A high temperature resistant controlled release coating material, coated compound fertilizer and controlled release fertilizer

Abstract

The present invention belongs to the technical field of polymer materials and controlled-release fertilizers, and specifically relates to a high-temperature resistant controlled-release coating material, a coated compound fertilizer and a controlled-release fertilizer. The high-temperature resistant controlled-release coating material comprises the following components in weight proportions: 20 to 40 parts of diols, 50 to 70 parts of diisocyanates, and 5 to 10 parts of cyclodextrins. The controlled-release fertilizer comprises the following components in weight proportions: 30 to 80 parts of coated compound fertilizers, 30 to 60 parts of potassium humate, 5 to 20 parts of porous silica-loaded carbon quantum dots, and 1 to 10 parts of water retaining agents. The present invention uses macromolecular cyclodextrin to replace conventional polyols as cross-linking agents for polyurethane coating agents, and the obtained coating material can achieve stable controlled release under high temperature (above 30°C). The coated compound fertilizer is further compounded with potassium humate and porous silica-loaded carbon quantum dots to prepare a controlled-release fertilizer, which can simultaneously achieve the effects of improving salinity and improving fertilizer efficiency and fertilizer retention capacity.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and controlled-release fertilizers, and in particular relates to a high-temperature resistant controlled-release coating material, a coated compound fertilizer and a controlled-release fertilizer. Background Art

[0002] Controlled-release fertilizers refer to fertilizers that are coated, wrapped, and added with inhibitors to prolong the decomposition and release time of fertilizers, which is beneficial to improve the utilization rate of fertilizer nutrients, thereby extending the effective period of fertilizers and promoting agricultural production. Common coated controlled-release fertilizers are mainly sulfur-coated controlled-release fertilizers and polyurethane-coated controlled-release fertilizers. Sulfur-coated controlled-release fertilizers are fertilizers that evenly coat the surface of fertilizer particles with sulfide solution, and gradually dissolve to achieve slow release of fertilizers, improve fertilizer efficiency and reduce the risk of fertilizer spillage. Sulfur-coated controlled-release fertilizers have a fast release rate, and most of the fertilizer components can usually be released within 1 to 2 months, which is suitable for the growth of short-cycle crops. Polyurethane-coated controlled-release fertilizers are fertilizer particles that are coated with polyurethane and then the release rate of fertilizers is controlled to reduce nutrient loss and improve fertilizer utilization. The release rate of polyurethane-coated controlled-release fertilizers is usually slow, and is suitable for crops with a long growing season, such as rice, rapeseed, corn, soybeans, etc.

[0003] At present, the polyurethane coating material used in polyurethane coated controlled-release fertilizers is generally obtained by curing reaction of isocyanate compounds and polyols, and cross-linked by small molecule cross-linking agents to improve its strength and water resistance, thereby improving its coating performance. However, the polyurethane coating material prepared by conventional small molecule cross-linking agents has poor elasticity and film-forming properties, and is easy to shrink and produce micropores during film formation, thereby affecting the coating performance. In order to achieve the specified release period, the amount of coating material needs to be increased, which increases the cost of fertilizers. In addition, the existing controlled-release fertilizer polyurethane coating materials generally have the problem of fast high-temperature release. Specifically, the Ministry of Agriculture and Rural Affairs defines the release period as the number of days when the release rate reaches 80% under 25°C extraction. However, the temperature in the southern region is high, and the soil temperature in summer can reach 30°C or even higher, so the release period of the controlled-release fertilizer will be much shorter. In addition, during the storage process of controlled-release fertilizers in high-temperature areas, the coating material membrane shell is generally aged, the gloss is poor, and the controlled-release fertilizer that has been placed for more than 2 years will have a release period shorter than theory.

[0004] Therefore, developing a controlled-release coating material with good coating performance, low coating material usage, and strong high-temperature (above 30° C.) controlled-release stability is a technical problem that needs to be solved by those skilled in the art.

