in step S1, the concentration of sulfuric acid is 1% to 5%, and the concentration of urea is 2% to 10%.

[0009] Further, the high-protein feed ingredient is prepared by the following method: deionized water is added to a mixing tank, the mixing tank is stirred at a speed of 50-80 r / min, the mass ratio of deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea is 5-10:10-20:20-30:5-10:1-2:2-3, the deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea are added to the mixing tank, and the stirring time is 20-30 min, thus obtaining the high-protein feed ingredient.

[0010] Furthermore, the high-protein feed ingredients are tested for pH value using pH test paper, and the pH value needs to be controlled within the range of 4.5 to 6.5.

[0011] Further, the high-protein feed ingredients are pumped into a high-pressure hydrolysis reactor with a volume of 50L to 100L and a pressure of 0.3MPa to 0.5MPa. The reactor is heated to 120℃ to 150℃, and the stirring speed is 30 to 50 r / min. The hydrolysis reaction is maintained at this temperature for 4 to 6 hours. The organic materials, namely feather meal, soybean meal, and mushroom bran powder, are fully hydrolyzed under subcritical conditions. After the reaction is completed, the pressure is released for 20 to 30 minutes. After the pressure is released, the reactor is cooled to 50 to 80℃ to obtain the separated hydrolysate.

[0012] Further, the specific steps for solid-liquid separation of the hydrolysate through filtration using a plate filter and centrifuge are as follows: the clarified filtrate is injected into the plate filter, the filter cloth of the plate filter has a precision of 5-10 μm, the pressure is 0.3-0.5 MPa, and the filtration time is 1-2 h to complete the filtration of the clarified filtrate. The filtered clarified filtrate is then added to a centrifuge, the centrifuge speed is 3000-5000 r / min, and the centrifugation time is 15-25 min. After centrifugation, the supernatant is collected.

[0013] Furthermore, the transmittance of the supernatant filtrate is 85%–95%, and the water content of the supernatant residue is 1%–5%.

[0014] Further, the supernatant is pumped into a neutralization tank and stirred at a speed of 60–90 r / min for 30–60 min. While stirring, sodium hydroxide solution is slowly added to the neutralization tank. The concentration of the sodium hydroxide solution is 10%–30%, and the amount added is 1%–5% of the volume of the supernatant, until the pH value of the supernatant is adjusted to 6.5–7.5, thus completing the acid-base neutralization reaction.

[0015] Furthermore, in step S4, during the concentration process, the concentration temperature is 60℃~80℃, the concentration pressure is -0.08MPa~-0.05MPa, and the concentration of the concentrated solution obtained from the concentration process is 40%~60%; during the crystallization process, the crystallization temperature is 0℃~10℃, the crystallization time is 4~6h, and the stirring speed is 40~60r / min, to obtain the water-soluble fertilizer product.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, feather meal is rich in keratin, and its addition can be decomposed into amino acids and short-chain peptides during subcritical hydrolysis, providing a readily available nitrogen source that plants can directly absorb. At the same time, it releases sulfur, making up for the lack of sulfur in traditional fertilizers. Soybean meal contains essential amino acids such as lysine and tryptophan, which are converted into small molecule peptides and free amino acids after subcritical hydrolysis, complementing the amino acid profile of feather meal to form a more comprehensive plant nitrogen source. In addition, bacterial bran contains a large amount of lignin and cellulose, which can be degraded into monosaccharides such as glucose and xylose by subcritical hydrolysis, providing a carbon source for microbial fermentation.

[0017] 2. This invention, by employing subcritical hydrolysis technology, effectively improves the utilization rate of raw materials and the purity of products, while reducing energy consumption and environmental pollution. The water-soluble fertilizer prepared using this process has high nutrient content, good solubility, and is easily absorbed and utilized by plants, thereby improving fertilizer utilization and crop yield and quality. In addition, the preparation method is simple to operate, has a short process flow, and is suitable for large-scale industrial production. Furthermore, its ingredients use common organic waste materials available on the market, which can reduce resource waste and increase economic benefits.

