Integrated low-temperature preparation method of plant source multifunctional nano composite fertilizer particles

Abstract

This invention provides an integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles, relating to the field of fertilizer manufacturing technology. The method includes the following steps: S1: Preparation of functional nano-slurry, mixing a plant-derived active composition with an amino acid metal chelate, adding a citric acid-modified halloysite nanotube carrier, and subjecting a loading composite reaction at 25-45°C for 2-3 hours under shear force to obtain the functional nano-slurry; the citric acid-modified halloysite nanotubes are obtained by dispersing halloysite nanotubes in a 0.5-2.0 wt% citric acid solution and stirring at 40-50°C for 1-2 hours; S2: Low-temperature binding and granulation, using the functional nano-slurry obtained in step S1 as a binder. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles provided by this invention has the advantages of efficient protection of active ingredients, strong bonding, continuous and efficient process, and high product uniformity.

Description

Technical Field

[0001] This invention relates to the field of fertilizer manufacturing technology, and in particular to a continuous, low-temperature preparation method for preparing multifunctional nanocomposite fertilizer particles with a core-shell structure. Background Technology

[0002] When preparing functional fertilizers containing heat-sensitive active ingredients (such as plant extracts and amino acid chelates), traditional high-temperature granulation (such as high-tower melt granulation, with temperatures >100℃) or strong shear extrusion granulation processes can lead to the deactivation of a large number of active ingredients.

[0003] In the existing technology, in order to protect the activity, a step-by-step method of "granulation first, then impregnation or surface spraying" is often adopted. However, this method has problems such as uneven functional layer loading, weak bonding, and easy detachment. In addition, the process is long and energy consumption is high.

[0004] Halloysite nanotubes (HNTs), as a natural nanotube mineral, are widely used for loading active substances due to their unique tubular structure and good biocompatibility. Existing technologies, such as patent document CN118878372A, disclose a method for chemically modifying halloysite nanotubes through multiple steps including sulfuric acid treatment, silane modification, and chitosan modification, followed by loading into compound fertilizers. However, this method involves multiple chemical reactions, is complex, and does not solve the problem of firmly binding the active ingredients to the fertilizer matrix.

[0005] Amino acid metal chelates have been widely used as highly efficient micronutrient fertilizers. For example, existing technologies, such as the patent document with publication number CN102627498A, disclose a method for preparing micronutrient fertilizers by chelating amino acids and micronutrients. However, there is no publicly disclosed technical solution for an integrated low-temperature process in which amino acid chelates and plant-derived active ingredients are co-loaded onto a nanocarrier and used as a binder in granulation.

[0006] Therefore, there is a need to develop a continuous preparation method that can efficiently and uniformly integrate active ingredients into the interior of fertilizer granules while maintaining a low-temperature environment throughout the process, so as to achieve a balance between product functionality and production economy. Summary of the Invention

[0007] The present invention aims to provide a low-temperature preparation method for multifunctional nanocomposite fertilizers that features a continuous process, high activity retention rate, and good product uniformity, in order to solve the core process challenges in the industrial production of heat-sensitive functional fertilizers.