[0005] In addition, existing studies have found that controlled-release fertilizers have a better yield-increasing effect on saline-alkali land than on normal soil, mainly because coated controlled-release special fertilizers can slow down the dissolution rate of nitrogen, phosphorus, and potassium, and reduce the superposition of salt damage to seeds and seedlings caused by quick-acting fertilizers and saline-alkali ions in the saline-alkali soil. However, controlled-release fertilizers generally do not have the effect of improving salinity, and when used on saline-alkali land, they generally need to be used in conjunction with organic fertilizers or soil conditioners. Therefore, providing a controlled-release fertilizer with a saline-alkali improvement effect has good application prospects. Summary of the invention

[0006] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a high temperature resistant controlled release coating material.

[0007] Another object of the present invention is to provide a coated compound fertilizer and a preparation method thereof.

[0008] Another object of the present invention is to provide a controlled-release fertilizer.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A high temperature resistant controlled release coating material comprises the following components in parts by weight:

[0011] 20-40 parts of diol, 50-70 parts of diisocyanate, and 5-10 parts of cyclodextrin.

[0012] Preferably, the diol is selected from one or a mixture of two or more of ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol with a molecular weight of 200 to 800, and polypropylene glycol with a molecular weight of 200 to 800.

[0013] Preferably, the diisocyanate is selected from one or a mixture of two or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate and lysine diisocyanate.

[0014] A method for preparing coated compound fertilizer comprises the following preparation steps:

[0015] (1) heating a diol and cyclodextrin to dissolve in a diluent solvent, cooling to room temperature, adding diisocyanate to dissolve uniformly, and obtaining a coating solution;

[0016] (2) The obtained coating liquid is evenly sprayed on the surface of the compound fertilizer particles, and dried to form a film to obtain the coated compound fertilizer.

[0017] Preferably, the dilution solvent is N,N-dimethylformamide or dimethyl sulfoxide; the solid content of the coating solution is 5% to 15% (mass percentage).

[0018] Preferably, the compound fertilizer particles are compound fertilizers with a particle size of 1 to 5 mm, comprising at least two of nitrogen fertilizers (urea, ammonium carbonate, ammonium sulfate, ammonium chloride, etc.), phosphate fertilizers (superphosphate, calcium magnesium phosphate, etc.), and potash fertilizers (potassium chloride, potassium sulfate, and potassium nitrate, etc.), or compound fertilizers containing at least two elements of nitrogen, phosphorus, and potassium.

[0019] Preferably, the drying and film-forming temperature is 60-80°C.

[0020] Preferably, the coating amount of the coating material in the coated compound fertilizer is 4% to 8% (the mass percentage of the coating material in the obtained coated compound fertilizer).

[0021] A coated compound fertilizer is prepared by the method.

[0022] A controlled-release fertilizer comprises the following components in parts by weight:

[0023] 30-80 parts of coated compound fertilizer, 30-60 parts of potassium humate, 5-20 parts of porous silica loaded carbon quantum dots, 1-10 parts of water retaining agent;

[0024] The porous silica-supported carbon quantum dots are prepared by the following method:

[0025] 1) adding the acid solution and the antibiotic residue into a hydrothermal reactor and mixing them evenly, heating them to 160-200° C. in a closed environment for a first hydrothermal reaction; after the reaction, centrifugally separating and taking the supernatant, adjusting the pH to neutral, and putting them into the hydrothermal reactor again for a second hydrothermal reaction by heating them to 160-200° C. in a closed environment; after the reaction, filtering and taking the filtrate to obtain a carbon quantum dot solution;

[0026] 2) adding porous silica to the carbon quantum dot solution of step (1) for stirring and adsorption treatment, and vacuum spray drying the mixed solution to obtain porous silica loaded with carbon quantum dots.

[0027] Preferably, the acid solution in step 1) is a nitric acid solution or a sulfuric acid solution with a concentration of 0.2 to 2 mol / L; the antibiotic residue refers to an antibiotic residue with a water content of 20% to 90% and an antibiotic content of 20 to 500 mg / kg, including but not limited to tetracycline residue, cephalosporin residue, penicillin residue, and vancomycin residue; the mass ratio of the acid solution to the antibiotic residue is 1 to 5:1.