[0018] 3. In this invention, after subcritical hydrolysis, sodium hydroxide solution is added to the supernatant obtained through filtration and separation. This effectively adjusts the pH value, thereby promoting the transformation of organic matter in the supernatant into a form that is more easily absorbed and utilized by plants. At the same time, the addition of sodium hydroxide also helps to remove some impurities in the supernatant, improving the purity and stability of the final product. In addition, this step can optimize the component ratio of the supernatant, ensuring that the prepared water-soluble fertilizer has a balanced nutrient content and meets the needs of different crops at different growth stages. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that all raw materials used in the following experiments are commercially available. Example

[0021] A method for preparing water-soluble fertilizer using subcritical hydrolysis technology includes the following steps: S1: Ingredient selection: animal raw material feathers are selected, steamed and crushed to obtain feather powder; plant raw material soybean meal is selected, crushed and deoiled to obtain soybean meal powder; microbial raw material mushroom bran is selected, dried and crushed to obtain mushroom bran powder; deionized water, sulfuric acid and urea are selected.

[0022] In step S1, the feather powder has a particle size of 1 mm and a high protein content of 80%; the soybean meal is powdered to 80 mesh and has a sieving rate of 85%; the residual oil rate of the soybean meal after degreasing is 1%; the moisture content of the mushroom bran after drying is 1%; and the particle size of the mushroom bran after powdering is 1 mm.

[0023] In step S1, the concentration of sulfuric acid is 1% and the concentration of urea is 2%.

[0024] S2: Ingredient processing: Add 5 parts of deionized water to the mixing tank and stir. Then add 10 parts of feather meal, 20 parts of soybean meal powder, 5 parts of mushroom bran powder, 1 part of sulfuric acid and 2 parts of urea in sequence and stir. After mixing, a high-protein feed ingredient is obtained.

[0025] S3: Hydrolysis reaction. High-protein feed ingredients are pumped into a 50L high-pressure hydrolysis vessel at a pressure of 0.3MPa, heated to 120℃, stirred at 30r / min, and maintained at this temperature for 6 hours. The feather meal, soybean meal, and bran powder are fully hydrolyzed under subcritical conditions. After the reaction, the pressure is released for 20 minutes, followed by cooling to 50℃ to obtain the separated hydrolysate. The separated hydrolysate is injected into a plate filter with a filter cloth precision of 5μm, a pressure of 0.3MPa, and a filtration time of 1 hour to complete the filtration of the clarified filtrate. The clarified filtrate is then added to a centrifuge at 3000r / min for 15 minutes. After centrifugation, the supernatant with a transmittance of 85% is collected.

[0026] The high-protein feed ingredient is prepared by the following method: deionized water is added to a mixing tank, the mixing tank is stirred at a speed of 50 r / min, the mass ratio of deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea is 5:10:20:5:1:2, the deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea are added to the mixing tank, and the stirring time is 20 min, thus obtaining the high-protein feed ingredient.

[0027] The pH value of the high-protein feed ingredients was tested using pH test paper, and the pH value needed to be controlled within the range of 4.5.

[0028] S4: Neutralization and Adjustment. The supernatant is pumped into a neutralization tank and stirred at 60 rpm for 60 minutes. While stirring, sodium hydroxide solution (10% concentration, 1% of the supernatant volume) is slowly added to the neutralization tank until the pH of the supernatant is adjusted to 6.5, completing the acid-base neutralization reaction. The supernatant after the acid-base neutralization reaction is poured into a concentration device using vacuum distillation. The concentration temperature is set to 60℃, and the concentration pressure to -0.08 MPa, resulting in a concentrate concentration of 40%. After concentration, the concentrate is introduced into a crystallization device for crystallization. The temperature inside the crystallization device is gradually reduced to 0℃. To ensure the purity and uniform particle size distribution of the crystals, continuous stirring is required during crystallization at 40 rpm for 4 hours. After crystallization, the water-soluble fertilizer crystals are removed from the crystallization device and dried to obtain the final water-soluble fertilizer product. Example

[0029] A method for preparing water-soluble fertilizer using subcritical hydrolysis technology includes the following steps: S1: Ingredient selection: animal raw material feathers are selected, steamed and crushed to obtain feather powder; plant raw material soybean meal is selected, crushed and deoiled to obtain soybean meal powder; microbial raw material mushroom bran is selected, dried and crushed to obtain mushroom bran powder; deionized water, sulfuric acid and urea are selected.