[0008] To solve the above-mentioned technical problems, the integrated low-temperature preparation method of plant-derived multifunctional nanocomposite fertilizer particles provided by the present invention includes the following steps: S1: Preparation of functional nanoparticle paste. First, halloysite nanotubes are modified with citric acid: Halloysite nanotubes are dispersed in a 0.5-2.0 wt% citric acid solution and stirred at 40-50℃ for 1-2 hours. After centrifugation, washing, and drying, surface carboxylated modified halloysite nanotubes are obtained. Citric acid treatment can increase the carboxyl group density on the surface of halloysite nanotubes under mild conditions, enhancing their adsorption capacity for amino acid metal chelates and plant-derived active ingredients, while avoiding the environmental impact of strong acids or organic solvents. The plant-derived active composition (a mixture of Scutellaria baicalensis extract and Melia toosendan extract) was mixed with an amino acid metal chelate in the liquid phase, and the modified halloysite nanotubes were added. The mixture was subjected to a loading composite reaction at 25-45℃ for 2-3 hours under shear force to obtain a uniform functional nanoslurry. S2: Low-temperature binding granulation. The functional nano-slurry obtained in step S1 is used as a binder and mixed with nitrogen, phosphorus, and potassium basic fertilizer powder in a fluidized bed granulator. The inlet air temperature is controlled at 45-48℃. The functional nano-slurry is sprayed into the fluidized basic fertilizer powder through an atomizing nozzle. The mass ratio of slurry to powder is 1:3-5. The material fluidizes, binds, and grows in the bed to form wet particles of 1-2 mm. S3: Fluidized bed drying and coating. The wet particles obtained in step S2 are placed in a vibrating fluidized bed and dried under the condition that the air inlet temperature in the drying zone is 45-50℃. Then, they enter the coating zone and a film-forming material solution (potassium humate, sodium lignosulfonate or polyacrylate emulsion) is sprayed by atomization. The air inlet temperature in the coating zone is 40-45℃. Under the condition of ≤50℃, an outer protective layer is formed on the particle surface, and finally, the dried coated particles are obtained.

[0009] Further, in step S1, the amino acid metal chelate is prepared in situ: an amino acid (at least one of glycine, glutamic acid, and lysine) is reacted with a soluble metal salt (soluble salts of zinc, iron, and manganese) in an aqueous solution at pH 5.8-6.2 and temperature 58-62℃ for 1-1.5 hours to directly obtain the chelate solution.

[0010] Furthermore, the halloysite nanotubes have an outer diameter of 50-70 nm, an inner diameter of 10-20 nm, and a length of 0.5-1.5 μm; after citric acid treatment, the surface carboxyl group density increases by 20-30%, which is beneficial for the complexation and fixation of amino acid metal chelates.

[0011] Furthermore, the baicalin content of the Scutellaria baicalensis extract in the plant-derived active composition is ≥20%, and the azadirachtin content of the Melia toosendan extract is ≥5%.

[0012] Further, in step S1, the shear force is provided by a high-speed dispersion device with a rotation speed of 2000-3000 rpm, and the mass ratio of the plant-derived active composition, the amino acid metal chelate and the modified halloysite nanotubes is 1-2:1-2:1.

[0013] Furthermore, in step S2, the basic fertilizer powder is a mixed powder of urea, monoammonium phosphate, and potassium sulfate, with a particle size ≤100 mesh.

[0014] Furthermore, the concentration of the film-forming material solution is 5-10 wt%.

[0015] Furthermore, from step S1 to the end of step S3, the maximum heating temperature of the material does not exceed 50°C.

[0016] The plant-derived multifunctional nanocomposite fertilizer particles prepared by the above method have a core-shell structure, wherein the core is a composite of modified halloysite nanotubes loaded with plant-derived active composition and amino acid metal chelates and basic fertilizer, and the outer shell is a film-forming material layer.

[0017] Compared with related technologies, the integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles provided by this invention has the following beneficial effects: 1. Mild modification, green and environmentally friendly: Citric acid is used to modify halloysite nanotubes, avoiding the use of strong acids or organic solvents. The process is mild (40-50℃), which increases the surface carboxyl group density while maintaining the integrity of the tubular structure of halloysite nanotubes. The modification process is matched with the temperature of subsequent processes, which is conducive to integrated continuous production.

[0018] 2. Synergistic loading and strong bonding: The carboxyl groups introduced by citric acid modification can form complexes with amino acid metal chelates, enhancing their fixation on the nanotube surface; simultaneously, the functional nano-slurry is used as a granulation binder, ensuring that the nanocarriers carrying active ingredients are uniformly distributed within the particles (bulk phase), solving the problem of easy functional layer detachment in traditional post-processing methods. Comparative experiments show that the functional component detachment rate of particles prepared by the method of this invention is <5%, while the detachment rate of traditional post-impregnation methods is as high as 35% or more.