[0028] Preferably, the time of the first hydrothermal reaction in step 1) is 3 to 10 hours, and the time of the second hydrothermal reaction is 1 to 5 hours.

[0029] Preferably, the particle size of the porous silica in step 2) is 5 to 6 μm, and the pore size is 5 to 20 nm; the amount of the porous silica added is 5% to 30% of the mass of the carbon quantum dot solution.

[0030] Preferably, the stirring adsorption treatment time in step (2) is 6 to 48 hours; the vacuum spray drying temperature is 100 to 120° C., and the vacuum degree is >0.09 MPa.

[0031] Preferably, the potassium humate is a highly efficient organic potassium fertilizer commonly used in the art, and its potassium content (in terms of K 2 O) is 5% to 12%.

[0032] Preferably, the water retaining agent is sodium polyacrylate.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention uses macromolecular cyclodextrin to replace conventional polyols as the crosslinking agent of the polyurethane coating agent. The macromolecular cyclodextrin contains a large number of hydroxyl groups distributed on the outside of the molecule, which can form a large number of crosslinking sites with isocyanate, thereby improving the strength and water resistance of the coating material. At the same time, cyclodextrin has good film-forming properties and can improve the film-forming properties and coating effect of the polyurethane coating material. In addition, cyclodextrin also has a relatively hydrophobic and loose inner cavity structure, which can improve the elasticity of the polyurethane coating material while improving water resistance, reduce shrinkage holes during film formation, and further improve the coating effect. The obtained coating material can achieve stable controlled release under high temperature (above 30°C).

[0035] (2) The present invention further prepares a controlled-release fertilizer by compounding the coated compound fertilizer with potassium humate and porous silica-loaded carbon quantum dots, which can simultaneously achieve the effects of improving salinity and alkali and improving fertilizer efficiency and fertilizer retention capacity.

[0036] (3) The preparation process of the controlled-release fertilizer of the present invention can also achieve the degradation treatment and resource utilization of antibiotic bacterial residues, which has good environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a TEM detection image of the carbon quantum dots obtained in the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0039] The porous silica-supported carbon quantum dots used in the following examples were prepared by the following method:

[0040] (1) A nitric acid solution with a concentration of 1 mol / L and tetracycline residue (water content of 82.5%, tetracycline content of 102 mg / kg) were added to a hydrothermal reactor at a mass ratio of 3:1 and mixed evenly. The mixture was heated to 180°C in a closed environment for the first hydrothermal reaction for 5 hours. After the reaction, the supernatant was centrifuged and separated, and the pH was adjusted to neutral with potassium hydroxide. The supernatant was placed in a hydrothermal reactor again and heated to 180°C in a closed environment for the second hydrothermal reaction for 2 hours. After the reaction, the filtrate was filtered to obtain a carbon quantum dot solution. The average particle size of the obtained carbon quantum dots was 4.7 nm, and its TEM detection image was as shown in FIG. Figure 1 After the treatment in this step, the reduction rate of tetracycline residue was 92.5% ((dry basis content of original tetracycline residue - dry basis content of solid residue remaining after treatment) / dry basis content of original tetracycline residue * 100%), and no tetracycline was detected in the remaining solid residue and the carbon quantum dot solution (HPLC detection), indicating that tetracycline has been completely degraded.

[0041] (2) Porous silica (particle size of 5 to 6 μm, pore size of 5 to 20 nm) is added to the carbon quantum dot solution of step (1) for stirring and adsorption treatment for 12 hours. The amount of porous silica added is 20% of the mass of the carbon quantum dot solution. The mixed solution is spray-dried at a temperature of 100 to 120° C. and a vacuum degree of >0.09 MPa to obtain porous silica-loaded carbon quantum dots.

