Composite slow-release fertilizer and preparation method thereof

Abstract

The application relates to the technical field of fertilizers, and discloses a kind of compound slow-release fertilizer and a preparation method thereof, wherein the compound slow-release fertilizer is obtained by spraying a coating liquid on the surface of urea particles; the coating liquid is prepared from modified starch, deionized water, chitosan, an aqueous acetic acid solution, organically modified montmorillonite and glycerol; the organically modified montmorillonite is prepared from sodium-based montmorillonite, deionized water and an aqueous cetyltrimethylammonium bromide solution; and the modified starch is prepared from cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate. The application can realize slow release of nutrients.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, specifically to a compound slow-release fertilizer and its preparation method. Background Technology

[0002] Chemical fertilizers play a vital role in agricultural production by increasing crop yields and improving crop quality. Urea, as the solid nitrogen fertilizer with the highest nitrogen content, is widely used in various crop cultivation scenarios due to its advantages such as readily available raw materials, low cost, and direct fertilizer effect. However, traditional urea fertilizers suffer from drawbacks such as rapid nutrient release and low utilization rate after application. Its nitrogen is easily lost through soil leaching, volatilization, and microbial decomposition, making it difficult for crops to effectively absorb.

[0003] Patent CN117902942B discloses a corn yield-increasing functional fertilizer, which comprises the following raw materials in parts by weight: 30-35 parts nitrogen, phosphorus, and potassium fertilizer; 20-25 parts organic matter agent; 10-15 parts continuous modifier; 8-12 parts sodium humate; 6-9 parts blending agent modified with nano-silica; 1-3 parts γ-aminobutyric acid; and 1-3 parts chitosan oligosaccharide. However, this fertilizer has a high nutrient release rate, which leads to the crop's inability to absorb nutrients in a timely manner, resulting in resource waste. Summary of the Invention

[0004] The purpose of this invention is to provide a compound slow-release fertilizer and its preparation method to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A compound slow-release fertilizer is obtained by spraying a coating solution onto the surface of urea granules; the coating solution is prepared from modified starch, deionized water, chitosan, aqueous acetic acid solution, organically modified montmorillonite, and glycerol; the organically modified montmorillonite is prepared from sodium montmorillonite, deionized water, and an aqueous solution of hexadecyltrimethylammonium bromide; the modified starch is prepared from cassava starch, deionized water, sodium hypophosphite, and citric acid monohydrate.

[0006] Furthermore, the degree of deacetylation of the chitosan is not less than 85%, and the viscosity is 50-200 mPa·s.

[0007] Furthermore, the particle size of urea particles is 2-4 mm.

[0008] Furthermore, the mass fraction of the hexadecyltrimethylammonium bromide aqueous solution is 10%-15%.

[0009] A method for preparing a compound slow-release fertilizer includes the following steps: (1) Add cassava starch and deionized water to the reactor and stir at 200-300 rpm for 20-30 minutes. Then add sodium hypophosphite and continue stirring for 20-30 minutes. Heat to 85-95℃ and continue stirring for 15-20 minutes. Then slowly add citric acid monohydrate over 30-40 minutes and continue stirring for 90-120 minutes. Cool, filter, wash with deionized water until neutral, and then vacuum dry at 55-65℃ for 8-12 hours. After pulverizing, pass through a 100-200 mesh sieve to obtain modified starch. (2) Sodium montmorillonite with a particle size of 200-400 mesh is added to deionized water and stirred at 5000-8000 rpm for 30-40 minutes at 60-70℃. Then, hexadecyltrimethylammonium bromide aqueous solution is slowly added over 30-40 minutes and stirred at 70-80℃ for 240-300 minutes. After that, it is allowed to stand and age for 10-12 hours. The supernatant is discarded, and the lower slurry is vacuum dried at 85-95℃ for 8-12 hours. After grinding, it is passed through a 200-300 mesh sieve to obtain organic modified montmorillonite. (3) Mix modified starch and deionized water at a mass ratio of 1:5-7, and stir at 300-500 rpm for 30-40 minutes at 85-90℃ to obtain a modified starch dispersion; mix chitosan and a 2-3% acetic acid aqueous solution at a mass ratio of 1:18-22, and stir at 200-400 rpm for 2-3 hours at 25-30℃ to obtain a chitosan solution; mix organically modified montmorillonite and deionized water at a mass ratio of 1:18-22, and disperse under ultrasonic power of 300-400W for 20-30 minutes to obtain... To obtain the organically modified montmorillonite dispersion; after cooling the modified starch dispersion to 30-40℃, place it in a reaction vessel, and slowly add chitosan solution over 30-40 minutes while stirring at 300-400 rpm, then slowly add the organically modified montmorillonite dispersion over 30-40 minutes, followed by the addition of glycerol, and stir at 8000-10000 rpm for 5-10 minutes. Finally, adjust the pH value to 4.5-5.5 with a 1-2% (w / w) aqueous acetic acid solution or a 1-2% (w / w) aqueous sodium hydroxide solution to obtain the coating solution; (4) Place the urea granules in a fluidized bed, spray the coating liquid onto the surface of the urea granules, and after spraying, continue fluidizing and drying at 55-65℃ for 30-45 minutes, then discharge the material to obtain the compound slow-release fertilizer.