[0030] In step S1, the feather powder has a particle size of 2 mm and a high protein content of 87%; the soybean meal is powdered to 90 mesh and has a sieve passing rate of 87%; the residual oil rate of the soybean meal after degreasing is 1.5%; the mushroom bran has a moisture content of 7% after drying and a particle size of 2 mm after powdering.

[0031] In step S1, the concentration of sulfuric acid is 3% and the concentration of urea is 6%.

[0032] S2: Ingredient processing: Add 7 parts of deionized water to the mixing tank and stir. Then add 15 parts of feather meal, 25 parts of soybean meal powder, 7 parts of mushroom bran powder, 1.5 parts of sulfuric acid and 2.5 parts of urea in sequence and stir. After mixing, a high-protein feed ingredient is obtained.

[0033] S3: Hydrolysis reaction. High-protein feed ingredients are pumped into a 75L high-pressure hydrolysis vessel at a pressure of 0.4MPa, heated to 135℃, stirred at 40r / min, and maintained at this temperature for 5 hours. The feather meal, soybean meal, and bran powder are fully hydrolyzed under subcritical conditions. After the reaction, the pressure is released for 25 minutes, followed by cooling to 65℃ to obtain the separated hydrolysate. The specific steps for solid-liquid separation of the separated hydrolysate through a plate filter and centrifuge are as follows: The clarified filtrate is injected into the plate filter. The plate filter cloth has a precision of 7.5μm, the pressure is 0.4MPa, and the filtration time is 1.5 hours to complete the filtration of the clarified filtrate. The filtered clarified filtrate is added to a centrifuge at a speed of 4000r / min for 20 minutes. After centrifugation, the supernatant is collected. The transmittance of the supernatant is 90%.

[0034] The high-protein feed ingredient is prepared by the following method: deionized water is added to a mixing tank, the mixing tank is stirred at a speed of 65 r / min, the mass ratio of deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea is 7:15:25:7:1.5:2.5, the deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea are added to the mixing tank, and the stirring time is 25 min, thus obtaining the high-protein feed ingredient.

[0035] The pH value of the high-protein feed ingredients was tested using pH test paper, and the pH value needed to be controlled within the range of 5.5.

[0036] S4: Neutralization and Adjustment. Pump the supernatant into a neutralization tank and stir at 75 rpm for 45 minutes. While stirring, slowly add sodium hydroxide solution (20% concentration, 3% of the supernatant volume) until the pH of the supernatant reaches 7.0, completing the acid-base neutralization reaction. Pour the supernatant from the acid-base neutralization process into a concentration device using vacuum distillation. Set the concentration temperature to 70℃ and the concentration pressure to -0.06 MPa, resulting in a 50% concentrated solution. After concentration, transfer the concentrated solution to a crystallization device for crystallization. Gradually reduce the temperature in the crystallization device to 5℃. To ensure crystal purity and uniform particle size distribution, continuous stirring is required during crystallization at 50 rpm for 5 hours. After crystallization, remove the water-soluble fertilizer crystals from the crystallization device and dry them to obtain the final water-soluble fertilizer product. Example

[0037] A method for preparing water-soluble fertilizer using subcritical hydrolysis technology includes the following steps: S1: Ingredient selection: animal raw material feathers are selected, steamed and crushed to obtain feather powder; plant raw material soybean meal is selected, crushed and deoiled to obtain soybean meal powder; microbial raw material mushroom bran is selected, dried and crushed to obtain mushroom bran powder; deionized water, sulfuric acid and urea are selected.