[0042] Example 1

[0043] A method for preparing coated compound fertilizer comprises the following preparation steps:

[0044] (1) Weigh the raw materials by weight, heat and dissolve 20 parts of propylene glycol, 10 parts of polyethylene glycol-400 and 8 parts of α-cyclodextrin in N,N-dimethylformamide solvent, cool to room temperature, add 60 parts of hexamethylene diisocyanate and dissolve evenly to obtain a coating solution with a solid content of 12%.

[0045] (2) The obtained coating liquid is evenly sprayed onto the compound fertilizer particles (compound fertilizer particles of urea and diammonium phosphate with a particle size of 1 to 5 mm, containing 26.2% N and 26.2% P) in a vacuum drum coating machine through an atomizing nozzle. 2 O 5 12.5%) surface, the temperature of the compound fertilizer particles is controlled at 70-75° C., the nozzle feed temperature is controlled at 75-80° C., the coating liquid spraying amount is controlled to be 6% (the coating material accounts for the mass percentage of the obtained coated compound fertilizer), and after the spraying is completed, the rotary drying is continued for 10 minutes to obtain the coated compound fertilizer.

[0046] A controlled-release fertilizer is obtained by uniformly mixing the following components by weight:

[0047] 50 parts of coated compound fertilizer, potassium humate (K 2 O 8.7%) 40 parts, porous silica-supported carbon quantum dots 10 parts, sodium polyacrylate water retaining agent 5 parts.

[0048] The controlled-release fertilizer obtained in this embodiment meets the requirements of ecological-grade fertilizer after testing (total cadmium <0.5 mg / kg, total mercury <0.5 mg / kg, total arsenic <5 mg / kg, total lead <10 mg / kg, total chromium <50 mg / kg, total thallium <1.0 mg / kg, total nickel <300 mg / kg, total cobalt <50 mg / kg, total vanadium <200 mg / kg, total antimony <10 mg / kg, biuret <1.5%, phenyl[a]pyrene <0.01 mg / kg, total petroleum hydrocarbon content ≤0.20%, total phthalate content ≤10 mg / kg, total antibiotic content <1.0 mg / kg, ascaris egg mortality rate 100%, fecal coliform count ≤100 / g).

[0049] Example 2

[0050] A method for preparing coated compound fertilizer comprises the following preparation steps:

[0051] (1) Weigh each raw material by weight, heat and dissolve 20 parts of butanediol and 10 parts of β-cyclodextrin in N,N-dimethylformamide solvent, cool to room temperature, add 50 parts of isophorone diisocyanate and dissolve evenly to obtain a coating solution with a solid content of 8%.

[0052] (2) The obtained coating liquid is evenly sprayed onto the compound fertilizer particles (compound fertilizer particles of urea, diammonium phosphate and potassium chloride with a particle size of 1 to 5 mm, containing 24.7% N and 1.5% P) in the vacuum drum through an atomizing nozzle. 2 O 5 11.6%, K 2 O 4.7%) surface, the temperature of the compound fertilizer particles is controlled at 70-75°C, the nozzle feed temperature is controlled at 75-80°C, the coating liquid spraying amount is controlled to be 4% (the mass percentage of the coating material in the obtained coated compound fertilizer), and after the spraying is completed, the rotary drying is continued for 10 minutes to obtain the coated compound fertilizer.

[0053] A controlled-release fertilizer is obtained by uniformly mixing the following components by weight:

[0054] 80 parts of coated compound fertilizer, potassium humate (K 2 O 8.7%) 30 parts, porous silica loaded carbon quantum dots 20 parts, sodium polyacrylate water retaining agent 10 parts.

[0055] The controlled-release fertilizer obtained in this embodiment meets the requirements of ecological-grade fertilizer after testing.

[0056] Example 3

[0057] A method for preparing coated compound fertilizer comprises the following preparation steps:

[0058] (1) Weigh each raw material by weight, heat and dissolve 30 parts of ethylene glycol, 10 parts of polypropylene glycol-600 and 5 parts of γ-cyclodextrin in N,N-dimethylformamide solvent, cool to room temperature, add 70 parts of isophorone diisocyanate and dissolve evenly to obtain a coating solution with a solid content of 15%.