[0010] Furthermore, in step (3), if the pH value of the mixture is higher than 5.5, it is adjusted with an aqueous solution of acetic acid with a mass fraction of 1-2%; if the pH value is lower than 4.5, it is adjusted with an aqueous solution of sodium hydroxide with a mass fraction of 1-2% until the pH value reaches 4.5-5.5, thus obtaining the coating solution.

[0011] Furthermore, in step (1), the mass ratio of cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate is 100:200-300:1.5-2.5:15-25.

[0012] Furthermore, in step (2), the mass ratio of sodium montmorillonite, deionized water and hexadecyltrimethylammonium bromide aqueous solution is 100:1800-2200:150-250.

[0013] Furthermore, in step (3), the mass ratio of modified starch dispersion, chitosan solution, organically modified montmorillonite dispersion and glycerol is 40-60:15-25:4-6:5-8.

[0014] Furthermore, in step (4), the mass ratio of urea particles to coating solution is 100:15-20.

[0015] Furthermore, in step (4), the inlet air temperature of the fluidized bed is set to 55-65℃.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. In this invention, the hydroxyl functional groups on the cassava starch molecular chain and the carboxyl functional groups on the citric acid molecule undergo an esterification reaction under heating and with the catalyst sodium hypophosphite. Two or three carboxyl groups on the citric acid can undergo esterification reactions with the hydroxyl groups on different starch molecular chains, thereby forming a cross-linked network structure that enhances its mechanical strength. The silicate lamellar structure of sodium-based montmorillonite contains exchangeable cations, which undergo cation exchange reactions with quaternary ammonium cations provided by hexadecyltrimethylammonium bromide. These quaternary ammonium cations enter the montmorillonite interlayers through ion exchange. Due to their relatively small molecular volume... The modified starch effectively increases the interlayer spacing of montmorillonite, improving its compatibility with organic polymers. The remaining hydroxyl and carboxyl functional groups on the modified starch molecular chain meet the amino and hydroxyl functional groups on the chitosan molecular chain under weakly acidic conditions. The protonated amino groups of chitosan carry a positive charge and interact electrostatically with the negatively charged carboxyl groups. Simultaneously, hydrogen bonds can form between the hydroxyl and amino groups, promoting their entanglement and forming a polymer network on the surface of urea particles, achieving slow nutrient release. The organically modified montmorillonite is dispersed within this polymer network, thus prolonging and hindering nutrient diffusion. Starch, sodium montmorillonite, and cassava starch are all environmentally friendly raw materials. Detailed Implementation

[0017] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0018] A compound slow-release fertilizer is obtained by spraying a coating solution onto the surface of urea granules; the coating solution is prepared from modified starch, deionized water, chitosan, aqueous acetic acid solution, organically modified montmorillonite, and glycerol; the organically modified montmorillonite is prepared from sodium montmorillonite, deionized water, and an aqueous solution of hexadecyltrimethylammonium bromide; the modified starch is prepared from cassava starch, deionized water, sodium hypophosphite, and citric acid monohydrate.

[0019] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0020] Example 1

[0021] (1) Add cassava starch and deionized water to the reactor and stir at 200 rpm for 20 minutes. Then add sodium hypophosphite and continue stirring for 20 minutes. Heat to 85°C and continue stirring for 15 minutes. Then slowly add citric acid monohydrate over 30 minutes and continue stirring for 90 minutes. Cool, filter, wash with deionized water until neutral, and then vacuum dry at 55°C for 8 hours. After pulverizing, pass through a 100-mesh sieve to obtain modified starch. The mass ratio of cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate is 100:200:1.5:15.