[0038] In step S1, the feather powder has a particle size of 3mm and a high protein content of 95%, the soybean meal is pulverized to 100 mesh and has a sieving rate of 95%, the residual oil rate of the soybean meal after degreasing is 2%, the moisture content of the dried mushroom bran is 5%, and the particle size of the pulverized mushroom bran is 3mm.

[0039] In step S1, the concentration of sulfuric acid is 5%, and the concentration of urea is 10%. S2: Ingredient processing: Add 10 parts of deionized water to the mixing tank and stir. Then add 20 parts of feather meal, 30 parts of soybean meal powder, 10 parts of mushroom bran powder, 2 parts of sulfuric acid and 3 parts of urea in sequence and stir. After mixing, a high-protein feed ingredient is obtained.

[0040] S3: Hydrolysis reaction. High-protein feed ingredients are pumped into a 100L high-pressure hydrolysis reactor at 0.5MPa. The reactor is heated to 150℃, stirred at 50r / min, and maintained at this temperature for 4 hours. The feather meal, soybean meal, and mushroom bran powder are fully hydrolyzed under subcritical conditions. After the reaction, the pressure is released for 30 minutes, followed by cooling to 80℃ to obtain the separated hydrolysate. The specific steps for solid-liquid separation of the separated hydrolysate through a plate filter and centrifuge are as follows: The clarified filtrate is injected into the plate filter (10μm filter cloth precision), the pressure is 0.5MPa, and the filtration time is 2 hours. The clarified filtrate is then added to a centrifuge at 5000r / min for 25 minutes. After centrifugation, the supernatant is collected. The transmittance of the supernatant is 95%. The high-protein feed ingredient is prepared by the following method: deionized water is added to a mixing tank, the mixing tank is stirred at 80 r / min, the mass ratio of deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea is 10:20:30:10:2:3, the deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea are added to the mixing tank, and the stirring time is 30 min, thus obtaining the high-protein feed ingredient.

[0041] The pH value of the high-protein feed ingredients was tested using pH test paper, and the pH value needed to be controlled within the range of 6.5.

[0042] S4: Neutralization and Adjustment. Pump the supernatant into a neutralization tank and stir at 90 rpm for 30 minutes. While stirring, slowly add sodium hydroxide solution (30% concentration, 5% of the supernatant volume) until the pH of the supernatant is adjusted to 7.5, completing the acid-base neutralization reaction. Pour the supernatant from the acid-base neutralization process into a concentration device using vacuum distillation. Set the concentration temperature to 80℃ and the concentration pressure to -0.05 MPa, resulting in a 50% concentrated solution. After concentration, transfer the concentrated solution to a crystallization device for crystallization. Gradually reduce the temperature in the crystallization device to 10℃. To ensure crystal purity and uniform particle size distribution, continuous stirring is required during crystallization at 60 rpm for 6 hours. After crystallization, remove the water-soluble fertilizer crystals from the crystallization device and dry them to obtain the final water-soluble fertilizer product.

[0043] Comparative Example 1: The difference between this comparative example and Experimental Example 1 is that no bacterial bran powder was added in this comparative example.

[0044] Comparative Example 2: The difference between this comparative example and Experimental Example 2 is that this comparative example uses ordinary hydrolysis. The hydrolysis conditions for ordinary hydrolysis are a temperature of 100℃, a pressure of 1.5MPa, and a hydrolysis time of 4h.

[0045] Comparative Example 3 differs from Experimental Example 3 in that the pH value was not neutralized or adjusted in this comparative example.

[0046] The test data is shown in the table below:

[0047] The following results were obtained from the three sets of examples and comparative examples: In Comparative Example 1, the amino acid and total nitrogen contents decreased by 13.6% and 15.4%, respectively, confirming the necessity of the microbial bran as a raw material to provide carbon and cellulose. The absence of the bran led to an imbalance in the carbon-nitrogen ratio of the hydrolysis system, affecting the efficiency of amino acid synthesis. The water-insoluble matter (6.0 g / L) exceeded the national standard, possibly due to the lack of dietary fiber adsorption by the microbial bran, resulting in increased impurity residues.