[0059] (2) The obtained coating liquid is evenly sprayed onto the compound fertilizer particles (compound fertilizer particles of urea and diammonium phosphate with a particle size of 1 to 5 mm, containing 26.2% N and 26.2% P) in the vacuum drum through an atomizing nozzle. 2 O 5 12.5%) surface, the temperature of the compound fertilizer particles is controlled at 70-75° C., the nozzle feed temperature is controlled at 75-80° C., the coating liquid spraying amount is controlled to be 8% (the coating material accounts for the mass percentage of the obtained coated compound fertilizer), and after spraying, it is continued to rotate and dry for 10 minutes to obtain the coated compound fertilizer.

[0060] A controlled-release fertilizer is obtained by uniformly mixing the following components by weight:

[0061] 30 parts of coated compound fertilizer, potassium humate (K 2 O 8.7%) 60 parts, porous silica-supported carbon quantum dots 5 parts, and sodium polyacrylate water retaining agent 1 part.

[0062] The controlled-release fertilizer obtained in this embodiment meets the requirements of ecological-grade fertilizer after testing.

[0063] Comparative Example 1

[0064] A method for preparing a coated compound fertilizer and a controlled-release fertilizer, compared with Example 1, an equal amount of pentaerythritol cross-linking agent is used to replace α-cyclodextrin, and the rest is the same.

[0065] The high temperature (35°C) nutrient release period of the coated compound fertilizer obtained in the above Examples 1 to 3 and Comparative Example 1 was measured (refer to HG / T 4215-2011, the time (d) required for the controlled-release nutrients to reach a cumulative nutrient release rate of 80% from the start of leaching in 35°C still water). The test results are shown in Table 1 below.

[0066] Table 1

[0067] Test Case Nutrient release period Example 1 136d Example 2 115d Example 3 148d Comparative Example 1 72d

[0068] It can be seen from the results in Table 1 that the coated compound fertilizer obtained by using cyclodextrin cross-linked polyurethane coating agent in the present invention has a significantly longer high temperature (35°C) nutrient release period than the coated compound fertilizer prepared by conventional polyol cross-linked polyurethane coating agent, and is very suitable for use in high temperature areas in the south.

[0069] Comparative Example 2

[0070] A controlled-release fertilizer, compared with Example 1, does not contain porous silica loaded carbon quantum dots, and the rest is the same.

[0071] Comparative Example 3

[0072] A controlled-release fertilizer, compared with Example 1, uses an equal amount of porous silicon dioxide (with a particle size of 5 to 6 μm and a pore size of 5 to 20 nm) to replace the porous silicon dioxide loaded carbon quantum dots, and the rest is the same.

[0073] Comparative Example 4

[0074] A controlled-release fertilizer, compared with Example 1, uses an equal amount of carbon quantum dots (obtained directly by vacuum spray drying a carbon quantum dot solution) to replace the porous silica-loaded carbon quantum dots, and the rest is the same.

[0075] The controlled-release fertilizer obtained in the above-mentioned Example 1 and Comparative Examples 2 to 4 is applied to saline-alkali land for fertilization treatment. The application method is to spread the controlled-release fertilizer on the saline-alkali land before planting crops, and the application amount is 28 kg of controlled-release fertilizer / mu. After fertilization, the soil is plowed and watered. After 24 hours, samples are taken to test the exchangeable sodium content, soil alkalinity (ESP) and soil EC value of the soil. Three parallel samples are tested for each group of samples, and the average value is taken. The saline-alkali land that has not been fertilized is used as the control group. The test results are shown in Table 2 below.

[0076] Table 2

[0077] Test sample <![CDATA[Exchangeable sodium content / cmol·kg -1 > ESP / % EC value / dS / m Example 1 6.7 6.5 9.2 Comparative Example 2 15.2 13.4 17.3 Comparative Example 3 10.9 9.8 14.8 Comparative Example 4 8.7 12.1 13.6 Control group 16.6 17.0 25.5

[0078] From the results in Table 2, it can be seen that the present invention uses porous silica loaded with carbon quantum dots as a synergist for compound fertilizer, which can effectively reduce the soil exchangeable sodium content, soil alkalinity (ESP) and soil EC value. At the same time, the loading combination of porous silica and carbon quantum dots has an obvious synergistic effect, which may be due to the combination of the two improving its pore transmission channel and adsorption active sites, effectively improving the adsorption and exchange of ions in saline-alkali soil, thereby achieving the effect of significantly reducing the soil exchangeable sodium content, soil alkalinity and soil EC value.