[0022] (2) Sodium montmorillonite with a particle size of 200 mesh was added to deionized water and stirred at 5000 rpm for 30 minutes at 60°C. Then, a 10% hexadecyltrimethylammonium bromide aqueous solution was slowly added over 30 minutes. The mixture was stirred at 70°C for 240 minutes. After that, it was allowed to stand for 10 hours. The supernatant was discarded, and the lower slurry was vacuum dried at 85°C for 8 hours. After grinding, it was passed through a 200-mesh sieve to obtain organically modified montmorillonite. The mass ratio of sodium montmorillonite, deionized water and hexadecyltrimethylammonium bromide aqueous solution was 100:1800:150.

[0023] (3) Modified starch and deionized water were mixed at a mass ratio of 1:5 and stirred at 300 rpm for 30 minutes at 85°C to obtain a modified starch dispersion; chitosan and a 2% acetic acid aqueous solution were mixed at a mass ratio of 1:18 and stirred at 200 rpm for 2 hours at 25°C to obtain a chitosan solution; organically modified montmorillonite was mixed with deionized water at a mass ratio of 1:18 and dispersed under ultrasonic power of 300W for 20 minutes to obtain an organically modified montmorillonite dispersion; the modified starch dispersion was cooled to 30°C and placed in a reaction vessel, and then subjected to 3... At a stirring speed of 00 rpm, chitosan solution was slowly added over 30 minutes, followed by organically modified montmorillonite dispersion over another 30 minutes. Glycerin was then added, and the mixture was stirred at 8000 rpm for 5 minutes. Finally, the pH was adjusted to 4.5 with a 1% (w / w) aqueous acetic acid solution or a 1% (w / w) aqueous sodium hydroxide solution to obtain the coating solution. The degree of deacetylation of the chitosan was not less than 85%, and the viscosity was 50 mPa·s. The mass ratio of modified starch dispersion, chitosan solution, organically modified montmorillonite dispersion, and glycerin was 40:15:4:5.

[0024] (4) Place urea granules with a particle size of 2 mm in a fluidized bed, set the inlet air temperature to 55°C, spray the coating liquid onto the surface of the urea granules, and after spraying, continue fluidizing and drying at 55°C for 30 minutes. Discharge the material to obtain the composite slow-release fertilizer. The mass ratio of urea granules to coating liquid is 100:15.

[0025] Example 2

[0026] (1) Add cassava starch and deionized water to the reactor and stir at 250 rpm for 25 minutes. Then add sodium hypophosphite and continue stirring for 25 minutes. Heat to 90°C and continue stirring for 17.5 minutes. Then slowly add citric acid monohydrate over 35 minutes and continue stirring for 105 minutes. Cool, filter, wash with deionized water until neutral, and then vacuum dry at 60°C for 10 hours. After pulverizing, pass through a 150-mesh sieve to obtain modified starch. The mass ratio of cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate is 100:250:2:20.

[0027] (2) Sodium montmorillonite with a particle size of 300 mesh was added to deionized water and stirred at 6500 rpm for 35 minutes at 65°C. Then, a 12.5% ​​hexadecyltrimethylammonium bromide aqueous solution was slowly added over 35 minutes. The mixture was stirred at 75°C for 270 minutes and then allowed to stand for 11 hours. The supernatant was discarded, and the lower slurry was vacuum dried at 90°C for 10 hours. After grinding, the mixture was passed through a 250-mesh sieve to obtain organically modified montmorillonite. The mass ratio of sodium montmorillonite, deionized water, and hexadecyltrimethylammonium bromide aqueous solution was 100:2000:200.

[0028] (3) Modified starch and deionized water were mixed at a mass ratio of 1:6 and stirred at 400 rpm for 35 minutes at 87.5°C to obtain a modified starch dispersion; chitosan and a 2.5% acetic acid aqueous solution were mixed at a mass ratio of 1:20 and stirred at 300 rpm for 2.5 hours at 27.5°C to obtain a chitosan solution; organically modified montmorillonite and deionized water were mixed at a mass ratio of 1:20 and dispersed under ultrasonic power of 350W for 25 minutes to obtain an organically modified montmorillonite dispersion; the modified starch dispersion was cooled to 35°C and placed in a reaction vessel, and then subjected to 3... Chitosan solution was slowly added over 35 minutes at a stirring speed of 50 rpm, followed by slow addition of organically modified montmorillonite dispersion over another 35 minutes. Glycerin was then added, and the mixture was stirred at 9000 rpm for 7.5 minutes. Finally, the pH was adjusted to 5.0 with a 1.5% (w / w) aqueous acetic acid solution or a 1.5% (w / w) aqueous sodium hydroxide solution to obtain the coating solution. The degree of deacetylation of the chitosan was not less than 85%, and the viscosity was 125 mPa·s. The mass ratio of modified starch dispersion, chitosan solution, organically modified montmorillonite dispersion, and glycerin was 50:20:5:6.5.