[0048] In Comparative Example 2, the amino acid and total nitrogen contents were only 51.8% and 60% of those in Example 2, respectively. This indicates that the high mass transfer characteristics of subcritical water (lower dielectric constant and higher ion product under high temperature and high pressure) significantly accelerated the hydrolysis rate of proteins and cellulose. The transmittance (75%) and pH value (5.0) were poor, reflecting that ordinary hydrolysis cannot effectively control the stability of the reaction system, resulting in insufficient degradation of products and accumulation of acidic substances.

[0049] Comparative Example 3: The lack of neutralization and adjustment resulted in a pH value that was too acidic, with a pH value of 4.0 (acidic), which deviated from the suitable range for crops (5.5~8.0). This inhibited the absorption of nutrients by crops, affected the soil micro-ecology, and the lack of impurity removal by sodium hydroxide led to a slight excess of water-insoluble matter and a decline in product quality.

[0050] Amino acid content measurement and calculation method: The ninhydrin colorimetric method was used for determination. 1 mL of supernatant sample was taken, 2 mL of ninhydrin colorimetric reagent was added, and the mixture was heated in a boiling water bath for 15 min. After cooling, the volume was adjusted to 25 mL with deionized water. The absorbance was measured at 570 nm using a UV-Vis spectrophotometer. The total content was calculated based on the amino acid standard curve, and the result is expressed in g / L.

[0051] Total nitrogen content measurement and calculation method: The Kjeldahl method was used for determination. 2 mL of the supernatant sample was taken, and a catalyst and 10 mL of concentrated sulfuric acid were added for digestion until a clear blue-green color was obtained. After cooling, the sample was transferred to a Kjeldahl distillation apparatus, distilled with sodium hydroxide solution, and the distillate was absorbed with boric acid solution. The final product was then titrated with a standard hydrochloric acid solution. The total nitrogen content was calculated using the formula, and the result was expressed in g / L.

[0052] Transmittance measurement and calculation method: The ultraviolet-visible spectrophotometer was used for measurement. The supernatant sample was diluted 10 times with deionized water. Using deionized water as a reference, the transmittance was measured at a wavelength of 600 nm. The value was read directly and the result was expressed as a percentage.

[0053] Method for measuring and calculating water-insoluble matter: Gravimetric method was used. 100 mL of the supernatant sample was filtered through a pre-weighed 0.45 μm microporous membrane. The membrane was rinsed three times with deionized water and dried in a 105℃ oven until constant weight. The ratio of membrane weight gain to sample volume was calculated, and the result is expressed in g / L.

[0054] pH measurement method: Use a precision pH meter to measure: Insert the pH meter electrode into the supernatant sample after neutralization and adjustment in step S4, and record the pH value directly after the reading stabilizes. Calibrate the instrument with a standard buffer solution before measurement. Method for measuring and calculating the moisture content of the residue: The drying loss method is used. Take the filtered residue sample, weigh the initial mass, place it in an oven at 105℃ and dry it to constant weight, then weigh the mass after drying. Calculate the moisture content according to the formula, and the result is expressed as a percentage (%).