[0019] 3. Low-temperature protection throughout the entire process: From halloysite modification, slurry preparation, granulation to drying and coating, the maximum heating temperature of the material does not exceed 50℃, which maximizes the protection of the structural stability of heat-sensitive active substances such as baicalin and azadirachtin, as well as amino acid chelates, with an active ingredient retention rate of ≥92%.

[0020] 4. Continuous and efficient process: The process of "carrier modification - slurry preparation - granulation - drying - coating" is organically integrated, which shortens the process, reduces material transfer loss, and reduces energy consumption by more than 30% compared with traditional processes.

[0021] 5. Excellent slow-release performance: Uniform coating using a vibrating fluidized bed creates a core-shell structure that allows for nutrient release over a period of more than 6 weeks, meeting the nutritional needs of crops throughout their growth cycle. Attached Figure Description

[0022] Figure 1 A flowchart of the integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles provided by the present invention; Figure 2 The infrared spectra of halloysite nanotubes before and after citric acid modification show that the characteristic peaks of carboxyl groups are enhanced after modification. Figure 3 This is a complete morphology image of the fertilizer granules prepared according to the present invention under a low-magnification scanning electron microscope; Figure 4 The image shows the cross-sectional morphology of the fertilizer granules prepared according to the present invention under a high-magnification scanning electron microscope. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Please refer to the following: Figures 1-4 ,in, Figure 1 A flowchart of the integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles provided by the present invention; Figure 2 The infrared spectra of halloysite nanotubes before and after citric acid modification show that the characteristic peaks of carboxyl groups are enhanced after modification. Figure 3 The image shows the complete morphology of the fertilizer granules prepared in this invention under a low-magnification scanning electron microscope. The granules are approximately spherical with a uniform particle size distribution, mainly in the range of 1.5-3.0 mm. Figure 4 The image shows the cross-sectional morphology of the fertilizer particles prepared in this invention under a high-magnification scanning electron microscope, clearly displaying the core-shell structure: the core is a composite of functional nano-slurry and basic fertilizer, and the outer shell is a dense film-forming material layer.

[0025] Example 1: The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles includes the following steps: (1) Citric acid modification of halloysite nanotubes: 10g of halloysite nanotubes (outer diameter 50-70nm, inner diameter 10-20nm, length 0.5-1.5μm) were dispersed in 200mL of 1.0wt% citric acid solution, stirred at 45℃ for 1.5 hours, centrifuged, washed three times with deionized water, and vacuum dried at 60℃ for 12 hours to obtain citric acid-modified halloysite nanotubes. Infrared spectroscopy showed that the modified halloysite nanotubes showed a high chromaticity at 1720 nm. The characteristic absorption peak of carboxyl group C=O appears at the point, and the surface carboxyl group density increases by about 25%.

[0026] (2) Preparation of amino acid metal chelate: Glycine and zinc sulfate were mixed at a molar ratio of 2.5:1, dissolved in deionized water, and the pH was adjusted to 6.0. The mixture was reacted in a water bath at 60°C for 1 hour to obtain glycine zinc chelate solution.

[0027] (3) Preparation of functional nano-slurry: Scutellaria baicalensis water extract with 20% baicalin content and Melia toosendan extract with 5% azadirachtin content were mixed at a mass ratio of 1:1 to obtain a plant-derived active composition. 10g of the above plant-derived active composition and glycine zinc chelate (equivalent to 10g solid content) were mixed, and 5g of citric acid modified halloysite nanotubes were added. The mixture was dispersed at high speed of 2500rpm and reacted at 38℃ for 2.5 hours to obtain functional nano-slurry.