[0029] (4) Place urea granules with a particle size of 3 mm in a fluidized bed, set the inlet air temperature to 60°C, spray the coating liquid onto the surface of the urea granules, and after spraying, continue fluidizing and drying at 60°C for 37.5 minutes. Discharge the material to obtain the composite slow-release fertilizer. The mass ratio of urea granules to coating liquid is 100:17.5.

[0030] Example 3

[0031] (1) Add cassava starch and deionized water to the reactor and stir at 300 rpm for 30 minutes. Then add sodium hypophosphite and continue stirring for 30 minutes. Heat to 95°C and continue stirring for 20 minutes. Then slowly add citric acid monohydrate over 40 minutes and continue stirring for 120 minutes. Cool, filter, wash with deionized water until neutral, and then vacuum dry at 65°C for 12 hours. After pulverizing, pass through a 200-mesh sieve to obtain modified starch. The mass ratio of cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate is 100:300:2.5:25.

[0032] (2) Sodium montmorillonite with a particle size of 400 mesh was added to deionized water and stirred at 8000 rpm for 40 minutes at 70°C. Then, a 15% hexadecyltrimethylammonium bromide aqueous solution was slowly added over 40 minutes. The mixture was stirred at 80°C for another 300 minutes. After that, it was allowed to stand for 12 hours. The supernatant was discarded, and the lower slurry was vacuum dried at 95°C for 12 hours. After grinding, it was passed through a 300-mesh sieve to obtain organically modified montmorillonite. The mass ratio of sodium montmorillonite, deionized water and hexadecyltrimethylammonium bromide aqueous solution was 100:2200:250.

[0033] (3) Modified starch and deionized water were mixed at a mass ratio of 1:7 and stirred at 500 rpm for 40 minutes at 90°C to obtain a modified starch dispersion; chitosan and a 3% acetic acid aqueous solution were mixed at a mass ratio of 1:22 and stirred at 400 rpm for 3 hours at 30°C to obtain a chitosan solution; organically modified montmorillonite was mixed with deionized water at a mass ratio of 1:22 and dispersed under ultrasonic power of 400W for 30 minutes to obtain an organically modified montmorillonite dispersion; the modified starch dispersion was cooled to 40°C and placed in a reaction vessel, and then stirred at 40°C... Chitosan solution was slowly added over 40 minutes at a stirring speed of 0 rpm, followed by slow addition of organically modified montmorillonite dispersion over another 40 minutes. Glycerin was then added, and the mixture was stirred at 10,000 rpm for 10 minutes. Finally, the pH was adjusted to 5.5 with a 2% (w / w) aqueous acetic acid solution or a 2% (w / w) aqueous sodium hydroxide solution to obtain the coating solution. The degree of deacetylation of the chitosan was not less than 85%, and the viscosity was 200 mPa·s. The mass ratio of modified starch dispersion, chitosan solution, organically modified montmorillonite dispersion, and glycerin was 60:25:6:8.

[0034] (4) Place urea granules with a particle size of 4 mm in a fluidized bed, set the inlet air temperature to 65°C, spray the coating liquid onto the surface of the urea granules, and after spraying, continue fluidizing and drying at 65°C for 45 minutes. Discharge the material to obtain the composite slow-release fertilizer. The mass ratio of urea granules to coating liquid is 100:20.

[0035] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that citric acid monohydrate is not added.

[0036] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no aqueous solution of hexadecyltrimethylammonium bromide was added.

[0037] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the chitosan solution is omitted.

[0038] Nutrient release performance test: Referring to GB / T23348-2009 Slow-release Fertilizer, the cumulative release rate of nitrogen nutrients was tested using the static water extraction method.

[0039] Table 1 below shows the performance analysis results of the embodiments and comparative examples of the present invention.

[0040] Table 1

[0041] Experimental data from the examples and comparative examples show that the protonated amino groups of chitosan in this invention are positively charged and interact electrostatically with the negatively charged carboxyl groups. At the same time, hydrogen bonds can be formed between the modified starch and the hydroxyl and amino groups of chitosan, thereby promoting their entanglement and forming a polymer network on the surface of urea particles, which realizes the slow release of nutrients. The organically modified montmorillonite is dispersed in the above polymer network, thereby prolonging and hindering the diffusion of nutrients.