[0079] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A controlled-release fertilizer, characterized in that: The composition comprises the following components by weight: 30-80 parts of coated compound fertilizer, 30-60 parts of potassium humate, 5-20 parts of porous silica loaded carbon quantum dots, 1-10 parts of water retaining agent; The coated compound fertilizer is prepared by the following method: (1) heating the diol and cyclodextrin to dissolve in a diluent solvent, cooling to room temperature, adding diisocyanate and dissolving evenly to obtain a coating solution; (2) spraying the obtained coating liquid evenly on the surface of compound fertilizer particles, drying to form a film, and obtaining coated compound fertilizer; The porous silica-supported carbon quantum dots are prepared by the following method: 1) Add the acid solution and the antibiotic residue into a hydrothermal reactor and mix them evenly, and heat them to 160-200°C in a closed environment for the first hydrothermal reaction; after the reaction, centrifuge and separate the supernatant, adjust the pH to neutral, put it into the hydrothermal reactor again, heat it to 160-200°C in a closed environment for the second hydrothermal reaction, and filter the filtrate after the reaction to obtain a carbon quantum dot solution; 2) adding porous silica to the carbon quantum dot solution of step (1) for stirring and adsorption treatment, and vacuum spray drying the mixed solution to obtain porous silica loaded with carbon quantum dots.

2. A controlled-release fertilizer according to claim 1, characterized in that: The weight ratio of the components in the coating solution in step (1) is: 20-40 parts of diol, 50-70 parts of diisocyanate, and 5-10 parts of cyclodextrin.

3. A controlled-release fertilizer according to claim 1, characterized in that: The diol in step (1) is selected from one or a mixture of two or more of ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol with a molecular weight of 200 to 800, and polypropylene glycol with a molecular weight of 200 to 800; the diisocyanate is selected from one or a mixture of two or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate and lysine diisocyanate.

4. A controlled-release fertilizer according to claim 1, characterized in that: The dilution solvent in step (1) is N,N-dimethylformamide or dimethyl sulfoxide; the solid content of the coating solution is 5% to 15%.

5. The controlled-release fertilizer according to claim 1, characterized in that: The compound fertilizer particles in step (2) have a particle size of 1-5 mm, and contain a compound fertilizer of at least two of nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer, or a compound fertilizer containing at least two elements of nitrogen, phosphorus and potassium; the drying and film forming temperature is 60-80° C.; and the coating amount of the coating material in the coated compound fertilizer is 4%-8%.

6. A controlled-release fertilizer according to claim 1, characterized in that: The acid solution in step 1) is a nitric acid solution or a sulfuric acid solution with a concentration of 0.2-2 mol / L; the antibiotic bacterial residue refers to an antibiotic bacterial residue with a water content of 20%-90% and an antibiotic content of 20-500 mg / kg; the mass ratio of the acid solution to the antibiotic bacterial residue is 1-5:1; the time for the first hydrothermal reaction is 3-10 hours, and the time for the second hydrothermal reaction is 1-5 hours.

7. The controlled-release fertilizer according to claim 1, characterized in that: The particle size of the porous silica in step 2) is 5-6 μm, and the pore size is 5-20 nm; the amount of the porous silica added is 5%-30% of the mass of the carbon quantum dot solution; the time of the stirring adsorption treatment is 6-48 hours; the temperature of the vacuum spray drying is 100-120° C., and the vacuum degree is >0.09 MPa.

8. The controlled-release fertilizer according to claim 1, characterized in that: The potassium content of the potassium humate is 5% to 12% in terms of K2O; and the water retaining agent is sodium polyacrylate.

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