[0028] (4) Low-temperature bonding and granulation: Urea, monoammonium phosphate, and potassium sulfate are mixed in a mass ratio of 2:1:1 and pulverized through a 100-mesh sieve to obtain basic fertilizer powder. 500g of basic fertilizer powder is put into a fluidized bed granulator, and the air inlet temperature is controlled at 48℃. The functional nano-slurry obtained in step (3) (containing about 25g of solids) is diluted with water to 120mL and sprayed into the fluidized bed granulator at a rate of 8mL / min and an atomization pressure of 0.2MPa. The material is fluidized, bonded, and grows in the bed to form wet particles of 1-2mm.

[0029] (5) Fluidized bed drying and coating: The wet particles are transferred to a vibrating fluidized bed. The air inlet temperature of the drying zone is 48°C, and the particles are dried for 10 minutes until the moisture content is ≤3%. An 8% potassium humate solution is prepared as the coating solution and sprayed by atomization at an air inlet temperature of 43°C in the coating zone. The coating weight gain is about 5%. After coating, hot air at 40°C is continued to be introduced for drying for 5 minutes. The particles are then sieved to obtain finished particles with a size of 1.5-3.0 mm.

[0030] Example 2: Based on Example 1, the following adjustments were made: the concentration of citric acid solution in step (1) was adjusted to 0.5wt%, and the treatment time was 2 hours; the amino acid metal chelate in step (3) was manganese glutamic acid (molar ratio 2:1); and the film-forming material in step (5) was 8% sodium lignosulfonate.

[0031] Example 3: Based on Example 1, the following adjustments were made: the concentration of citric acid solution in step (1) was adjusted to 2.0 wt%, and the treatment time was 1 hour; lysine iron (molar ratio 3:1) was used as the amino acid metal chelate in step (3); and 6% polyacrylate emulsion was used as the film-forming material in step (5).

[0032] Comparative Example 1: Referring to the patent document with publication number CN118878372A in the prior art, the following method was used to prepare a slow-release compound fertilizer: sulfuric acid treatment, acryloyloxypropyltrimethoxysilane modification, modified chitosan-modified halloysite nanotubes, loaded with compound fertilizer, and then coated with modified rubber and modified polyvinyl alcohol.

[0033] Comparative Example 2: The traditional post-impregnation method was used for preparation: basic fertilizer granules were prepared by conventional high-temperature (80°C) fluidized bed granulation, and then impregnated in the same functional nano-slurry as in Example 1. After removal, they were dried at 50°C.

[0034] Performance testing: 1. Active ingredient shedding rate test 10g of each of the particles prepared in Examples 1-3 and Comparative Example 2 were placed in a shaker and shaken at 50rpm for 30 minutes (simulating transport abrasion). The particles and eluent were separated by filtration, and the content of baicalin in the eluent was determined. The shedding rate was calculated. The results are shown in Table 1.

[0035] Table 1

[0036] 2. Active ingredient retention rate test The changes in baicalin content during the preparation process (from raw materials to finished product) of each example were measured, and the retention rate was calculated. The results are shown in Table 2.

[0037] Table 2

[0038] 3. Nutrient release cycle test Using a soil incubation method, the particles from each embodiment were buried in soil at a constant temperature and humidity of 25°C. The available nitrogen and zinc content in the surrounding soil was measured periodically, and the release cycle (the time required for cumulative release ≥80%) was calculated. The results are shown in Table 3.

[0039] Table 3

[0040] Results analysis: As shown in Table 1, the functional component loss rate of the particles prepared by the method of the present invention (Examples 1 to 3) is less than 5%, which is far better than the 36.7% of the traditional post-impregnation method (Comparative Example 2). This proves that the integrated process of using functional nano-slurry as a binder has achieved a strong bond between the functional components and the fertilizer matrix.

[0041] As shown in Table 2, the low-temperature process of the present invention ensures that the retention rate of heat-sensitive active ingredients is above 92%, while in Comparative Example 1, due to the involvement of high-temperature treatment steps, the loss of active ingredients is relatively large.