[0042] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A compound slow-release fertilizer, characterized in that, The compound slow-release fertilizer is obtained by spraying a coating solution onto the surface of urea granules; the coating solution is prepared from modified starch, deionized water, chitosan, acetic acid aqueous solution, organically modified montmorillonite, and glycerol; the organically modified montmorillonite is prepared from sodium montmorillonite, deionized water, and hexadecyltrimethylammonium bromide aqueous solution; the modified starch is prepared from cassava starch, deionized water, sodium hypophosphite, and citric acid monohydrate.

2. The compound slow-release fertilizer according to claim 1, characterized in that: The degree of deacetylation of the chitosan is not less than 85%, and the viscosity is 50-200 mPa·s.

3. The compound slow-release fertilizer according to claim 1, characterized in that: The particle size of urea granules is 2-4 mm.

4. The compound slow-release fertilizer according to claim 1, characterized in that: The mass fraction of the aqueous solution of hexadecyltrimethylammonium bromide is 10%-15%.

5. A method for preparing a compound slow-release fertilizer, applied to the compound slow-release fertilizer according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Add cassava starch and deionized water to the reactor and stir at 200-300 rpm for 20-30 minutes. Then add sodium hypophosphite and continue stirring for 20-30 minutes. Heat to 85-95℃ and continue stirring for 15-20 minutes. Then slowly add citric acid monohydrate over 30-40 minutes and continue stirring for 90-120 minutes. Cool, filter, wash with deionized water until neutral, and then vacuum dry at 55-65℃ for 8-12 hours. After pulverizing, pass through a 100-200 mesh sieve to obtain modified starch. (2) Sodium montmorillonite with a particle size of 200-400 mesh is added to deionized water and stirred at 5000-8000 rpm for 30-40 minutes at 60-70℃. Then, hexadecyltrimethylammonium bromide aqueous solution is slowly added over 30-40 minutes and stirred at 70-80℃ for 240-300 minutes. After that, it is allowed to stand and age for 10-12 hours. The supernatant is discarded, and the lower slurry is vacuum dried at 85-95℃ for 8-12 hours. After grinding, it is passed through a 200-300 mesh sieve to obtain organic modified montmorillonite. (3) Mix modified starch and deionized water at a mass ratio of 1:5-7, and stir at 300-500 rpm for 30-40 minutes at 85-90℃ to obtain a modified starch dispersion; mix chitosan and a 2-3% acetic acid aqueous solution at a mass ratio of 1:18-22, and stir at 200-400 rpm for 2-3 hours at 25-30℃ to obtain a chitosan solution; mix organically modified montmorillonite and deionized water at a mass ratio of 1:18-22, and disperse under ultrasonic power of 300-400W for 20-30 minutes to obtain... To obtain the organically modified montmorillonite dispersion; after cooling the modified starch dispersion to 30-40℃, place it in a reaction vessel, and slowly add chitosan solution over 30-40 minutes while stirring at 300-400 rpm, then slowly add the organically modified montmorillonite dispersion over 30-40 minutes, followed by the addition of glycerol, and stir at 8000-10000 rpm for 5-10 minutes. Finally, adjust the pH value to 4.5-5.5 with a 1-2% (w / w) aqueous acetic acid solution or a 1-2% (w / w) aqueous sodium hydroxide solution to obtain the coating solution; (4) Place the urea granules in a fluidized bed, spray the coating liquid onto the surface of the urea granules, and after spraying, continue fluidizing and drying at 55-65℃ for 30-45 minutes, then discharge the material to obtain the compound slow-release fertilizer.

6. The method for preparing a compound slow-release fertilizer according to claim 5, characterized in that: In step (1), the mass ratio of cassava starch, deionized water, sodium hypophosphite and citric acid monohydrate is 100:200-300:1.5-2.5:15-25.

7. The method for preparing a compound slow-release fertilizer according to claim 5, characterized in that: In step (2), the mass ratio of sodium montmorillonite, deionized water and hexadecyltrimethylammonium bromide aqueous solution is 100:1800-2200:150-250.

8. The method for preparing a compound slow-release fertilizer according to claim 5, characterized in that: In step (3), the mass ratio of modified starch dispersion, chitosan solution, organically modified montmorillonite dispersion and glycerol is 40-60:15-25:4-6:5-8.

9. The method for preparing a compound slow-release fertilizer according to claim 5, characterized in that: In step (4), the mass ratio of urea granules to coating solution is 100:15-20.

10. The method for preparing a compound slow-release fertilizer according to claim 5, characterized in that: In step (4), the inlet air temperature of the fluidized bed is set to 55-65℃.

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