[0055] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing water-soluble fertilizer using subcritical hydrolysis technology, characterized in that: Includes the following steps: S1: Ingredient selection: animal raw material feathers are selected, steamed and crushed to obtain feather powder; plant raw material soybean meal is selected, crushed and deoiled to obtain soybean meal powder; microbial raw material mushroom bran is selected, dried and crushed to obtain mushroom bran powder; deionized water, sulfuric acid and urea are selected. S2: Ingredient processing: Deionized water is added to the mixing tank and stirred. Then, feather meal, soybean meal powder, mushroom bran powder, sulfuric acid and urea are added in sequence and stirred. After mixing, high-protein feed ingredients are obtained. S3: Hydrolysis reaction. High-protein feed ingredients are added to the reaction vessel and a subcritical hydrolysis reaction is carried out to obtain a separated hydrolysate. The separated hydrolysate is then filtered through a plate filter and a centrifuge to separate the solid and liquid, and a supernatant is obtained. S4: Neutralization and adjustment. The supernatant is pumped into a neutralization tank and stirred. Sodium hydroxide solution is added during stirring to adjust the pH value to the neutral range and to concentrate the solution. After the treatment, crystallization is carried out to obtain the water-soluble fertilizer product.

2. The method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: In step S1, the feather powder has a particle size of 1-3 mm and a high protein content of 80%-95%, the soybean meal is powdered to 80-100 mesh and has a sieving rate of 85%-95%, the residual oil content of the soybean meal after degreasing is 1%-2%, the moisture content of the dried mushroom residue is 1%-15%, and the particle size of the powdered mushroom residue is 1-3 mm.

3. The method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: In step S1, the concentration of sulfuric acid is 1% to 5%, and the concentration of urea is 2% to 10%.

4. The method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: The high-protein feed ingredient is prepared by the following method: deionized water is added to a mixing tank, the mixing tank is stirred at a speed of 50-80 r / min, the mass ratio of deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea is 5-10:10-20:20-30:5-10:1-2:2-3, the deionized water, feather meal, soybean meal powder, probiotic, sulfuric acid and urea are added to the mixing tank, and the stirring time is 20-30 min, thus obtaining the high-protein feed ingredient.

5. A method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 4, characterized in that: The pH value of the high-protein feed ingredients was tested using pH test paper, and the pH value needed to be controlled within the range of 4.5 to 6.

5.

6. The method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: High-protein feed ingredients are pumped into a high-pressure hydrolysis reactor with a volume of 50L to 100L and a pressure of 0.3MPa to 0.5MPa. The reactor is heated to 120℃ to 150℃, and the stirring speed is 30 to 50 r / min. The hydrolysis reaction is maintained at this temperature for 4 to 6 hours. The organic materials, namely feather meal, soybean meal, and mushroom bran powder, are fully hydrolyzed under subcritical conditions. After the reaction is completed, the pressure is released for 20 to 30 minutes. After the pressure is released, the reactor is cooled to 50 to 80℃ to obtain the separated hydrolysate.

7. The method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: The specific steps for separating the hydrolysate through filtration using a plate filter and centrifuge are as follows: The clarified filtrate is injected into the plate filter. The filter cloth of the plate filter has a precision of 5–10 μm, the pressure is 0.3–0.5 MPa, and the filtration time is 1–2 h to complete the filtration of the clarified filtrate. The filtered clarified filtrate is then added to a centrifuge. The centrifuge speed is 3000–5000 r / min, and the centrifugation time is 15–25 min. After centrifugation, the supernatant is collected.

8. A method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1 or 7, characterized in that: The transmittance of the supernatant filtrate is 85%–95%.

9. A method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: The supernatant is pumped into a neutralization tank and stirred at a speed of 60–90 r / min for 30–60 min. While stirring, sodium hydroxide solution is slowly added to the neutralization tank. The concentration of the sodium hydroxide solution is 10%–30%, and the amount added is 1%–5% of the volume of the supernatant, until the pH value of the supernatant is adjusted to 6.5–7.5, thus completing the acid-base neutralization reaction.

10. A method for preparing water-soluble fertilizer using subcritical hydrolysis technology according to claim 1, characterized in that: In step S4, during the concentration process, the concentration temperature is 60℃~80℃, the concentration pressure is -0.08MPa~-0.05MPa, and the concentration of the concentrated liquid obtained from the concentration process is 40%~60%; during the crystallization process, the crystallization temperature is 0℃~10℃, the stirring speed is 40~60r / min, and the crystallization time is 4~6h, to obtain the water-soluble fertilizer product.

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