[0042] As shown in Table 3, the nutrient release cycle of the particles prepared by this invention is more than 6 weeks, which is better than that of Comparative Example 1, indicating that the dual slow-release structure formed by citric acid modified halloysite nanotubes and coating layer has a synergistic effect.

[0043] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles, characterized in that, Includes the following steps: S1: Preparation of functional nano-slurry: A plant-derived active composition is mixed with an amino acid metal chelate, and a citric acid-modified halloysite nanotube carrier is added. The mixture is subjected to a loading and composite reaction at 25-45℃ for 2-3 hours under shear force to obtain the functional nano-slurry. The citric acid-modified halloysite nanotubes are prepared by dispersing halloysite nanotubes in a 0.5-2.0wt% citric acid solution and stirring at 40-50℃ for 1-2 hours. S2: Low-temperature bonding granulation. The functional nano slurry obtained in step S1 is used as a binder and mixed with the basic fertilizer powder in a fluidized bed granulator for granulation. The air inlet temperature is controlled at 45-48℃. The functional nano slurry is atomized and sprayed into the fluidized basic fertilizer powder to form wet granules. S3: Fluidized bed drying and coating. The wet particles obtained in step S2 are dried in a vibrating fluidized bed at 40-50°C, and a film-forming material solution is atomized and sprayed to form an outer protective layer at ≤50°C.

2. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S1, the plant-derived active composition is a mixture of Scutellaria baicalensis extract and Melia toosendan extract, wherein the Scutellaria baicalensis extract contains ≥20% baicalin and the Melia toosendan extract contains ≥5% azadirachtin.

3. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S1, the amino acid metal chelate is prepared by reacting amino acids with soluble metal salts in situ in an aqueous phase at pH 5.8-6.2 and 58-62°C for 1-1.5 hours; the amino acid is selected from at least one of glycine, glutamic acid, and lysine, and the metal salt is a soluble salt of zinc, iron, or manganese.

4. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S1, the halloysite nanotubes have an outer diameter of 50-70 nm, an inner diameter of 10-20 nm, and a length of 0.5-1.5 μm; after citric acid treatment, the surface carboxyl group density of the halloysite nanotubes increases by 20-30%.

5. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S1, the shear force is provided by a high-speed dispersion device with a rotation speed of 2000-3000 rpm, and the mass ratio of the plant-derived active composition, amino acid metal chelate and modified halloysite nanotubes is 1-2:1-2:

1.

6. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S2, the basic fertilizer powder is a mixed powder of urea, monoammonium phosphate, and potassium sulfate with a particle size ≤100 mesh, and the mass ratio of functional nano-slurry to basic fertilizer powder is 1:3-5.

7. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, In step S3, the inlet air temperature of the vibrating fluidized bed drying zone is 45-50℃, and the inlet air temperature of the vibrating fluidized bed coating zone is 40-45℃.

8. The integrated low-temperature preparation method for plant-derived multifunctional nanocomposite fertilizer particles according to claim 1, characterized in that, The film-forming material solution is at least one of potassium humate, sodium lignosulfonate, or polyacrylate emulsion, with a concentration of 5-10 wt%.

9. The integrated low-temperature preparation method of plant-derived multifunctional nanocomposite fertilizer particles according to any one of claims 1-8, characterized in that, From step S1 to the end of step S3, the maximum heating temperature of the material shall not exceed 50°C.

10. The integrated low-temperature preparation method of plant-derived multifunctional nanocomposite fertilizer particles according to claim 9, characterized in that, Plant-derived multifunctional nanocomposite fertilizer particles have a core-shell structure, in which the core is a composite of modified halloysite nanotubes loaded with plant-derived active compositions and amino acid metal chelates and basic fertilizer, and the outer shell is a film-forming material layer.

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